Title of Invention

CASTING MOULD PRODUCED FROM AN AGE-HARDENABLE COPPER ALLOY

Abstract

The invention concerns an age-hardenable copper alloy of - expressed in percentage by weight respectively - 0.4% to maximum 2% cobalt, which can be partially replaced by nickel, 0.1% to 0.5% beryllium, 0.03% to 0.5% zirconium as desired, 0.005 % to 0.1 % magnesium and, if necessary, maximum 0.15% of at least one element from the group consisting of niobium, manganese, tantalum, vanadium, titanium, chromium, cerium and hafnium. The rest is made up of copper, including impurities associated with the production and the usual processing alloys. This copper alloy serves as material for the production of casting moulds, especially for the casing of continuous casting and rolling as component of a double roll casting plant.

Full Text

The invention concerns a casting mould produced from an age-hardenable copper alloy. The universal goal, especially of the steel industry, is to cast wrought products as closely as possible to final dimensions, in order to economise on the hot and/or cold forming steps, has lead since about 1980 to a series of developments, for example in one- and two-roll continuous casting method. During these casting methods, very high surface temperatures arise on the water-cooled cylinders or rolls for the casting of alloy steels, nickel, copper as well as alloys, which can be hot rolled only with difficulty, in the casting-in zone of the melt. These lie, for example for the casting of an alloy steel close to the final dimensions, at 350°C to 450°C, in which the cast rolling casing is of a CuCrZr-material with an electrical conductivity of 48 Sm/mm2 and caloric conductivity of approximately 320 W/mK. Materials based on CuCrZr were previously used primarily for thermally high demanding continuously cast ingot moulds and casting wheels. The surface temperature is reduced to about 150°C to 200°C just before the casting-in zone for these materials by the cooling of the casting rollers cyclically for each rotation. On the other hand, it remains to a large extent constant at about 30°C to 40°C on the cooled rear side of the casting rollers during the rotation. The temperature gradient between the surface and the rear side in combination with the cyclical alteration of the surface temperature of the casting rollers cause thermal stresses in the surface area of the casing material. According to investigations of the fatigue behaviour on the previously used CuCrZr-material at different temperatures with a strain amplitude of ± 0.3% and a frequency of 0.5 Hertz - these parameters correspond approximately to the rotational speed of the casting rollers of 30 RPM -, under most favourable conditions a life of 3000 cycles can be expected before the formation of cracks for a maximum surface temperature, for example, of 400 °C, corresponding to a wall thickness of 25 mm above the water-cooling. Therefore, the casting rollers have to be reworked already after a relatively short operation time of about 100 minutes, for the purpose of remedying the surface cracks. Moreover, the life between the reworks is essentially dependent, among others, on the effectiveness of the lubricant/stripping agent at the casting surfaces, the constructional and process-required cooling as well as the casting rate. The casting machine must be stopped and the casting cycle interrupted for changing the casting rollers. A further disadvantage of the field-proven CuCrZr ingot mould material is the relatively low hardness of about 110 HBW to 130 HBW. But it is not possible to avoid the splashes from reaching the roller surface before the casting-in region in the case of a one- or two-roller continuous casting process. Then, the solidified steel particles are pressed into the relatively soft surfaces of the casting rollers, whereby the surface quality of the cast strips is considerably affected from about 1.5 mm to 4 mm thickness. Also, the lower electrical conductivity of a standard CuNiBe-alloy with an addition of up to 1 % niobium leads to a higher surface temperature in comparison to a CuCrZr-alloy. Since the electrical conductivity is approximately proportional to the caloric conductivity, the surface temperature in the casing of a casting roller made from CuNiBe-alloy is raised to about 540 °C in comparison to a casting roller with a casing of CuCrZr with a maximum temperature of 400 °C at the surface and 30 °C on the rear side. Although ternary CuNiBe- or CuCoBe-alloys have basically a Brinell hardness of above 200 HBW. however the electrical conductivity of the standard wrought products out of these materials, like for example rods for the production of resistance welding electrodes or plates and strips for the production of springs or lead frames, reach at the most values lying in the range of 26 Sm/mm2 to about 32 Sm/mm2. Under optimum conditions, only a surface temperature of about 585 °C would be attained on the casing of a casting roller with these standard materials. Also, there are no indications that conductivity values of > 38 Sm/mm2 can be attained in combination with a minimum hardness of 200 HBW with the targeted selection of the alloy components for the CuCoBeZr- or CuNiBeZr-alloys, as fundamentally known from the US-patent 4,179,314. Further, the use of an age-hardenable copper alloy consisting of 1.0 % to 2.6 % nickel that can be partially or totally replaced by cobalt, 0.1 % to 0.45 % beryllium, 0.05 % to 0.25 % zirconium as desired and, if necessary, maximum 0.15 % of at least one element from the group consisting of niobium, tantalum, vanadium, titanium, chromium, cerium and hafnium, the rest copper, including impurities associated with the production and the usual processing alloys, with a Brinell hardness of minimum 200 HBW and an electrical conductivity above 38 Sm/mm2 as material for the production of casting rollers and casting wheels is considered within the scope of EP 0 548636 Bl, as per the state-of-art technology. Alloys with these compositions, like for example the alloys CuCo2Be0.5 or CuNi2Be0.5, have disadvantages of hot formabiliry due to the relatively high alloying element contents. However, high degree of hot forming are necessary to achieve a fine-grained product with a grain size structure with a grain size of several millimetres. Till now, sufficiently large cast ingots 01 desired quality coula be produced at very high expenditure, especially for large sized casting rollers; however hardly any industrial forming equipments are available to carry out a sufficiently high hot kneading for the re-crystallisation of the cast structure to a fine-grained structure with reasonable expenditure. The invention is based upon the task-starting from the state-of-the-art technology-to produce an age-hardenable copper alloy as material for the production of cast moulds, which is insensitive to changing temperature requirements even at high casting rates or has a high fatigue resistance at the working temperature for a mould. This task is solved by an age-hardenable copper alloy according to the instant invention. Accordingly, the present invention provides a casting mould produced from an age-hardenable copper alloy made of expressed, in each case, in % by weight 0.4% to 2.0% cobalt, which can be partly replaced by up to 0.6% nickel, 0.1% to 0.5% beryllium, 0.03% to 0.5% zirconium, 0.005% to 0.1% magnesium and optionally a maximum of 0.15% of at least one element from the group comprising niobium, manganese, tantalum, vanadium, titanium, chromium, cerium and hafnium, the remainder copper comprising production-related impurity and conventional processing additives, wherein the casting mould is produced within a time period of 4 to 32 hours by the processing steps of casting, hot working, solution annealing at 850°C to 980°C, cold working up to 30% and age-hardening at 400°C to 550°C and in an age-hardened state of the copper alloy, the casting mould has an average grain size of 30 urn to 500 urn to ASTM E 112, a hardness of at least 185 HBW, a conductivity between 30 and 36 Sm/mm2, a 0.2% yield point of at least 450 MPa and an elongation at break of at least 12%. The instant invention provides for an age-hardenable copper alloy comprising of 0.4 % to maximum 2 % by weight of cobalt, which can be partially replaced by nickel, 0.1% to 0.5 % by weight of beryllium, 0.03 % to 0.5% by weight of zirconium, 0.005% to 0.1% by weight of magnesium and, if necessary, maximum 0.15 % by weight of at least one element from the group consisting of niobium, manganese, tantalum, vanadium, titanium, chromium, cerium and hafnium, the rest being copper and the usual impurities associated with the production and the processing of the alloys, as a material for the production of cast moulds. On the one hand, a still sufficient hardenability of the material is ensured for the attainment of a higher strength, hardness and conductivity by the use of a CuCoBeZr(Mg)-alloy with selectively low graded Co- and Be-content. On the other hand, only low degrees of hot forming are required for the complete re-crystallisation of the cast structure and conversion to a fine-grained structure with sufficient plasticity. Thanks to this type of material produced for a mould, it is possible to step up the casting rate to more than double the conventional rate. Besides, a visibly improved surface quality of the cast strip is achieved. Also, a considerably longer life of the mould is ensured. By moulds are understood not only stationary moulds, like e.g. plate- or tubular moulds, but also revolving ingot moulds, like, for example, casting rollers. A further improvement of the mechanical properties of the mould, especially an increase of the tensile strength, can be achieved advantageously by the copper alloy containing 0.03 % to 0.35 % zirconium and 0.005 % to 0.05 % magnesium. According to a further embodiment, the copper alloy contains a proportion of 0.3 % zirconium. It is further advantageous if the ratio of cobalt to beryllium lies between 2 and 15 in the copper alloy. Especially, this ratio of cobalt to beryllium amounts to 2.2 to 5. As per the invention it is permissible to have copper alloy containing up to 0.6 % nickel, besides cobalt. Further improvements of the mechanical properties of the mould can be achieved if, the copper alloy contains up to maximum 0.15% of at least one element from the group comprising niobium, manganese, tantalum, vanadium, titanium, chromium, cerium and hafnium. The mould is produced advantageously through the processing steps of casting, hot forming, solution annealing at 850° C to 980° C, cold forming up to 30 % as well as hardening at 400 °C to 550 °C within a period of 2 to 32 h, whereby it has a maximum average grain size of 1.5 mm as per ASTM E 112, a hardness of minimum 170 HBW and an electrical conductivity of minimum 26 Sm/mm2. It is especially advantageous if the mould, exhibits in the hardened condition an average grain size of 30 μm to 500 μm as per ASTM E 112, a hardness of minimum 185 HBW, a conductivity between 30 and 36 Sm/mm2, a 0.2 % proof stress of minimum 450 Mpa and a breaking elongation of minimum 12 %. The copper alloy as per the invention is suitable, especially for the production of the casing of casting rollers of a double roll casting plant, which are subject to a changing temperature requirement under high rolling pressure for the casting close to the final dimensions of strips made from nonferrous metals, especially strips out of aluminium or aluminium alloys. In this case, each casing can be provided with a diathermancy reducing coating. Furthermore, this can improve the product quality of the strip, cast out of a nonferrous metal, however especially out of aluminium or an aluminium alloy. The coating, depending on the operational behaviour of the casing made from a copper alloy with especially an aluminium strip, is formed as follows. An adhesion layer is formed at the beginning of a casting and rolling process from the combination of copper with aluminium on the surface of the casing, from which aluminium penetrates into the copper surface during the further course of the casting process and thereby forms a stable robust diffusion layer, whose thickness and property are essentially determined by the casting speed and cooling conditions. This improves the surface quality of the aluminium band and consequently the product quality is unambiguously improved. The invention is explained in detail below. Based on the seven alloys (alloys A to G) and three alloys for comparison (H to J), it is shown how critical the composition is to achieve the combination of properties strived for. All alloys were molten in a crucible furnace and cast into round ingots of same form. The composition in percentage by weight is given in the following Table 1. The addition of magnesium serves for the pre- deoxidation of the melt and the zirconium addition operates positively on the hot-plasticity. The alloys were subsequently pressed to flat bars with a low pressing ratio (= cross-section of the ingots / cross-section of the pressing bar) of 5.6:1 on an extruder at 950 °C. Thereafter, the alloys were subject to a minimum of 30 minute solution annealing above 850 °C followed by a water quenching and subsequently hardened for 2 to 32 h in the temperature range between 400 °C and 550 °C. The combinations of properties shown in the Table 2 below were achieved. As can be seen from the combination of properties, the alloys as per the invention achieve, especially for the production of a casing of a cast roller, the re-crystallised fine-grained structure with the relevant desired high breaking elongation. The reference alloys H to J have a grain size of over 1.5 mm, because of which the plasticity of the material is reduced. An additional increase in strength can be achieved by cold forming before hardening. In the following Table 3, combination of properties are again given for the alloys A to J, which are attained by solution annealing of the pressed material for minimum 30 minutes at above 850 °C followed by water quenching, 10 % to 15 % cold rolling (cross sectional reduction) and finally hardening for 2 to 32 hours in the temperature range between 400 "C and 550 °C. The alloys A to G as per the invention once again show higher breakage elongation and a grain size below 0.5 mm, while the reference alloys H to J have a coarse grain with a grain size above 1.5 mm and lower breakage elongation values. Consequently, these copper alloys have definite processing advantages for the production of casings, especially for larger cast rollers of double roll casting plants, whereby it is possible to produce a fine-grained end product with optimum basic properties for the range of application. WE CLAIM : 1. Casting mould produced from an age-hardenable copper alloy made of expressed, in each case, in % by weight 0.4% to 2.0% cobalt, which can be partly replaced by up to 0.6% nickel, 0.1% to 0.5% beryllium, 0.03% to 0.5% zirconium, 0.005% to 0.1% magnesium and optionally a maximum of 0.15% of atleast one element from the group comprising niobium manganese tentalum vanadium titanium chromium, cerium and hafnium, the remainder copper comprising production-related impurity and conventional processing additives, wherein the casting mould is produced within a time period of 4 to 32 hours by the processing steps of casting, hot working, solution annealing at 850°C to 980°C, cold working up to 30% and age-hardening at 400°C to 550°C and in an age-hardened state of the copper alloy, the casting mould has an average grain size of 30 urn to 500 urn to ASTM E 112, a hardness of at least 185 HBW, a conductivity between 30 and 36 Sm/mm2, a 0.2% yield point of at least 450 MPa and an elongation at break of at least 12%. 2. Casting mould as claimed in claim 1, wherein the copper alloy contains 0.03% to 0.35%/zirconium)and 0.005% to 0.05% magnesium. 3. Casting mould as claimed in either of claims 1 or 2, the copper alloy containing less than 1.0% cobalt, 0.15% to 0.3% beryllium and 0.15% to 0.3% zirconium. 4. Casting mould as claimed in any one of claims 1 to 3, wherein the ratio of cobalt to beryllium in the copper alloy is between 2 and 15. 5. Casting mould as claimed in claim 4, wherein the ratio of cobalt to beryllium in the copper alloy is between 2.2 and 5. 6. Casting mould as claimed in at least one on claims 1 to 5, wherein the copper alloy contains up to a maximum of 0.15% of at least one of the elements from the group comprising niobium, manganese tantalum, vanadium, titanium, chromium, cerium and hafnium. 7. Casting mould, substantially as herein described. The invention concerns an age-hardenable copper alloy of - expressed in percentage by weight respectively - 0.4% to maximum 2% cobalt, which can be partially replaced by nickel, 0.1% to 0.5% beryllium, 0.03% to 0.5% zirconium as desired, 0.005 % to 0.1 % magnesium and, if necessary, maximum 0.15% of at least one element from the group consisting of niobium, manganese, tantalum, vanadium, titanium, chromium, cerium and hafnium. The rest is made up of copper, including impurities associated with the production and the usual processing alloys. This copper alloy serves as material for the production of casting moulds, especially for the casing of continuous casting and rolling as component of a double roll casting plant.

Documents:

604-CAL-2002-CORRESPONDENCE.pdf

604-CAL-2002-FORM 27.pdf

604-cal-2002-granted-abstract.pdf

604-cal-2002-granted-claims.pdf

604-cal-2002-granted-correspondence.pdf

604-cal-2002-granted-description (complete).pdf

604-cal-2002-granted-examination report.pdf

604-cal-2002-granted-form 1.pdf

604-cal-2002-granted-form 18.pdf

604-cal-2002-granted-form 2.pdf

604-cal-2002-granted-form 3.pdf

604-cal-2002-granted-form 5.pdf

604-cal-2002-granted-gpa.pdf

604-cal-2002-granted-priority document.pdf

604-cal-2002-granted-reply to examination report.pdf

604-cal-2002-granted-specification.pdf

604-cal-2002-granted-translated copy of priority document.pdf