JPH0125381B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a method for stably, uniformly, and inexpensively manufacturing cold-rolled steel sheets that are processed into various shapes and used. Conventional Technology Conventionally, cold-rolled steel sheets have been manufactured by batch (box) annealing, but in recent years continuous annealing has been increasingly used to streamline the process. However, when producing a cold rolled steel sheet for drawing by the continuous annealing method, there are two major problems as described below, which have been obstacles to its application. During hot rolling, it is necessary to perform high-temperature coiling, and during the cooling process of continuous annealing, long-term overaging treatment is required. This is done to improve the drawability, especially the r-value, of continuously annealed materials, as shown in Figure 2. However, when high-temperature winding is performed, product characteristics may vary due to differences in thermal history depending on the coil position, and scale may increase. There was a problem that it became thick and impeded pickling efficiency. On the other hand, for over-aging treatment, as described in Japanese Patent Publication No. 49-1969, it is necessary to hold at a temperature of 300 to 500°C for 10 seconds or more, essentially 1 to 5 minutes, to precipitate C. It is. When this precipitation of C is insufficient, a large amount of solid solution C remains in the product, causing strain aging deterioration of the product. It goes without saying that if it is possible to shorten this overaging treatment time, the length of the continuous annealing furnace can be shortened, which is industrially desirable. Problems to be Solved by the Invention The purpose of the present invention is to solve the above-mentioned problems of the prior art.More specifically, even when low-temperature winding is performed, it is possible to achieve good aging resistance with a short overaging treatment. It is an object of the present invention to provide a method for producing a cold-rolled steel sheet for processing, which allows a product to be obtained and a good r value to be ensured. Means for Solving the Problems In order to solve the above problems, according to the present invention, C: 0.01 to 0.10% by weight, Mn: 0.02 to 0.40% by weight, Sol.Al: 0.001 to 0.08% by weight, N: 0.001 -0.007% by weight, Ti: 0.002-0.020% by weight, and the content of N and Ti has the following relationship, -0.001% by weight<N-14/48Ti<0.001% by weight,
After hot-rolling a steel that satisfies the above requirements and the remainder consists of Fe and unavoidable impurities, it is rapidly cooled and coiled at a temperature of 270°C or less, then cold-rolled at a reduction rate of 50% or more, and further heated at a heating rate of 50% or more. Provided is a method for producing a cold-rolled steel sheet for processing, characterized in that continuous annealing is performed at 1 to 100°C/second at a soaking temperature of 650 to 850°C. Furthermore, according to the present invention, it contains C: 0.01 to 0.10% by weight, Mn: 0.02 to 0.40% by weight, Sol.Al: 0.001 to 0.08% by weight, N: 0.001 to 0.007% by weight, Ti: 0.002 to 0.020% by weight. Furthermore, Si: 0.05 to 0.5% by weight, P: 0.03
~0.11% by weight and B: 0.0002 to 0.0010% by weight, and contains N and Ti.
The content of is in the following relationship, −0.001% by weight<N-14/48Ti<0.001% by weight,
After hot-rolling a steel that satisfies the above requirements and the remainder consists of Fe and unavoidable impurities, it is rapidly cooled and coiled at a temperature of 270°C or less, then cold-rolled at a reduction rate of 50% or more, and further heated at a heating rate of 50% or more. Provided is a method for producing a cold-rolled steel sheet for processing, characterized in that continuous annealing is performed at 1 to 100°C/second at a soaking temperature of 650 to 850°C. Effects To explain the above-mentioned method for manufacturing a cold rolled steel sheet of the present invention from a metallurgical perspective, the method of the present invention significantly lowers the coiling temperature of the hot-rolled steel sheet to below a specific temperature. By leaving a large amount of solid solution C in the steel, performing cold rolling in that state, and then performing rapid heating and annealing, cementite is finely precipitated during recovery and recrystallization of the cold rolled structure, improving the r value. It is based on the technical idea of obtaining a desirable recrystallized texture. Since the above-mentioned finely precipitated cementite acts as a C precipitation site during cooling, the precipitation of C during overaging treatment is accelerated, resulting in a cold rolled steel sheet with good aging resistance even with a shorter overaging treatment time than conventional ones. It will be done. Conventionally, it was thought that performing hot-rolling at high temperatures to coarsen the cementite in the hot-rolled sheet was a necessary condition for obtaining a high r value after continuous annealing, but basic research by the present inventors A method for manufacturing cold-rolled steel sheets for processing has been discovered that can increase the r value by adopting a method based on an idea that is completely opposite to the conventional method. Another feature of the present invention is that a small amount of Ti is added,
The point is that the solid solution N in the cryogenic rolled material is reduced, resulting in TiN precipitates. The basics of this technical idea are described in JP-A-53-13708, but the inventors have found that the above-mentioned effect of Ti can be obtained even if the coiling temperature of the hot strip is lower than previously thought possible. It was confirmed that it is possible and can be used effectively. As described above, the present invention utilizes the effects of conventionally known alloy components to develop an inexpensive manufacturing method for cold-rolled steel sheets for drawing using a completely new method. The problem is alleviated and the technical effect is great. Below, reasons for limiting the constituent elements of the present invention will be individually explained. Steel component C: This is an element that is inevitably contained in steel, and is also a cause of the aging properties of cold-rolled steel sheets. Therefore, although good properties can be obtained for steel with a C content of less than 0.01% by weight without employing the method of the present invention, the production cost of steel with a C content of less than 0.01% by weight is extremely high, making it economically difficult. Not on point. On the other hand, if the C content exceeds 0.10% by weight, the steel becomes hard and workability deteriorates. Mn: Mn is an element effective in preventing hot embrittlement caused by S, and is preferably contained in an amount of 0.02% by weight or more. However, if it exceeds 0.40% by weight, the steel becomes hard and its workability deteriorates. Also r
The value also decreases. Sol.Al: Al is added as a deoxidizing agent and is effective in providing a beautiful steel surface without surface defects, so it is preferably contained at 0.001% by weight or more. However, if the content exceeds 0.08% by weight,
The inclusions deteriorate the surface quality, harden the steel product, and deteriorate workability. N: In order to reduce the N content to less than 0.001% by weight, special treatment such as vacuum degassing treatment is required, which increases manufacturing costs. The application of the present invention is limited to economically produced steel types with an N content of 0.001% by weight or more;
It is exhibited at 0.001% by weight or more. however,
If it exceeds 0.007% by weight, the amount of TiN increases and becomes hard, resulting in poor workability. Ti: Added for the purpose of fixing N as a precipitate even if low-temperature winding is performed during rolling and reducing the amount of solid solution N in the finished product. If it is less than 0.002% by weight, the effect of addition is insufficient, and if it exceeds 0.02% by weight, the product becomes hard and processability deteriorates. Value of N-14/48Ti: Theoretically, this value should ideally be zero. When this value is zero, all Ti and N are stoichiometrically combined. When this value is negative, solid solution Ti or TiC precipitates in the steel and the product hardens; when it is positive, N is not completely fixed and the product undergoes strain aging. be. As shown in FIG. 1, if this value is within the range of ±10 ppm, the above-mentioned deterioration is small and there is no problem in terms of the characteristics of the product. P, Si: These elements are added as necessary when strength characteristics are required. 0.05 each
If Si is less than 0.03% by weight and P is less than 0.03% by weight, the strength-increasing effect will not be significant. On the other hand, if Si exceeds 0.5% by weight, the surface properties of the steel plate will deteriorate, and if P exceeds 0.11% by weight, the steel will become brittle. . B: B is added as necessary to stabilize the properties, but it has no effect at less than 2 ppm, and at 10 ppm
Addition in excess of this amount only increases manufacturing costs and has little effect. Hot-rolling coiling temperature: This is the most important requirement in the method of the present invention, and low-temperature coiling is performed for the purpose of leaving solid solution C in the hot-rolled sheet. If winding is performed at a temperature exceeding 270°C, a large amount of C will precipitate as Fe ₃ C and the r value will decrease. Winding at a temperature below 270°C is effective in imparting particularly excellent aging resistance to the finished product. In the present invention, the winding temperature may be room temperature as long as it is below 270°C. Cold rolling reduction ratio: If it is less than 50%, the degree of work is low, so r
value decreases. Therefore, it was decided to perform cold rolling at a rolling reduction of 50% or more. Conditions for continuous annealing Heating rate: The heating rate during continuous annealing is also an important factor in the method of the present invention. If the heating rate is less than 1° C./sec, fine precipitation of cementite cannot be obtained during recrystallization, resulting in a decrease in the r value. On the other hand, if the heating rate exceeds 100° C./sec, the fine precipitation of cementite will not occur in time, and the effect cannot be expected, the r value will become low, and the object of the present invention cannot be achieved. As shown in experiments in Examples below, 5
Heating rates in the range ˜50° C./sec are particularly preferred to obtain good r values. Soaking temperature: Soaking at a temperature of less than 650°C results in insufficient recrystallization and decreases elongation, while when it exceeds 850°C, γ (austenite) phase precipitates and the r value decreases. As detailed above, according to the present invention, the steel strip is rapidly cooled after hot rolling, wound into a coil at a temperature of 270°C or less, then cold rolled at a rolling reduction of 50% or more, and further heated at a heating rate of 1 to 50%. 100℃/sec, soaking temperature 650-850℃
After continuous annealing, followed by short-time overaging treatment, cooling to room temperature, and temper rolling,
Ship the finished product. Hereinafter, the present invention will be explained by examples, but these examples are merely illustrative of the method of the present invention,
This is not intended to limit the technical scope of the present invention in any way. Example 1 C: 0.03% by weight, Mn: 0.18% by weight, Sol.Al:
0.02% by weight, N: 0.0018% by weight, Ti: 0.006% by weight, P: 0.006% by weight, S: 0.004% by weight, Si:
0.01% by weight, N-14/48Ti = 0.0001% by weight, and the balance was essentially Fe. This was divided into eight parts, and a hot rolling simulation was performed in a laboratory. That is, a steel slab with the above composition was soaked at 1200°C for 1 hour, then hot rolled at 850°C or above to a finishing thickness of 3 mm, immediately quenched to various temperatures between 50 and 700°C, and then rolled at each of these temperatures. The sample was placed in a holding furnace, held for 30 minutes, and then cooled at a cooling rate of 20°C/hour. The above processing corresponds to the temperature history of a coil that was hot rolled in an actual hot rolling factory and coiled at the various temperatures mentioned above. After descaling these steel strips, they were cold rolled to 0.8 mm at a reduction rate of 73%, then heated to 700 °C at a heating rate of 10 °C/sec, held at this temperature for 40 seconds,
Next, it is cooled at a cooling rate of 10℃/second and subjected to overaging treatment.
The test was carried out at 350°C for 2 minutes. After these treatments, which correspond to continuous annealing, the steel strip was temper-rolled at an elongation rate of 1%, and the obtained steel sheet was subjected to a JIS No. 5 tensile test, and the r value and aging index (AI) were measured. The aging index is measured by the amount of increase in yield stress when heat treatment is performed at 100℃ for 1 hour after applying 10% tension, and this value is an indicator of the room temperature aging property of the steel plate. . Figure 2 shows the results of these tests, and as can be seen from this, the aging index is low when the coiling temperature is below 270°C, and gradually increases when it exceeds 270°C. On the other hand, the r value is highest when the winding temperature is 700°C, but an r value of 1.2 or more is obtained even at a winding temperature of 270°C or lower, and it has formability that can withstand press working for many uses. As described above, by selecting the winding temperature, heating rate, etc. according to the present invention, excellent aging resistance and sufficient formability are guaranteed even with a short overaging treatment time of 2 minutes as described above. It becomes possible to produce cold-rolled steel sheets with an r value of 100%. Example 2 C: 0.018% by weight, Mn: 0.06% by weight, Sol.Al:
0.070% by weight, N: 0.0033% by weight, Ti: 0.013% by weight, P: 0.020% by weight, S: 0.016% by weight, Si:
A steel containing 0.02% by weight, N-14/48Ti = -0.0005% by weight, and the balance substantially consisting of Fe was melted in a converter furnace and made into a 200 mm thick slab. It was subsequently hot rolled into a 3.2 mm steel strip. The heating temperature of the slab was 1100°C, the hot rolling finishing temperature was 840°C, the coiling temperature was 150°C, and the time required from the end of hot rolling to coiling was 15 seconds. This hot rolled steel strip was cold rolled to a thickness of 0.8 mm at a rolling reduction of 75%. The thus obtained cold rolled steel plate was heated to 680°C or 800°C at various heating rates in the laboratory, held at these temperatures for 40 seconds, and then heated to 400°C.
It was cooled at a rate of 10°C/second, held at 400°C for 2 minutes, and then cooled to room temperature. Then, after 1% temper rolling, the r value was measured. Figure 3 shows the change in r value compared to the heating rate during annealing. As shown in FIG. 3, a high r value is obtained when annealing is performed at a heating rate of 1 to 100° C./sec according to the method of the present invention. Example 3 In order to investigate the influence of steel components on formability and aging resistance, steels with the components shown in Table 1 were melted in a laboratory, and only the coiling temperature was changed to produce Example 1.
Hot rolling, cold rolling, continuous annealing, and temper rolling were performed using the same simulation method as above, and the r value and aging index were measured. The time required from the end of hot rolling to winding was 10 to 20 seconds.

[Table] As shown in Table 1, the properties of cold-rolled steel sheets manufactured from steel with chemical composition within the range of the invention are r≧
1.2, AI<4.0Kg/ ^mm2 , which is sufficient for processing, but steel compositions outside the scope of the present invention are r
<1.2 or AI>4.0Kg/ ^mm2 , making it unsuitable for use as a cold-rolled steel sheet for press working. That is, since the steel of sample number 12 has a high C content, the r value is as low as 1.03, and the formability is poor. sample
Steel No. 13 has a large (N-14/48Ti) value of 0.0016% by weight, and the Ti content is low compared to the N content.
N was not sufficiently fixed by Ti, and the aging resistance deteriorated. On the other hand, the steel of sample number 14 is (N-14/
48Ti) is -0.0015% by weight, which is too large in the negative direction, and solid solution Ti or TiC precipitates in the steel, resulting in low formability, that is, r value. Effects of the Invention As described above, the method of the present invention significantly lowers the coiling temperature of the hot rolled sheet to leave a large amount of solid solution C in the hot rolled sheet, performs cold rolling in that state, and then rapidly rolls the hot rolled sheet. By heating and annealing, the cold-rolled structure can be recovered and
Cementite is finely precipitated during recrystallization, and the finely precipitated cementite is used as a C precipitation site during cooling, allowing C to rapidly precipitate during overaging treatment. As a result, good aging resistance is achieved even with a shorter overaging treatment time than conventional methods. Moreover, we succeeded in providing a cold-rolled steel sheet with excellent formability. The steel types to which the method of the present invention is applied have normal levels of C and N, can be melted economically, and the overaging treatment time is short, so the length of the treatment furnace can be shortened, which is industrially advantageous. It is.

[Brief explanation of drawings]

Figure 1 shows the N and
It is a graph showing the content range of Ti. Figure 2 shows
2 is a graph showing the experimental results of Example 1 and showing the relationship between heating rate and r value in continuous annealing. Third
The figure shows the experimental results of Example 2, and is a graph showing the relationship between hot rolling winding temperature and r value.

Claims (1)

[Claims] 1 C: 0.01 to 0.10% by weight, Mn: 0.02 to 0.40% by weight, Sol.Al: 0.001 to 0.08% by weight, N: 0.001 to 0.007% by weight, Ti: 0.002 to 0.020% by weight, and the content of N and Ti is in the following relationship, -0.001% by weight<N-14/48Ti<0.001% by weight,
After hot-rolling a steel that satisfies the above requirements and the remainder consists of Fe and unavoidable impurities, it is rapidly cooled and coiled at a temperature of 270°C or less, then cold-rolled at a reduction rate of 50% or more, and further heated at a heating rate of 50% or more. A method for producing a cold-rolled steel sheet for processing, characterized in that continuous annealing is performed at a soaking temperature of 650 to 850°C at a rate of 1 to 100°C/second. 2 Contains C: 0.01 to 0.10% by weight, Mn: 0.02 to 0.40% by weight, Sol.Al: 0.001 to 0.08% by weight, N: 0.001 to 0.007% by weight, Ti: 0.002 to 0.020% by weight, and further contains Si. :0.05-0.5% by weight, P:0.03
~0.11% by weight and B: 0.0002 to 0.0010% by weight, and contains N and Ti.
The content of is in the following relationship, −0.001% by weight<N-14/48Ti<0.001% by weight,
After hot-rolling a steel that satisfies the above requirements and the remainder consists of Fe and unavoidable impurities, it is rapidly cooled and coiled at a temperature of 270°C or less, then cold-rolled at a reduction rate of 50% or more, and further heated at a heating rate of 50% or more. A method for producing a cold-rolled steel sheet for processing, characterized in that continuous annealing is performed at a soaking temperature of 650 to 850°C at a rate of 1 to 100°C/second.