Title of Invention

"A SOFT TINNED BLACK PLATE AND PRODUCTION METHOD FOR THE SAME"

Abstract

Soft blackplates for tinning comprise (wt.%) up to 0.006 C, 0.10-0.20 Mn, 0.025-0.075 Al, up to 0.03 Si, 0.03-0.08 Ti, up to 0.015 P, up to 0.015 S, up to 0.003 N, up to 0.004 O, and the balance Fe and other inevitable impurities. The method for producing the soft blackplates involves steelmaking, continuous casting, hot rolling, combination of pickling and cold tandem rolling, continuous annealing, and temper rolling. The main process parameters in the method are as follows: slab delivering temperature is between 1190 deg. C and 1250 deg. C, final rolling temperature is between 880 deg. C and 920 deg. C, coiling temperature is between 550 deg. C and 630 deg. C, deformation of cold rolling is 82-92%, annealing temperature is 720-770 deg. C, holding time is 25-50 seconds, temper elongation of T-ICA is 0.8-1.8%, temper elongation of .0 T-2CA is 1.8-3.0%.

Full Text

Soft Blackplate for Tinning and Production Method For the Same Technical Field The present invention relates to a soft blackplate for tinning and its manufacture method, in particular D relates to a soft blackplate for tinning having a hardness FIR 30T of 49±3 (hereinafter referred to as T-1CA) and 53±3 (hereinafter called T-2CA) respectively, and their manufacture method. This soft blackplate for tinning are prepared using a method of continuously annealing Ti -IF steel, mainly used in production of a bucket of flower baskets with expanded diameter, a can-cup with complicated deformation and a can produced by punch deformation. Background In accordance with Japanese Industrial Standard JIS G 3303, the range of hardness HR 30T of tinDplating steel plate of various tempering grades is shown in Tab.l, wherein grades T-l to T-3 are for soft blackplate for tinning, while grades T-4 to T-6 are for hard plates . Table 1 Hardness range of various grades of plates for tinning (Table Removed)In the prior art, tin-plated steel plate is produced mainly using low-carbon aluminum killed-steel. Japanese Parent No. 8073943 issued to Japan Steel Pipe Co. Ltd on March 19,1996 employs low-carbon aluminum killed steel for production of soft black plate for tinning with HR 30T hardness of less than or equal to 54-60, which is the HR 30T hardness of grade T-3, It comprises chemical components as follows: 0.050%30n/sDand aged for more than 30 seconds When producing tin-plated plate using low-carbon aluminum killed steel, significant aging takes place. After aging, product hardness will increase, while subsequent processing performance will become poor, and defects such as cracking, slip-line, cross-hatch, bending, cording in surface will readily occur under conditions of deep punching, large expanded diameter, great deformation such as serious bending. Moreover, the unavoidable aging problem of low-carbon steel leads to the fact that tinplating plate tends to be wrinkled and corded during bending and produce slip-lines after punching or drawing deformation, thus difficult to satisfy user's requirement. Further, low-carbon aluminum killed steel is not suitable to production of very soft tinplating plate. With development of production technique of IF steel, the developed countries abroad have earlier begun to use IF steel incorporated with Nb in large-batch production of tin-plated steel plate. Be cause of inherent good shapeable property and aging resistance, tin-plated IF steel product have shown strong competitive power in market. JP D D719192 (Japan Steel Pipe Co. Ltd) published in August 1,1995 discloses production of soft black plate for tinning having the following composition: C employs Nb-IF steel and has specific requirement with respect to Nb content. Because Nb-IF steel is very sensitive to processing parameters, especially to parameters of hot-rolling, so the product properties are not stable and not uniform. Moreover, its re-crystallization temperature is high, so its annealing temperature is required to be high as well., In the production of this product, larger amount of transition coils and longer transition time are required. In particular, within continuously annealing furnace, curve easily occurs and even strip brokening. As a result, performance of running continuous strips poor. Further due to large heat energy consumption and high price of niobium as an alloy element, production cost is relatively higher. In addition, Nb-IF steel has poor plasticity. Although its anisotropy is not large, its overall mechanical property is poorer than Ti-IF steel. Finally, during mining and smelting, Nb shows radio D activity to a certain extent, so there exists dispute as to whether it is harmful to human body for tin-plated plate incorporated with Nb to be mainly used in food industry. Meanwhile, although said patent discloses that the coiling of hot-rolling is carried out at 600-800 D . This coiling temperature especially upper limit (800D) is too high to be practiced. The range of coiling temperature claimed in this patent is obviously unreasonable, because when the coiling is performed near 800D, steel plate is seriously oxidized. Even above 630D, oxidization scale obviously thickens, which not only affects picking speed in subsequent procedures, but also affects surface quality of final product. In addition, said patent discloses that the annealing is performed at 670-800D. However, because Nb-IF steel is used to produce soft blackplate for tinning in said patent, when annealing at a temperature near 670 D within the annealing temperature range given in said patentnfor example, 670-740DD, it is difficult for steel plate to accomplish re-crystallization at a regular line speed. That is, it is impossible to produce an accepted soft blackplate for tinning. Thus, the annealing temperature range claimed in said patent is obviously unreasonable. Disclosure of Invention The object of the present invention is to provide T-1CA and T-2CA soft blackplate for tinning, produced by continuously-annealing using Ti-IF steel. For said purpose, the present invention provides T-1CA and T-2CA soft blackplate for tinning having chemical components in weight percentages as follows: C Al: 0.025-0.075%, preferably Al: 0.030-0.060% SiSO.03%, Ti:0.03-0.08%, preferably Ti:0.05-0.07% P the rest is iron and some unavoidable impurity elements. Functions and descriptions of main elements of the present invention are described as follows. C content With the increase of C content, hardness of soft blackplate for tinning increases, while its plasticity decreases on the other hand. In order to stably control hardness FIR 30T to lower than 56 and to ensure shapeable property of material, the present invention requires C content to be The preferable C content is ≤0.004% Mn content: 0.10-0.20% Mn is a main reinforcement element for the soft blackplate for tinning. The higher its content, the higher the hardness of product. But the price of Mn is relatively expensive. In order to reduce cost , on the premise of satisfactory properties, the smaller its amount, the more economical and feasible it is. When its content is controlled as lower than 0.20%, for T-2CA soft blackplate for tinning which requires a higher hardness, the requirement may be satisfied via enhancing temper-rolling elongation conveniently and economically. But when its content is lower them 0.10%, nature of the material become too soft. On the other hand, there is a certain amount of Mn in steel itself. So, if requiring Mn content less than 0.10%, Mn content in steel must be reduced, resulting in a great increase of the cost. The present invention, therefore, limits Mn content to be within the range of 0.10-0.20%. Ti content: 0.03-0.08% Ti is mainly used to fix free C in steel to form TiC, and Ti is favorable to enhancing aging resistance of material, especially its punching shapeable property. Moreover, Tic also has a function of dispersion reinforcement to a certain extent, thus resulting in increase of strength and hardness of the material. The price of Ti, however, is expensive (even though much lower than Nb), and thus its content directly affect manufacture cost. Therefore, its content must be strictly under control. In the present invention, it is enough for Ti content to be controlled lower than 0.08% for satisfying requirement. But when its content is lower than 0.03%, it is impossible to fix all free C and small amount of N in steel. The present invention, therefore , requires Ti content to be within the range of 0.03-0.08%, preferably 0.05-0.07%. Al content: 0.025-0.075% Al is a killing element, also a strong nitride-forming element, mainly used to fix N atom, favorable to increasing the aging resistance of material. In addition, Al is also an indispensable deoxidizing agent during steel smelting, If its content is lower than 0.025%, requirement on quality cannot be met, and if higher than 0.075, not only the cost is high, but also crystal grain growth of re-crystallization in the annealing will be suppressed. The present invention, there fore, requires Al content to be 0.025-0.075%, preferably 0.030-0.060% Si content: Although Si has a certain reinforcement function, but concomitantly impair erosion resistance, so the lower its content, the better the effect of present invention is. Therefore, it requires Si content below 0.03%. When Si content exceeds 0.03%, erosion resistance is significantly deteriorated . Content of Other elements: P≤0.015%, S≤0.015%,N≤0.003%, O≤0.004% Element P, S, N and O are detrimental impurity elements and should be strictly under control. The lower contents of these elements, the better of the product of current invention. Otherwise, mechanical properties and erosion resistance of soft blackplate for tinning will be affected. Provided that their contents are within the limit ranges of the present invention, soft blackplate for tinning satisfying requirement can be produced. T-1CA and T-2CA soft tinning plate are produced using a process comprising the following steps: smelting-continuously casting→hot-rolling→pickling and cold-rolling→ continuously armealing-»temper-rolling→tinning. Other process can also be employed, comprising steps of: smelting→continuously casting →hot-rolling→pickling→continuously cold-rolling→continuously annealing→temper-rolling→tinning; or a process comprising steps of smelting-continuously casting→hot-rolling→pickling→ multiple reversible cold-rolling→continuously annealing-→temper-rolling→tinning. The key points of main procedures are described as follows. Steel smelting Molten steel is RH refined, and vacuum degassed, concomitantly taking corresponding measures to control impurities. Finally, a continuous cast slab is obtained through conventional continuous cast procedure, and followed by hot-rolling. Hot-rolling: In the hot-rolling step of the present invention, the temperature for heating the slab (i.e. the tapping temperature) is 1220±30n, and the final temperature of the hot-rolling is 900±20. It is proved in theory and production practice that when the final temperature is higher than 920 D, the surface of steel strip is oxidized seriously, leading to a poor surface quality. On the other hand, if lower than 880, the hot-rolling steel strip tends to give a duplex grain structure when two phases formed inside the strip during rolling, and leading to non-uniform structure property of final product. When the final temperature of hot-rolling is controlled at 900 ±20 , surface oxidation of steel strip is alleviated and duplex grain structure does not occur in steel strip, leading to a uniform structure property of final product. The final temperature of hot-rolling is preferably controlled at 885-915 D so as to give a more uniform properties and a better surface quality. The cooling temperature of hot-rolling of the present invention is controlled at 590±40. Increase of the coiling temperature may reduce hardness of hot-rolling substrate plate, and consequently lower hardness of final product and enhance the shapeable property of final product. However, when the coiling temperature is greater than 630 , the oxidization scale on surface of steel strip tends to thicken easily, thereby resulting in a difficult pickling step, and impacting surface quality of the product. When the coiling temperature is lower than 550, crystal grains of hot-rolling intermediate product is too fine, structure and property of final product is affected thereby. It also results in a final product with fine crystal grains, increased strength and hardness, and a poor plasticity. So for T-1CA and T-2CA soft tinned plate of current invention produced by continuously annealing, if the coiling temperature of hot-rolling is controlled at 590±40, the amount of oxidization scale on surface of steel strip after the coiling procedure is small, pickling is more easy to perform, and surface quality of final product is good. The coiling temperature of hot-rolling is preferably controlled at 570-610 so as to obtain a good plasticity and better surface quality. Pickling and cold-rolling: Pickling and cold-rolling combination line can be used, or pickling is performed first, and then continuously cold-rolling or multiple reversible cold-rolling is performed. But it is preferably to use the pickling and cold-rolling combination line so as to increase production efficiency. During pickling procedure, line speed should be regulated according to the pickling capacity of the line to ensure a good pickling result. When the cold-rolling is carried out continuously using five stands. Total reduction ratio of cold-rolling is 82-92%. Cold-rolling reduction ratio will affect mechanical properties of strip material Moreover, an appropriate cold-rolling reduction ratio is favorable to guarantee precise dimension of hard material and control of strip shape. A too small reduction ratio leads to a poor shapeable property of strip material, while a too large reduction ratio leads to an increase of consumption in the cold-rolling procedure and a poor strip shape of hard strip material, influencing stability of continuous strip running at a high speed during subsequent procedure of continuous anneal. Continuous annealing: The present invention uses a continuous anneal to produce T-1CA and T-2CA soft tinned plate with an annealing temperature of 720-770 n and a holding time of 25-50s. A preferable annealing temperature is 735-765 . Although a soft blackplate for tinning can also be produced employing a cover anneal, mechanical property of the head, the middle and tail parts of a large coil of tin-plated product produced via a cover anneal is non-uniform, and the strip shape and surface quality of the product is far inferior to the soft blackplate for tinning produced by continuously annealing. The present invention prepares T-1CA and T-2CA soft tinned plate via a continuous anneal using Ti-IF steel, the mechanical properties of the product thus obtained are uniform, and surface quality is good. The product can well meet user requirement, it therefore has a strong market competitive power. When the annealing temperature is higher than 770 DD steel strip tends to become curved and even broken in annealing furnace in case steel strip is wide and thin due to soft nature of strip steel. At the same time, energy consumption also increases. When the annealing temperature is lower than 720 D, under conditions of normal continuous anneal line speed, it is difficult to guarantee accomplishment of re-crystallization of steel strip, and hardness of product is increased and shapeable property of product becomes poor. According to the present invention, a soft blackplate for tinning is prepared by continuously-annealing using Ti-IF steel at a lower anneal temperature as compared with continuous annealing of Nb-IF steel, ( according to the result of simulation annealing tests, none but the anneal temperature of Ni-IF steel is 750-800D sufficient re-crystallization can be guaranteed). Therefore, in arrangement of production, the amount of transition coil used may be decreased, and time for increasing and lowering the temperature may be shortened so as to raise production efficiency and to reduce production cost. In addition, the probability of curving and brokening of steel strip in annealing furnace is greatly reduced due to drop of temperature. Holding time and annealing temperature interact each other. Increase of annealing temperature facilitates to shorten the holding time. But the holding tine can not be shorter than 25s, otherwise grain growth in re-crystallization is not sufficient and results in a material too hard. At the same time, in case the line speed is a little higher, steel strip tends to run off track. On the other hand, the holding time cannot last too long. If longer than 50s, production efficiency is decreased due to a too low line speed of continuous anneal , and crystal grains grow too larger, resulting in a material with soft nature. Further, the steel strip tends to curve and even broken in annealing furnace . Temper-rolling: After accomplishment of re-crystallization of Ti-IF steel, the amount of temper-rolling deformation greatly impacts property, nature and quality of the material. With increase of amount of deformation, strength and hardness obviously enhance. For T-1CA soft tinned plate produced by continuously annealing according to the present invention, temper-rolling is performed with two stands after annealing. Temper-rolling elongation is controlled at 0.8-1.8%. For T-2CA tin-plating soft plate, temper-rolling elongation is controlled at 1.8-3.0%. The range of temper-rolling elongation of T-1CA and T-2CA mentioned above may be adjusted appropriately according to the thickness of product. Smaller temper-rolling elongation is adopted for thinner steel strip; and larger temper-rolling elongation for thicker steel strip. Tinning: T-1CA and T-2CA soft tinned plate prepared by continuously annealing according to the present invention can be plated with tin with conventional tinning technology for ordinary tinned plates. The tinned soft steel strip having the chemical components of present invention, which is produced with Ti-IF steel according to the present invention, has no aging problem, and is not sensitive to the processing parameters of hot-rolling as well. The re-crystallization temperature of soft blackplate for tinning produced with Ti-IF steel according to the present invention is lower than that prouced with Nb-IF, leading to a lower thermal energy consumption of furnace, a shorter transition time of temperature in normal production, a reduced amount of transition coil or re-annealing coil used, and thereby reducing production cost. Moreover, during continuous anneal in furnace, steel strip does not tend to become curved, and performance of running continuous strip is good, and risk of strip brokering is small. The soft blackplate for tinning produced using Ti-IF steel according to the present invention has more stable mechanical properties than that produced using Nb-IF steel. In addition, in preparation of soft blackplate for tinning of the present invention, on the premise of guaranteeing uniform property, nature and quality of the material, hot-rolling uses a lower final temperature and coiling temperature, the amount of oxidization scale on surface of steel strip after hot-rolling is small, the subsequent pickling is easy to be performed, resulting in a good surface quality of final product. Examples Exemplary description of soft blackplate for tinning produced according to the present invention is recorded as follows. Examples 1-6: T-1CA tinned soft steel plate is prepared using Ti-IF steel. Molten steel is subjected to RH refining and vacuum degassing, taking various measures for controlling impurities. Finally, a continuous cast slab is prepared by conventional continuous casting technology. Chemical compositions of the molten steel are given in Tab. 2, Other unavoidable impurity elements are also present in the steel, the rest is Fe. Tab.2 Chemical Components of Plates of Examples 1-6 (wt %) (Table Removed)Before hot-rolling, the continuous cast slab is heated to the temperature for start rolling of the hot-rolling. It is subjected to rough rolling, finish rolling and laminar flow cooling, and followed by coiling. After cooled at room temperature for 2-3 days, it is subjected to pickling and continuous cold-rolling, using combination line of CDCM line (for pickling) and continuously cold-rolling line to prepare a cold-rolling plate.. The specific processing parameters are given in Tab 3. Table 3 Main process parameters of Examples 1-6 (Table Removed)The cold-rolled steel strip is continuously annealed on CAPL line (for continuous anneal), and temper-rolled on temper-rolling line, followed by conventional tinning, thus a tinned plate is obtained. Annealing process parameters, temper-tolling elongation, and hardness of final product are given in Tab 4. Tab .4 Annealing Parameters, Temper-rolling Elongation and Hardness of Product of Examples 1-6 (Table Removed)Mechanical properties of final product are given in Tab5. Tab. 5 Mechanical Properties of Examples 1-6 (Table Removed)Examples 7-12 T-2CA soft blackplate for tinning is prepared using Ti- IF steel. Molten steel is subjected to RH refining and vacuum degassing, taking various measures for controlling impurities. Finally, a continuous cast slab is prepared by conventional continuous casting technology. Chemical compositions of the molten steel are given in Tab. 6. Other unavoidable impurity elements are also present in the steel, the rest is Fe. Tab.6 Chemical components of Plates of Examples 7-12 (Table Removed)Before hot-rolling, the continuous cast slab is heated to the temperature for start rolling of the hot-rolling. It is subjected to rough rolling, finish rolling and laminar flow cooling, and followed by coiling. After cooled at room temperature for 2-3 days, it is subjected to pickling and continuous cold-rolling, using combination line of CDCM line (for pickling) and continuously cold-rolling line to prepare a cold-rolling plate. The specific processing parameters are given in Tab 7. Table 7 Main process parameters of Examples 7-12 (Table Removed)The cold-rolled steel strip is continuously annealed on CAPL line (for continuous anneal), and temper-rolled on temper-rolling line, followed by conventional tinning, thus a tinned plate is obtained. Annealing process parameters, temper-tolling elongation, and hardness of final product are given in Tab 8. Table 8 Annealing Parameters, Temper-rolling Elongation and Hardness of Product of Examples 7-12 (Table Removed)Mechanical properties of final product are given is Tab.9 Tab.9 Mechanical Properties of Examples 7-12 (Table Removed) We claim. 1 A soft blackplate for tinning, comprising the following components in percentage by weight: C≤O.006%, Mn: 0.10-0.20%, Al: 0.025-0.075%, Si≤O.03%, Ti: 0.03-0.08%, P≤O.015%, S≤O.015%, N 2. The soft blackplate for tinning of claim 1, wherein C content is 0.004%. 3. The soft blackplate for tinning of claim 1, wherein said Al content is 0.030-0.060% . 4. The soft blackplate for tinning of claim 1, wherein said Ti content is 0.05-0.07%. 5. The soft blackplate for tinning of claim 1, wherein said steel plate is prepared by a continuously annealing method. 6. A method for preparing the soft blackplate for tinning of Claim 1, comprising steps of: steel-smelting, continuously casting, hot-rolling, →pickling and cold-rolling, →continuously annealing, →temper-rolling, and plating with tin. 7. The method of Claim 6, wherein the step of pickling and cold-rolling is carried out with a combination line of pickling and continuously cold-rolling. 8. The method of Claim 6, wherein the step of pickling and cold-rolling may be replaced with a step of pickling and followed by continuously cold-rolling or multiple reversible cold-rolling. 9. The method of any of Claims 6-8, wherein in the step of hot-rolling, tapping temperature of slab is controlled at 1190-1250, final rolling temperature of slab is controlled at 880-920coiling temperature of slab is controlled at 550-630 . 10. The method of Claim 9, wherein final temperature of hot-rolling is controlled at 885-915 coiling temperature is controlled at 570-610D D 11. The method of any of Claims 6-8, wherein in said step of cold-rolling, cold-rolling reduction percentage is controlled at 82-92%. 12. The method of any of claims 6-8, wherein in said continuously annealing step, annealing temperature is controlled at 720-770, holding time is controlled at 25-50s. 13. The method of Claim 12, wherein said annealing temperature is controlled at 73 5-765 D. 14. The method of any of Claims 6-8, wherein the step of temper-rolling is carried out using a single temper-rolling mill or double temper-rolling mills. 15. The method of any of Claims 6-8, wherein in the step of temper-rolling, temper-rolling elongation is 0.8-3.0%. 16. The method of Claim 15, wherein when preparing a soft blackplate for tinning having a hardness HR 30T of 49±3, said temper-rolling elongation is controlled at 0.8-1.8% . 17. The method of Claim 15, wherein when preparing a soft blackplate for tinning having a hardness HR 30T of 53±3, said temper-rolling elongation is controlled at 1.8-3.0% . 18. A soft blackplate for tinning substantially as herein described with reference to the foregoing examples.

Documents:

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60-delnp-2008-Abstract-(18-03-2013).pdf

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60-delnp-2008-Correspondence Others-(18-03-2013).pdf

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