JPH01263220A - Production of cold rolled steel sheet having excellent workability by continuous annealing - Google Patents

Abstract

PURPOSE:To produce the cold rolled steel sheet having excellent workability by heating and hot rolling a steel slab consisting of a specific compsn. and cooling and coiling the slab under specific conditions, then subjecting the slab to cold rolling and continuous annealing. CONSTITUTION:The slag contg., by weight, 0.010-0.040% C, 0.05-0.25% Mn, 0.004-0.020% S, 0.020-0.080% Al, and <=0.0030% N, and consisting of the balance Fe and inevitable impurities is heated and hot rolled. The slag is then cooled at <=30 deg.C/sec cooling rate in a 900-670 deg.C temp. region and thereafter, the slab is coiled at >=600 deg.C. This slab is then subjected to the cold rolling and continuous annealing. The cold rolled steel sheet having the good deep drawability and pickling property is thereby obtd.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention provides A! This relates to the manufacturing method of killed cold-rolled steel sheets, in which hot-rolled hot-rolled sheets are cooled by applying a specific cooling rate in a specific temperature range. The present invention provides a method for improving the workability of a steel plate.

(Conventional technology) Conventionally, in order to manufacture steel plates with good workability by continuous annealing,
A method of fixing C in steel has been carried out by reducing the amount of C in steel to about 0.005 wtχ or less and adding carbide-forming elements such as Ti and Nb. This increases the number of steps, leading to increased costs.

There is also a method of using IV-killed steel in order to reduce material costs, but for that purpose, hot-rolled sheets with 650~
Winding must be performed at a high temperature of 700° C. or higher, which increases the scale thickness and increases the cost of pickling. Furthermore, in high-temperature winding, the cooling rate of the top and bottom parts after winding is fast, which causes problems such as deterioration of the material and a drop in yield.

In order to avoid this problem, it is necessary to perform coiling at a low temperature of 650°C or lower, but cold rolling may result in insufficient precipitation of AZN or insufficient agglomeration of Fe5C in the hot-rolled sheet stage. The workability of the steel plate is poor.

Currently, as a solution to this problem, as disclosed in JP-A-60-115156, Cl in steel is reduced to 0.020wt.
A method has been proposed to reduce the Cl
There remains the problem that aging deterioration is likely to occur when the Also, JP-A-61-249
Mn, S, N as disclosed in Publication No. 443.

Although there is a method of limiting the amount of N within a certain range,
In order to sufficiently aggregate e and C, Mni must be 0.1wt.
% or less. In this case, there is a drawback that cracks are likely to occur during hot rolling depending on the sl. Also,
Due to At and N'FJ limitations, even winding temperatures below 650℃ can be achieved! Although it is possible to precipitate N, Cl must be reduced to 0.020 wt% or less for Fe5C to coagulate, and the above-mentioned problem of aging deterioration remains.

Like this, to! The conventional method of hot-rolling using killed steel and then winding it at a low temperature of 650° C. or lower is difficult to actually apply due to the severe composition conditions.

(Problems to be Solved by the Invention) Therefore, in the present invention, low carbon killed steel is used, and even if coiling is performed at a low temperature of 600 to 650'C after hot rolling, 65
The objective is to produce cold-rolled steel sheets with excellent workability equivalent to those rolled at high temperatures of 0°C or higher.

(Means for Solving the Problems) The present inventors cooled a hot-rolled sheet immediately after hot rolling in a temperature range of 900 to 670°C according to the conditions shown below, and then rolled it at a temperature of 600°C or higher. It has been found that the above object can be achieved by subsequently performing cold rolling and continuous annealing.

■. Temperature range from 900 to 670'C at 30° (:/s
Cool at a cooling rate of ec or less.

2. Temperature range from 900 to 720℃ is 100'C/sec
After cooling at any cooling rate below, further 720-670
The temperature range of 0.degree. C. is cooled at a cooling rate of 15.degree. C./sec or less.

The gist of the first invention is as follows. That is, C: 0.010 to 0.040%, Y
In: 0.05-0.25%, S: 0.004-0
．． 020%, Al: 0, 020-0.080%, Al:
After heating and hot rolling a slab containing 0.0030% or less and the remainder consisting of Pe and unavoidable impurities,
The process includes a step of cooling in a temperature range of 670°C at a cooling rate of 30°C/sec or less, a subsequent step of winding at a temperature of 600°C or more, and a subsequent step of cold rolling and continuous annealing. This is a method for producing cold-rolled steel sheets with excellent workability.

The gist of the second invention is as follows. That is, C: 0.010 to 0.040%, M
n: 0.05-0.25%, S: 0.004-0.
020%, eight! :0.020~0.080%, Al:0
．． After heating and hot rolling a slab containing 0.030% or less and the remainder consisting of Fe and unavoidable impurities,
A step of cooling a temperature range of 20° C. at a cooling rate of 100° (:/sec or less), a step of cooling a temperature range of 720 to 670° C. at a cooling rate of 15° (:/sec or less), and then a step of cooling a temperature range of 720 to 670° C. at a cooling rate of 15° (:/sec or less); a step of winding at a temperature of C or higher;
This method of manufacturing a cold rolled steel sheet with excellent workability is characterized by comprising the steps of thereafter performing cold rolling and continuous annealing.

First, the reason for limiting the chemical composition of steel to which the method of the present invention is applied will be explained.

If C is less than 0.010%, it is not desirable because aging deterioration after continuous annealing is large. Moreover, if it exceeds 0.040%, the deep drawability of the product will deteriorate. Therefore, the amount of C should be 0.010~
It was limited to 0.040%. 0.010 to 0.0 in order to more fully agglomerate FetC in the hot-rolled sheet stage.
A range of 28% is preferred.

Mn is a necessary component to prevent hot brittleness, but 0
．． If it is less than 0.05%, FeS will be generated and there will be no effect. Moreover, if it exceeds 0.25%, deep drawability deteriorates. Therefore, the amount of Mn was limited to 0.05 to 0.25%. The content is preferably in the range of 0.10 to 0.20% in order to make MnS, which becomes the precipitation nucleus of cementite, to a more appropriate size during overaging during continuous annealing.

If S exceeds 0.020%, it causes hot embrittlement, so it must be less than this. In addition, in order to utilize MnS as precipitation nuclei of cementite during over-aging during continuous annealing, the content is preferably 0.004% or more.

At least 0.020% of AI is required in order to precipitate N as AfN after deoxidation and winding. However, 0.
If it exceeds 0.080%, workability deteriorates. AZ to precipitate
In order to coarsen the size of N and improve workability, the range is preferably from 0.030 to 0.080%.

Further, since AfN also deteriorates workability, it is better to have a smaller amount, and the Ni content was set to 0.0030% or less.

Furthermore, the slab used in the manufacturing method of the present invention is Si,
It can contain P and other elements.

The present inventors melted steel within the above composition range, hot-rolled it, cooled it in various temperature ranges at various cooling rates, and
It was wound at a temperature of 0-850'C.

Furthermore, the material was subjected to cold rolling and continuous annealing at a recrystallization temperature of 800° C., and the material properties were investigated. Representative results are shown in FIGS. 1 and 2. Figure 1 shows the weight ratio of C:
0.020%, Si: 0.010%, Mn: 0.1
5%, P: 0.007%, S: 0.011%,
sol, AI: 0.050%, N: 0.0015%
, Fe: After hot rolling the steel with a composition consisting of the remainder at 900'C,
This figure shows the effect of the cooling rate on the r value when the material was cooled at a cooling rate of 5 to 100°C/see, then wound up at 650°C, and then cold rolled and continuously annealed.

Figure 2 shows the steel with the above composition being hot-rolled at a finishing temperature of 900°C and then rolled at 20″C/se between 900 and 720°C.
c and I When coiled at 650°C after cooling at a cooling rate of OO'C/sec and subsequently cooling at various cooling rates between 720 and 670°C from 5 to 80°C/sec, a good depth was obtained. The cooling rate range in which drawability is obtained is indicated by diagonal lines.

From these results, it was found that in order to obtain a steel sheet with excellent deep drawability, the following cooling and winding conditions must be met.

■The temperature range of 900 to 670℃ of the hot-rolled sheet after hot rolling is 3.
600℃ after cooling at a cooling rate of 0°(:/Sec or less)
Winding is performed at the above temperature.

2. Temperature range from 900 to 720℃ to 100℃ (: /
After cooling at a cooling rate of 720 to 670°C, cooling is performed at a cooling rate of 7 seconds or less, and winding is performed at a temperature of 600°C or higher.

When the precipitation state of FezC in the hot-rolled sheet was investigated using an optical microscope, it was found that the condition of the FezC according to the conditions of the present invention was sufficiently agglomerated.
The distribution interval is wide, whereas if either or both of the cooling conditions and coiling temperature conditions after hot rolling deviate from the conditions of the present invention, the degree of agglomeration is insufficient, and the distribution interval is It turns out that there is a close relationship between the two countries.

The cold rolling reduction may be as usual, but a high cold rolling reduction of 70% or more is preferred in order to develop the (111) texture after continuous annealing and improve deep drawability.

Next, the continuous annealing conditions will be described. The heating temperature needs to be higher than the recrystallization temperature. If the material is hot-rolled, cold-rolled, etc. according to the present invention, sufficient deep drawability can be obtained even by low-temperature annealing. Therefore, currently the temperature is mainly 700 to 830℃.
However, even if annealing is performed at a higher temperature than this temperature, deep drawability will not be improved. In addition, in order to improve the aging characteristics, it is preferable to set the primary cooling rate to 50° (:/sec or higher) and then perform overaging treatment in the temperature range of 250 to 350°C. This depends on the slab temperature history conditions mentioned above. This is because the distribution of MnS in the steel is just right for it to act as precipitation nuclei of cementite during overaging, and its effect is particularly effective under these overaging conditions.

The cold-rolled sheet produced as described above has superior deep drawability compared to conventional directly hot-rolled materials.

Example I C: 0.022%, Si: 0.013%, Mn: 0.
15%, P: 0.008%, S: 0.012%
, sol, 8/: 0.040%, Al: 0.0
Steel having a composition of 020%, Fe: balance was melted and hot rolled at a finishing temperature of 900°C to a plate thickness of 4.0 m.
After cooling at various temperature ranges at various cooling rates, it was wound up at a temperature of 500 to 730°C. Furthermore, cold rolling and continuous annealing at a recrystallization temperature of 800° C. were performed, and the material properties were investigated. Table 1 shows the cooling conditions and winding conditions after hot rolling, and the material test results.

Samples A, B, C, D, and E were cooled in a temperature range of 9oO to 670°C at a cooling rate within the range of the present invention. Sample F
, G and H are cooled in the temperature range of 900 to 720°C at 30, 50, and 80°C/sec, respectively, and then cooled to 720 to 720°C.
The temperature range of 670°C was cooled at 10'C/sec.

Samples A, B, and C were all subjected to a winding process at 650'C for 1 hour, and then cooled at 30'C/hr. For sample sample and E, the winding temperature was set to 600℃ and 7℃, respectively.
The temperature was 30'C.

Sample 1. The cooling rate of J and K in the temperature range of 900 to 670°C is faster than that of the present invention.

The cooling rate of the samples M and N in the temperature range of 900 to 670°C is within the range of the present invention, but the coiling temperature is lower than the range of the present invention.

In addition, the amount of N dissolved in the steel after winding was 8! It precipitates as N and becomes coarse, so it does not affect the workability of the finished plate, and there is no adverse effect of solid solution N and AIN.

After pickling, these hot-rolled sheets were rolled to 0.8 m at a rolling reduction of 80%.
Cold rolled to a thickness of m, and further heated to a temperature of 800'
Continuous annealing was performed at C for 1 minute.

The resulting cold-rolled steel sheet was subjected to a tensile test using a JIS No. 5 tensile test piece, and the r value, yield strength, and elongation were measured. The results of these measurements are also shown in Table 1.

From the results shown in Table 1, if the cooling conditions in the temperature range of 900 to 670°C are out of the range of the present invention, the material has sufficient r value, yield strength, and/or elongation to perform deep drawing. It is clear that when this is within the range of the present invention, the material has sufficient r value, yield strength, and elongation to perform deep drawing.

When the distribution of Fe and C in the hot-rolled steel sheet was investigated, the following findings were found.

When the cooling conditions in the temperature range of 900 to 670°C after hot rolling or the coiling temperature are outside the range of the present invention (sample 1. J,
The Fe3C distribution of K, L, M, and N is within the range of the present invention (Sample A), whereas it precipitates in large numbers in a dot array at the grain boundaries and is not agglomerated.

Fe1C of B, C, D, E, F, G and H) is aggregated and precipitated, the distribution interval is wide and the number is small.

That is, by keeping the cooling conditions in the temperature range of 900 to 670°C after hot rolling within the range of the present invention, agglomeration of Fe5C in the hot rolled steel sheet when performing low temperature coiling, which was difficult in the past, can be prevented. This makes it possible to produce cold-rolled steel sheets with excellent deep drawability.

Example 2 Steel having the composition shown in Table 2 was melted and finished at a finishing temperature of 900.
After hot rolling at ℃ to 4.0 mm thickness, 900 to 67
After cooling in a temperature range of 0°C at a cooling rate of 30°C/sec, it was wound up at a temperature of 650°C. Furthermore, cold rolling and
Continuous annealing was performed at a recrystallization temperature of 800°C, and the material properties were investigated. The material test results are shown in Table 3.

Sample 0. Although the composition of P and Q is within the scope of the present invention,
Samples R, S, T, U and V all deviate from the scope of the invention with respect to the underlined components.

After pickling, these hot-rolled sheets were rolled to 0.8 m at a rolling reduction of 80%.
The sheet was cold rolled to a thickness of m, and further annealed continuously at a temperature of 800° C. for 1 minute.

The resulting cold-rolled steel sheet was subjected to a tensile test using a JIS No. S tensile test piece, and the r value, yield strength, and elongation were measured. The results of these measurements are shown in Table 3.

From the results shown in Table 3, it can be seen that if the composition is outside the range of the present invention, a material with sufficient r value, yield strength, and elongation, or all of them, for deep drawing cannot be obtained.

Table 3 (Effects of the Invention) As is clear from the above explanation, according to the method of the present invention, after hot rolling M-killed steel, the temperature is lower than that of the conventional method.
Cold-rolled steel sheets with excellent deep drawability can be produced even when coiling is performed at 650°C. In addition, according to this method, since the material is wound at a low temperature, the scale thickness is thinner than when winding at a high temperature, and good pickling properties are obtained, resulting in a reduction in the cost of pickling. Furthermore, the material of the top and bottom parts after winding is less likely to deteriorate.
Yield is also good.

[Brief explanation of the drawing]

Figure 1 shows 900~6 after hot rolling, which provides good deep drawability.
The cooling rate range between 70'C and 70'C is indicated by diagonal lines. Figure 2 shows that after hot rolling, cooling is performed between 900 and 720°C at a cooling rate of 20°C/sec and 100°C/sec, and then
The cooling rate range in which good deep drawability is obtained when the material is cooled at various cooling rates of 5 to 8 Q'C/sec between 20 and 670°C and then coiled at a temperature of 650°C is indicated by diagonal lines. It is. Figure 1 Figure 2 720-670℃Φ cooling failure

Claims (2)

[Claims] (1) C: 0.010-0.040%, Mn by weight ratio
:0.05~0.25%, S:0.004~0.020
%, Al: 0.020-0.080%, N: 0.003
0% or less, with the balance consisting of Fe and unavoidable impurities, is heated, hot rolled, cooled at a cooling rate of 30°C/sec or less in the temperature range of 900 to 670°C, and then heated to 600°C or more. A method for producing a cold-rolled steel sheet with excellent workability by continuous annealing, which comprises winding at a high temperature, followed by cold rolling and continuous annealing. (2) C: 0.010-0.040%, Mn in weight ratio
:0.05~0.25%, S:0.004~0.020
%, Al: 0.020-0.080%, Al: 0.00
After heating and hot rolling a slab containing 30% or less and the remainder consisting of Fe and unavoidable impurities, the temperature is 900 to 720°C.
The temperature range is cooled at a cooling rate of 100℃/sec or less, and the temperature range from 720 to 670℃ is cooled at a cooling rate of 15℃/sec.
A method for producing a cold-rolled steel sheet with excellent workability by continuous annealing, which comprises cooling at the following cooling rate, then winding at a temperature of 600° C. or higher, followed by cold rolling and continuous annealing.