JPH11302739A - Method for producing ferritic stainless steel with excellent surface properties and low anisotropy - Google Patents

Abstract

(57) [Problem] To provide a method for producing a ferritic stainless steel capable of improving workability of a ferritic stainless steel and improving ridging characteristics. SOLUTION: In wt%, C: 0.0005 to 0.010%, S: 0.0010 to
0.040%, P: 0.025% or less, Cr: 10.0 to 20.0%, Ti: 0.4% or less, N: 0.0005 to 0.020%, O: 0.01% or less, 2 ≦ S / C
When hot rolling a ferritic stainless steel satisfying ≦ 4 and 1.5 (P + S) +4 (C + N + O) ≦ Ti, the heating temperature should be 1
250 ° C or less, and the total rolling reduction of the rough rolling is 80% or more,
After finishing the rough rolling at 1000 ° C. or more with the final three passes of the rough rolling at a cumulative rolling reduction of 60% or more, the total strain of the rough rolling (logarithmic strain: εr) and the total strain of the finish rolling (logarithmic strain: εf) are determined. After performing finish rolling so that εr ≦ εf, winding at a temperature of less than 600 ° C., pickling without performing hot-rolled sheet annealing, cold-rolling, and performing excellent surface characteristics characterized by performing annealing,
A method for producing ferritic stainless steel with low anisotropy.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a ferritic stainless steel having excellent surface characteristics and low anisotropy.

[0002]

2. Description of the Related Art Ferritic stainless steel is widely used in kitchen appliances, automobile exhaust parts, and the like because of its lower Ni content and lower price than austenitic stainless steel.

[0003] The properties required for working into such products include press workability and surface properties after working. Ferritic stainless steels have better workability and surface properties than austenitic stainless steels. The fact is that it is inferior in the point.

[0004] In the case of ferritic stainless steel, an r value is mentioned as a characteristic value indicating press workability. The higher the r-value, the better the deep drawing properties. However, ferritic stainless steels have a large in-plane anisotropy, and in particular, 4% in the rolling direction.
Generally, the r value in the 5 ° direction is lower than the r value in the rolling direction or the direction perpendicular to the rolling direction.

For this reason, from the viewpoint of improving the workability, it has been studied to increase the overall r value. However, when the r-value in the 45 ° direction is low, the workability is affected by the r-value in the 45 ° direction. Therefore, a steel sheet having a small in-plane anisotropy is preferable from the viewpoint of workability.

[0006] It is known that surface irregularities called ridging occur when processed.
Since this ridging increases in proportion to the degree of processing, the aesthetic appearance is significantly impaired in the case of strong processing. Further, when the steel sheet is subjected to secondary processing after being formed once, the processing conditions may be locally changed due to unevenness and may cause a crack. Therefore, a steel sheet having good ridging resistance is desired.

[0007] Many studies have been made on the above. That is, from the viewpoint of processability improvement,
Japanese Patent Application Laid-Open No. 99151/99 discloses that a reduction rate of 900 ° C. or less
%, And rolling at a finishing temperature of 800 ° C. or less.
A method is disclosed in which winding is performed at a temperature of 00 ° C. or higher to perform hot-rolled sheet annealing. Japanese Patent Application Laid-Open No. 5-98352 also discloses a method in which the finish rolling temperature is set to 800 ° C. or less and the hot-rolled sheet is annealed. Further, Japanese Unexamined Patent Publication No. 9-235
No. 621 discloses a method in which the components are specified and the film is wound at 600 ° C. or higher.

As a measure against ridging, Japanese Patent Application Laid-Open No. 9-5315
No. 5 discloses an alloy having good ridging resistance. However, as shown in the Examples, hot rolling is performed and then hot rolled sheet annealing is performed. This results in an increase in cost due to performing, and an increase in pickling cost due to an increase in scale due to annealing.

Therefore, adding a new process to the conventional process to reduce ridging has a great possibility of losing the advantage of inexpensive ferritic stainless steel, and provides a ferritic stainless steel having good ridging resistance and workability. If it can be manufactured by a so-called ordinary steel process in which hot-rolled sheet annealing is omitted, ferritic stainless steel can be provided at lower cost.

[0010]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a method for producing a ferritic stainless steel capable of improving anisotropy of the ferritic stainless steel and improving ridging resistance.

[0011]

Means for Solving the Problems The present inventors have used a so-called two-time cold-rolling method in which hot-rolled sheet annealing performed in a conventional process or intermediate annealing between cold-rolling is performed. A method that can improve ridging resistance and workability at least was studied. As a result, they have found that the ridging resistance and workability can be simultaneously improved by consistently and appropriately adjusting the rolling conditions after hot rolling and the winding conditions after hot rolling by defining the trace components, and completed the present invention. .

That is, the gist of the present invention is as follows. (1) C: 0.0005 to 0.010%, S: 0.0010 to 0.040%, P: 0.025% or less, Cr: 10.0 to 20.0%, Ti: 0 by weight% 0.4% or less, N: 0.0005 to 0.020%, O: 0.01% or less, 2 ≦ S / C ≦ 4 and 1.5 (P + S) +4
When hot rolling a ferritic stainless steel satisfying (C + N + O) ≦ Ti, the heating temperature is set to 1250 ° C. or less, the total rolling reduction of the rough rolling is 80% or more, and the final rolling of the final three passes of the rough rolling is the cumulative rolling reduction. After the rough rolling is completed at 1000 ° C. or more as 60% or more, the total strain of the rough rolling (logarithmic strain: εr)
And finish rolling such that the total strain of the finish rolling (logarithmic strain: εf) becomes εr ≦ εf, then rolled up at less than 600 ° C., pickled without performing hot-rolled sheet annealing, cold-rolled, A method for producing ferritic stainless steel having excellent surface characteristics and low anisotropy, characterized by performing annealing.

(2) Further, by weight%, B: 0.0003
(1) The method for producing a ferritic stainless steel having excellent surface characteristics and small anisotropy according to the above (1), wherein the ferrite-based stainless steel contains 0.1 to 0.0020%.

(3) Further, in weight%, Mg: 0.000
The method for producing a ferritic stainless steel having excellent surface properties and small anisotropy according to the above (1) or (2), characterized by containing 5 to 0.0050%.

(4) Mo: 0.05-2.0%, Nb: 0.05-2.0%, Zr: 0.05-2.0%, W: 0.05-% 2.0%, V: 0.05 to 2.0%, and the surface characteristics described in any one of (1) to (3) above are excellent. Method for producing ferritic stainless steel with low resistance.

(5) In the hot rolling, lubrication is performed so that the average friction coefficient between the roll and the rolled plate in the finish rolling is 0.2 or less. A method for producing a ferritic stainless steel having excellent surface properties and low anisotropy as described in the section.

[0017]

DETAILED DESCRIPTION OF THE INVENTION
-0.002 to 0.007C -0.004 to 0.015
A 50 kg ingot of ferritic stainless steel containing N-Ti-added steel as a basic component is melted and subjected to a hot rolling test to obtain 3 to 5 mm.
The hot rolled sheet was manufactured, and pickling-cold rolling-annealing was performed. The r-value was measured after a 15% tensile test by taking JIS No. 5 test specimens from the product sheet at 0, 45, and 90 ° C with respect to the rolling direction. The ridging characteristics were obtained by taking a JIS No. 5 test specimen from the rolling direction of the product sheet, performing a 16% tensile test, and then measuring roughness by a roughness meter in a direction perpendicular to the rolling direction. The effects of components and hot rolling conditions on these characteristic values were investigated, and it was possible to improve the surface characteristics and workability by controlling the components and hot rolling consistently.

Hereinafter, the present invention will be described in detail. In the component, P is set to 0.02 from the viewpoint of improving ridging resistance and workability.
5% or less, and S and C, P, S, and
It has been found that ridging satisfying the relationship between C, N, O and Ti and the r value are improved. 2 ≦ S / C ≦ 4 and 1.5 (P + S) +4 (C + N +
O) ≦ Ti If this formula is satisfied as a component, the precipitation during heating to hot rolling can be stabilized, grain growth during heating can be prevented, and recrystallization during rough rolling can be promoted. And the destruction of the cast structure can be promoted.

In the present invention, the reason why the heating temperature is set to 1250 ° C. or less is that the particle size becomes coarse at a high temperature heating exceeding 1250 ° C., recrystallization during hot rolling is delayed, and the component control of the present invention is not performed. Even if it is performed, the precipitate dissolves during heating, and during hot rolling or winding, or re-precipitates during annealing after cold rolling,
In order to delay recrystallization, the temperature is set to 1250 ° C. or lower.

Although the lower limit of the heating temperature is not particularly defined,
If the temperature is lower than 0 ° C., recrystallization during rolling cannot be utilized, and the rolling temperature is lowered, so that flaws due to seizure are likely to occur. Therefore, the lower limit of the heating temperature is considered to be practically 1000 ° C.

In the rough rolling, it is important to destroy the cast structure and make it recrystallized before the finish rolling. For this purpose, in the rough rolling, a rolling reduction of 80% or more with respect to the initial sheet thickness is required. Also, in order to promote recrystallization sufficiently from rough rolling to finish rolling, the cumulative rolling reduction in the final three passes of rough rolling (the rolling reduction relative to the thickness before the final three passes) is 60% or more, and the rough rolling is completed. By setting the temperature to 1000 ° C. or higher, it is possible to eliminate structural anisotropy such as a mixed grain structure as a structure before finish rolling.

Regarding the finish rolling, the finish rolling is carried out so as to satisfy the above-mentioned rough rolling conditions and to satisfy the following conditions: εr ≦ εf, the total strain (logarithmic strain εr) of the rough rolling and the total strain (logarithmic strain εf) of the finish rolling. Doing so reduces the anisotropy of the r value,
It is also effective for improving ridging.

In addition, since the application of lubricating rolling has the effect of preventing the shear deformation of the surface layer of the hot-rolled sheet, the workability can be improved by performing the finishing rolling. At this time, it is important to perform lubricating rolling as a finish rolling so that the average friction coefficient between the roll and the rolled plate becomes 0.2 or less. Here, the reason why the friction coefficient between the roll and the rolled plate is set to 0.2 or less is that it is possible to reduce the influence of shear strain due to frictional force. Become.

It is desirable that the cooling after hot rolling is as rapid as possible, and the winding is performed at a temperature lower than 600 ° C. 600
If the winding temperature is higher than ℃, recovery and recrystallization occur during cooling after winding, the r value of the product plate in the 45 ° direction decreases, the anisotropy increases, and the heat during cooling of the coil decreases. This is because the hysteresis changes in the longitudinal direction, causing variations in workability. In the present invention, winding at a temperature lower than 600 ° C. can prevent variations in characteristics in the coil.

As a result of examining the above relationship while expanding the component range, it has been found that the present invention can be realized by the following component systems. That is, in the ferritic stainless steel of the present invention, C: 0.0005 to 0.010%, S: 0.0010 to 0.040%, P: 0.025% or less, and Cr: 10.0% by weight. ２20.0%, Ti: 0.4% or less, N: 0.0005 to 0.020%, O: 0.01% or less, and, if necessary, B: 0.0020% or less, Mg: 0 0.0005% to 0.0050%, or one or more of the following elements can be added as selective elements. Mo: 0.05 to 2.0%, Nb: 0.05 to 2.0%, Zr: 0.05 to 2.0%, W: 0.05 to 2.0%, V: 0.05 to 2.0%

The reasons for limiting the components in the present invention are described below. C: C is harmful in terms of workability and corrosion resistance, and particularly has a bad influence on the corrosion resistance of the welded portion.
At present, the production cost is high if the content is less than 0.0005%, and processability,
Since the toughness and corrosion resistance deteriorate, C is 0.0005 to
It was 0.01%.

S: In the present invention, S is an important element for improving processability and ridging characteristics, and is regulated by the relationship with C. Therefore, the lower limit is 0.0010%, and the upper limit is 0.04%.
%. If added in excess of this, the effect of improving properties is small, and the yield strength increases, resulting in poor workability.

P: P is detrimental to ridging resistance and processability in the present invention, and the smaller the content, the better, the content being 0.025% or less.

Cr: Cr is a main element of the ferritic stainless steel of the present invention, and it is necessary to add 10% or more from the viewpoint of corrosion resistance. However, even if added over 20%, the corrosion resistance is improved, but the cost is large and the workability and toughness are deteriorated. Therefore, the upper limit of Cr is set to 20%.

Ti: In the present invention, from the viewpoints of ridging resistance and workability, Ti is an element necessary for fixing C, N, P, S, and O.
+ S) +4 (C + N + O) or more. Further, if the content is excessive, the toughness is reduced and the workability is reduced.
4% or less.

N: As in the case of C, the smaller the content of N, the better the corrosion resistance and workability. However, it is industrially difficult to reduce the content to less than 0.0005%. If added, the workability and toughness deteriorate, so that N is set to 0.1.
It is added in the range of 0005 to 0.02%.

O: O degrades the toughness of the hot-rolled sheet, causes clogging of nozzles and scratches during casting, and causes the deterioration of the toughness of the hot-rolled sheet.

B: B is an element that is easily segregated at the grain boundary,
It is added in order to improve the processability as in the present invention.
It is effective for secondary cracking, and is added at 0.0003% or more. Also, if added over 0.0020%,
To delay recrystallization during hot rolling or after cold rolling annealing to deteriorate workability and ridging resistance, 0.0003 to 0.00
Add at 20%.

Mg: Mg is effective for refining the solidification structure, and is added in an amount of 0.0005% or more. Also, 0.0050
%, The effect is saturated.
005-0.0050%.

In the present invention, Mo, N
Any one or more of b, Zr, W, and V can be added. Mo: Mo is an element effective also in the case of corrosion resistance and when high-temperature strength is required as an exhaust material.
% Or more. Further, even if added in excess of 2.0%, the effect is saturated and the cost is high.
2.0%.

Nb: Nb is an element that fixes C and N and is preferable from the viewpoint of corrosion resistance, and is also an effective element when high-temperature strength is required as an exhaust material, and can be added at 0.05% or more. . Further, even if added in excess of 2.0%, the effect is saturated and the cost becomes high.
%.

Zr: Zr is used to fix C and N. In particular, Zr is used to improve the corrosion resistance by suppressing the precipitation of Cr carbonitride at the welded portion, and when high-temperature strength is required as an exhaust material. Is also an effective element and can be added at 0.05% or more. Further, even if added in excess of 2.0%, the effect is saturated and the cost increases, so the content was set to 0.05 to 2.0%.

W: In order to fix C and N, W suppresses the precipitation of Cr carbonitride particularly at the welded portion to improve corrosion resistance, and also requires a high-temperature strength as an exhaust material. Is also an effective element and can be added at 0.05% or more. Further, even if added in excess of 2.0%, the effect is saturated and the cost increases, so the content was set to 0.05 to 2.0%.

V: V is used to fix C and N, and in particular, to suppress the precipitation of Cr carbonitride at the welded portion to improve corrosion resistance, and to require high-temperature strength as an exhaust material. Is also an effective element and can be added at 0.05% or more.
Also, even if added over 2.0%, the effect is saturated,
Further, since it is expensive, the content is set to 0.05 to 2.0%.

In the present invention, Si, Mn, or Al, which is generally used as a deoxidizing element, may be used. In this case, the following component ranges are desirable as ranges that do not affect the characteristics of the present invention. Si: 0.01 to 1.0%, Mn: 0.01 to 1.0%, Al: 0.005 to 0.05%

Si: If Si is less than 0.01% as a deoxidizing agent, it has no sufficient effect, and if it exceeds 1%, the workability of the present invention is deteriorated. desirable. Mn: Mn as a deoxidizing element has insufficient effect if it is less than 0.01%, and its effect is saturated even if it is added more than 1%, so that 0.01 to 1.0% is desirable. Al: Al is effective as a deoxidizing element at 0.005% or more, and even if it exceeds 0.05%, the degree of deoxidizing is saturated.
0.005% to 0.05% is desirable.

[0042]

Next, embodiments of the present invention will be described. Using a ferrite stainless steel slab having a thickness of 250 mm having the components shown in Table 1, heating and hot rolling were performed under the conditions shown in Table 2, followed by hot rolling to produce a hot-rolled sheet of 3 to 5 mm. Thereafter, the hot rolled sheet annealing was performed. Except for B, the hot rolled sheet annealing was omitted and pickling and cold rolling were performed to evaluate workability and ridging characteristics. Hot rolled sheet annealing material No. The annealing condition of the hot-rolled sheet of B is 820
The temperature was set to 6 ° C. × 6 h, and the annealing was performed by box annealing. The rolling reduction of the cold rolling is set to 80%, and the finish annealing is performed at 800 to 1070 ° C for 30 to 30%.
60 seconds.

From the obtained product, r value, anisotropy Δr and ridging height were measured by the following methods. The r value and the measure of anisotropy {r} are 0 ° with respect to the rolling direction, 45 °.
JIS No. 5 test specimens were sampled from the ゜ direction and the 90 ° direction, subjected to a 15% tensile test, and determined by the following formula. r value = (rL + 2rD + rC) / 4 Δr = (rL−2rD + rC) / 2 where rL: r value in the rolling direction, rD: r value in the 45 ° direction with respect to the rolling direction, rC: rolling direction Is the r value in the 90 ° direction. As long as the r value is 1.5 or more and {r} is 0.3 or less, there is no problem in workability deterioration due to insufficient r value in the 45 ° direction.

The ridging characteristics are determined according to the rolling direction of the product sheet.
IS5 tensile test specimen was collected and subjected to a 16% tensile test.
Irregularities were measured in the direction perpendicular to the rolling direction using a roughness meter.

The ridging was evaluated as follows: A: less than 7 μm, B:
7 μm or more to less than 15 μm, C: 15 μm or more to 30 μm
m, D: 30 μm or more. There is no problem for the A and B ranks in practical use.

As a result, the steel of the present invention had a workability and an r value of 1.
It is 5 or more, and Δr showing anisotropy is 0.3 or less, which is extremely good as compared with a hot-rolled sheet annealing process material or a material that does not satisfy the conditions of the present invention, and also has good ridging characteristics. Indicated.

[0047]

[Table 1]

[0048]

[Table 2]

[0049]

As described above, according to the present invention, by controlling the components and the hot rolling conditions consistently in a simple process in which the hot-rolled sheet annealing is omitted, the difference in workability, which is an issue of ferritic stainless steel, is obtained. A ferritic stainless steel with improved anisotropy and improved ridging characteristics can be manufactured.

Continuing from the front page (72) Inventor Takehide Senuma 20-1 Shintomi, Futtsu-shi, Chiba Nippon Steel Corporation Technology Development Division

Claims (5)

[Claims] C: 0.0005 to 0.010%, S: 0.0010 to 0.040%, P: 0.025% or less, Cr: 10.0 to 20.0% by weight% Ti: 0.4% or less, N: 0.0005 to 0.020%, O: 0.01% or less, 2 ≦ S / C ≦ 4 and 1.5 (P + S) +4
When hot rolling a ferritic stainless steel satisfying (C + N + O) ≦ Ti, the heating temperature is set to 1250 ° C. or less, the total rolling reduction of the rough rolling is 80% or more, and the final rolling of the final three passes of the rough rolling is the cumulative rolling reduction. After the rough rolling is completed at 1000 ° C. or more at 60% or more, the total strain of the rough rolling (logarithmic strain: εr
) And finish rolling so that the total strain (logarithmic strain: ff) of 圧 延 r satisfies rr ≤ ff, then winds up at less than 600 ° C, pickles without performing hot-rolled sheet annealing, and cold-rolls. A method for producing ferritic stainless steel having excellent surface characteristics and small anisotropy, characterized by performing annealing. 2. B: 0.0003-% by weight
The method for producing a ferritic stainless steel having excellent surface properties and small anisotropy according to claim 1, characterized by containing 0.0020%. 3. The composition further comprises Mg: 0.0005 to 5% by weight.
The method for producing a ferritic stainless steel having excellent surface characteristics and small anisotropy according to claim 1 or 2, which contains 0.0050%. 4. Further, in terms of% by weight, Mo: 0.05 to 2.0%, Nb: 0.05 to 2.0%, Zr: 0.05 to 2.0%, W: 0.05 to 2 And at least one of V: 0.05 to 2.0%.
The method for producing a ferritic stainless steel having excellent surface characteristics and low anisotropy according to any one of the above. 5. The hot-rolling apparatus according to claim 1, wherein lubrication is performed so that the average friction coefficient between the roll and the rolled plate in the finish rolling is 0.2 or less. A method for producing ferritic stainless steel with excellent surface properties and low anisotropy.