JPS631374B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a method for manufacturing soft surface-treated steel sheets with a temper level of 3 or less, such as soft tinplates, which are subjected to surface treatments such as tin plating and chromic acid treatment.
The present invention relates to a method for manufacturing a soft surface treated steel plate with excellent fruching resistance by continuous annealing. (Prior Art) The degree of tempering of tin-plated tinplate is defined as a guideline that can be selected as appropriate depending on the quality of the material required for various uses. In other words, the temper degree is Rockwell surface hardness (HR30T
or HR15T), from the softest one, Symbol Hardness T-1 46~52 T-2 50~56 T-3 54~60 T-4 58~64 T-5 62~68 T-6 67 ~73. These tinplates are generally manufactured by hot-rolling a hot-rolled coil made from a billet of low-carbon steel, cold-rolling it to a specified thickness, annealing it, and tin-plating it on a temper-rolled tin plate. . Among these manufacturing processes, batch annealing and continuous annealing are used for annealing, but T-1 to T-3 tin plates are conventionally annealed using the batch annealing method.
It is also classified by JIS. Continuous annealing is an annealing cycle consisting of rapid heating, short-time soaking, and rapid cooling, so it has conventionally been applied to the production of hard tinplates of T-4 or higher. However, continuous annealing has advantages such as being able to efficiently manufacture steel sheets and having small variations in the material of the manufactured steel sheets. Various studies have been conducted on the production of By the way, in order to manufacture a soft tin plate by continuous annealing, it is necessary to prevent grain refinement, reduce supersaturated solid solution C and solid solution N, in other words, reduce aging properties. . First, in order to prevent grain refinement, the finishing temperature during hot rolling is set at a low temperature near or below the Ar ₃ point, and the winding temperature is set at a high temperature, and the steel composition is adjusted. . In order to reduce supersaturated solid solution C, an overaging treatment is performed in the cooling process following short-time soaking during continuous annealing.
In addition, in order to reduce supersaturated solid solution N, Al, B,
Measures such as adding Nb _etc. have been taken.
For these reasons, recently, continuous annealing has been applied to some soft tinplates of T-3 or lower. However, in recent years, the requirements for soft tinplate materials have become increasingly strict, and it is important not only to guarantee a stable degree of temper, but also to ensure that processing defects such as bending do not occur during processing after the paint baking process by the customer. There is a growing tendency to demand more. Waist bending is a phenomenon in which tinplate bends into a broken line when it is bent, and is called fluting. Up until now, fluting has been closely related to aging properties, and it is sufficient to keep the elongation at yield point to about 4% or less. It is said that. However, since tinplate is heated to about 210℃ during the painting baking process,
At this time, a severe aging phenomenon occurs and yield point elongation is unavoidable, for example, yield point elongation of 6 to 12%. For these reasons, the problem of fluting has not yet been solved satisfactorily. (Objective of the Invention) An object of the present invention is to provide a method for manufacturing a soft surface-treated steel sheet that performs continuous annealing and has excellent fluting properties. (Structure and operation of the invention) In order to manufacture a surface-treated steel sheet that is T-3 or less soft and free of fluting by applying continuous annealing, the inventors of the present application have devised the overall manufacturing process, including the steel components. We considered the following. As a result, the heating temperature of the slab made of Al-killed steel and once cooled to below the Ar ₁ transformation point was set to 1150°C or lower, but above 950°C, and the winding temperature during hot rolling was lowered. 620 to 700℃ to promote the precipitation of AlN and C, and in continuous annealing after cold rolling, soaking is carried out in the temperature range above the Ac ₁ transformation point, which has been generally avoided until now, and then the overaging treatment temperature is Rapid cooling is performed at, for example, 30°C/second or more, preferably 100°C/second or more, and an overaging treatment is performed at a temperature of 300 to 500°C to greatly reduce solid solute C and solid solute N, and Steel sheets manufactured by a manufacturing method that involves increasing the precipitation density of carbides and acting as a dislocation source, for example, as shown in Figure 1, have a yield point elongation of several percent or more due to the aging phenomenon during paint baking, as shown in Figure 1. It was found that fruiting does not occur even if it occurs more than that. In addition, the test material in Fig. 1 has a C: 0.045~
0.070%, Mn: 0.20~0.30%, acid soluble Al: 0.040~
0.060%, N: 0.0030 to 0.0060%, and the conditions of hot rolling, continuous annealing, paint baking treatment, etc. are as shown in Table 1. 〇 is a surface-treated steel sheet manufactured by the method of the present invention, and ● is a surface-treated steel sheet manufactured by a comparative example (slab heating temperature and continuous annealing temperature are outside the range of the method of the present invention).

[Table] The present invention was made based on the above findings, and the gist of the present invention is as follows: C: 0.04-0.10%, Mn: 0.05-0.60%, acid soluble
Al: 0.03% or more and 0.150% or less, N: 0.010% or less,
A steel billet, the remainder of which is iron and unavoidable impurity elements, is continuously cast or bloomed and cooled to below the Ar ₁ transformation point, then heated to a temperature of 950°C to 1150°C, hot-rolled to a temperature of 620 to 700°C. Rolled at temperature, then descaled, cold rolled, and then continuously annealed to Ac ₁
Heated to a temperature above the transformation point and below 850℃, rapidly cooled to the overaging temperature range, and then heated at a temperature of 300 to 500℃ for 10
This is a method for producing a soft surface-treated steel sheet with excellent fluting resistance by continuous annealing, which is characterized by performing an over-aging treatment for more than a second and then skin-pass rolling. The present invention will be explained in detail below. The present invention is made of Al-killed steel, and first the steel components will be described. If the content of C is small, solid solution C tends to remain during continuous annealing, so the lower limit is set at 0.04%. On the other hand, if the content is too high, it will become hard.
0.10% or less. Mn is contained in an amount of 0.05% or more in order to prevent hot brittleness and ensure smooth hot rolling. If its content increases, it becomes hard, so it should be kept at 0.60% or less. Al is contained as acid-soluble Al (hereinafter referred to as SolAl) in an amount of 0.03% or more in order to fix N. The upper limit is set at 0.15% from the perspective of cost reduction. N makes the steel hard and also contributes to aging properties, so it should be kept at 0.010% or less. The basic steel composition is as above, but if necessary
When deoxidizing with Si before adding Al, 0.1 to 0.2%
Contains. In addition, one or more elements from B, Ti, Nb, Zr, and V are added in a total of 0.0003 to 0.02% to promote grain growth and reduce solute C and N.
May be added. After the steel made of the above components is melted in a converter, electric furnace, etc., it is made into a slab by continuous casting or ingot-forming and blooming. The slab is once cooled below the Ar ₁ transformation point to completely precipitate AlN. The slab is heated to a temperature of 1150°C or lower prior to hot rolling to prevent AlN from remelting. On the other hand, if the slab heating temperature becomes less than 950°C, the hot rolling finish temperature will decrease, the hot rolled sheet will have a mixed grain structure, and the steel will harden, so the lower limit is set at 950°C. In hot rolling, finish rolling is carried out at a normal finishing temperature, and winding is carried out in a temperature range of 620 to 700°C. lower limit
The reason for setting the temperature to 620°C is to promote precipitation of AlN. On the other hand, if the winding temperature becomes high, the pickling properties deteriorate, so the upper limit is set at 700°C. Next, it is descaled and cold rolled, and the rolling reduction ratio is determined arbitrarily so as to obtain a predetermined product thickness. After cold rolling, continuous annealing is performed, and the soaking temperature is
Ac ₁ Metamorphosis point or higher. So far, the soaking temperature for general tin plate annealing is around 630-700℃.
Although the temperature was below the Ac ₁ transformation point, in the present invention, the temperature is set to be above the Ac ₁ transformation point in order to greatly reduce the solid solution C in conjunction with the subsequent rapid cooling and overaging treatment.
On the other hand, if this temperature exceeds 850°C, continuous annealing operation becomes difficult, so the upper limit is set at 850°C. At conventional soaking temperatures, on the contrary, solid solution C increases.
The soaking time in the method of the present invention does not need to be particularly specified, but is approximately 10 seconds to 5 minutes. Then, for example, 30℃/second or more, preferably 100℃/second
It is rapidly cooled to an overaging treatment temperature range at a cooling rate of seconds or more, and overaging treatment is performed at a temperature range of 300 to 500°C. The reason for rapid cooling is not only to reduce solid solution C through the subsequent over-aging treatment, but also to increase the precipitation of carbides within the grains, which act as dislocation sources, thereby preventing the occurrence of fluting. The lower limit of the overaging treatment temperature is set at 300° C., since it takes a long time for solid solution C to precipitate at low temperatures. on the other hand,
When the temperature becomes high, C becomes solid solution in equilibrium.
Since the amount is large, the upper limit is set at 500℃. The overage processing time shall be 10 seconds or more. This is because at the above-mentioned overaging temperature of 300 to 500°C, the amount of solid solution C is reduced in 10 seconds or more. After this continuous annealing, skin pass rolling is performed to adjust the temper degree. Next, examples will be shown. The sample steels of Examples 1 to 8 of the present invention and Comparative Examples 9 to 13 shown in Table 2 were processed under the hot rolling conditions and continuous annealing conditions shown in the same table, respectively. Then, the hardness after temper rolling is H _R 30T.
And, the fruiting after the paint baking treatment was measured. Sample number 9 of the comparative example in Table 2 has a continuous annealing temperature outside the range of the method of the present invention, and sample number 10 has a continuous annealing temperature outside the range of the method of the present invention, and sample number 10 has a Sample No. 11 has the acid-soluble Al content and continuous annealing temperature, Sample No. 12 has the slab heating temperature and winding continuous annealing temperature, and Sample No. 13 has the slab heating temperature, winding temperature, and overaging temperature. Temperature is out of range. As is clear from the fruching values in this table, the steel sheet produced by the method of the present invention has superior fruching resistance compared to the steel sheet of the comparative example.

【table】

【table】 [Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between yield point elongation and fruching property after paint baking treatment.

Claims (1)

[Claims] 1% by weight: C: 0.04-0.10%, Mn: 0.05-0.60%, acid-soluble Al: 0.03% to 0.150%, N: 0.010
% or less, the balance consisting of iron and unavoidable impurity elements. After continuous casting or blooming, a steel billet is cooled to below the Ar ₁ transformation point, and then heated to a temperature of 950°C to 1150°C,
Hot rolled and rolled at a temperature of 620~700℃, then descaled, cold rolled, and then continuously annealed.
It is characterized by heating to a temperature above Ac ₁ transformation point and below 850℃, rapidly cooling to the overaging treatment temperature range, performing overaging treatment at a temperature of 300 to 500℃ for 10 seconds or more, and then performing temper rolling. A method for producing steel sheets for soft surface treatment with excellent fruching resistance through continuous annealing.