JPH08253818A - Production of ferritic stainless steel strip reduced in inplane anisotropy and excellent in balance between strength and elongation - Google Patents

Abstract

PURPOSE: To produce a ferritic stainless steel strip excellent in r-value and ridging resistance, reduced in the inplane anisotropy of r-value, and having superior balance between strength and elongation. CONSTITUTION: A ferritic stainless steel stock is subjected to hot rolling consisting of roughing and finish rolling, to cold rolling, and to finish annealing, by which the stainless steel strip is produced. In this method, the value of γp, computed from the chemical composition of the ferritic stainless steel and represented by equation γp=288 (Cwt.%)+350 (Nwt.%)+22 (Niwt.%) +7.5(Mnwt.%)=18.75(Crwt.%)-54(Siwt.%)+338.5, is regulated to 20-80. Moreover, rolling of at least one pass in the roughing stage is done under the conditions of 970-1150 deg.C rolling temp., <=0.3 friction coefficient, and 40-75% draft. Further, holding is done at 750-950 deg.C for >=1hr in the hot rolled plate annealing stage, and also holding is done at 600-750 deg.C for >=1hr in the course of its temp. fall.

Description

Detailed Description of the Invention

[0001]

The present invention has a small in-plane anisotropy,
The present invention also relates to a method for producing a ferritic stainless steel strip having an excellent strength-elongation balance.

[0002]

2. Description of the Related Art Ferritic stainless steel strips are usually
After the continuously cast slab is heated, it is manufactured through the steps of hot rolling (rough rolling and finish rolling), hot-rolled sheet annealing, cold rolling and finish annealing. The ferritic stainless steel strip produced in this manner is generally used widely in various fields such as kitchen appliances and automobile parts because it is excellent in stress corrosion cracking resistance and inexpensive. However, it has a drawback in that it is slightly inferior in press workability (strength and elongation) as compared with austenitic stainless steel, and has wrinkles called ridging during press work. Therefore, ferritic stainless steel is
If its strength and elongation (represented by tensile strength TS × elongation El, abbreviated as “strength-elongation balance”; the same applies below) and ridging are improved, it is difficult to perform the processing which was difficult to apply in the past. Even in places, it will be used instead of austenitic stainless steel.

By the way, many attempts have been made so far in order to improve the press workability of ferritic stainless steel. For example, Japanese Unexamined Patent Publication No. 53-48018 and Japanese Examined Patent Publication No. 2-7391 describe ultra-low C and N steels.
A technique for improving the r value by adding Nb or Ti has been proposed. However, this technique has a problem that although the r value is improved, the in-plane anisotropy (Δr) of the r value is large and the strength-elongation balance is poor.
Further, Japanese Patent Laid-Open No. 62-10217 discloses a strain rate of 15 in a hot rolling process of a ferritic stainless steel piece.
A technique has been proposed for improving the ridging resistance by regulating the relationship between the strain rate and the friction coefficient of 0 1 / sec or more. However, this technique also improves ridging resistance, but is insufficient in terms of in-plane anisotropy of r value, and is not a technique for improving strength-elongation balance.

[0004]

As described above, the above-mentioned known technique can improve the r value or the ridging resistance in terms of the improvement of pressability, but on the other hand, the in-plane anisotropy of the r value is They had a common problem of making them larger. Moreover, in any of these known techniques, no attention has been paid to the strength-elongation balance to improve the characteristics.

Therefore, a main object of the present invention is to establish a technique for producing a ferritic stainless steel strip which does not cause the above-mentioned problems of the above-mentioned known technique even if the r value and the ridging resistance are improved. Especially. Another object of the present invention is to provide a method for producing a ferritic stainless steel strip having excellent r-value and ridging resistance, small in-plane anisotropy of r-value, and excellent strength-elongation balance. . A more specific object of the present invention is that the in-plane anisotropy (Δr) of the r value is 0.3 or less, the strength-elongation balance (TS ×
An object of the present invention is to provide a method for producing a ferritic stainless steel strip having El) of 18,000 or more.

[0006]

Means for Solving the Problems Now, as a result of earnest research toward realization of the above-mentioned object, the inventors have found that the chemical composition of ferritic stainless steel and hot rolling conditions, especially its rough rolling conditions, and hot rolling. If the plate annealing conditions are properly controlled, r
In addition to the improvement of the value and ridging resistance, it was found that the in-plane anisotropy and the strength-elongation balance can be improved, and the present invention has been completed.

The gist of the present invention is the following configuration embodying the above findings. (1) The ferritic stainless steel material is subjected to hot rolling consisting of rough rolling and finish rolling, and then hot rolled sheet annealing,
In the method for producing a stainless steel strip by performing pickling, cold rolling and finish annealing, γp represented by the following formula (1) calculated from the chemical composition of the ferritic stainless steel is 20 to 80. At least one pass of the rough rolling step is performed at a rolling temperature of 970 to 1150.
℃, the friction coefficient is 0.3 or less and the rolling reduction is 40 to 75%, and further 750 to 9 in the hot rolled sheet annealing step.
A ferritic stainless steel strip with small in-plane anisotropy and excellent in strength-elongation balance characterized by holding for 1 hr or more at 50 ° C. and holding for 1 hr or more at 600 to 750 ° C. in the temperature lowering process. Production method. Note γp = 288 (Cwt%) + 350 (Nwt%) + 22 (Niwt%) + 7.5 (Mn wt%)-18.75 (Crwt%)-54 (Siwt%) + 338.5 ... (1)

(2) A ferritic stainless steel material is hot-rolled by rough rolling and finish rolling, then hot-rolled sheet is annealed, pickled, cold-rolled and then finish annealed to obtain a stainless steel strip. In the method for producing the above, γp represented by the following formula (1) calculated from the chemical composition of the ferritic stainless steel is set to 20 to 80, and at least one pass of the rough rolling step is performed at a rolling temperature. 97
0 to 1150 ° C, friction coefficient of 0.3 or less and rolling reduction of 40 to
It is carried out under the condition of 75%, and at least one pass of the finish rolling step is performed at a rolling temperature of 600 to 950.
C., a reduction rate of 20 to 45%, further holding at 750 to 950.degree. C. for 1 hr or more in the hot rolled sheet annealing step, and 600 to 750.degree. C. in the temperature decreasing process.
The method for producing a ferritic stainless steel strip having a small in-plane anisotropy and an excellent strength-elongation balance, which is characterized by holding for 1 hr or more. Note γp = 288 (Cwt%) + 350 (Nwt%) + 22 (Niwt%) + 7.5 (Mn wt%)-18.75 (Crwt%)-54 (Siwt%) + 338.5 ... (1)

In each of the above inventions, the temperature range for rough rolling is 900 to 1300 ° C., and the temperature range for finish rolling is 550 to 550.
It is desirable that the 1000 ℃. In addition, in each of the above inventions, the preferable range of the composition of the ferritic stainless steel satisfying γp of 20 to 80 is as follows.
C: 0.1 wt% or less, more preferably 0.0010 to 0.080 wt%
, Si: 1.5 wt% or less, more preferably 0.10 to 0.80 wt
%, Mn: 1.5 wt% or less, more preferably 0.10 to 1.50 wt
%, Cr: 11 to 20 wt%, more preferably 14 to 19 wt%, Ni:
2.0 wt% or less, more preferably 0.01 to 1.0 wt%, P: 0.
08wt% or less, more preferably 0.010 to 0.080wt%,
S: 0.0100 wt% or less, more preferably 0.0010 to 0.0080 wt
%, N: 0.1 wt% or less, more preferably 0.002 to 0.08 wt
%, And if necessary, Nb: 0.050 to 0.30 wt%, Ti:
0.050 to 0.30wt%, Al: 0.010 to 0.20wt%, V: 0.050
~ 0.30wt%, Zr: 0.050 ~ 0.30wt%, Mo: 0.50 ~ 2.5
wt%, Cu: 0.50 to 2.5 wt% Steel containing one or more selected from the group consisting of Fe and inevitable impurities.

[0010]

First, the results of the experimental research that triggered the present invention will be described. Ferrite stainless steel with different γp in the high frequency vacuum melting furnace (C: 0.010 to
0.080-wt%, Si: 0.20-0.60 wt%, M
n: 0.20 to 0.70 wt%, P: 0.032 wt%,
S: 0.0029 wt%, Cr: 16.3 wt%, Ni:
0.09-0.30 wt%, N: 0.012-0.060
wt%, A1: 0.01 wt%) was melted to form a block piece having a thickness of 200 mm. These were heated to 1230 ° C. and subjected to hot rolling consisting of 4 passes of rough rolling and 5 to 7 passes of finish rolling to obtain 4.0 mm thick hot rolled steel sheets. Here, the final pass R4 in the rough rolling (rolling temperature: 1030 to 1080
(° C) rolling coefficient and friction coefficient between roll and rolled material (μ)
And the value of the reduction ratio of the final pass F5 or F7 in the finish rolling (rolling temperature: 800 to 870 ° C.) (18%, 3
0%) was changed. In addition, hot-rolled sheet annealing was performed at 850 ° C for 4
After the temperature was maintained, the temperature was lowered at 700 ° C. for 2 hours in the cooling process (cooling rate: 20 ° C./hr), and then 50% at the above cooling rate.
Cooled to 0 ° C. However, some of them were not held and cooled from 850 ° C to 500 ° C at the above cooling rate. The hot rolled steel sheet obtained by the above method is pickled-cold rolled-
A 0.7 mm-thick cold-rolled annealed plate was obtained through the process of finish annealing. A test piece was sampled from this cold-rolled annealed plate, and mechanical properties (tensile strength, elongation) and in-plane anisotropy (Δr) of r value were measured. In addition, Δr is Δr = (r _L −2r _D + r _C ).
Calculated from / 2. However, r _L , r _D, and r _C represent r values in the rolling direction, the direction of 45 ° with respect to the rolling direction, and the direction of 90 ° with respect to the rolling direction, respectively. 1 and 2 show the influence of hot rolling conditions and hot rolled sheet annealing conditions on the strength-elongation balance and Δr obtained by the above method, respectively.
Shown in

From FIG. 1, when γp is in the range of 20 to 80, when the rough rolling is rolled under one large rolling lubrication, the strength-elongation balance becomes large, and the effect is that the rolling reduction in the final rolling final pass is large. The higher the value, the more prominent. It is said that if TS × El is 18,000 or more, the press formability is greatly improved. Further, from FIG. 2, when γp is in the range of 20 to 80, when rough rolling is performed under lubrication-large reduction and finish rolling is performed under large pressure, and further, 700 ° C. is maintained during the temperature reduction process of hot-rolled sheet annealing, Although the in-plane anisotropy becomes very small, it can be seen that the in-plane anisotropy exceeds 0.3 when large reduction rolling is not performed or 700 ° C. holding is omitted.

Next, in the present invention, the reason why the manufacturing conditions of the ferritic stainless steel strip are limited to the above-mentioned constitution will be explained. (1) γp: 20 to 80 If γp represented by the above formula (1) is less than 20, the strength decrease is greater than the increment of elongation, while if it exceeds 70, the strength is increased but the elongation is significantly reduced. . Therefore, in either case, the balance between strength and elongation is poor, and press formability deteriorates. Therefore, the range of γp is set to 20-80. The preferable range is 40 to 70.

(2) Rolling temperature of rough rolling: 970 to 1150
C. If the rolling temperature of the rough rolling is less than 970.degree. C., recrystallization of the ferritic stainless steel is less likely to proceed, the workability is inferior, the in-plane anisotropy is not improved, and the roll life during the large reduction rolling is significantly shortened. On the other hand, when the temperature exceeds 1150 ° C., the ferrite grains have a structure extending in the rolling direction and the in-plane anisotropy increases. Therefore, the rolling temperature of rough rolling is 97
It is necessary to adjust the temperature to 0 to 1150 ° C. The preferable temperature range is 1000 to 1100 ° C.

(3) Rolling reduction of rough rolling: 40 to 75% If the rolling reduction of rough rolling is less than 40%, a large amount of unrecrystallized structure remains in the central portion of the plate thickness, resulting in poor workability. The internal anisotropy is not improved either. However, rolling over 75% may cause seizure or defective biting. Therefore, the reduction ratio of rough rolling is 40 to
Must be 75%. The preferable range of the rolling reduction is 45 to 60%.

(4) Coefficient of Coefficient of Rough Rolling: 0.30 or Less When the coefficient of friction of rough rolling exceeds 0.30, recrystallization occurs in the high shear strain region of the surface layer of the steel sheet, but large at the center of the thickness. Since the part remains as an unrecrystallized structure, the workability is poor,
The in-plane anisotropy is not improved either. Moreover, the seizure between the steel sheet and the roll significantly deteriorates the surface properties of the steel sheet. Therefore, the coefficient of friction of rough rolling needs to be 0.30 or less, preferably 0.2 or less. The lubrication method for reducing the friction coefficient may be any method such as mixing a low melting glass lubricant with water and spraying it on a steel plate or roll .

(5) Hot-rolled sheet annealing Annealing of the hot-rolled sheet at a temperature of 750 to 950 ° C. for at least 1 hr is performed by recrystallization of the steel sheet and the transformation phase remaining in the hot-rolled sheet is ferrite phase. The purpose is to decompose into carbides. If the annealing condition is less than 750 ℃,
If it is less than hr, the recrystallization temperature and the decomposition of the transformation phase are insufficient, so that the strength-elongation balance decreases. Meanwhile 950
If the temperature exceeds ℃, the γ phase is precipitated, so that the cold rolling property is deteriorated and the strength-elongation balance is also deteriorated. When the temperature is held at 600 to 750 ° C. for 1 hour or more, the r value is improved and the in-plane anisotropy is decreased.
This is because C and N in the steel are Cr during holding at 600 to 750 ° C.
It is considered that since it precipitates as carbonitrides, the solid solution C and N before cold rolling were reduced, and the r value and the in-plane anisotropy (Δr) were improved. Holding condition is less than 600 ℃, lh
If it is less than r, the precipitation amount of Cr carbonitride is small and the r value is lowered. On the other hand, when the temperature exceeds 750 ° C., there is almost no precipitation of Cr carbonitride and C and N in the steel are in a solid solution state, so that the r value is remarkably lowered.

At least one pass of the rough rolling satisfying the conditions (2), (3) and (4) is performed on the ferritic stainless steel of the above component (1), and then the hot rolled sheet annealing (5) is performed. By doing so, the strength-elongation balance of the product is excellent, and the in-plane anisotropy is also improved. The above 1 pass may be performed in any of the rough rolling steps. Subsequent to such rough rolling and hot-rolled sheet annealing, further finish rolling satisfying the following conditions makes it possible to further improve the in-plane anisotropy.

(6) Rolling temperature for finish rolling: 600 to 95
If the rolling temperature of 0 ° C. finish rolling is less than 600 ° C., it is difficult to secure a reduction rate of 20%, and the roll wear becomes severe. On the other hand, when the rolling temperature exceeds 950 ° C, the effect of improving the in-plane anisotropy cannot be expected because the rolling strain is less accumulated. Therefore, the rolling temperature for finish rolling is 6
It should be in the range of 00 to 950 ° C, preferably 7
The range of 50 to 900 ° C is preferable.

(7) Rolling ratio of finish rolling: 20 to 45% If the rolling ratio of finish rolling is less than 20%, the in-plane anisotropy is not improved. On the other hand, if the rolling ratio exceeds 45%, the steel sheet Surface quality deteriorates. Therefore, the rolling reduction of finish rolling must be in the range of 20 to 45%, and preferably 2
The range of 5 to 35% is preferable.

In the present invention, manufacturing conditions other than the above-mentioned processing conditions may be in accordance with a conventional method. For example, slab heating is from 1050 to 1300 ° C., and a temperature range of rough rolling is 900.
~ 1300 ℃, finish rolling temperature range 550 ~ 105
0 degreeC, and 750-1000 degreeC of cold-rolled board annealing are preferable.
Also, the type of lubricating oil and the lubricating method may be appropriately determined according to a conventional method.

The present invention can be applied to any ferritic stainless steel satisfying γp of 20 to 80 regardless of the component composition, but the following component composition can be applied more advantageously. C: 0.1 wt% or less, more preferably 0.00
10 to 0.080 wt%, Si: 1.5 wt% or less, more preferably
0.10 to 0.80 wt%, Mn: 1.5 wt% or less, more preferably 0.
10 to 1.50 wt%, Cr: 11 to 20 wt%, more preferably 14 to 19
wt%, Ni: 2.0 wt% or less, more preferably 0.01 to 1.0 wt
%, P: 0.08 wt% or less, more preferably 0.010 to 0.080 w
t%, S: 0.0100 wt% or less, more preferably 0.0010 to
0.0080 wt%, N: 0.1 wt% or less, more preferably 0.002
~ 0.08wt%, if necessary, Nb: 0.050 ~ 0.30wt
%, Ti: 0.050 to 0.30 wt%, Al: 0.010 to 0.20 wt%,
V: 0.050 to 0.30 wt%, Zr: 0.050 to 0.30 wt%, Mo: 0.
50-2.5 wt%, Cu: 0.50-2.5 wt% 1
A steel containing one or more kinds, and the balance being Fe and inevitable impurities.

[0022]

Example 1 Steels A to F having the chemical compositions shown in Table 1 were melted into slabs, heated to 1200 ° C., and then hot-rolled with 4 rough stands and 7 finish stands. A hot rolled plate having a plate thickness of 4.0 mm was used. At this time, the temperature of the fourth stand of the rough rolling, the reduction ratio,
The friction coefficient was changed. The friction coefficient was adjusted by changing the concentration of the lubricant (low melting glass lubricant). The rolling reductions of the other stands for rough rolling were all made smaller than the rolling reduction of the fourth stand. Further, the hot-rolled sheet annealing was held at 850 ° C. for 4 hours and then cooled (cooling rate: 20
C./hr) at 700.degree. C. for 2 hours, and then cooled to 500.degree. C. at the above cooling rate. However, some of them were not held and cooled from 850 ° C to 500 ° C at a cooling rate of 20 ° C / hr. This hot-rolled sheet was pickled, cold-rolled and finish-annealed (850 ° C x
By 60 seconds), a cold rolled steel sheet having a sheet thickness of 0.7 mm was obtained.

[0023]

[Table 1]

Using the steel sheet obtained by the above method as a test material, the characteristic values of strength-elongation balance, r value, Δr and ridging were measured by the following methods. The stainless steel manufactured by the conventional method has an absolute value of 0.4 to 0.4.
Since it is about 0.8, it can be said that it is good if the absolute value is 0.3 or less. -Strength / elongation balance Using JIS No. 13B test piece, tensile strength TS (N / mm
² ) and the elongation El (%) were calculated. -R value After applying a 15% tensile strain using JIS No. 13B test piece, the average r value by the 3-point method was determined. -Δr From the r value in each direction obtained by the above method, Δr = (r _L -2r
_D + r _C ) / 2. However, r _L , r _D, and r _C are 45 ° with respect to the rolling direction and the rolling direction, respectively.
And the r value in the direction of 90 ° to the rolling direction. -Ridging After applying a tensile strain of 20% to the JIS No. 5 test piece taken from the rolling direction, the ridging height was measured.

Table 2 shows the above-mentioned rough rolling conditions and hot-rolled sheet annealing conditions and the obtained characteristic values. In addition, all the steel sheets manufactured by the method of the present invention were good without any deterioration in surface quality, defective biting, or defective shape.

[0026]

[Table 2]

From Table 2, the steel plates to which the method of the present invention is applied are:
Δr is small in the range of −0.30 to 0.30, and T
It can be seen that S × El is 18,000 or more, and the r value and ridging resistance are excellent.

Example 2 Steels A to F having the chemical compositions shown in Table 1 were smelted into slabs, heated to 1230 ° C., and then rolled by a hot rolling mill consisting of coarse 4 stands and finishing 7 stands. The hot-rolled sheet had a thickness of 4.0 mm. At this time, the temperature of the fourth stand of the rough rolling, the reduction ratio,
The friction coefficient was changed. The friction coefficient was adjusted by changing the concentration of the lubricant (low melting glass lubricant). The rolling reductions of the other stands for rough rolling were all made smaller than the rolling reduction of the fourth stand. Further, the temperature and the rolling reduction in the final pass of finish rolling were also changed. However,
The rolling reductions of the other stands in finish rolling were all smaller than the rolling reduction of the final stand. The hot rolled sheet annealing is 8
After holding at 50 ° C for 4 hours, the temperature decreasing process (cooling rate: 20 ° C /
After holding for 2 hours at 700 ° C. in hr), it was cooled to 500 ° C. at the above cooling rate. However, some of them do not hold this temperature, from 850 ℃ to 500 ℃, 20 ℃
It was cooled at a cooling rate of / hr. This hot-rolled sheet was pickled, cold-rolled and finish-annealed (850 ° C x 60
Seconds) to obtain a cold rolled steel sheet having a thickness of 0.7 mm. Using the steel sheet obtained by the above method as a test material, TS × El, r
Values, Δr, and ridging characteristic values were measured in the same manner as in Example 1.

Table 3 shows the above-mentioned rough rolling conditions and hot-rolled sheet annealing conditions and the obtained characteristic values. In addition, all the steel sheets manufactured by the method of the present invention were good without any deterioration in surface quality, defective biting, or defective shape.

[0030]

[Table 3]

From Table 3, the steel plates to which the method of the present invention is applied are:
Δr is small in the range of −0.30 to 0.30, and T
It can be seen that S × El is 18,000 or more, and the r value and ridging resistance are excellent.

[0032]

As described above, according to the method of the present invention, r
It is possible to manufacture a ferritic stainless steel strip having a small in-plane anisotropy, excellent strength-elongation balance, and excellent r value and ridging resistance. Therefore, according to the present method, it becomes possible to apply the ferritic stainless steel to a processed member, which has been difficult to apply conventionally, which contributes to the quality improvement and cost reduction of stainless steel products.

[Brief description of drawings]

FIG. 1 is a graph showing the effects of γp, hot rolling, and annealing conditions on TS × El.

FIG. 2 is a graph showing the influence of γp, hot rolling, and annealing conditions on the in-plane anisotropy of r value.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Uki Ko, 1 Kawasaki-cho, Chuo-ku, Chiba, Chiba Prefecture Inside the Technical Research Laboratory, Kawasaki Steel Co., Ltd. (72) Inventor Makoto Kobayashi 1 Kawasaki-cho, Chuo-ku, Chiba-shi Kawasaki Steel Co., Ltd. Chiba Steel Works (72) Inventor Shohei Kanari 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Kawasaki Steel Co., Ltd.

Claims (2)

[Claims] 1. A stainless steel strip is obtained by subjecting a ferritic stainless steel material to hot rolling consisting of rough rolling and finish rolling, followed by hot-rolled sheet annealing, pickling, cold rolling and finish annealing. In the manufacturing method, γp represented by the following formula (1) calculated from the chemical composition of the ferritic stainless steel is set to 20 to 80, and at least one pass of the rough rolling step is performed at a rolling temperature of 970. ~ 1150 ° C, friction coefficient 0.3 or less and rolling reduction 4
It is carried out under the condition of 0 to 75%, and further, it is held for 1 hr or more at 750 to 950 ° C. in the hot-rolled sheet annealing step, and is held for 1 hr or more at 600 to 750 ° C. in the temperature decreasing process. A method for producing a ferritic stainless steel strip having a small in-plane anisotropy and an excellent strength-elongation balance. Note γp = 288 (Cwt%) + 350 (Nwt%) + 22 (Niwt%) + 7.5 (Mn wt%)-18.75 (Crwt%)-54 (Siwt%) + 338.5 (1) 2. A stainless steel strip is obtained by subjecting a ferritic stainless steel material to hot rolling consisting of rough rolling and finish rolling, followed by hot rolling sheet annealing, pickling, cold rolling and finish annealing. In the manufacturing method, γp represented by the following formula (1) calculated from the chemical composition of the ferritic stainless steel is set to 20 to 80, and at least one pass of the rough rolling step is performed at a rolling temperature of 970. ~ 1150 ° C, friction coefficient 0.3 or less and rolling reduction 4
The rolling temperature is 600 to 95 at least 1 pass of the finish rolling step.
It is carried out under the conditions of 0 ° C. and a reduction rate of 20 to 45%, and further, it is held at 750 to 950 ° C. for 1 hour or more in the hot rolled sheet annealing step, and 600 to 750 in the temperature lowering process.
A method for producing a ferritic stainless steel strip having a small in-plane anisotropy and an excellent strength-elongation balance, which is characterized by holding at 0 ° C for 1 hour or more. Note γp = 288 (Cwt%) + 350 (Nwt%) + 22 (Niwt%) + 7.5 (Mn wt%)-18.75 (Crwt%)-54 (Siwt%) + 338.5 ... (1)