JPH11100617A - Production of cold rolled ferritic stainless steel sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a cold rolled steel sheet excellent in ridging resistance by using a ferritic stainless steel represented by SUS430. SOLUTION: A ferritic stainless steel, having a composition which consists of, by weight, 16.00-18.00% Cr, 0.004-0.1% Ti, <=0.08% C, <=1.00% Si, <=1.00% Mn, <=0.030% S, <=1.00% Ni, <=0.1% N, and the balance Fe with inevitable impurities and in which the value of γ-potential represented by (γ- potential)=700[C(%)]+800[N(%)]+10[Mn(%)]+20[Ni(%)]-9.2[Si(%)]-6.2[Cr(% )]+63.2 is regulated to 30 to 60, is used. A continuously castslab of this steel is heated to 1,050 to 1,230 deg.C, and reduction is applied at 1 to 30% in a slab-width direction at the time of hot roughing and also reduction is applied at 65 to 80% in total in a thickness direct ion at the last pass but two and at the last pass. Subsequently, finish rolling is performed at 700 to 950 deg.C to form a hot coil, followed by hot rolled plate annealing at 800 to 850 deg.C. After cold rolling, the resultant cold rolled sheet is finish-annealed at 800 to 850 deg.C by continuous annealing.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a cold-rolled steel sheet of ferritic stainless steel represented by SUS430 and having good ridging resistance.

[0002]

2. Description of the Related Art Ferritic stainless cold-rolled steel sheets represented by SUS430 have become widespread in recent years as inexpensive stainless steels in bathtubs, sinks, tableware, electric appliances, and the like, and their production tends to increase. However, the cold-rolled ferritic stainless steel sheet is hot-rolled without transformation of the solidification structure (columnar crystal) formed by continuous casting, and the subsequent hot-rolled sheet annealing and columnar crystals are formed on the steel sheet surface after cold rolling. There is a defect called ridging in which traces of undulations are undulated in a line parallel to the rolling direction, and there is a disadvantage that the commercial value of appearance is significantly impaired. Further, the ridging is promoted by a distortion pattern called roping due to unevenness in the rolling direction due to 20% tension, and may cause a problem such as an extra polishing step. This is referred to as a wrinkle pattern generated when a product is formed by processing, and significantly reduces the commercial value of appearance.

[0003] As a method for preventing the ridging, the ridging is relaxed by annealing and recrystallizing a hot-rolled sheet for a long time. Ridging caused by columnar crystals generated by continuous casting has been used. Is not valid for Further, a method has been proposed in which a small amount of elements such as Ti and Zr are added to reduce columnar crystals during continuous casting to increase equiaxed crystals and reduce ridging (Japanese Patent Publication No. 53-21994). However, the magnetic properties are deteriorated, which is not practical.

As another method for preventing ridging, for example, an unsolidified molten steel is agitated by electromagnetic force during continuous casting, and a slab center region corresponding to a non-recrystallization center region at the time of hot rolling determined by hot rolling conditions is determined. To reduce ridging by equiaxed crystallization in the range (JP-B-57-159)
No. 69), the final pass of rough rolling in hot rolling is 900 ° C.
A method in which the ridging of the product plate is eliminated by ending the rolling under the high-pressure rolling of 50 to 70% and finishing the subsequent finishing rolling in the low temperature region of 850 to 720 ° C (Japanese Patent Publication No. Sho 56-43091). In addition, mixing of impurities in steel is suppressed as much as possible, and for at least one of Ti and Zr, according to the total amount of Si and Al, ΔTi (%) +
0.5Zr (%)｝ ≦ 0.022 / ｛Si (%) + Al
(%) The method of suppressing ridging by reducing it to within the limit range (制 限) has been proposed (JP-B-56-31846).

[0005]

SUMMARY OF THE INVENTION The above-mentioned Japanese Patent Publication No. 57-15 / 1982
According to the method disclosed in Japanese Patent No. 969, it is extremely difficult to produce a 100% equiaxed slab, and it is impossible to completely eliminate ridging in a continuous cast slab in which columnar crystals remain. Further, the method disclosed in Japanese Patent Publication No. Sho 56-43091 does not completely eliminate ridging. Furthermore, the method disclosed in Japanese Patent Publication No. 56-31846, like the method disclosed in Japanese Patent Publication No. 53-211994, causes deterioration of magnetic characteristics and is not practical.

An object of the present invention is to provide a method for manufacturing a cold-rolled ferritic stainless steel sheet which can solve the above-mentioned disadvantages of the prior art and can eliminate ridging caused by columnar crystals during continuous casting.

[0007]

Means for Solving the Problems The present inventors have conducted research and studies to achieve the above object, and as a result, have found that the chemical component is γ-
By increasing the ratio of the austenite forming element by controlling the potential, it is possible to suppress the growth of ferrite grains and increase the number of fine grains, and to set a predetermined amount in both the width direction and the thickness direction at a predetermined temperature during hot rough rolling. By applying the rolling, it was determined that the columnar crystals of the continuous casting slab were broken at the completion of the rough rolling, a recrystallized structure was generated, and the ridging was significantly reduced.

[0008] The method for producing a cold rolled ferritic stainless steel sheet according to claim 1 of the present invention is as follows: C: 0.08% or less;
1.00% or less, Mn: 1.00% or less, S: 0.03
0% or less, Cr: 16.00% to 18.00%,
Ni: 1.00% or less, N: 0.1% or less, Ti: 0.
004% or more and 0.1% or less, with the balance being Fe and unavoidable impurities, and γ determined by the following equation (1).
-A continuous cast slab of ferritic stainless steel having a potential of 30 or more and 60 or less is used.
C. or less, and a reduction of 1% or more and 30% or less is applied in the slab width direction during hot rough rolling, and a total reduction of 65% or more and 80% or less is applied in the thickness direction before the final two passes and in the final pass. Next, finish rolling is performed at 700 ° C. or more and 950 ° C. or less to form a hot-rolled coil, and after hot-rolled sheet annealing is performed at 800 ° C. or more and 850 ° C. or less, cold rolling is performed.
Finish annealing by continuous annealing is performed at a temperature of not more than ℃. γ-potential = 700 [C (%)] + 800 [N (%)] + 10 [Mn (%)] + 20 [Ni (%)]-9.2 [Si (%)]-6.2 [Cr (% )] + 63.2 Equation (1) As described above, the hot-rolled coil obtained by hot-rolling the continuous cast slab of the ferritic stainless steel having the above-mentioned chemical composition under the above-mentioned conditions is continuously rolled when the rough rolling is completed. Since the columnar crystals of the cast slab are broken and a recrystallized structure is generated, ridging does not occur during cold rolling, and a ferritic stainless steel cold-rolled steel sheet without ridging can be manufactured.

The method for producing a cold-rolled ferritic stainless steel sheet according to claim 2 of the present invention is characterized in that: C: 0.08% or less;
Si: 1.00% or less, Mn: 1.00% or less, S:
0.030% or less, Cr: 16.00% or more and 18.00
%, Ni: 1.00% or less, N: 0.1% or less, T
i: 0.004% or more and 0.1% or less, with the balance being F
e and unavoidable impurities, and the γ-potential determined by the above equation (1) is heated from 1050 ° C to 1230 ° C. A reduction of 1% or more and 30% or less is applied in the slab width direction, and a total of 65% or more and 80% in the thickness direction before the final two passes and in the final pass.
The following reduction was applied, and then finish rolling was performed at 700 ° C. or more and 950 ° C. or less to form a hot-rolled coil.
After hot-rolled sheet annealing at 0 ° C. or less, cold rolling is performed with one or two or more intermediate annealings interposed therebetween, and finish annealing by continuous annealing at 800 ° C. or more and 850 ° C. or less is performed. As described above, a hot-rolled coil obtained by hot rolling a continuous cast slab of ferritic stainless steel having the above chemical composition under the above conditions, upon completion of rough rolling, columnar crystals of the continuous cast slab are destroyed and a recrystallization structure is obtained. Since it is generated, ridging does not occur during cold rolling, and a ferritic stainless cold-rolled steel sheet without ridging can be manufactured.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The reasons for limiting the chemical components of steel in the present invention are as follows. C is 0.08%
If it exceeds 0.008%, it causes work hardening during cold working and deteriorates moldability.

If Si is contained in excess of 1.00%, the ductility is deteriorated and a breakage problem occurs during rolling. Therefore, the content of Si is set to 1.00% or less.

If Mn is contained in excess of 1.00%, work hardening occurs during cold working, and MnS precipitates, which significantly impairs hot and cold workability.
1.00% or less.

When S is contained in excess of 0.030%, a sulfide mainly composed of MnS is formed, and the hot workability is remarkably reduced. Therefore, the content of S is set to 0.030% or less.

If the Cr content is less than 16%, the corrosion resistance deteriorates. If the Cr content exceeds 18%, the hot workability deteriorates due to the precipitation of the σ phase and the cost increases.
16% or more and 18% or less.

If Ni is contained in excess of 0.1%, the yield strength and tensile strength increase, and the workability during molding decreases.

If N is contained in excess of 0.1%, a large amount of nitride precipitates at the grain boundaries and the hot workability is reduced.
0.1% or less.

If the content of Ti is less than 0.004%, the effect of refining the crystal grains is reduced, and the sulfide is increased to deteriorate the bending workability. In order to deteriorate the surface properties, cleanliness, etc. by forming nitrides, the content is made 0.004% or more and 0.1% or less.

When the γ-potential obtained by the above equation (1) is less than 30, the amount of ferrite produced increases, and
The crystal grains become coarse and significantly impair ridging resistance.
If it exceeds 60, on the contrary, the amount of austenite generated increases, the proof stress and tensile strength increase, and the workability during molding decreases.

The continuous cast slab of ferritic stainless steel is heated to a temperature of 1050 ° C. or more and 1230 ° C. or less, and 1% or more in a slab width direction using a width reduction press such as a sizing press during rough rolling in hot rolling. A reduction of 30% or less is applied, and a total reduction of 65% or more and 80% or less is applied in the thickness direction before the final two passes and in the final pass, followed by finish rolling at 700 ° C or more and 950 ° C or less to obtain a hot-rolled coil. .

The heating temperature of the continuous casting slab is 105
If the temperature is lower than 0 ° C., it is difficult to secure the finishing temperature, and the temperature is 1230 ° C.
If it exceeds 90, the columnar crystals are coarsened and precipitates such as MnS are redissolved, deteriorating hot workability and ridging resistance.
The temperature was set to 50 ° C or higher and 1230 ° C or lower. Further, the slab width reduction is indispensable for breaking the columnar crystals. However, under the width reduction by the vertical roll, the columnar crystals are not sufficiently broken down to the center in the width direction due to the occurrence of dog bone, etc. It is preferable to use a width reduction press such as a sizing press. As shown in FIG. 1, when the width reduction ratio is less than 1%, there is no effect on ridging prevention, and when it exceeds 30%, width reduction becomes difficult. Therefore, the width reduction ratio in the hot rough rolling is 1% or more. % Or less. Furthermore, if the total rolling reduction in the thickness direction before and after the final two passes in the hot rough rolling is less than 65%, there is no effect on ridging prevention, and when it exceeds 80%, rolling becomes difficult. The total rolling reduction in the thickness direction before the final two passes and in the final pass in rolling was 60% or more and 80% or less. Furthermore, when the finish rolling temperature is less than 700 ° C., the rolling load increases and the finish rolling becomes difficult, and when it exceeds 950 ° C., the crystal grains become coarse due to recrystallization, and the ridging resistance deteriorates. The temperature was set to 700 ° C. or more and 950 ° C. or less.

The hot-rolled coil is pickled and then 800
After hot-rolled sheet annealing at a temperature of 850 ° C or higher and 850 ° C or lower,
Cold rolling or cold rolling with one or two or more intermediate annealing steps is performed, and finish annealing by continuous annealing is performed at a temperature of 800 ° C or more and 850 ° C or less. Hot rolled sheet annealing is 800
When the temperature is lower than 850 ° C., there is no effect because recrystallization is not performed. When the temperature is higher than 850 ° C., crystal grains are recrystallized and then coarsened to deteriorate ridging resistance.
Further, the intermediate annealing in the cold rolling has no effect because it is not recrystallized below 800 ° C., and if it exceeds 850 ° C., the crystal grains are recrystallized and then coarsened to deteriorate the ridging resistance. Further, in the finish annealing by continuous annealing, if the temperature is lower than 800 ° C., a sufficient recrystallization structure cannot be obtained and there is no ridging prevention effect, and if the temperature exceeds 850 ° C., the crystal grains are recrystallized and then coarsened to deteriorate ridging resistance. , 800 ° C or higher, 850
° C or less.

[0022]

EXAMPLES Ferrite stainless steels of the present invention of steel types A to E shown in Table 1 and comparative ferritic stainless steels of steel types F to J in which the chemical components indicated by * are out of the range of the present invention are 227 mm thick and 1000 mm wide. The continuous cast slab of the present invention was subjected to hot rolling under hot rolling conditions shown in Table 2 in the present invention and Table 3 in the comparative example to obtain a hot-rolled coil having a thickness of 2.3 mm.
In the example of the present invention, a hot-rolled sheet was annealed and pickled under the conditions shown in Table 4 and Table 5 in the comparative example, and then cold-rolled under the conditions shown in Tables 4 and 5 to obtain a 0.40 mm-thick cold-rolled steel. Obi and none, then 85
Recrystallization annealing was performed by continuous annealing at a temperature of 0 ° C. A test specimen was collected from each of the obtained ferritic stainless steel cold-rolled steel strips, subjected to a 20% tensile test, visually inspected for a striped state called roping on the surface, and evaluated on a five-point scale of 1 to 5. At the same time, the surface defect of each ferritic stainless steel cold rolled steel strip coil was evaluated by x for barge flaws and ○ for none. The results are shown in Tables 4 and 5. The results of coil roping are as follows: 1 and 2 are unacceptable, and 3 to 5 are good and pass.

[0023]

[Table 1]

[0024]

[Table 2]

[0025]

[Table 3]

[0026]

[Table 4]

[0027]

[Table 5]

As shown in Tables 1, 2 and 4, Test No. In each of Examples 1 to 24 of the present invention, 3 to 5 of acceptable lines were obtained as a result of coil roping, and no barbed flaw was observed in the coil. On the other hand, as shown in Tables 1, 3 and 5, steel grades F to
Test No. J using No. J In the comparative examples 25 to 31, the test N in which 3 to 5 of the acceptable lines were obtained in the coil roping results
o. In Test Nos. 26, 27 and 29-31, the coil had barbed flaws and the coil had no barbed flaws.
o. In 25 and 28, the coil roping result was 2 in the reject line.

[0029]

The method for producing a cold rolled ferritic stainless steel sheet according to claim 1 of the present invention is characterized in that a continuous cast slab having a predetermined chemical composition is heated to 1050 ° C. to 1230 ° C. , A reduction of 65% to 80% in total in the thickness direction before the final two passes and in the final pass.
Finish rolling at 0 ° C or more and 950 ° C or less to form a hot-rolled coil, hot-rolled sheet annealing at 800 ° C or more and 850 ° C or less, cold rolling, and finish annealing by continuous annealing at 800 ° C or more and 850 ° C or less. By doing so, the hot-rolled coil subjected to hot rolling, at the time of rough rolling completion, columnar crystals of the continuous casting slab are destroyed and a recrystallized structure is generated, so that ridging does not occur during cold rolling, A ferritic stainless cold-rolled steel sheet without ridging can be manufactured.

In the method for producing a cold rolled ferritic stainless steel sheet according to claim 2 of the present invention, the continuous cast slab having a predetermined chemical composition is heated to 1050 ° C. or more and 1230 ° C. or less,
At the time of hot rough rolling, a reduction of 1% or more and 30% or less is applied in the slab width direction, and a total reduction of 65% or more and 80% or less is applied in the thickness direction before the final two passes and in the final pass, and then 700 ° C or more and 950 ° C or less. Finish rolling is performed below to form a hot-rolled coil, hot-rolled sheet annealing at 800 ° C or more and 850 ° C or less, and cold rolling with one or two or more intermediate annealings sandwiched between 800 ° C and 850 ° C or less By performing finish annealing by continuous annealing at the time of cold rolling, the hot-rolled coil subjected to hot rolling has a recrystallized structure generated when the rough rolling is completed and the columnar crystals of the continuous cast slab are destroyed. Ridging does not occur, and a cold rolled ferritic stainless steel sheet without ridging can be manufactured.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between width reduction and ridging in hot rough rolling according to the present invention.

[Procedure amendment]

[Submission date] October 24, 1997

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0020

[Correction method] Change

[Correction contents]

The heating temperature of the continuous casting slab is 105
If the temperature is lower than 0 ° C., it is difficult to secure the finishing temperature, and the temperature is 1230 ° C.
If it exceeds 90, the columnar crystals are coarsened and precipitates such as MnS are redissolved, deteriorating hot workability and ridging resistance.
The temperature was set to 50 ° C or higher and 1230 ° C or lower. Further, the slab width reduction is indispensable for breaking the columnar crystals. However, under the width reduction by the vertical roll, the columnar crystals are not sufficiently broken down to the center in the width direction due to the occurrence of dog bone, etc. It is preferable to use a width reduction press such as a sizing press. As shown in FIG. 1, when the width reduction ratio is less than 1%, there is no effect on ridging prevention, and when it exceeds 30%, width reduction becomes difficult. Therefore, the width reduction ratio in the hot rough rolling is 1% or more. % Or less, but preferably 5% or more and 30% or less.
%, More preferably 10% or more and 30% or less .
Further, if the total rolling reduction in the thickness direction before the final two passes and in the final pass in the hot rough rolling is less than 65%, there is no effect on ridging prevention, and if it exceeds 80%, rolling becomes difficult, so The total rolling reduction in the thickness direction before the final two passes and in the final pass in rolling was 60% or more and 80% or less. Furthermore, when the finish rolling temperature is less than 700 ° C., the rolling load increases and the finish rolling becomes difficult.
If the temperature exceeds 50 ° C., the crystal grains become coarse due to recrystallization, and the ridging resistance deteriorates.
° C or less.

Claims (2)

[Claims] 1. C: 0.08% or less, Si: 1.00%
Hereinafter, Mn: 1.00% or less, S: 0.030% or less,
Cr: 16.00% to 18.00%, Ni: 1.
And the balance is composed of Fe and inevitable impurities. The γ-potential obtained by the following equation (1) is: A continuous cast slab of ferritic stainless steel of 30 or more and 60 or less is heated to 1050 ° C or more and 1230 ° C or less, and a rolling reduction of 1% or more and 30% or less is applied in the slab width direction during hot rough rolling, and before the final two passes. And in the final pass, apply a total reduction of 65% or more and 80% or less in the thickness direction,
Next, finish rolling is performed at 700 ° C. or more and 950 ° C. or less to form a hot-rolled coil, hot-rolled sheet annealing is performed at 800 ° C. or more and 850 ° C. or less, and then cold-rolled, and finish annealing by continuous annealing is performed at 800 ° C. or more and 850 ° C. or less. A method for producing a cold rolled ferritic stainless steel sheet, comprising: γ-potential = 700 [C (%)] + 800 [N (%)] + 10 [Mn (%)] + 20 [Ni (%)]-9.2 [Si (%)]-6.2 [Cr (% )] + 63.2 ... (1) 2. C: 0.08% or less, Si: 1.00%
Hereinafter, Mn: 1.00% or less, S: 0.030% or less,
Cr: 16.00% to 18.00%, Ni: 1.
And the balance is composed of Fe and inevitable impurities. The γ-potential obtained by the following equation (1) is: A continuous cast slab of ferritic stainless steel of 30 or more and 60 or less is heated to 1050 ° C or more and 1230 ° C or less, and a rolling reduction of 1% or more and 30% or less is applied in the slab width direction during hot rough rolling, and before the final two passes. And in the final pass, apply a total reduction of 65% or more and 80% or less in the thickness direction,
Next, finish rolling is performed at 700 ° C or more and 950 ° C or less to form a hot-rolled coil, hot-rolled sheet annealing is performed at 800 ° C or more and 850 ° C or less, and then cold-rolled with one or two or more intermediate annealings interposed therebetween. A method for producing a cold-rolled ferritic stainless steel sheet, comprising performing a finish annealing by continuous annealing at a temperature of 800 ° C or more and 850 ° C or less. γ-potential = 700 [C (%)] + 800 [N (%)] + 10 [Mn (%)] + 20 [Ni (%)]-9.2 [Si (%)]-6.2 [Cr (% )] + 63.2 ... (1)