JP2001098328A - Method of producing ferritic stainless steel sheet excellent in ductility, workability and ridging resistance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of producing a ferritic stainless steel sheet for working combining excellent ductility, workability and ridging resistance. SOLUTION: A steel stock containing, by mass, 0.02 to 0.12% C, 0.02 to 0.12% N, 16 to 18% Cr, 0.01 to 0.15% V and <=0.03% Al is heated and is subjected to hot rolling in which the rolling finishing temperature FDT is controlled to the range of 1,050 to 750 deg.C, within 2 sec after the finish of the hot rolling, cooling is started, the stock is cooled to <=550 deg.C at a cooling rate of 10 to 150 deg.C/s and is thereafter coiled to form its structure into the one of ferrite+martensite, or is moreover subjected to a preliminary rolling stage in which the same is subjected to cold or warm rolling at a draft of 2 to 15% and is subjected to hot rolled sheet annealing. It is also possible that, instead of the rapid cooling after the hot rolling, the same is rapidly cooled after the coiling to form its structure into the one of ferrite+martensite.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to an exterior material for a building,
The present invention relates to a method for producing a ferritic stainless steel sheet suitable for use in kitchen appliances, chemical plants, water tanks, heat-resistant members for automobiles, and the like, and more particularly, to improvement of ductility, workability, and ridging resistance. The steel sheet in the present invention includes a steel sheet and a steel strip.

[0002]

2. Description of the Related Art A stainless steel sheet has a beautiful surface and excellent corrosion resistance, and is therefore widely used for building exterior materials, kitchen appliances, chemical plants, water tanks and the like. In particular, austenitic stainless steel sheets have been widely used in the above-mentioned applications because of their excellent ductility and excellent press formability without ridging.

On the other hand, the formability of ferritic stainless steel sheets has been improved due to the progress of steel purification technology, and recently, austenitic stainless steel sheets such as SUS304 and SUS316 have been applied to the above-mentioned applications. Are being considered. This is a feature of ferritic stainless steel, for example, low thermal expansion coefficient, small stress corrosion cracking susceptibility, and is inexpensive because it does not contain expensive Ni,
Such advantages have become widely known.

[0004] However, in consideration of application to molded products, this ferritic stainless steel sheet has poor ductility compared to austenitic stainless steel plates, and has irregularities on the surface of the processed product called ridging. There is a problem that the appearance of the processed product is spoiled and the load of surface polishing is increased. For this reason, in order to further expand the use of ferritic stainless steel sheets, improvement in ductility and workability and improvement in ridging resistance have been required.

In response to such a demand, for example, Japanese Patent Laid-Open No.
-24913 discloses that, by weight%, C: 0.03 to 0.08%, N:
A ferritic stainless steel having excellent workability and containing 0.01% or less and Al: 2 × N% or more and 0.2% or less has been proposed. In the technology described in JP-A-52-24913,
By reducing the contents of C and N and further adding Al at least twice the N content, the amount of dissolved N is reduced, and the crystal grains can be further refined, ductility, ridging resistance, and secondary processing. It is said that the nature is improved.

Japanese Patent Application Laid-Open No. 54-112319 discloses that, by weight, (C + N): 0.02 to 0.06%, Zr: 0.2 to 0.6%, Zr: 10 (C + N) ± 0.15%, A heat-resistant ferritic stainless steel having improved ductility and r value and excellent in press formability has been proposed. JP-A-57-70223 discloses that, in terms of% by weight, sol Al: 0.08 to 0.5%, and B,
Production of ferritic stainless steel sheet with excellent workability by hot rolling a ferritic stainless steel slab containing one or more of Ti, Nb, V and Zr, then cold rolling and then final annealing A method has been proposed.

However, in the techniques described in JP-A-52-24913, JP-A-54-112319, and JP-A-57-70223, although the workability is greatly improved, Ridging properties are not yet sufficient, and when performing processing such as press molding, polishing for improving aesthetic appearance is required, and there has been a problem that the polishing load increases and the cost increases.

On the other hand, for improvement of ridging resistance, for example, JP-A-1-111816 discloses that hot rolling is performed at a finishing temperature of 850 ° C. or more, and immediately after completion of rolling, quenched at 10 ° C./s or more and 550 ° C. Winding at the following temperature, then the cumulative draft
A method for producing a cold rolled ferritic stainless steel sheet having excellent ridging resistance, which is subjected to cold rolling of 50% or more and then annealed, is disclosed. According to the technique described in JP-A-1-111816, ridging resistance is improved by changing the structure to ferrite + martensite by quenching after hot rolling. However, in the technique described in JP-A-1-111816, although ridging resistance is improved, both ductility and workability have not been sufficiently improved. With respect to such a problem, there have been proposed some techniques for achieving both ductility, workability, and ridging resistance. Japanese Patent Application Laid-Open No. 2-170923 discloses that
Hot rolled sheet obtained by hot rolling a chromium stainless steel slab containing 20.0 wt% is subjected to preliminary cold rolling at a rolling reduction of 2 to 30%, followed by continuous annealing, descaling, cold rolling, Also disclosed is a method for producing a cold rolled chromium stainless steel sheet having excellent ridging resistance and press workability subjected to finish annealing. According to the method described in Japanese Patent Application Laid-Open No. 2-170923, a strong reduction by cold rolling is applied before annealing to promote recrystallization behavior during annealing, enable continuous annealing, and improve workability and ridging resistance. I have to.

Japanese Patent Application Laid-Open No. 9-111354 discloses that, by weight%, C: 0.02 to 0.05%, N: 0.02 to 0.05%, Cr: 15 to
A slab containing 18% and Al: 0.10 to 0.30% is subjected to hot rolling at a final pass exit temperature: 950 ° C. or higher, and then a cooling rate: 20
Cooled to 500 to 650 ° C at ~ 80 ° C / s to obtain a hot rolled sheet having a composite structure of ferrite + martensite.
Anneal for 180 to 300 sec in the temperature range of 850 to 980 ° C, then quench at a cooling rate of 15 ° C / s or more, then apply cold rolling and finish annealing. Excellent in ridging resistance and press formability. A method for producing a ferritic stainless steel sheet having good surface properties is disclosed.

Japanese Patent Application Laid-Open No. Hei 10-53817 discloses that, by weight, Cr: 11 to 25%, C: 0.005% or less, N: 0.008 to 0.4%.
Ferritic stainless steel slabs containing 03% and Ti in the range of 1 to 5 times C + N have a total reduction of 50% for one or more passes in a temperature range of 1100 to 950 ° C.
Above and the end temperature: 950 ℃ or more rough rolling,
10 seconds or more after rough rolling, the total rolling reduction of the last two passes: 40
%, Finishing temperature: 850 ° C or more
A method for producing a ferritic stainless steel sheet excellent in roping resistance, ridging resistance and formability with an average cooling rate of 25 ° C./s or less for 5 seconds immediately after rolling is disclosed. According to the technique described in Japanese Patent Application Laid-Open No. Hei 10-53817, a strong reduction in hot rolling is effective in improving ridging resistance.

[0011]

However, JP-A-2-170923, JP-A-9-111354 and JP-A-10-110354 disclose the problems to be solved.
There is still room for improvement in the technology described in -53817. The technique described in Japanese Patent Application Laid-Open No. 2-170923 has a problem that the ridging height is not more than 5 μm and the ridging resistance and the high r value are not both improved.

In the technique described in Japanese Patent Application Laid-Open No. 9-111354, it is necessary to add a large amount of Al, the amount of inclusions in the steel increases, and the generation of surface defects due to this problem cannot be avoided. In addition, the amount of martensite is 10-20%
However, the degree of improvement in ridging resistance is insufficient, and the improvement in ductility is still insufficient.

Further, in the technique described in Japanese Patent Application Laid-Open No. Hei 10-53817, the ridging resistance is not sufficiently improved because the ridging grade 1 having the highest rating is included up to 20 μm. The problem that was left.
Furthermore, in the technology described in JP-A-10-53817,
It is necessary to add a sufficient amount of Ti to fix carbon and carbon to make the carbon extremely low, and in addition to the problem that the production cost increases, the problem that the generation of surface defects due to the large addition of Ti is inevitable. was there.

It is an object of the present invention to solve the above-mentioned problems of the prior art and to propose a method for producing a ferritic stainless steel sheet for processing having excellent ductility, workability and ridging resistance.

[0015]

Means for Solving the Problems The present inventors have made various studies to achieve the above-mentioned object, and as a result, the structure of the hot-rolled sheet contains 20 to 70% (vol%) of a martensite phase. It has been found that by performing hot-rolled sheet annealing as a two-phase structure of ferrite and martensite, ductility, workability, and ridging resistance are all improved. Although the detailed mechanism of this property improvement has not been fully elucidated at present, it is sheared when the austenite phase is transformed to the martensite phase due to the inclusion of 20-70% of martensite phase. This is presumably because the accumulated strain increases with the increase in temperature, and recrystallization during annealing of the hot-rolled sheet is promoted.

Further, when the structure of the hot-rolled sheet is a two-phase structure of ferrite + martensite, and a relatively low rolling strain is imparted during warm or cold, and then the hot-rolled sheet is annealed,
It has been found that the r value (workability) can be further increased without lowering ductility and ridging resistance.
The present inventors further adjusted the chemical composition and forcedly cooled after hot rolling to make the hot-rolled sheet structure before the hot-rolled sheet annealing a two-phase structure of ferrite and martensite. It has also been found that it is most effective to perform a cooling treatment or a forced cooling treatment after winding, in which the coil is forcibly cooled after being wound on the coil.

The present invention has been completed based on the above findings and further studies. That is, in the first present invention, in mass%, C: 0.02 to 0.12%, N: 0.02 to 0.
A steel material containing 12%, Cr: 16 to 18%, V: 0.01 to 0.15% and Al: 0.03% or less is heated, and the rolling end temperature FDT is in the range of 1050 to 750 ° C. Hot rolling to form a hot-rolled sheet, and cooling is started within 2 seconds after the completion of hot rolling, at a cooling rate of 10 to 150 ° C./s.
After the hot-rolled sheet is cooled to 550 ° C. or lower, the hot-rolled sheet is rolled up and then subjected to a forced cooling step. Fifteen
% Cold rolling of a hot-rolled sheet which has been subjected to a preliminary rolling step of rolling the steel sheet, followed by annealing the hot-rolled sheet, and cold-rolling the hot-rolled sheet after the hot-rolled sheet annealing step. A method for producing a ferritic stainless steel sheet excellent in ductility, workability and ridging resistance, comprising sequentially performing a step and a finish annealing step of finish annealing the cold-rolled sheet.

In the second invention, the mass% and C: 0.
02-0.12%, N: 0.02-0.12%, Cr: 16-18%
Further, a steel material containing V: 0.01 to 0.15% and adjusted to Al: 0.03% or less is formed into a hot-rolled sheet by hot rolling, and is subjected to a hot-rolling step of winding at a winding temperature of 1000 to 700 ° C. ,
Cooling is started until the temperature of the rolled hot-rolled sheet falls by 50 ° C. from the winding temperature, and 500 ° C. from the cooling start temperature.
Cooling rate in the temperature range up to ℃: 10 to 150 ℃ / s to cool to 500 ℃ or less, perform a forced cooling step after winding, or further perform rolling at a cold or warm rolling reduction: 2 to 15% Performing a pre-rolling step, then annealing the hot-rolled sheet, annealing the hot-rolled sheet, cold-rolling the hot-rolled sheet after the hot-rolled sheet annealing step into a cold-rolled sheet, Ductility characterized by sequentially performing a finish annealing step of finish annealing the sheet,
This is a method for producing a ferritic stainless steel sheet having excellent workability and ridging resistance.

Further, in the first invention and the second invention, the steel material is mass%, C: 0.02 to 0.12%,
N: 0.02 to 0.12%, Cr: 16 to 18%, V: 0.01 to 0.15%,
Al: 0.03% or less, Si: 1.0% or less, Mn:
It is preferable to use a steel material containing 1.0% or less and having a composition consisting of the balance of Fe and unavoidable impurities. Further, in the present invention, in addition to the above-described respective compositions, further, in mass%,
B: 0.0002 to 0.0050%, Ca: 0.0005 to 0.010%, Mg: 0.
One or more selected from 0002 to 0.0050% may be contained. The inevitable impurities include ma
In ss%, Ni: 1.0% or less, P: 0.05% or less, S: 0.01%
The following are allowed:

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, the reasons for limiting the composition of the steel material used in the present invention will be described. Hereinafter, mass% in the composition is simply described as%. C: 0.02 to 0.12% In the present invention, C is preferably reduced as much as possible to improve ductility. However, if the C content is excessively reduced, the ridging resistance is deteriorated, and irregularities are formed in a processed portion during processing such as press molding, and the appearance of the product is impaired. It becomes difficult to secure.
In order to secure the amount of martensite (20% or more by volume and 70% or less by volume) required in the present invention, at least 0.02%
%, The lower limit of the C content is set to 0.02%. On the other hand, if it is contained in excess of 0.12%, the ductility is reduced, and a de-Cr layer, which is a starting point of rust,
Coarse precipitates and inclusions increase. For this reason, the upper limit of the C content is set to 0.12%.

N: 0.02 to 0.12% N, like C, is preferably reduced as much as possible for improving ductility. However, when the N content is excessively reduced, the ridging resistance is deteriorated, and irregularities are generated in a processed portion during processing such as press molding, and the appearance of the product is impaired. It becomes difficult to secure. In order to secure the amount of martensite (more than 20%) required in the present invention, an N content of at least 0.02% is required. Therefore, the lower limit of the N content is set to 0.02%. On the other hand, 0.
If it is contained in excess of 12%, ductility will decrease and
Cr-free layer, coarse precipitates and inclusions, which are the starting points of rusting, increase. Therefore, the upper limit of the N content is set to 0.12%.

Cr: 16 to 18% Cr is an effective element for improving corrosion resistance, and has an appropriate amount of martensite (20% by volume) before annealing of a hot-rolled sheet.
~ 70%) is an important element to secure. In order to obtain sufficient corrosion resistance and an appropriate amount of martensite before annealing of the hot-rolled sheet, the content of Cr must be at least 16%. on the other hand,
If the content exceeds 18%, the workability decreases. For this reason, Cr was limited to the range of 16 to 18%.

Al: 0.03% or less Al acts as a deoxidizing agent, but excessive content causes many surface defects due to inclusions such as oxides and reduces the amount of martensite before annealing of hot-rolled sheet. Let it. Therefore, in the present invention, Al is adjusted to 0.03% or less. Preferably, 0.
01% or less.

V: 0.01 to 0.15% V combines with C and N to form carbides, nitrides or carbonitrides, reduces the amount of solute C and solute N, and further suppresses coarsening of crystal grains. Is an element that has the effect of Such an effect is recognized when the content of V is 0.01% or more. On the other hand, 0.15
%, The cold workability is reduced, and a large amount increases production cost and is economically disadvantageous. For this reason, V is limited to the range of 0.01 to 0.15%.
In addition, preferably, it is 0.03 to 0.15%.

The components of the steel material other than the above-mentioned chemical components are preferably in the following ranges. Si: 1.0% or less Si is an element acting as a deoxidizing agent, but if contained in a large amount, ductility and cold workability are reduced. For this reason, Si
It is preferably set to 1.0% or less. In addition, more preferably, it is 0.03 to 0.50%.

Mn: 1.0% or less Mn is an effective element that combines with S to reduce solid solution S, thereby suppressing segregation at the grain boundaries of S and preventing cracking during hot rolling. Contains causes a decrease in cold workability and corrosion resistance. Therefore, Mn is preferably limited to 1.0% or less. Incidentally, the content is more preferably 0.05 to 0.8%.

Ni: 1.0% or less Ni is an element for improving corrosion resistance and can be contained as necessary. However, when the content exceeds 1.0%, the cold workability is lowered and the production cost is increased, which is disadvantageous economically. Therefore, when adding, 1.0
% Is preferable. From the viewpoint of workability, Ni is more preferably set to 0.7% or less. In addition to the case where Ni is added as necessary, Ni is inevitably contained, but the inevitable content is allowed up to about 0.4%.

P: 0.05% or less P is an element that deteriorates hot workability and generates pits, and is preferably reduced as much as possible. Up to 0.05%, its adverse effect is not significant, so up to 0.05% is acceptable. S: 0.01% or less S is an element that forms sulfides, lowers the cleanliness of steel, becomes a starting point of rust as MnS, and further segregates at crystal grain boundaries to promote grain boundary embrittlement. Is preferred. Up to 0.01%, the adverse effect is not significant and is acceptable.

B: 0.0002-0.0050%, Ca: 0.0005-0.01
0%, Mg: one or two or more selected from 0.0002 to 0.0050% B, Ca, and Mg each have an effect of improving workability, and are selected as necessary, and may be used alone or in combination. Can be contained. B improves workability through improvement of secondary work brittleness resistance, but no effect is observed at less than 0.0002%. On the other hand, if the content exceeds 0.0050%, workability is rather lowered. For this reason, B is preferably limited to the range of 0.0002 to 0.0050%. Ca improves workability through control of inclusion morphology, but no effect is observed at less than 0.0005%. On the other hand, if the content exceeds 0.010%, surface defects due to oxides occur frequently and the surface quality deteriorates. For this reason, Ca
Preferably, it is limited to the range of 0.0005 to 0.010%. Further, Mg has an effect of improving hot workability,
The effect is recognized at a content of 0002% or more. On the other hand, 0.00
If the content exceeds 50%, the surface quality deteriorates. For this reason, Mg is preferably limited to the range of 0.0002 to 0.0050%.

The balance of the steel material used in the present invention other than the above components is Fe and inevitable impurities. Next, a method for obtaining a ferritic stainless steel sheet having excellent ductility, workability, and ridging resistance using the steel material having the above composition will be described. First, molten steel of the above composition is
After smelting in a commonly known smelting furnace such as a converter or an electric furnace, it is further smelted by a known smelting method such as vacuum degassing (RH method), VOD method, AOD method, and then continuous casting method or smelting method. It is preferable to cast into a slab or the like by the lump method to obtain a steel material.

The steel material is then heated and hot rolled into a hot rolled sheet. The heating temperature of the steel material does not need to be particularly limited, but needs to be a predetermined finish rolling end temperature or a temperature at which a predetermined winding temperature can be secured. Therefore, in the present invention, the heating temperature of the steel material is 1000 to 1250
C. is preferred. First, the first present invention will be described.

In the first aspect of the present invention, in order to make the structure of the hot-rolled sheet into a ferrite + martensite two-phase structure, forced cooling is performed immediately after completion of hot rolling. For this reason, in the hot rolling step of the first invention, the finish rolling end temperature FDT of hot rolling is set in a range of 1050 to 750 ° C. If the FDT exceeds 1050 ° C., the strain accompanying the subsequent forced cooling increases, and the steel sheet shape becomes poor. On the other hand, when the FDT is lower than 750 ° C., the martensitic transformation does not occur even by the subsequent forced cooling. For this reason, the FDT was set in the range of 1050 to 750 ° C.

The hot-rolled sheet after the hot-rolling step is started to be cooled within 2 seconds after the completion of the hot rolling, and the cooling rate is 10 to 10 seconds.
After being cooled to 550 ° C or less at 150 ° C / s, it is subjected to a forced cooling process after hot rolling. In order to obtain a sufficient amount of martensite, it is necessary to start cooling within 2 seconds after hot rolling so that redistribution and precipitation of C and N do not occur. If the start of forced cooling exceeds 2 seconds after the end of hot rolling, there is a problem that rearrangement of solid solution C and N and precipitation of carbon / nitride may occur and martensitic transformation may not sufficiently occur. For this reason, the start time of forced cooling was set within 2 seconds after the end of hot rolling.

When the cooling rate of the forced cooling is less than 10 ° C./s, the amount of martensite generated at the time of cooling is small. On the other hand, when the cooling rate exceeds 150 ° C./s, the shape of the steel sheet is poor due to distortion accompanying cooling. Becomes For this reason, the cooling rate of the forced cooling was limited to the range of 10 to 150 ° C./s. If the cooling stop temperature exceeds 550 ° C., the amount of martensite generated during cooling is small and the desired effect cannot be expected. Therefore, the cooling stop temperature is limited to 550 ° C. or lower. However, when winding into a coil after forced cooling, the cooling stop temperature
If the temperature is lower than 400 ° C., it may be difficult to wind up. Therefore, the cooling stop temperature is preferably set to 400 ° C. or higher.

In the first aspect of the present invention, the hot-rolled sheet obtained through the above steps is then subjected to a hot-rolled sheet annealing step. In the first aspect of the present invention, the hot-rolled sheet that has undergone the above-described hot-rolled sheet quenching step is subjected to descaling treatment as necessary, and is further subjected to cold or warm rolling at a rolling reduction of 2 to 15%. After performing the preliminary rolling step, the hot-rolled sheet annealing step may be performed.

Next, a description will be given of the experimental results that were the basis for determining the pre-rolling process conditions. 0.063wt%
C-0.033 wt% N-0.27 wt% Si-0.60 wt% Mn-16.3 wt%
A ferritic stainless steel material having a composition containing Cr-0.33wt% Ni-0.001wt% Al-0.061wt% V is hot-rolled at a finish rolling temperature of 975 ° C to form a hot-rolled sheet. , At a cooling rate of 50 ° C./s to 550 ° C., and thereafter, cold rolling is performed at a rolling reduction of 0 to 20% to impart a rolling strain. C. (holding 1 min.) And then cold rolling so that the total draft of the hot rolled sheet after hot rolling becomes 75%, and then finish annealing at 830 ° C. for 30 sec. To obtain a cold rolled ferritic stainless steel sheet.

With respect to these ferritic stainless steel cold-rolled steel sheets, changes in average elongation El _mean , average r value (Rankford value) r _mean and ridging grade were examined. The result is shown in FIG. As shown in FIG. 1, the average elongation El _mean : 33% or more, r value: 1.5 or more, ridging grade: A (wave height 5 μm) Below), elongation, r-value,
It can be seen that both the ridging resistance and the ridging resistance are improved.

For this reason, prior to annealing of the hot-rolled sheet, the hot-rolled sheet having a two-phase structure of ferrite and martensite is subjected to descaling treatment, if necessary, and then subjected to a preliminary rolling step for imparting rolling strain. As a result, it is understood that the r value is improved without lowering the elongation and the ridging resistance. In the preliminary rolling step, rolling is performed at a rolling reduction of 2 to 15% in a cold or warm state. By this rolling, rolling distortion is introduced, and the elongation, r value, and ridging resistance are all improved by a combination of the subsequent hot rolled sheet annealing, cold rolling, and cold rolled sheet annealing. When the rolling reduction is less than 2%, the improvement in elongation, r value and ridging resistance is small. On the other hand, when it exceeds 15%, both the elongation, r value and ridging resistance deteriorate. For this reason, the rolling reduction in the preliminary rolling step is limited to the range of 2 to 15%. The rolling in the pre-rolling step is performed in a cold region or a warm region of less than 450 ° C.
When the rolling temperature is 450 ° C. or higher, the rolling distortion introduced by the rolling is recovered, and the effect of the preliminary rolling is reduced.

In the first invention, a forced cooling step after hot rolling,
Alternatively, the hot rolled sheet obtained through the preliminary rolling step is
Next, a hot-rolled sheet annealing step is performed. As the annealing in the hot-rolled sheet annealing step, both box annealing and continuous annealing are suitable.
The annealing temperature of hot-rolled sheet annealing is 700 ° C or more at which recrystallization occurs.
Preferably, it is carried out at a temperature of 750 to 950 ° C.

The hot-rolled sheet that has undergone the hot-rolled sheet annealing step is subjected to descaling treatment if necessary, and then is cold-rolled by cold rolling in the cold-rolling step. In cold rolling in the cold rolling process, the rolling reduction
It is preferably at least 30%. Incidentally, more preferably 50
~ 95%. If the rolling reduction is less than 30%, the r value and ridging resistance may be insufficient.

After the cold rolling step, in the finish annealing step, the cold rolled sheet is subjected to finish annealing. Finish annealing is preferably performed at a temperature of 600 ° C. or more at which recrystallization occurs in order to improve workability. The more preferable temperature range of the finish annealing is 70.
0-900 ° C. The finish annealing is preferably a continuous annealing in consideration of productivity. In the present invention, the cold rolling step and the finish annealing step may be repeated two or more times. By repeating the cold rolling step and the finish annealing step, the r value, elongation, and ridging resistance are further improved.

The finish of the cold-rolled sheet may be 2
Needless to say, various finishes such as D finish, 2B finish, and BA finish can be made. Next, the second present invention will be described. In the second aspect of the present invention, similarly to the first aspect, the above-mentioned steel material is hot-rolled into a hot-rolled sheet, and is subjected to a hot-rolling step of winding at a winding temperature of 1000 to 700 ° C. Cooling is started until the temperature of the hot rolled sheet falls by 50 ° C. from the winding temperature, and a cooling rate in a temperature range from the cooling starting temperature to 500 ° C .: 10 to 150 ° C./s
After cooling to 500 ° C or less, a forced cooling step is performed. In the second aspect of the present invention, in order to make the structure of the hot-rolled sheet into a ferrite + martensite two-phase structure, the hot-rolled sheet wound into a coil after hot rolling is subjected to a forced cooling step. In the forced cooling step after winding, cooling is started until the temperature of the hot rolled sheet falls by 50 ° C. from the winding temperature, and the cooling rate in a temperature range from the cooling start temperature to 500 ° C .: 10 to 150 ° C
Cool at / s.

When the winding temperature exceeds 1000 ° C., the distortion accompanying the subsequent cooling increases, and the steel sheet shape becomes poor. On the other hand, if the winding temperature is less than 700 ° C., the martensitic transformation does not sufficiently occur in the subsequent cooling. From such a thing,
In the second aspect of the present invention, the winding temperature during hot rolling is set to 1000 to 700 ° C.
Limited to. It is preferable to adjust the hot rolling conditions so that the winding temperature falls within a predetermined range.

The rolled hot rolled sheet starts cooling until the temperature of the hot rolled sheet drops by 50 ° C. from the winding temperature. If the cooling start is lower than the above-mentioned temperature, an appropriate amount of martensite will not be formed in the subsequent cooling. It is preferable that the forced cooling step after winding is started within about 10 minutes after the winding of the hot rolled sheet. In addition, the winding temperature of the hot-rolled sheet referred to in the present invention is 1/1 in the width direction near the center in the longitudinal direction of the hot-rolled sheet.
The temperature of the hot rolled sheet measured at the position of No. 2 shall be referred to.

When the rolled hot rolled sheet is cooled, if the cooling rate in the temperature range from the temperature at the start of forced cooling to 500 ° C. is less than 10 ° C./s, the amount of martensite generated is small. If the speed exceeds 150 ° C / s, the shape of the steel plate becomes poor due to the strain caused by cooling. From such a thing,
The cooling rate for forced cooling was limited to the range of 10 to 150 ° C / s. When the cooling stop temperature exceeds 500 ° C., the amount of martensite generated is small and the desired effect cannot be expected.

For rapid cooling, the coil may be immersed in a water tank after hot rolling. In the second aspect of the present invention, the hot-rolled sheet obtained through the above-described steps is subjected to descaling treatment as in the first aspect of the present invention, or is further subjected to a reduction ratio of 2 to 15 in cold or warm conditions. % Rolling is performed, and then a hot-rolled sheet annealing step is performed. The conditions of the pre-rolling step and the hot-rolled sheet annealing step are the same as those in the first invention.

The hot-rolled sheet is subjected to hot-rolled sheet annealing, and then is subjected to a cold-rolling step and a finish annealing step under the same conditions as those of the first invention, to obtain a product sheet.

[0048]

EXAMPLE Molten steel having the composition shown in Table 1 was smelted in a converter-secondary refining process and made into a slab by a continuous casting method. After reheating these slabs, hot rolling was performed at the finish rolling end temperature shown in Table 2 to obtain a hot rolled sheet. Immediately after the completion of the hot rolling, a forced cooling step after hot rolling under the conditions shown in Table 2 or a rolled heat After the rolled sheet was wound under the conditions shown in Table 2, a forced cooling step was performed. A part of the hot rolled sheet that had undergone the forced cooling step after hot rolling or the forced cooling step after winding was further subjected to pickling and then subjected to a preliminary rolling step under the conditions shown in Table 2.

A hot rolled sheet that has undergone a forced cooling step after hot rolling or a forced cooling step after winding, or a hot rolled sheet that has further undergone a pre-rolling step, is subjected to a hot rolled sheet annealing step under the conditions shown in Table 2 and a cold rolling step. Rolling process and finish annealing process are sequentially performed to achieve a thickness of 0.
An 8 mm cold-rolled annealed plate was used. In the cold rolling process after pickling the hot rolled sheet, the cold rolling reduction is adjusted so that the total rolling reduction to the hot rolled sheet after hot rolling is 75 to 85%, and the sheet thickness becomes 0.8 mm. I did it. Annealing in the final annealing step was continuous annealing, and kept at 830 ° C. for 1 minute.

A test piece was collected from the obtained cold-rolled annealed plate,
A tensile test was performed to measure elongation El, r value, and ridging grade. The methods for measuring elongation, r value, and ridging grade are as follows. (1) Elongation Each direction of each cold-rolled annealed sheet (rolling direction, 45 ° to the rolling direction)
Direction, a direction perpendicular to the rolling direction), take a JIS No. 13 B test piece, conduct a tensile test, and elongate El (E
_{l 0, El 45, El 90} ) were measured. The average elongation El _mean was determined from the elongation El in each direction by the following equation.

El _mean = (El ₀ + 2El ₄₅ + El ₉₀ ) / 4 (where El ₀ is the elongation in the rolling direction, El ₄₅ is the elongation in the 45 ° direction with respect to the rolling direction, and El ₉₀ is the 90 ° in the rolling direction. (Right angle)
Direction. (2) r value Each direction of each cold-rolled annealed sheet (rolling direction, 45 ° to rolling direction)
Direction, a direction perpendicular to the rolling direction). When a 15% uniaxial tensile prestrain was applied to these test pieces, the width strain and the thickness strain of each test piece were determined, and the ratio of the width strain to the thickness strain r = ln (w / w ₀ ) / ln (T / t ₀ ) (where w ₀ and t ₀ are the width and thickness of the test piece before the tensile test, and w and t are the width and thickness of the test piece after the tensile test). The r value in each direction is determined, and the following equation is given: r _mean = (r ₀ + 2r ₄₅ + r ₉₀ ) / 4 (where r ₀ is the r value in the rolling direction, r ₄₅ is the r value in a 45 ° direction with respect to the rolling direction, r ₉₀ is 90 ° (right angle) to the rolling direction
The r value in the direction. ) To determine the average r value r _mean . (3) Ridging grade Samples of JIS No. 5 were taken from the rolling direction of each cold rolled annealed sheet,
One side of this test piece was finish-polished with # 600 abrasive paper. Next, after applying a uniaxial tensile prestrain of 20% to these test pieces, the height of undulation (ridging irregularities) generated on the test pieces was measured at the center of the test pieces by a roughness meter. The degree of ridging was evaluated from the height of the undulation.

The degree of ridging was evaluated on a four-point scale, with the undulation height being 5 μm or less for A, 5 μm to 10 μm for B, 10
C was determined to be greater than 20 μm, and D was determined to be greater than 20 μm. In the case of A and B in this evaluation standard, the ridging resistance at the time of press molding is good. The hot-rolled sheet after hot rolling after hot rolling or forced cooling after winding was cut out, polished and etched (aqua regia), and subjected to an optical microscope (magnification: 200 times).
The tissue was observed at. At a 1/4 position in the thickness direction, a tissue photograph was taken (magnification: 200 times, 20 visual fields), the area ratio of the martensite phase was determined by image analysis, and the average martensite amount (vol%) was measured.

Table 2 shows the obtained results.

[0054]

[Table 1]

[0055]

[Table 2]

[0056]

[Table 3]

[0057]

[Table 4]

Each of the examples of the present invention has an El _{mean of} 32% or more, a r _mean value of 1.30 or more, a ridging grade of A, and has good properties in ductility, r value and ridging resistance. On the other hand, the comparative examples out of the range of the present invention are ductility, r
Either value or ridging resistance is reduced.

[0059]

According to the present invention, a ferritic stainless steel sheet having excellent ductility, workability, and ridging resistance can be manufactured efficiently and at low cost, and the industrially remarkable effect is obtained.

[Brief description of the drawings]

FIG. 1 shows the preliminary rolling reduction, the average elongation El _mean (a),
It is a graph which shows the relationship between an average r value r _mean (b) and a ridging grade (c).

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Kouki Uki 1 Kawasaki-cho, Chuo-ku, Chiba City, Chiba Prefecture Inside the Technical Research Institute of Kawasaki Steel Corp. (72) Susumu Sato Susumu 1 Kawasaki-cho, Chuo-ku, Chiba City, Chiba Prefecture Kawasaki 4K032 AA00 AA01 AA02 AA03 AA04 AA05 AA08 AA13 AA16 AA21 AA23 AA27 AA29 AA31 AA36 BA01 CA02 CA03 CC03 CC04 CD03 CE01 CE02 CF03 CG01 CG02 CH04 CH05 EA03 EA01 EA15 EA18 EA20 EA23 EA25 EA27 EA32 EB06 EB08 EB09 EB14 FA02 FA03 FC03 FC04 FC05 FD03 FD04 FE01 FE03 FE05 FF03 FG01 FH01 FH03 FJ04 FJ05 FJ06 FM02 HA06

Claims (2)

[Claims] 1. Mass%, C: 0.02 to 0.12%, N: 0.02%
0.12%, Cr: 16-18%, V: 0.01-0.15
% And Al: 0.03% or less.
A hot rolling step of heating and performing hot rolling such that the finish rolling end temperature FDT is in the range of 1050 to 750 ° C. to form a hot rolled sheet; cooling is started within 2 seconds after the completion of hot rolling;
After the hot-rolled sheet is cooled to 550 ° C. or less at 0 ° C./s and then rolled up, a forced cooling step is performed after hot rolling, or the hot-rolled sheet that has passed through the hot-rolling sheet quenching step is further cold- or cold-rolled. rate:
A pre-rolling step of performing rolling of 2 to 15% is performed, and then a hot-rolled sheet annealing step of annealing the hot-rolled sheet, and a hot-rolled sheet that has passed through the hot-rolled sheet annealing step is cold-rolled into a cold-rolled sheet. Cold rolling process,
A method for producing a ferritic stainless steel sheet having excellent ductility, workability, and ridging resistance, comprising sequentially performing a finish annealing step of finish annealing the cold-rolled sheet. 2. Mass%, C: 0.02 to 0.12%, N: 0.02%
0.12%, Cr: 16-18%, V: 0.01-0.15
%, And a steel material adjusted to not more than 0.03% in Al is formed into a hot-rolled sheet by hot rolling, and is subjected to a hot-rolling step of winding at a winding temperature of 1000 to 700 ° C. Cooling is started until the temperature of the rolled sheet falls by 50 ° C. from the winding temperature. After the winding, perform a forced cooling step, or further perform a preliminary rolling step of performing rolling at a rolling reduction of 2 to 15% in a cold or warm state, and then perform a hot-rolled sheet annealing step of annealing the hot-rolled sheet, The ductility, workability and resistance to heat are characterized by sequentially performing a cold rolling step of cold-rolling the hot-rolled sheet through the hot-rolled sheet annealing step into a cold-rolled sheet, and a finish annealing step of finish annealing the cold-rolled sheet. Method for producing ferritic stainless steel sheet with excellent ridging properties.