JPH0152451B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a method for manufacturing a plated original plate for hard tin plate that does not generate stretcher strain. Here, the plated original plate for hard tinplate includes the case where it is used for so-called stain-free steel. According to JISG3303, regarding the tempering degree of tinplate,
Depending on the target Rockwell T hardness (HR30T), T-1 (H _R 30T: 49±3) to T-6 (H _R
30T: up to 70±3), and for these, in addition to the case using the box annealing method, especially T-
4CA to T-6CA (H _R 30T: 61±3 to 70±3), and the continuous annealing method is specified. The present invention relates to the last of the above categories, hard tin tin and similar stain-free steels. (Prior art) Conventionally, T-1 to T-4 grade tin plates are made of low carbon aluminum killed steel containing C: 0.01 to 0.10% by weight (hereinafter, the steel composition is simply expressed in percentage). For T-5 and T-6, low carbon aluminum killed steel was mainly used, aiming at increasing hardness by adding P or N. The relationship between the annealing method applied to these plated original plates and the properties of tinplate is as follows. Box annealing method: After completion of recrystallization (550 to 700°C), the steel is slowly cooled to near room temperature over several days, so that most of the C in the steel precipitates as carbides. Mata Hagane N
precipitates as aluminum nitride during heating. In other words, since C and N in steel do not exist in a solid solution state, strain aging does not occur even after temper rolling and tin alloying treatment after tin tinting (so-called reflow treatment, held at 230 to 250 degrees Celsius for several seconds). No elongation at yield point occurs. Continuous annealing method: The material is rapidly heated to 600-730°C at a rate of 10-30°C/second, held for several tens of seconds to allow recrystallization, and then rapidly cooled to room temperature at a rate of 5-50°C/second. , C, and N are mostly present in a solid solution state. Therefore, dislocations are introduced into the steel by temper rolling, and then by the tin alloying treatment after tin-plating, solid solution C and N precipitate on the dislocation lines, causing strain age hardening. Therefore, when this steel sheet is processed into cans, etc., a streak pattern (called stretcher strain) occurs due to elongation at the yield point, which significantly impairs the aesthetic appearance. That is, hard tinplates with a tempering degree of T-4 to T-6, which were conventionally manufactured by the continuous annealing method, had a considerable amount of stretcher strain, which caused problems. By the way, by combining continuous annealing and temper rolling, T
Japanese Patent Publication No. 56-3413 is known as a technique for producing hard tin plate having a heat treatment degree of -4 to T-6. The same publication describes the materials as C: 0.1% or less (example 0.04%), Si: 0.05% or less, Mn: 0.05 to 0.4
%, acid soluble Al: 0.01-0.1%, N: 0.002-0.01%
The material is aluminum killed steel, hot rolling finish temperature 700~900℃, cold rolling reduction rate 75~93%, surface hardness H _R 30T43~58, surface hardness 44.
A wet tempering of 1.5% to 35% is disclosed depending on the desired degree of tempering ranging from ~75%. Although it can be easily inferred that the desired degree of tempering can be achieved by temper rolling in this method by considering work hardening in temper rolling, the material properties required for the first time in this prior disclosure are Even if the hardness is satisfied, there is no mention of measures to prevent stretcher strain that occurs during processing. However, when continuous annealing is performed using a material with the above-mentioned components, as mentioned above, a large amount of C remains in the steel in a solid solution state, so strain is introduced in the subsequent temper rolling process, causing strain. This creates a situation where the statute of limitations is likely to run out. In other words, after applying tinting to a temper-rolled plate, it is then subjected to alloying treatment at 230 to 300°C for a few seconds, or for drying when chromium plating is applied to make stain-free steel. However, this problem was still unsolved, as strain aging occurs due to heating, resulting in significant stretcher strain during processing such as can manufacturing. (Problems to be Solved by the Invention) The inventors have conducted studies to stably obtain a hard tin plate that does not cause stretcher strain during temper rolling and subsequent tin alloying treatment after tin plating. As a result, C as material: 0.003
Especially using ultra-low carbon aluminum killed steel of less than %,
It has been found that by combining this with continuous annealing and temper rolling, the object intended by the present invention can be advantageously achieved. (Means for Solving the Problems) This invention contains C: 0.0030% or less, Si: 0.1% or less, Mn: 0.5% or less, Al: 0.010 to 0.080%,
N: 0.0050% or less, or even 0.10% or less
at least one of Nb and 0.20% or less of Ti,
In addition to S with a Mn/S ratio of 10 or more and limited to 0.030% or less, a steel material with a composition containing 0.030% or less of P and other unavoidable impurities is hot rolled and then cold rolled. to obtain an ultra-low carbon cold-rolled aluminum-killed steel sheet; and heating this cold-rolled sheet to a temperature higher than the recrystallization temperature through continuous annealing, cooling it, and then temper rolling at a rate of 10% to 50%. Particularly advantageously, the combination with the stage T-4 to T-6 can be carried out without the risk of stretcher strains.
It was discovered that hard tinplate or stain-free steel with a heat treatment level of 100% can be obtained. In this invention, the steel composition of the plated original plate is particularly C.
The behavior of is important. As already mentioned, conventionally the C content was 0.01
Due to the high content of ~0.10%, a large amount of solid solution C exists in the steel due to rapid cooling during continuous annealing, and this solid solution C is removed on dislocation lines by skin pass rolling and plating alloying treatment after plating. This causes stretcher strain. Therefore, in order to investigate the relationship between the amount of C contained in the steel and the stretcher strain after plating and alloying treatment, vacuum melted steels with different amounts of C were melted in the laboratory and the following basic experiments were conducted. (Basic experiment) C was varied as a component of the material from 0.0008% to 0.040%, and other components were Si: 0.01% to 0.02%, Mn:
0.23%, P: 0.011-0.012%, S: 0.007-0.009
%, Al: 0.028-0.030%, N: 0.0023-0.0025%
It is almost common. This steel is forged into a 30mm thick sheet bar, then hot rolled by heating the sheet bar to 1150℃, finishing at a finishing temperature of 860℃ to form a 2.6mm hot rolled steel plate, and then immediately placed in a 560℃ furnace. A process equivalent to a coil winding temperature of 560°C was performed by charging and slowly cooling for 30 minutes. After pickling, this steel plate was cold rolled to 0.32 mm using a small rolling mill, and further recrystallized annealed using a continuous annealing cycle. In other words, cold-rolled steel sheets are processed using a heat treatment simulator.
It was rapidly heated to 710°C at a rate of 15°C/second, held at this temperature for 30 seconds, and then rapidly cooled to room temperature at a rate of 10°C/second. After this, after 12% temper rolling, in order to reproduce the plating and post-plating alloying treatment in the laboratory, it was held in an oil bath at 250℃ for 3 seconds and then water-cooled. Ivy. This sample was processed into a JIS No. 5 tensile test piece, a tensile test was conducted, and the hardness of some of the samples was also measured. In addition to observing the occurrence of stretcher strain at 1% tension, the center line average roughness (Ra; cutoff value: 0.8 mm) of the steel plate surface was measured. Figure 1 shows the effect of C content on yield point elongation, hardness, stretcher strain generation behavior, and steel sheet surface roughness in a tensile test. As shown in Figure 1, when the yield point elongation is 0.003%C or less, the elongation at yield is suppressed to 10% or less, and there is almost no stretcher strain. This is also clear from the fact that the skin roughness caused by this phenomenon is extremely small. (Function) According to the results of the basic experiment described above, in this invention, the amount of C in the steel must be 0.003% or less. Next, regarding the components Si, Mn, S and P in the steel of this invention, adding large amounts of these elements suppresses grain growth during continuous annealing, hardens the steel, and reduces the rolling load during subsequent temper rolling. Not only does this cause an increase in the corrosion resistance of the tin plate, but it can also be a factor that inhibits the corrosion resistance of tinplate, so the lower the content, the better; Si: 0.1% or less, Mn:
Must be 0.5% or less, S: 0.030% or less, P: 0.030% or less. However, since Mn needs to fix S, which causes embrittlement during hot rolling, as MnS, Mn/S
10 is required. Al is necessary to fix N as aluminum nitride, and is required at a minimum of 0.010%. Adding a large amount increases costs, so the upper limit is set at 0.080%. Also, like C, if N exists in a solid solution state after continuous annealing, it will cause stretcher strain during product processing, so the less it is, the better. can. In addition to the above, Nb and Ti contain C in solid solution at 0.10% or less and 0.20% or less, respectively.
It plays the role of fixing NbC and TiC. Again in Figure 1, ☆ and ★ indicate Nb = 0.01% when C = 0.0023% and C
= 0.0026%, Ti = 0.028% was added under the same conditions, but the yield point elongation was 0 for all steels, and there was no problem of stretcher strain. In other words, Nb and Ti have the same effect on preventing stretcher strain, which is the object of this invention. Note that the upper limits of these contents are Nb: 0.10%, Ti: 0.20%, taking into account the cost increase due to addition.
It should be %. In order to particularly expect the effects of Nb and Ti, Nb: 0.005%,
Ti: Useful from 0.01%. Before the molten steel whose composition has been adjusted as described above reaches the process step of the present invention, it is suitably subjected to hot rolling and cold rolling to form a slab that has been subjected to blooming rolling using an agglomeration method, or more preferably a slab that has been continuously cast. However, there is no need to particularly limit the hot rolling conditions and cold rolling conditions, and conventional methods may be followed. Regarding continuous annealing conditions after this cold rolling, in order to obtain uniform material properties in the longitudinal and width directions of the strip, the present invention is particularly effective in continuous annealing, which is superior to box annealing. However, the continuous annealing conditions themselves do not need to be particularly limited as long as the annealing temperature is equal to or higher than the recrystallization temperature. Furthermore, there are no particular limitations on the cooling rate to near room temperature. On the other hand, temper rolling is the most important component in determining the hardness of tinplate. This invention uses ultra-low carbon aluminum killed steel with C: 0.0030% or less as a material, and after continuous annealing and temper rolling of 10% or more, tin-plating and tin-alloying treatment or stain-free steel. Through corresponding processing, we have newly announced that we can manufacture hard tin or stain-free steel with a temper degree of T-4 to T-6, which has the specificity of not causing stretcher strain caused by elongation at the yield point. This is what we propose. The continuously annealed steel sheet here is extremely soft because it is made of ultra-low carbon Al-killed steel.
Reductions of 10% or more can be easily achieved with a temper rolling mill. That is, the following experiment was conducted to confirm the effect of the rolling reduction in temper rolling. Materials are C=0.0018%, Si=0.01%, Mn=0.23
%, Al=0.031%, N=0.0023%, P=0.011%,
Steel containing S = 0.007% was produced in the laboratory by vacuum melting, and the steps up to continuous annealing were the same as those described in the basic experiment. After continuous annealing, the steel plate was subjected to 8-50% temper rolling, then held at 250℃ for 3 seconds in an oil bath, and then processed into JIS No. 5 test pieces and subjected to a tensile test. The yield point elongation and hardness were measured. Figure 2 shows the results. The yield point elongation is 0.5 at any temper rolling reduction rate.
% or less, and there is no problem with stretcher strain. In addition, when the temper rolling reduction is less than 10 to 20%, it is almost T-4 temper, and when it is 20 to 30%, it is T-5 temper.
Furthermore, it can be seen that various hard tinplates with a T-6 heat refining degree can be obtained at 40 to 50%. Based on the above experimental results, the skin pass rolling reduction ratio in the present invention was limited. If the reduction rate is less than 10%, it is difficult to ensure a heat treatment degree of T-4 or higher, so the lower limit was set at 10%. Furthermore, even if a reduction of more than 50% is applied, there is no major change in the material, and it only unnecessarily increases the load on the rolling mill, which can easily lead to operational troubles such as breakage of the steel plate during rolling. Therefore, the upper limit was set at 50%. As described above, this invention is based on a completely new idea of using ultra-low carbon Al killed steel with C: 0.0030% or less and combining it with temper rolling. Or, an advantageous refining method for stain-free steel has been established. The rolling mill used for temper rolling is not limited to the one-stand or two-stand temper rolling mill that has been commonly used in the past.
Any type of rolling mill may be used as long as it is capable of rolling by 10% or more. (Example) Steel having the components shown in Table 1 was melted in a converter and made into a slab by continuous casting. The slab was finished to 2.3 mm under the hot rolling conditions shown in Table 1.

[Table] After pickling, it was cold rolled to 0.3mm using a tandem rolling mill. Next, continuous annealing was performed in a continuous annealing furnace using the heat cycle shown in FIG. This steel plate was subjected to 15, 25, and 45% temper rolling in a temper rolling mill, then No. 25 tin plated in an electroplating line, and then plated and alloyed. These steel plates were processed into JIS No. 5 test pieces and the yield point elongation and hardness (H _R 30T) were determined when a tensile test was performed.
are shown in Table 2.

【table】

[Table] The sample materials (A) to (G) according to the present invention all have a C content of 0.003% or less, a yield point elongation as small as 1% or less, and no stretcher strain is observed. However, the C content of sample materials (H) to (J) was 0.003%.
Since the yield point elongation exceeds 1.0%,
The roughness of the surface of the steel plate is strongly manifested, and the beauty of the surface of the Sn-plated plate is significantly impaired. (Effects of the Invention) As described above, the present invention makes it possible to obtain hard tin or similar products that do not suffer from stretcher strain caused by yield point elongation that occurs during processing of tin or similar products. Needless to say, bending defects during processing due to elongation at yield point do not occur.

[Brief explanation of drawings]

Figures 1 and 2 are graphs showing the effects of C content and skin pass rolling/reduction ratio on yield point elongation and hardness (H _R 30T), respectively, and Figure 3 is a graph showing the effects of C content and skin pass rolling/reduction ratio on yield point elongation and hardness (H R 30T), and Figure 3 is a This is the heat cycle of a continuous annealing furnace.

Claims (1)

[Claims] 1 C: 0.0030% by weight or less, Si: 0.1% by weight or less, Mn: 0.5% by weight or less, Al: 0.010 to 0.080% by weight, N: 0.0050% by weight or less, Mn/S ratio of 10 or more. A steel material having a composition containing S limited to 0.030% by weight or less, 0.030% by weight or less P, and other unavoidable impurities is hot rolled, and then cold rolled to produce ultra-low carbon aluminum killed steel. A stretcher strain that combines the step of obtaining a sheet and the step of continuously annealing the cold-rolled sheet to a temperature higher than the recrystallization temperature, cooling it, and then temper-rolling it at a rate of 10% or more and 50% or less. A method for manufacturing a plated original plate for hard tinplate that does not generate. 2 C: 0.0030 weight% or less, Si: 0.1 weight% or less, Mn: 0.5 weight% or less, Al: 0.010 to 0.080 weight%, N: 0.0050 weight% or less, and further 0.10 weight% or less Nb, 0.20% or less A steel material having a composition containing at least one type of Ti at a Mn/S ratio of 10 or more and S limited to 0.030% by weight or less, as well as 0.030% by weight or less of P and other unavoidable impurities. A step of hot rolling and then cold rolling to obtain an ultra-low carbon aluminum killed steel cold rolled sheet; heating this cold rolled sheet by continuous annealing to a temperature higher than the recrystallization temperature, and then cooling it; A method for producing a plated original plate for hard tinplate that does not generate stretcher strain that is combined with the step of applying temper rolling of 50% or less.