Title of Invention	HIGH CORROSION RESISTANCE GALVANNEALED STEEL MATERIAL HAVING HAIRLINE APPEARANCE
Abstract	The present invention provides a high corrosion resistance galvannealed steel material having a hairline appearance able to be used for the same applications as applications for stainless steel material, that is, a high corrosion resistance galvannealed steel material having a hairline appearance having a plating layer with a plating deposition of 10 to 600 g/m2, containing Al: 1 to 60 mass%, Mg: 0.1 to 10 mass%, and a balance of Zn and unavoidable impurities, and having hairlines formed on the surface, said hairlines having a surface roughness Ra of 0.2 to 2.5 urn and a peaks per inch PPI of 50 to 400 in a direction perpendicular to the hairlines, having a surface roughness Ra of 0.1 to 1.2 urn and a peaks per inch PPI of 1 to 100 in the hairline direction, and having a surface roughness Ra in a direction perpendicular to the hairlines of 1.2 times or more the surface roughness Ra in the hairline direction and a PPI in a direction perpendicular to the hairlines of 2.0 times or more the PPI in the hairline direction.

Title of Invention

HIGH CORROSION RESISTANCE GALVANNEALED STEEL MATERIAL HAVING HAIRLINE APPEARANCE

Abstract

The present invention provides a high corrosion resistance galvannealed steel material having a hairline appearance able to be used for the same applications as applications for stainless steel material, that is, a high corrosion resistance galvannealed steel material having a hairline appearance having a plating layer with a plating deposition of 10 to 600 g/m2, containing Al: 1 to 60 mass%, Mg: 0.1 to 10 mass%, and a balance of Zn and unavoidable impurities, and having hairlines formed on the surface, said hairlines having a surface roughness Ra of 0.2 to 2.5 urn and a peaks per inch PPI of 50 to 400 in a direction perpendicular to the hairlines, having a surface roughness Ra of 0.1 to 1.2 urn and a peaks per inch PPI of 1 to 100 in the hairline direction, and having a surface roughness Ra in a direction perpendicular to the hairlines of 1.2 times or more the surface roughness Ra in the hairline direction and a PPI in a direction perpendicular to the hairlines of 2.0 times or more the PPI in the hairline direction.

Full Text	DESCRIPTION GORReSlON RESISTANCE GALVANNBALED STEEL MATERIAL HAVING HAIRLINE APPEARANCE" TECHNICAL FIELD The present invention relates to a high corrosion resistance galvannealed steel material having a hairline appearance used for interior materials or exterior materials of buildings, cars, etc., surface materials of electrical equipment, etc. BACKGROUND ART As conventional steel materials having a hairline appearance, stainless steel materials are well known. That is, as a surface finish of stainless steel materials, a "hairline finish (HL finish)" is defined in JIS G 4305 and 4307. A "hairline finish", as defined by "a finish obtained by polishing by a polishing material of a suitable particle size to give a continuous polished grain", means a surface finish where the polished surface continues long like with hairs. FIG. 1 is a view showing an outline of a hairline finish. The ordinary hairline finish method, as shown in FIG. I, comprises rotating at a high speed an endless paper polishing belt 3 strung between a contact wheel 1 and an idler roll 2 by rotating the contact wheel so as to polish the surface of a stainless steel material 6 moving from an uncoiler 4 to a coiler 5 by the polishing belt (for example, see Japanese Patent Publication (A) No. 1-306162 and Japanese Patent Publication (B) No. 7- 96183). A hairline finished stainless steel material has corrosion resistance and has a unique surface pattern, so is being widely used for interior materials or external materials of buildings where design is stressed, surface materials of electrical equipment, etc. However, stainless steel materials are expensive, so a new inexpensive steel material taking the place of stainless steel materials, that is, a steel material having a hairline appearance provided with a high corrosion resistance similar to a stainless steel material and suitable for use for building materials or electrical equipment, is desired. Therefore, the inventors took note of the inexpensive galvanized steel materials with their excellent corrosion resistance similar to stainless steel materials and studied how to give them a hairline finish. As conventional art for giving a plating layer a hairline finish, art has been proposed for solving the problem of the underlayer of the plating coated layer being exposed, the corrosion resistance becoming poor, and stable good quality materials not being able to be obtained if forming a plating coating layer on the surface of a thin, light-weight magnesium-based member and applying a hairline finish to try to form a hairline pattern on the surface of the plating coated layer. That is, there is the art of giving a hairline finish to the surface of an Mg-based part on which the dry plating method is used to form a plating coated layer (1) selected from Cu, a Cu alloy, Au, an Au alloy, Al, or an Al alloy and over said plating coated layer (1) the wet plating method is used to form a plating coated layer (2) selected from Cu, Ni, Au, Cr, Zn, Pa, Pt, Rh, Fe, Co, Sn, Cd, Ru, and their alloys (for example, see Japanese Patent Publication (A) No. 2000-219977). However, this art requires that two thick plating coated layers be provided. Further, the dry plating method and wet plating method have to be combined, so this art is difficult to apply as is to a galvanized steel material. Further, various inventions have been made regarding high corrosion resistance galvannealed steel sheets. For example, a Zn-Al-Mg-based alloy plated steel sheet plated using a plating bath comprised of, by mass%, Al: 3 to 17%, Mg: 1 to 5%, and the balance of Zn and a plated steel sheet plated using a plating bath of this plus Ti and B (for example, see Japanese Patent Publication (A) No. 10-306357) or a Zn-Al-Mg-Si-based alloy plated steel sheet plated having a plating layer including, by mass%, Al: 5 to 81, Mq: I to 10%, Si: 0.01 to 2%, and, if needed, Fe: 1% or less or further Sn: 0.1 to 2% are known (for example, see Japanese Patent Publication (A) No. 2001-355053). DISCLOSURE OF THE INVENTION The present invention has as its object the provision of a high corrosion resistance galvannealed steel material having a hairline appearance which can be used similarly for the same applications as the applications of a stainless steel material having a hairline appearance. The inventors engaged in in-depth research on giving a hairline finish to a galvanized steel material, which is a material less expensive than a stainless steel material but having a similar corrosion resistance, as a material for taking the place of a stainless steel material having a hairline appearance. As a result, they found that if giving a pure galvanized steel material a hairline finish, since the zinc is soft, the hairlines formed are easily crushed and, further, the hairline finish polishing belt easily becomes clogged at the time of the processing work, so good hairlines could not be obtained and a hairline finish was difficult. Further, the hairline finished galvanized steel material had the problem of formation of white rust on the zinc surface in the atmosphere. If white rust formed, the hairline appearance ended up disappearing and the effect of formation of the hairlines ended up being lost. Therefore, in the present invention, the inventors took note of high corrosion resistance galvannealing process introducing a hard phase in the plating layer and discovered that if applying a hairline finish to this, a good high corrosion resistance galvanized steel material having a hairline appearance can be obtained and thereby completed the present invention. The present invention has as its gist the following: (1) A high corrosion resistance galvannealed steel material having a hairline appearance having a plating layer with a plating deposition of 10 to 600 g/m2, containing Al: 1 to 60 mass%, Mg: 0.1 to 10 mass%, and a balance of Zn and unavoidable impurities, and having hairlines formed on the surface, said hairlines having a surface roughness Ra of 0.2 to 2.5 (am and a peaks per inch PPI of 50 to 400 in a direction perpendicular to the hairlines, having a surface roughness Ra of 0.1 to 1.2 jjm and a peaks per inch PPI of 1 to 100 in the hairline direction, and having a surface roughness Ra in a direction perpendicular to the hairlines of 1.2 times or more the surface roughness Ra in the hairline direction and a PPI in a direction perpendicular to the hairlines of 2.0 times or more the PPI in the hairline direction. (2) A high corrosion resistance galvannealed steel material having a hairline appearance having a plating layer with a plating deposition of 10 to 600 g/m2, containing Al: 1 to 60 mass%, Mg: 0.1 to 10 mass%, and a balance of Zn and unavoidable impurities, and having hairlines formed on the surface, said hairlines having a peaks per inch PPI of 50 to 400 in a direction perpendicular to the hairlines, having a peaks per inch PPI of 1 to 100 in the hairline direction, and having a PPI in a direction perpendicular to the hairlines of 2.0 times or more the PPI in the hairline direction. (3) A high corrosion resistance galvannealed steel material having a hairline appearance having a plating layer with a plating deposition of 10 to 600 g/m2, containing Al: 1 to 60 mass%, Mg: 0.1 to 10 mass%, and a balance of Zn and unavoidable impurities, and having hairlines formed on the surface, said hairlines having a surface roughness Ra of 0.1 to 2.5 \|j,m and a peaks per inch PPI of: 50 to 400 in a direction perpendicular to the hairlines, having a surface roughness Ra of 0.1 to 1.2 \|j.m and a peaks per inch PPI of 1 to 100 in the hairline direction, and having a surface roughness Ra in a direction perpendicular to the hairlines of 1.2 times or more the surface roughness Ra in the hairline direction and a PPI in a direction perpendicular to the hairlines of 2.0 times or more the PPI in the hairline direction. (4) A high corrosion resistance galvannealed steel material having a hairline appearance as set forth in any one of (1) to (3), characterized in that the plating layer further contains Si in an amount of 0.001 to 3 ma s s %. (5) A high corrosion resistance galvannealed steel material having a hairline appearance as set forth in any one of (1) to (4), characterized in that the plating layer further contains one or two of Ti in an amount of 0.0001 to 0.1 mass% and B in an amount of 0.0001 to 0.1 ma s s % . (6) A high corrosion resistance galvannealed steel material having a hairline appearance as set forth in any one of (1) to (5), characterized in that plating layer is comprised of a Zn and Al binary eutectic in a volume ratio of 1 to 80 vol% and a Zn, Al, and ZnMg alloy ternary eutectic in a volume ratio of 10 to 90 vol%, with the total of the two being at least 50%. (7) A high corrosion resistance galvannealed steel material having a hairline appearance as set forth in any one of (1) to (6), characterized in that plating layer has a chromate treated layer of 1 to 1000 mg/m2 on its surface. (8) A high corrosion resistance galvannealed steel material having a hairline appearance as set forth in any one of (1) to (6), characterized in that plating layer surface has a chromate-free treated layer of 1 to 200 mg/m"" not containing any chrome on its surface. (9) A high corrosion resistance galvannealed steel material having a hairline appearance as set forth in any one of (1) to (8), characterized by having a transparent resin coating layer of a thickness of 0.5 to 100 \|o.m on its surface. (10) A high corrosion resistance galvannealed steel material having a hairline appearance as set forth in any one of (1) to (9), characterized in that the vicinity of the interface between the plating layer surface and chromate-free treated layer not containing any chrome has a layer of a deposit of one or more of Co, Fe, Ni, Pt, and Mn in a metal state or hydroxide state of 0.1 to 10 mg/m2 and the blackening resistance in a wet environment is excellent. BRIEF1 DESCRIPTION OF THE DRAWINGS FIG. 1 is a view showing an outline of a hairline finish. FIG. 2 gives views of the structure of a Zn-based alloy plating layer of the present invention, wherein (a) is a micrograph of a Zn-based alloy plating layer of the present invention and (b) is a schematic view of its structure. FIG. 3 is a micrograph of the cross-section of the surface of a hairline finished high corrosion resistance galvannealed steel material (Zn-ll%Al-3Mg-0.2Si plating, plating weight: 90 g/m2) after #80 emery polishing (magnification: 1000X). BEST MODE FOR CARRYING OUT THE INVENTION Below, the present invention will be explained in detail. As steel materials having a hairline appearance, there are hairline finished stainless steel materials, but stainless steel materials are expensive. Therefore, the inventors focused on the galvanized/galvannealed plated steel materials providing a high corrosion resistance like that of stainless steel materials and studied giving galvanized/galvannealed steel materials a hairline finish. If giving a galvanized steel material a hairline finish, the ridges of the hairlines become deformed and the hairlines are crushed, so a good hairline appearance cannot be obtained. There are also parts where the base metal is exposed. Further, the problem arises of clogging of the hairline finishing polishing belt. Further, there is the problem that if leaving the material in the atmosphere after giving it the hairline finish, white rust is formed and the hairline appearance ends up being lost. A good hairline appearance cannot be obtained in this way probably due to the fact that the galvanized layer has a hardness of about 50 Hv, i.e., is soft. Therefore, the inventors focused on galvannealed layers including hard phases and found that if giving these a hairline finish, a good hairline appearance could be obtained. As galvannealed layers including hard phases, they learned that a galvannealed layer containing Al and Mg which contains Zn and Al binary eutectic and Zn, Al, and ZnMg alloy ternary eutectic hard layers is suitable. The plating layer should be one comprising, as ingredients, by mass%, Al: 1.0 to 60%, Mg: 0.1 to 10%, and the balance of Zn and unavoidable impurities, further selectively including, as needed, Si: 0.001 to 3.0% to improve the corrosion resistance and one or both of Ti: 0.0001 to 0.1% and B: 0.0001 to 0.1% to improve the appearance. The reasons for limitation of the ingredients of the galvannealed layer will be explained next. Al forms a hard phase Zn/Al binary eutectic and Zn/Al/Zn2Mg ternary eutectic in the plating layer and acts to improve the corrosion resistance of the plating layer and suppress the formation of dross in the plating bath. If Al is less than 1.0%, the volume fraction of the binary eutectic and ternary eutectic forming the hard phase becomes insufficient, a good hairline appearance cannot be obtained by a hairline finish, and the plated steel material becomes inferior in corrosion resistance. On the other hand, if Al is over 60%, the plated surface is formed with whisker-shaped relief shapes, a plating layer with a uniform appearance cannot be obtained, the effect of improvement of the corrosion resistance becomes saturated, and simultaneously the sacrificial corrosion action on the base iron is lost so the corrosion resistance of flawed parts deteriorates. Therefore, the Al content was made 1.0 to 60%. Mg is an ingredient required for forming the ternary eutectic and has the effect of forming corrosion products on the plated surface to improve the corrosion resistance of the plated steel material. If Mg is less than 0.1%, the volume fraction of the ternary eutectic becomes insufficient, a good hairline appearance cannot be obtained by a hairline finish, and the corrosion products required for improving the corrosion resistance cannot be formed. On the other hand, if Mg exceeds 10%, the plating bath proceeds to oxidize due to contact with the air, black oxides (dross) are produced making treatment difficult, and the effect of improvement of the corrosion resistance becomes saturated. Therefore, the Mg content was made 0.1 to 10%. Si is added as needed to improve the corrosion resistance and improve the plating adhesion. If the amount; of addition is less than 0.001%, these effects are not obtained, while if over 3.0%, these effects become saturated and conversely the production of dross increases, so the amount of addition of Si was made 0.001 to 3.0%. Ti is an ingredient added as needed for forming the nuclei for precipitation of the primary crystal Al phase, increasing the fineness of the structure, and improving the appearance. At least 0.0001% must be added. However, if adding over 0.1%, the solubility in the plating bath is exceeded, Ti-Al-based precipitates grow, the plating layer is formed with relief shapes on its surface, and the quality of the appearance deteriorates, so Ti was made 0.0001 to 0.1%. B, like Ti, has the effect of improving the plating appearance, but if less than 0.0001%, that effect cannot be obtained, while if over 0.1%, that effect becomes saturated, so B was made 0.0001 to 0.1%. With a plating deposition of less than 10 g/m2, the corrosion resistance becomes inferior, so this was made the lower limit, while with one of more than 600 g/m2, the uniformity of deposition of the plating layer deteriorates and a dripping appearance results, which is not preferred, and bending or the like easily results in cracks in the plating layer. Therefore, 600 g/m2 was made the upper limit. FIG. 2(a) is a micrograph of the structure of a Znbased alloy plating layer of the present invention, while FIG. 2(b) is a schematic view of the structure. As shown in FIG. 2(b), for example, the Zn-ll%Al- 3%Mg-0.2%Si high corrosion resistance Zn-based alloy plating layer has, in its cross-sectional structure, a structure of a [Zn/Al/Zn2Mg] ternary eutectic phase 7 in which a [Zn/Al] binary eutectic phase 8 is mixed and in which a [Zii2Mg single phase] 9 is present in island shapes. This ternary eutectic phase is comprised of a structure of soft Zn and Al phases in which hard Zn2Mg is dispersed. The structure as a whole features both consistency and hardness. If giving a hairline finish to plated steel material in which this type of phase is also present at the surface, the plated surface is easily peeled off from the plated surface by the polishing belt, a beautiful hairline appearance is obtained without deformation of the ridges of the hairlines, the polishing belt does not become clogged, and a good hairline appearance is obtained. FIG. 3 is a micrograph of the cross-section of the surface of a hairline finished high corrosion resistance galvannealed steel material (Zn-ll%Al-3Mg-0.2Si plating, plating deposition: 90 g/m2) after #80 emery polishing (magnification: 1000X). As shown in FIG. 3, this has a good appearance with no deformation of the hairline grooves. To give a high corrosion resistance galvannealed steel material a hairline finish to obtain a good hairline appearance, the plating layer is preferably structured with a [Zn/Al] binary eutectic phase in a volume fraction of 1 to 80 vol%, a [Zn/Al/Zn2Mg] ternary eutectic phase in a volume fraction of 10 to 90 vol%, and the balance of Zn, Zn2Mg alloy, Mg2Si, TiAl3, etc. The [Zn/Al] binary eutectic phase is soft compared with the ternary eutectic phase, but is hard compared with the Zn and Al single phases. Therefore, the smaller the volume fraction, the more improved the hairline finishability. If over 90 vol%, the plating layer as a whole softens and the hairline finishability deteriorates. Making it less than 1 vol% is difficult engineering wise. If the volume fraction of the ternary eutectic becomes small, the hardness and consistency characteristics of the plating layer deteriorate, the appearance at the time of hairline finishing deteriorates, and the scraps easily clog the abrasive material. Therefore, the lower limit of the volume fraction of the ternary eutectic was made 10 vol%. On the other hand, the upper limit is determined by the ease of formation of the Al phase and Zn2Mg phase in the process of solidification of the plating layer. 90 vol% was the upper limit in engineering production. Further, if the volume fraction of the two eutectic phases combined falls, the overall plating layer falls in hardness and consistency and the hairline appearance becomes poor, so this fraction was made 50% or more. The thickness of the plating layer suitable for application of a hairline finish is, in terms of plating deposition, 10 to 600 g/m2, preferably 100 to 500 g/m2. If the plating deposition is less than 10 g/m2, since the plating layer is thin, the corrosion resistance is insufficient and the hairline finishing ends up exposing the underlying steel material. If the plating deposition is over 600 g/m2, the plating layer is too thick and a plating layer with a uniform appearance cannot be obtained. Further, the plating layer easily peels off. This is also disadvantageous cost wise. Therefore, the plating deposition was made 10 to 600 g/m2. As the shape of the superior appearance hairlines formed on the plated steel material, in the direction perpendicular to the hairlines (C-direction), the surface roughness should be a surface roughness Ra of 0.2 to 2.5 HITI, preferably 1.2 to 1.8 ^m, and the peaks per inch PPI should be 50 to 400; in the hairline direction (Ldirection), the surface roughness should be Ra: 0.1 to 1.2 [o,m, preferably 0.5 to 1.0 jam, and the peaks per inch PPI should be I to 100; the Ra in the direction perpendicular to the hairlines (C-direction) should be 1.2 times or more the Ra in the hairline direction (Ldirection) (C-direction Ra/L-direction Ra>1.2); and the PPI in the direction perpendicular to the hairlines (Cdirection) should be 2 times or more the PPI in the hairline direction (L-direction) (C-direction PPI/LdirectionPPI 2) . If less than the limit limits of the C-direction and L-direction surface roughnesses Ra, peaks per inch PPI, and ratios prescribed here, the hairlines will no longer stand out and the hairline finish treatment will become wasted. Further, conversely, if more than the upper limits of the C-direction and L-direction surface roughnesses Ra and peaks per inch PPI, the hairlines will become too coarse, beautiful hairlines will not be obtained, the aesthetic design value of the hairlines will be lost, and the product will lose its value. Therefore, the present invention defines the shape of the hairlines as above by the surface roughnesses, peaks per .inch, and their ratios. Note that the surface roughness Ra was measured in accordance with the method of measurement prescribed in JIS B060 (1997) employing a reference length of 0.8 mm. Further, the peaks per inch PPI were measured in accordance with SAEJ911-1986 using a measured length of 1 inch and a width 2H between positive and negative reference levels of 50 \|j.inch. To form hairlines satisfying the requirements of the surface roughnesses, peaks per inch, and their ratios prescribed in the present invention, use of a #60 to #320 or so belt sander (polishing belt) for the hairline finish is preferable. After application of the hairline finish, the plating layer is preferably treated by chromate treatment or chromate-free treatment for primary rust proofing. A galvanized steel material is susceptible to white rust, so to prevent this, after the plating layer is given the hairline finish, it is treated by chromate treatment or chromate-free treatment to form a rustproofing coated layer for primary rust proofing. In the case of chromate treatment, a known chromate treatment, for example, chromate treatment by a chromate treatment solution containing chromic acid and a reaction accelerator as main ingredients can be applied. The amount of chromate deposition is made 1 to 200 mg/m2. If the amount of chromate deposition is less than 1 mg/m"', a sufficient rust proofing effect cannot be obtained. Further, if over 200 mg/m2, not only does the hairline finish no longer stand out, but also the rust proofing effect will end up becoming saturated and, economically, the cost will rise. Further, it is also possible to perform primary rust proofing by a known chromate-free treatment (nonchromate treatment) in the same way as a chromate treatment. The cnromate-free treatment (nonchromate treatment) uses a treatment solution not containing any environmentally harmful hexavalent chrome in the solution. For example, there are treatment solutions containing Zr, Ti salts, treatment solutions containing silane coupling agents, etc. Known chromate-free treatment solutions may be used for chromate-free treatment. In such chromate-free treatment, a chromatefree treated layer containing Ti, Zr, P, Ce, Si, Al, Li, and other main ingredients and not containing chromic acid is formed. The amount of deposition is preferably 1 to 1000 mg/m2. If the amount of deposition in the chromate-free treatment is less than 1 mg/m2, a sufficient rust preventing effect cannot be obtained. Further, if over 1000 mg/m2, not only does the hairline finish no longer stand out, but also the rust preventing effect ends up becoming saturated and, economically, the cost rises. E'urther, if giving a galvanized steel material a hairline finish and then leaving it in the atmosphere, the plated surface will oxidize and blacken. If blackening, the hairline finish will no longer stand out and the hairline appearance will be lost. Further, the galvanized layer will be easily damaged upon collision with a hard object. For this reason, if forming a transparent resin coated layer to a thickness of 0.5 to 100 \|im on the hairline finished plated surface, the blackening resistance and the defect resistance can be improved. The transparent resin coated layer may be formed using a conventional known organic clear coating and a conventional known coating method. As such organic clear coatings, specifically an acryl-based baked clear coating, urethane-based clear coating, epoxy-based clear coating, polyester-based clear coating, melamine alkydbased clear coating, etc. may be mentioned. Among these, polyester-based and acryl-based baked clear coatings are preferably used. As the method of coating an organic clear coating, specifically the roll coater method, curtain coater method, spray can method, electrostatic method, etc. may be mentioned. Among these, the roll coater method and the curtain coater method are preferable. To impart blackening resistance, it is possible to give the vicinity of the interface with the chromate and chromate-free treated layer a layer of a deposit of one or more of Co, Fe, Ni, Pt, and Mn in a metal state or hydroxide state of 0.1 to 10 mg/m2. This deposited layer should have an amount of deposition of 0.1 to 10 mg/m2, preferably 0.5 to 3.0 mg/m2. This treatment greatly improves the blackening resistance in a wet environment. If the amount of deposition is less than 0.1 mg/m2, the effect of the blackening resistance is not sufficient, while if over 10 mg/m2, the corrosion resistance deteriorates, so these are not preferred. The method of imparting this treated layer is not particularly limited, but as examples there are the above salt water solution dipping method or spraying method, the vacuum deposition method, etc. In the dipping method, the hairline finished plated steel sheet is dipped in a 0.1 to 10 g/liter metal salt aqueous solution for 0.5 to 10 seconds, then rinsed. EXAMPLES Below, examples will be used to explain the present invention in detail. Low carbon steel sheets of two different types of thicknesses, that is, sheet thicknesses of 0.8 mm and 1.6 mm, were used as the sheets for plating. The sheets were plated by heating, annealing, and plating by a continuous hot dip galvanization line of a non-oxidizing furnace type. The annealing atmosphere was made 10% hydrogen and the remaining 90% nitrogen gas. The dew point was made -30°C. The annealing temperature was made 730°C and the annealing time 3 minutes. The plating bath was comprised of, by mass%, Al: 11.0%, Mg: 3.0%, Si: 0.2%, and the balance of Zn and unavoidable impurities, while the plating bath temperature was 450°C. The plating deposition was adjusted by the ordinary nitrogen gas wiping method. After the plating, different number belt sanders (size 100 mmx915 mm) were used to give hairline finishes under condations of a belt speed of about 3.5/seconds and a polishing time of 3 to 4 seconds. After this, the surface roughness (Ra) and peaks per inch (PPI) were investigated. The results are shown in Table 1. As shown in Table 1, Nos. 1, 2, and 5 were the high corrosion resistance plated steel materials having a beautiful hairline appearance satisfying the surface roughnesses (Ra), peaks per inch (PPI), and their ratios prescribed in the present invention. As opposed to this, the #80 bead blasted No. 3 was formed with uniform fine relief over its surface, but the L-direction surface roughness and peaks per inch were small, the ratios of the surface roughness and peaks per inch were also small, and the requirements prescribed in the present invention were not satisfied. The bead blasting and hairline finish were clearly difficult. No. 4 was given a hairline finish, but the belt sander was a #600 type or too fine and therefore the requirements for hairlines prescribed in the present invention were not satisfied. Hairlines could not be clearly observed in the appearance. Further, No. 6 and No. 7 are cases with hairline finish given. In these cases, the C-direction surface roughness and peaks per inch were small and the ratios were also small. In these cases as well, naturally no hairlines were observed. From the above test results, only the plated steel sheets with hairline finishes satisfying the requirements prescribed in the present invention were plated steel sheets with beautiful hairline appearances. Next, the inventors prepared plated steel sheets with different compositions of plating layers then used a 80 belt sander (size 100 mmx915 mm) to give them a hairline finish at a belt speed of about 3.5/second and a polishing time of 3 to 4 seconds. The inventors investigated the hairline appearance and state of deposition of scraps at that time. The results are shown in Table 2. Nos. 1 to 17 have the plating compositions prescribed in the present invention and were good in terms of hairline appearance, clogging of sanders by scraps, and corrosion resistance. On the other hand, Nos. 18 to 20 had platings outside the composition prescribed by the present invention. While they had values of surface roughness satisfying the values prescribed in the present invention, the hairline appearance could not be clearly observed and the sheets were poor in terms of scrap production and corrosion resistance. The reason, why the hairline appearance could not be clearly observed is believed to be because of the production of scraps and deformation of the polishing marks etc. Further, the inventors performed plating while changing the volume fractions of the eutectic phases in the plating layers and investigated the resultant performances. The results are shown in Table 3. Nos. I to 5 had the phase structures prescribed in the present invention and were good in all of the hairline appearance, sander scrap clogging, and corrosion resistance. On the other hand, Nos. 6 and 7 had platings outside the phase structure prescribed by the present invention and were inferior in hairline appearance and poor in terms of production of scraps. Further, plated steel sheets having a composition of Zn-llAl-3Mg-0.2Si were used for chromate treatment, chromate-free treatment, clear coating treatment, and blackening resistance treatment. The chromate treatment comprised coating the sheet with a chromic acid 100 g/liter solution, then drying it in a 60°C hot air furnace for 30 seconds. The chromate-free treatment comprised coating the sheet with a chemical comprised of zirconium aluminum carbonate, cobalt nitrate, silica, and ammonium phosphate, then drying in a 60°C hot air furnace for 30 seconds. Further, sheets were coated with a melamine alkyd-based clear coating (solvent-based) and acryl-based clear coating (aqueous dispersion based) and heated until sheet temperatures of 220°C (melamine alkyd-based) and 150°C (acryl-based). The blackening resistance treatment comprised dipping the sheet in a 1 g/liter Ni sulfate aqueous solution for 3 seconds, then rinsing and drying it, then treating it by the chromate-free treatment and coating it by a melamine alkyd-based clear coating. The corrosion resistance of the flat parts was evaluated by the amount of formation of white rust after 240 hours of a JIS Z2331 salt water spray test with "Good" indicating 1% or less formation of white rust and "Poor" indicating 10% or more. The cross-cut parts were evaluated by the blisters after 1000 hours of a salt water spray test with "Good" indicating less than 2 mm and "Poor" 2 mm or more. The blackening resistance was evaluated by allowing a treated steel material to stand in a high humidity tank of a temperature of 60°C and a relative humidity of 85% for seven days and comparing the color difference 8E values before and after. The color difference 8E was measured in accordance with JIS Z8722. A 6E of 1 or less indicated no blackening or a good result (Good), 1 to 2 indicated slight observance or a fair result (Fair), and larger than 2 indicated blackening observed or a poor result (Poor). Nos. 1 to 46 satisfy the requirements of the blackening resistance treatment, pretreatment, and coating prescribed by the present invention and were excellent in corrosion resistance both at the flat parts and the cross-cut parts. Further, Nos. 23 and 46 treated for blackening resistance were also excellent in blackening resistance. On the other hand, Nos. 47 to 49 were outside the requirements of the present invention and were poor in corrosion resistance. (Table Removed) INDUSTRIAL APPLICABILITY The high corrosion resistance galvanized steel material having a hairline appearance of the present invention is provided with a good hairline appearance and is excellent in corrosion resistance as well, so can be used for applications similar to the applications of conventional stainless steel material having a hairline appearance. Further, it can be provided at less of a price than expensive stainless steel material. WE CLAIM: 1. A high corrosion resistance galvannealed steel material having a hairline appearance having a plating layer with a plating deposition of 10 to 600 g/m2, containing Al : 1 to 60 mass%, Mg : 0.1 to 10 mass%, and a balance of Zn and unavoidable impurities, and having hairlines formed on the surface, said hairlines having a surface roughness Ra of 0.2 to 2.5 urn and a peaks per inch PPI of 50 to 400 in a direction perpendicular to the hairlines, having a surface roughness Ra of 0.1 to 1.2 urn and a peaks per inch PPI of 1 to 100 in the hairline direction, and having a surface roughness Ra in a direction perpendicular to the hairlines of 1.2 times or more the surface roughness Ra in the hairline direction and a PPI in a direction perpendicular to the hairlines of 2.0 times or more the PPI in the hairline direction. 2. A high corrosion resistance galvannealed steel material having a hairline appearance having a plating layer with a plating deposition of 10 to 600 g/m2, containing Al: 1 to 60 mass%, Mg: 0.1 to 10 mass%, and a balance of Zn and unavoidable impurities, and having hairlines formed on the surface, said hairlines having a peaks per inch PPI of 50 to 400 in a direction perpendicular to the hairlines, having a peaks per inch PPI of 1 to 100 in the hairline direction, and having a PPI in a direction perpendicular to the hairlines of 2.0 times or more the PPI in the hairline direction. 3. A high corrosion resistance galvannealed steel material having a hairline appearance having a plating layer with a plating deposition of 10 to 600 g/m2, containing Al: 1 to 60 mass%, Mg: 0.1 to 10 mass%, and a balance of Zn and unavoidable impurities, and having hairlines formed on the surface, said hairlines having a surface roughness Ra of 0.1 to 2.5 µm and a peaks per inch PPI of 50 to 400 in a direction perpendicular to the hairlines, having a surface roughness Ra of 0.1 to 1.2 µm and a peaks per inch PPI of 1 to 100 in the hairline direction, and having a surface roughness Ra in a direction perpendicular to the hairlines of 1.2 times or more the surface roughness Ra in the hairline direction and a PPI in a direction perpendicular to the hairlines of 2.0 times or more the PPI in the hairline direction. 4. A high corrosion resistance galvannealed steel material having a hairline appearance as claimed in any one of claims 1 to 3, wherein the plating layer further contains Si in an amount of 0.001 to 3 mass%. 5. A high corrosion resistance galvannealed steel material having a hairline appearance as claimed in any one of claims 1 to 4, wherein the plating layer further contains one or two of Ti in an amount of 0.0001 to 0.1 mass% and B in an amount of 0.0001 to 0.1 mass%. 6. A high corrosion resistance galvannealed steel material having a hairline appearance as claimed in any one of claims 1 to 5, wherein plating layer is comprised of a Zn and Al binary eutectic in a volume ratio of 1 to 80 vol% and a Zn, Al, and ZnMg alloy ternary eutectic in a volume ratio of 10 to 90 vol%, with the total of the two being at least 50%. 7. A high corrosion resistance galvannealed steel material having a hairline appearance as claimed in any one of claims 1 to 6, wherein plating layer has a chromate treated layer of 1 to 1000 mg/m on its surface. 8. A high corrosion resistance galvannealed steel material having a hairline appearance as claimed in any one of claims 1 to 6, wherein plating layer surface has a chromate-free treated layer of 1 to 200 mg/m not containing any chrome on its surface. 9. A high corrosion resistance galvannealed steel material having a hairline appearance as claimed in any one of claims 1 to 8, comprising a transparent resin coating layer of a thickness of 0.5 to 100 µm on its surface. 10. A high corrosion resistance galvannealed steel material having a hairline appearance as claimed in any one of claims 1 to 9, wherein the vicinity of the interface between the plating layer surface and chromate-free treated layer not containing any chrome has a layer of a deposit of one or more of Co, Fe, Ni, Pt, and Mn in a metal state or hydroxide state of 0.1 to 10 mg/m2 and the blackening resistance in a wet environment is excellent.

Full Text

DESCRIPTION
GORReSlON RESISTANCE GALVANNBALED STEEL MATERIAL
HAVING HAIRLINE APPEARANCE"
TECHNICAL FIELD
The present invention relates to a high corrosion
resistance galvannealed steel material having a hairline
appearance used for interior materials or exterior
materials of buildings, cars, etc., surface materials of
electrical equipment, etc.
BACKGROUND ART
As conventional steel materials having a hairline
appearance, stainless steel materials are well known.
That is, as a surface finish of stainless steel
materials, a "hairline finish (HL finish)" is defined in
JIS G 4305 and 4307. A "hairline finish", as defined by
"a finish obtained by polishing by a polishing material
of a suitable particle size to give a continuous polished
grain", means a surface finish where the polished surface
continues long like with hairs.
FIG. 1 is a view showing an outline of a hairline
finish. The ordinary hairline finish method, as shown in
FIG. I, comprises rotating at a high speed an endless
paper polishing belt 3 strung between a contact wheel 1
and an idler roll 2 by rotating the contact wheel so as
to polish the surface of a stainless steel material 6
moving from an uncoiler 4 to a coiler 5 by the polishing
belt (for example, see Japanese Patent Publication (A)
No. 1-306162 and Japanese Patent Publication (B) No. 7-
96183). A hairline finished stainless steel material has
corrosion resistance and has a unique surface pattern, so
is being widely used for interior materials or external
materials of buildings where design is stressed, surface
materials of electrical equipment, etc.
However, stainless steel materials are expensive, so
a new inexpensive steel material taking the place of
stainless steel materials, that is, a steel material
having a hairline appearance provided with a high
corrosion resistance similar to a stainless steel
material and suitable for use for building materials or
electrical equipment, is desired.
Therefore, the inventors took note of the
inexpensive galvanized steel materials with their
excellent corrosion resistance similar to stainless steel
materials and studied how to give them a hairline finish.
As conventional art for giving a plating layer a
hairline finish, art has been proposed for solving the
problem of the underlayer of the plating coated layer
being exposed, the corrosion resistance becoming poor,
and stable good quality materials not being able to be
obtained if forming a plating coating layer on the
surface of a thin, light-weight magnesium-based member
and applying a hairline finish to try to form a hairline
pattern on the surface of the plating coated layer.
That is, there is the art of giving a hairline
finish to the surface of an Mg-based part on which the
dry plating method is used to form a plating coated layer
(1) selected from Cu, a Cu alloy, Au, an Au alloy, Al, or
an Al alloy and over said plating coated layer (1) the
wet plating method is used to form a plating coated layer
(2) selected from Cu, Ni, Au, Cr, Zn, Pa, Pt, Rh, Fe, Co,
Sn, Cd, Ru, and their alloys (for example, see Japanese
Patent Publication (A) No. 2000-219977). However, this
art requires that two thick plating coated layers be
provided. Further, the dry plating method and wet plating
method have to be combined, so this art is difficult to
apply as is to a galvanized steel material.
Further, various inventions have been made regarding
high corrosion resistance galvannealed steel sheets. For
example, a Zn-Al-Mg-based alloy plated steel sheet plated
using a plating bath comprised of, by mass%, Al: 3 to
17%, Mg: 1 to 5%, and the balance of Zn and a plated
steel sheet plated using a plating bath of this plus Ti
and B (for example, see Japanese Patent Publication (A)
No. 10-306357) or a Zn-Al-Mg-Si-based alloy plated steel
sheet plated having a plating layer including, by mass%,
Al: 5 to 81, Mq: I to 10%, Si: 0.01 to 2%, and, if
needed, Fe: 1% or less or further Sn: 0.1 to 2% are known
(for example, see Japanese Patent Publication (A) No.
2001-355053).
DISCLOSURE OF THE INVENTION
The present invention has as its object the
provision of a high corrosion resistance galvannealed
steel material having a hairline appearance which can be
used similarly for the same applications as the
applications of a stainless steel material having a
hairline appearance.
The inventors engaged in in-depth research on giving
a hairline finish to a galvanized steel material, which
is a material less expensive than a stainless steel
material but having a similar corrosion resistance, as a
material for taking the place of a stainless steel
material having a hairline appearance. As a result, they
found that if giving a pure galvanized steel material a
hairline finish, since the zinc is soft, the hairlines
formed are easily crushed and, further, the hairline
finish polishing belt easily becomes clogged at the time
of the processing work, so good hairlines could not be
obtained and a hairline finish was difficult. Further,
the hairline finished galvanized steel material had the
problem of formation of white rust on the zinc surface in
the atmosphere. If white rust formed, the hairline
appearance ended up disappearing and the effect of
formation of the hairlines ended up being lost.
Therefore, in the present invention, the inventors
took note of high corrosion resistance galvannealing
process introducing a hard phase in the plating layer and
discovered that if applying a hairline finish to this, a
good high corrosion resistance galvanized steel material
having a hairline appearance can be obtained and thereby
completed the present invention.
The present invention has as its gist the following:
(1) A high corrosion resistance galvannealed steel
material having a hairline appearance having a plating
layer with a plating deposition of 10 to 600 g/m2,
containing Al: 1 to 60 mass%, Mg: 0.1 to 10 mass%, and a
balance of Zn and unavoidable impurities, and having
hairlines formed on the surface, said hairlines having a
surface roughness Ra of 0.2 to 2.5 (am and a peaks per
inch PPI of 50 to 400 in a direction perpendicular to the
hairlines, having a surface roughness Ra of 0.1 to 1.2 jjm
and a peaks per inch PPI of 1 to 100 in the hairline
direction, and having a surface roughness Ra in a
direction perpendicular to the hairlines of 1.2 times or
more the surface roughness Ra in the hairline direction
and a PPI in a direction perpendicular to the hairlines
of 2.0 times or more the PPI in the hairline direction.
(2) A high corrosion resistance galvannealed steel
material having a hairline appearance having a plating
layer with a plating deposition of 10 to 600 g/m2,
containing Al: 1 to 60 mass%, Mg: 0.1 to 10 mass%, and a
balance of Zn and unavoidable impurities, and having
hairlines formed on the surface, said hairlines having a
peaks per inch PPI of 50 to 400 in a direction
perpendicular to the hairlines, having a peaks per inch
PPI of 1 to 100 in the hairline direction, and having a
PPI in a direction perpendicular to the hairlines of 2.0
times or more the PPI in the hairline direction.
(3) A high corrosion resistance galvannealed steel
material having a hairline appearance having a plating
layer with a plating deposition of 10 to 600 g/m2,
containing Al: 1 to 60 mass%, Mg: 0.1 to 10 mass%, and a
balance of Zn and unavoidable impurities, and having
hairlines formed on the surface, said hairlines having a
surface roughness Ra of 0.1 to 2.5 |j,m and a peaks per
inch PPI of: 50 to 400 in a direction perpendicular to the
hairlines, having a surface roughness Ra of 0.1 to 1.2 |j.m
and a peaks per inch PPI of 1 to 100 in the hairline
direction, and having a surface roughness Ra in a
direction perpendicular to the hairlines of 1.2 times or
more the surface roughness Ra in the hairline direction
and a PPI in a direction perpendicular to the hairlines
of 2.0 times or more the PPI in the hairline direction.
(4) A high corrosion resistance galvannealed steel
material having a hairline appearance as set forth in any
one of (1) to (3), characterized in that the plating
layer further contains Si in an amount of 0.001 to 3
ma s s %.
(5) A high corrosion resistance galvannealed steel
material having a hairline appearance as set forth in any
one of (1) to (4), characterized in that the plating
layer further contains one or two of Ti in an amount of
0.0001 to 0.1 mass% and B in an amount of 0.0001 to 0.1
ma s s % .
(6) A high corrosion resistance galvannealed steel
material having a hairline appearance as set forth in any
one of (1) to (5), characterized in that plating layer is
comprised of a Zn and Al binary eutectic in a volume
ratio of 1 to 80 vol% and a Zn, Al, and ZnMg alloy
ternary eutectic in a volume ratio of 10 to 90 vol%, with
the total of the two being at least 50%.
(7) A high corrosion resistance galvannealed steel
material having a hairline appearance as set forth in any
one of (1) to (6), characterized in that plating layer
has a chromate treated layer of 1 to 1000 mg/m2 on its
surface.
(8) A high corrosion resistance galvannealed steel
material having a hairline appearance as set forth in any
one of (1) to (6), characterized in that plating layer
surface has a chromate-free treated layer of 1 to 200
mg/m"" not containing any chrome on its surface.
(9) A high corrosion resistance galvannealed steel
material having a hairline appearance as set forth in any
one of (1) to (8), characterized by having a transparent
resin coating layer of a thickness of 0.5 to 100 |o.m on
its surface.
(10) A high corrosion resistance galvannealed steel
material having a hairline appearance as set forth in any
one of (1) to (9), characterized in that the vicinity of
the interface between the plating layer surface and
chromate-free treated layer not containing any chrome has
a layer of a deposit of one or more of Co, Fe, Ni, Pt,
and Mn in a metal state or hydroxide state of 0.1 to 10
mg/m2 and the blackening resistance in a wet environment
is excellent.
BRIEF1 DESCRIPTION OF THE DRAWINGS
FIG. 1 is a view showing an outline of a hairline
finish.
FIG. 2 gives views of the structure of a Zn-based
alloy plating layer of the present invention, wherein (a)
is a micrograph of a Zn-based alloy plating layer of the
present invention and (b) is a schematic view of its
structure.
FIG. 3 is a micrograph of the cross-section of the
surface of a hairline finished high corrosion resistance
galvannealed steel material (Zn-ll%Al-3Mg-0.2Si plating,
plating weight: 90 g/m2) after #80 emery polishing
(magnification: 1000X).
BEST MODE FOR CARRYING OUT THE INVENTION
Below, the present invention will be explained in
detail.
As steel materials having a hairline appearance,
there are hairline finished stainless steel materials,
but stainless steel materials are expensive. Therefore,
the inventors focused on the galvanized/galvannealed
plated steel materials providing a high corrosion
resistance like that of stainless steel materials and
studied giving galvanized/galvannealed steel materials a
hairline finish.
If giving a galvanized steel material a hairline
finish, the ridges of the hairlines become deformed and
the hairlines are crushed, so a good hairline appearance
cannot be obtained. There are also parts where the base
metal is exposed. Further, the problem arises of clogging
of the hairline finishing polishing belt. Further, there
is the problem that if leaving the material in the
atmosphere after giving it the hairline finish, white
rust is formed and the hairline appearance ends up being
lost.
A good hairline appearance cannot be obtained in
this way probably due to the fact that the galvanized
layer has a hardness of about 50 Hv, i.e., is soft.
Therefore, the inventors focused on galvannealed layers
including hard phases and found that if giving these a
hairline finish, a good hairline appearance could be
obtained. As galvannealed layers including hard phases,
they learned that a galvannealed layer containing Al and
Mg which contains Zn and Al binary eutectic and Zn, Al,
and ZnMg alloy ternary eutectic hard layers is suitable.
The plating layer should be one comprising, as
ingredients, by mass%, Al: 1.0 to 60%, Mg: 0.1 to 10%,
and the balance of Zn and unavoidable impurities, further
selectively including, as needed, Si: 0.001 to 3.0% to
improve the corrosion resistance and one or both of Ti:
0.0001 to 0.1% and B: 0.0001 to 0.1% to improve the
appearance.
The reasons for limitation of the ingredients of the
galvannealed layer will be explained next.
Al forms a hard phase Zn/Al binary eutectic and
Zn/Al/Zn2Mg ternary eutectic in the plating layer and acts
to improve the corrosion resistance of the plating layer
and suppress the formation of dross in the plating bath.
If Al is less than 1.0%, the volume fraction of the
binary eutectic and ternary eutectic forming the hard
phase becomes insufficient, a good hairline appearance
cannot be obtained by a hairline finish, and the plated
steel material becomes inferior in corrosion resistance.
On the other hand, if Al is over 60%, the plated surface
is formed with whisker-shaped relief shapes, a plating
layer with a uniform appearance cannot be obtained, the
effect of improvement of the corrosion resistance becomes
saturated, and simultaneously the sacrificial corrosion
action on the base iron is lost so the corrosion
resistance of flawed parts deteriorates. Therefore, the
Al content was made 1.0 to 60%.
Mg is an ingredient required for forming the ternary
eutectic and has the effect of forming corrosion products
on the plated surface to improve the corrosion resistance
of the plated steel material. If Mg is less than 0.1%,
the volume fraction of the ternary eutectic becomes
insufficient, a good hairline appearance cannot be
obtained by a hairline finish, and the corrosion products
required for improving the corrosion resistance cannot be
formed. On the other hand, if Mg exceeds 10%, the plating
bath proceeds to oxidize due to contact with the air,
black oxides (dross) are produced making treatment
difficult, and the effect of improvement of the corrosion
resistance becomes saturated. Therefore, the Mg content
was made 0.1 to 10%.
Si is added as needed to improve the corrosion
resistance and improve the plating adhesion. If the
amount; of addition is less than 0.001%, these effects are
not obtained, while if over 3.0%, these effects become
saturated and conversely the production of dross
increases, so the amount of addition of Si was made 0.001
to 3.0%.
Ti is an ingredient added as needed for forming the
nuclei for precipitation of the primary crystal Al phase,
increasing the fineness of the structure, and improving
the appearance. At least 0.0001% must be added. However,
if adding over 0.1%, the solubility in the plating bath
is exceeded, Ti-Al-based precipitates grow, the plating
layer is formed with relief shapes on its surface, and
the quality of the appearance deteriorates, so Ti was
made 0.0001 to 0.1%.
B, like Ti, has the effect of improving the plating
appearance, but if less than 0.0001%, that effect cannot
be obtained, while if over 0.1%, that effect becomes
saturated, so B was made 0.0001 to 0.1%.
With a plating deposition of less than 10 g/m2, the
corrosion resistance becomes inferior, so this was made
the lower limit, while with one of more than 600 g/m2, the
uniformity of deposition of the plating layer
deteriorates and a dripping appearance results, which is
not preferred, and bending or the like easily results in
cracks in the plating layer. Therefore, 600 g/m2 was made
the upper limit.
FIG. 2(a) is a micrograph of the structure of a Znbased
alloy plating layer of the present invention, while
FIG. 2(b) is a schematic view of the structure.
As shown in FIG. 2(b), for example, the Zn-ll%Al-
3%Mg-0.2%Si high corrosion resistance Zn-based alloy
plating layer has, in its cross-sectional structure, a
structure of a [Zn/Al/Zn2Mg] ternary eutectic phase 7 in
which a [Zn/Al] binary eutectic phase 8 is mixed and in
which a [Zii2Mg single phase] 9 is present in island
shapes.
This ternary eutectic phase is comprised of a
structure of soft Zn and Al phases in which hard Zn2Mg is
dispersed. The structure as a whole features both
consistency and hardness. If giving a hairline finish to
plated steel material in which this type of phase is also
present at the surface, the plated surface is easily
peeled off from the plated surface by the polishing belt,
a beautiful hairline appearance is obtained without
deformation of the ridges of the hairlines, the polishing
belt does not become clogged, and a good hairline
appearance is obtained.
FIG. 3 is a micrograph of the cross-section of the
surface of a hairline finished high corrosion resistance
galvannealed steel material (Zn-ll%Al-3Mg-0.2Si plating,
plating deposition: 90 g/m2) after #80 emery polishing
(magnification: 1000X). As shown in FIG. 3, this has a
good appearance with no deformation of the hairline
grooves.
To give a high corrosion resistance galvannealed
steel material a hairline finish to obtain a good
hairline appearance, the plating layer is preferably
structured with a [Zn/Al] binary eutectic phase in a
volume fraction of 1 to 80 vol%, a [Zn/Al/Zn2Mg] ternary
eutectic phase in a volume fraction of 10 to 90 vol%, and
the balance of Zn, Zn2Mg alloy, Mg2Si, TiAl3, etc. The
[Zn/Al] binary eutectic phase is soft compared with the
ternary eutectic phase, but is hard compared with the Zn
and Al single phases. Therefore, the smaller the volume
fraction, the more improved the hairline finishability.
If over 90 vol%, the plating layer as a whole softens and
the hairline finishability deteriorates. Making it less
than 1 vol% is difficult engineering wise. If the volume
fraction of the ternary eutectic becomes small, the
hardness and consistency characteristics of the plating
layer deteriorate, the appearance at the time of hairline
finishing deteriorates, and the scraps easily clog the
abrasive material. Therefore, the lower limit of the
volume fraction of the ternary eutectic was made 10 vol%.
On the other hand, the upper limit is determined by the
ease of formation of the Al phase and Zn2Mg phase in the
process of solidification of the plating layer. 90 vol%
was the upper limit in engineering production. Further,
if the volume fraction of the two eutectic phases
combined falls, the overall plating layer falls in
hardness and consistency and the hairline appearance
becomes poor, so this fraction was made 50% or more.
The thickness of the plating layer suitable for
application of a hairline finish is, in terms of plating
deposition, 10 to 600 g/m2, preferably 100 to 500 g/m2. If
the plating deposition is less than 10 g/m2, since the
plating layer is thin, the corrosion resistance is
insufficient and the hairline finishing ends up exposing
the underlying steel material. If the plating deposition
is over 600 g/m2, the plating layer is too thick and a
plating layer with a uniform appearance cannot be
obtained. Further, the plating layer easily peels off.
This is also disadvantageous cost wise. Therefore, the
plating deposition was made 10 to 600 g/m2.
As the shape of the superior appearance hairlines
formed on the plated steel material, in the direction
perpendicular to the hairlines (C-direction), the surface
roughness should be a surface roughness Ra of 0.2 to 2.5
HITI, preferably 1.2 to 1.8 ^m, and the peaks per inch PPI
should be 50 to 400; in the hairline direction (Ldirection),
the surface roughness should be Ra: 0.1 to
1.2 [o,m, preferably 0.5 to 1.0 jam, and the peaks per inch
PPI should be I to 100; the Ra in the direction
perpendicular to the hairlines (C-direction) should be
1.2 times or more the Ra in the hairline direction (Ldirection)
(C-direction Ra/L-direction Ra>1.2); and the
PPI in the direction perpendicular to the hairlines (Cdirection)
should be 2 times or more the PPI in the
hairline direction (L-direction) (C-direction PPI/LdirectionPPI
2) .
If less than the limit limits of the C-direction and
L-direction surface roughnesses Ra, peaks per inch PPI,
and ratios prescribed here, the hairlines will no longer
stand out and the hairline finish treatment will become
wasted. Further, conversely, if more than the upper
limits of the C-direction and L-direction surface
roughnesses Ra and peaks per inch PPI, the hairlines will
become too coarse, beautiful hairlines will not be
obtained, the aesthetic design value of the hairlines
will be lost, and the product will lose its value.
Therefore, the present invention defines the shape
of the hairlines as above by the surface roughnesses,
peaks per .inch, and their ratios. Note that the surface
roughness Ra was measured in accordance with the method
of measurement prescribed in JIS B060 (1997) employing a
reference length of 0.8 mm. Further, the peaks per inch
PPI were measured in accordance with SAEJ911-1986 using a
measured length of 1 inch and a width 2H between positive
and negative reference levels of 50 |j.inch.
To form hairlines satisfying the requirements of the
surface roughnesses, peaks per inch, and their ratios
prescribed in the present invention, use of a #60 to #320
or so belt sander (polishing belt) for the hairline
finish is preferable.
After application of the hairline finish, the
plating layer is preferably treated by chromate treatment
or chromate-free treatment for primary rust proofing.
A galvanized steel material is susceptible to white
rust, so to prevent this, after the plating layer is
given the hairline finish, it is treated by chromate
treatment or chromate-free treatment to form a
rustproofing coated layer for primary rust proofing.
In the case of chromate treatment, a known chromate
treatment, for example, chromate treatment by a chromate
treatment solution containing chromic acid and a reaction
accelerator as main ingredients can be applied. The
amount of chromate deposition is made 1 to 200 mg/m2.
If the amount of chromate deposition is less than 1
mg/m"', a sufficient rust proofing effect cannot be
obtained. Further, if over 200 mg/m2, not only does the
hairline finish no longer stand out, but also the rust
proofing effect will end up becoming saturated and,
economically, the cost will rise.
Further, it is also possible to perform primary rust
proofing by a known chromate-free treatment (nonchromate
treatment) in the same way as a chromate treatment.
The cnromate-free treatment (nonchromate treatment)
uses a treatment solution not containing any
environmentally harmful hexavalent chrome in the
solution. For example, there are treatment solutions
containing Zr, Ti salts, treatment solutions containing
silane coupling agents, etc. Known chromate-free
treatment solutions may be used for chromate-free
treatment. In such chromate-free treatment, a chromatefree
treated layer containing Ti, Zr, P, Ce, Si, Al, Li,
and other main ingredients and not containing chromic
acid is formed. The amount of deposition is preferably 1
to 1000 mg/m2.
If the amount of deposition in the chromate-free
treatment is less than 1 mg/m2, a sufficient rust
preventing effect cannot be obtained. Further, if over
1000 mg/m2, not only does the hairline finish no longer
stand out, but also the rust preventing effect ends up
becoming saturated and, economically, the cost rises.
E'urther, if giving a galvanized steel material a
hairline finish and then leaving it in the atmosphere,
the plated surface will oxidize and blacken. If
blackening, the hairline finish will no longer stand out
and the hairline appearance will be lost. Further, the
galvanized layer will be easily damaged upon collision
with a hard object. For this reason, if forming a
transparent resin coated layer to a thickness of 0.5 to
100 |im on the hairline finished plated surface, the
blackening resistance and the defect resistance can be
improved. The transparent resin coated layer may be
formed using a conventional known organic clear coating
and a conventional known coating method. As such organic
clear coatings, specifically an acryl-based baked clear
coating, urethane-based clear coating, epoxy-based clear
coating, polyester-based clear coating, melamine alkydbased
clear coating, etc. may be mentioned. Among these,
polyester-based and acryl-based baked clear coatings are
preferably used.
As the method of coating an organic clear coating,
specifically the roll coater method, curtain coater
method, spray can method, electrostatic method, etc. may
be mentioned. Among these, the roll coater method and the
curtain coater method are preferable.
To impart blackening resistance, it is possible to
give the vicinity of the interface with the chromate and
chromate-free treated layer a layer of a deposit of one
or more of Co, Fe, Ni, Pt, and Mn in a metal state or
hydroxide state of 0.1 to 10 mg/m2. This deposited layer
should have an amount of deposition of 0.1 to 10 mg/m2,
preferably 0.5 to 3.0 mg/m2. This treatment greatly
improves the blackening resistance in a wet environment.
If the amount of deposition is less than 0.1 mg/m2, the
effect of the blackening resistance is not sufficient,
while if over 10 mg/m2, the corrosion resistance
deteriorates, so these are not preferred. The method of
imparting this treated layer is not particularly limited,
but as examples there are the above salt water solution
dipping method or spraying method, the vacuum deposition
method, etc. In the dipping method, the hairline finished
plated steel sheet is dipped in a 0.1 to 10 g/liter metal
salt aqueous solution for 0.5 to 10 seconds, then rinsed.
EXAMPLES
Below, examples will be used to explain the present
invention in detail.
Low carbon steel sheets of two different types of
thicknesses, that is, sheet thicknesses of 0.8 mm and 1.6
mm, were used as the sheets for plating.
The sheets were plated by heating, annealing, and
plating by a continuous hot dip galvanization line of a
non-oxidizing furnace type. The annealing atmosphere was
made 10% hydrogen and the remaining 90% nitrogen gas. The
dew point was made -30°C. The annealing temperature was
made 730°C and the annealing time 3 minutes. The plating
bath was comprised of, by mass%, Al: 11.0%, Mg: 3.0%, Si:
0.2%, and the balance of Zn and unavoidable impurities,
while the plating bath temperature was 450°C. The plating
deposition was adjusted by the ordinary nitrogen gas
wiping method.
After the plating, different number belt sanders
(size 100 mmx915 mm) were used to give hairline finishes
under condations of a belt speed of about 3.5/seconds and
a polishing time of 3 to 4 seconds. After this, the
surface roughness (Ra) and peaks per inch (PPI) were
investigated.
The results are shown in Table 1.
As shown in Table 1, Nos. 1, 2, and 5 were the high
corrosion resistance plated steel materials having a
beautiful hairline appearance satisfying the surface
roughnesses (Ra), peaks per inch (PPI), and their ratios
prescribed in the present invention.
As opposed to this, the #80 bead blasted No. 3 was
formed with uniform fine relief over its surface, but the
L-direction surface roughness and peaks per inch were
small, the ratios of the surface roughness and peaks per
inch were also small, and the requirements prescribed in
the present invention were not satisfied. The bead
blasting and hairline finish were clearly difficult.
No. 4 was given a hairline finish, but the belt
sander was a #600 type or too fine and therefore the
requirements for hairlines prescribed in the present
invention were not satisfied. Hairlines could not be
clearly observed in the appearance.
Further, No. 6 and No. 7 are cases with hairline
finish given. In these cases, the C-direction surface
roughness and peaks per inch were small and the ratios
were also small. In these cases as well, naturally no
hairlines were observed.
From the above test results, only the plated steel
sheets with hairline finishes satisfying the requirements
prescribed in the present invention were plated steel
sheets with beautiful hairline appearances.
Next, the inventors prepared plated steel sheets
with different compositions of plating layers then used a
80 belt sander (size 100 mmx915 mm) to give them a
hairline finish at a belt speed of about 3.5/second and a
polishing time of 3 to 4 seconds. The inventors
investigated the hairline appearance and state of
deposition of scraps at that time.
The results are shown in Table 2. Nos. 1 to 17 have
the plating compositions prescribed in the present
invention and were good in terms of hairline appearance,
clogging of sanders by scraps, and corrosion resistance.
On the other hand, Nos. 18 to 20 had platings outside the
composition prescribed by the present invention. While
they had values of surface roughness satisfying the
values prescribed in the present invention, the hairline
appearance could not be clearly observed and the sheets
were poor in terms of scrap production and corrosion
resistance. The reason, why the hairline appearance could
not be clearly observed is believed to be because of the
production of scraps and deformation of the polishing
marks etc.
Further, the inventors performed plating while
changing the volume fractions of the eutectic phases in
the plating layers and investigated the resultant
performances. The results are shown in Table 3. Nos. I to
5 had the phase structures prescribed in the present
invention and were good in all of the hairline
appearance, sander scrap clogging, and corrosion
resistance. On the other hand, Nos. 6 and 7 had platings
outside the phase structure prescribed by the present
invention and were inferior in hairline appearance and
poor in terms of production of scraps.
Further, plated steel sheets having a composition of
Zn-llAl-3Mg-0.2Si were used for chromate treatment,
chromate-free treatment, clear coating treatment, and
blackening resistance treatment. The chromate treatment
comprised coating the sheet with a chromic acid 100
g/liter solution, then drying it in a 60°C hot air furnace
for 30 seconds. The chromate-free treatment comprised
coating the sheet with a chemical comprised of zirconium
aluminum carbonate, cobalt nitrate, silica, and ammonium
phosphate, then drying in a 60°C hot air furnace for 30
seconds. Further, sheets were coated with a melamine
alkyd-based clear coating (solvent-based) and acryl-based
clear coating (aqueous dispersion based) and heated until
sheet temperatures of 220°C (melamine alkyd-based) and
150°C (acryl-based). The blackening resistance treatment
comprised dipping the sheet in a 1 g/liter Ni sulfate
aqueous solution for 3 seconds, then rinsing and drying
it, then treating it by the chromate-free treatment and
coating it by a melamine alkyd-based clear coating. The
corrosion resistance of the flat parts was evaluated by
the amount of formation of white rust after 240 hours of
a JIS Z2331 salt water spray test with "Good" indicating
1% or less formation of white rust and "Poor" indicating
10% or more. The cross-cut parts were evaluated by the
blisters after 1000 hours of a salt water spray test with
"Good" indicating less than 2 mm and "Poor" 2 mm or more.
The blackening resistance was evaluated by allowing a
treated steel material to stand in a high humidity tank
of a temperature of 60°C and a relative humidity of 85%
for seven days and comparing the color difference 8E
values before and after. The color difference 8E was
measured in accordance with JIS Z8722. A 6E of 1 or less
indicated no blackening or a good result (Good), 1 to 2
indicated slight observance or a fair result (Fair), and
larger than 2 indicated blackening observed or a poor
result (Poor).
Nos. 1 to 46 satisfy the requirements of the
blackening resistance treatment, pretreatment, and
coating prescribed by the present invention and were
excellent in corrosion resistance both at the flat parts
and the cross-cut parts. Further, Nos. 23 and 46 treated
for blackening resistance were also excellent in
blackening resistance. On the other hand, Nos. 47 to 49
were outside the requirements of the present invention
and were poor in corrosion resistance.
(Table Removed)
INDUSTRIAL APPLICABILITY
The high corrosion resistance galvanized steel
material having a hairline appearance of the present
invention is provided with a good hairline appearance and
is excellent in corrosion resistance as well, so can be
used for applications similar to the applications of
conventional stainless steel material having a hairline
appearance. Further, it can be provided at less of a
price than expensive stainless steel material.

WE CLAIM:
1. A high corrosion resistance galvannealed steel material having a hairline appearance having a plating layer with a plating deposition of 10 to 600 g/m2, containing Al : 1 to 60 mass%, Mg : 0.1 to 10 mass%, and a balance of Zn and unavoidable impurities, and having hairlines formed on the surface, said hairlines having a surface roughness Ra of 0.2 to 2.5 urn and a peaks per inch PPI of 50 to 400 in a direction perpendicular to the hairlines, having a surface roughness Ra of 0.1 to 1.2 urn and a peaks per inch PPI of 1 to 100 in the hairline direction, and having a surface roughness Ra in a direction perpendicular to the hairlines of 1.2 times or more the surface roughness Ra in the hairline direction and a PPI in a direction perpendicular to the hairlines of 2.0 times or more the PPI in the hairline direction.
2. A high corrosion resistance galvannealed steel material having a hairline appearance having a plating layer with a plating deposition of 10 to 600 g/m2, containing Al: 1 to 60 mass%, Mg: 0.1 to 10 mass%, and a balance of Zn and unavoidable impurities, and having hairlines formed on the surface, said hairlines having a peaks per inch PPI of 50 to 400 in a direction perpendicular to the hairlines, having a peaks per inch PPI of 1 to 100 in the hairline direction, and having a PPI in a direction perpendicular to the hairlines of 2.0 times or more the PPI in the hairline direction.
3. A high corrosion resistance galvannealed steel material having a hairline appearance having a plating layer with a plating deposition of 10 to 600 g/m2, containing Al: 1 to 60 mass%, Mg: 0.1 to 10 mass%, and a balance of Zn and unavoidable impurities, and having hairlines formed on the surface, said hairlines having a surface roughness Ra of 0.1 to 2.5 µm and a peaks per inch PPI of 50 to 400 in a direction perpendicular to the hairlines, having a surface roughness Ra of 0.1 to 1.2 µm and a peaks per inch PPI of 1 to 100 in the hairline direction, and having a surface roughness Ra in a direction perpendicular to the hairlines of 1.2 times or more the surface roughness Ra in the hairline direction and a PPI in a direction perpendicular to the hairlines of 2.0 times or more the PPI in the hairline direction.
4. A high corrosion resistance galvannealed steel material having a hairline appearance as claimed in any one of claims 1 to 3, wherein the plating layer further contains Si in an amount of 0.001 to 3 mass%.
5. A high corrosion resistance galvannealed steel material having a hairline appearance as claimed in any one of claims 1 to 4, wherein the plating layer further contains one or two of Ti in an amount of 0.0001 to 0.1 mass% and B in an amount of 0.0001 to 0.1 mass%.
6. A high corrosion resistance galvannealed steel material having a hairline
appearance as claimed in any one of claims 1 to 5, wherein plating layer is comprised of a
Zn and Al binary eutectic in a volume ratio of 1 to 80 vol% and a Zn, Al, and ZnMg alloy
ternary eutectic in a volume ratio of 10 to 90 vol%, with the total of the two being at least
50%.
7. A high corrosion resistance galvannealed steel material having a hairline
appearance as claimed in any one of claims 1 to 6, wherein plating layer has a chromate
treated layer of 1 to 1000 mg/m on its surface.
8. A high corrosion resistance galvannealed steel material having a hairline appearance as claimed in any one of claims 1 to 6, wherein plating layer surface has a chromate-free treated layer of 1 to 200 mg/m not containing any chrome on its surface.
9. A high corrosion resistance galvannealed steel material having a hairline appearance as claimed in any one of claims 1 to 8, comprising a transparent resin coating layer of a thickness of 0.5 to 100 µm on its surface.
10. A high corrosion resistance galvannealed steel material having a hairline appearance as claimed in any one of claims 1 to 9, wherein the vicinity of the interface between the plating layer surface and chromate-free treated layer not containing any chrome has a layer of a deposit of one or more of Co, Fe, Ni, Pt, and Mn in a metal state or hydroxide state of 0.1 to 10 mg/m2 and the blackening resistance in a wet environment is excellent.

Documents:

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Patent Number

272461

Indian Patent Application Number

2302/DELNP/2007

PG Journal Number

15/2016

Publication Date

08-Apr-2016

Grant Date

04-Apr-2016

Date of Filing

23-Mar-2007

Name of Patentee

NIPPON STEEL & SUMITOMO METAL CORPORATION

Applicant Address

6-3, OTEMACHI 2-CHOME, CHIYODA-KU, TOKYO 100-8071, JAPAN.

Inventors:

#	Inventor's Name	Inventor's Address
1	AKIRA TAKAHASHI	C/O NIPPON STEEL CORPORATION KIMITSU WORKS, 1, KIMITSU, KIMITSU, KIMITSU-SHI, CHIBA 299-1141, JAPAN.
2	YOSHIO KIMATA	C/O NIPPON STEEL CORPORATION KIMITSU WORKS, 1, KIMITSU, KIMITSU, KIMITSU-SHI, CHIBA 299-1141, JAPAN.
3	SATORU TANAKA	C/O C/O NIPPON STEEL CORPORATION, 6-3, OTEMACHI 2-CHOME, CHIYODA-KU, TOKYO 100-8071, JAPAN

PCT International Classification Number

C23C 2/06

PCT International Application Number

PCT/JP2005/006975

PCT International Filing date

2005-04-04

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	2004-282443	2004-09-28	Japan
2	2005-031542	2005-02-08	Japan