JP2019044215A - Ferritic stainless steel sheet and manufacturing method therefor - Google Patents

Abstract

To provide a ferritic stainless steel sheet excellent in corrosion resistance, and further excellent in ridging resistance, and a manufacturing method therefor.SOLUTION: There is provided a ferritic stainless steel sheet containing, by mass%, C:0.001 to 0.040%, Si:0.05 to 0.30%, Mn:0.05 to 1.00%, P:0.040% or less, S:0.030% or less, Al:0.001 to 0.300%, Cr:10.5 to 14.5%, Ni:0.01 to 1.00%, N:0.001 to 0.100% and the balance Fe with inevitable impurities, and having ridging height of a surface of the steel sheet to which 20% tensile strain is added in a rolling direction of 1.5 μm or less.SELECTED DRAWING: None

Description

  The present invention relates to a ferritic stainless steel sheet excellent in corrosion resistance and further excellent in ridging resistance, and a method of manufacturing the same.

  Ferritic stainless steel sheets are used for various applications such as building materials, transportation equipment, household appliances and the like because they are materials excellent in explosion resistance. In particular, ferritic stainless steel plates are being applied to general household goods where price is important because the content of rare elements Cr and Ni is small compared to austenitic stainless steels. Furthermore, since it has magnetism unlike austenitic stainless steel, the application to the cooking appliance which can respond to IH (induction heating) system is increasing.

  Many cooking utensils represented by pots and the like are formed by pressing. However, ferritic stainless steel sheets have a problem that surface irregularities (riding) often occur on the surface during press-forming, which impair the appearance. In cooking utensils whose surface appearance greatly affects the commercial value, when ridging occurs, a polishing process for removing irregularities after molding is required. That is, if a large ridging occurs during molding, there is a problem that the manufacturing cost increases.

  In recent years, for household cooking appliances, cost reduction of material cost and manufacturing cost is required for further price reduction. That is, in order to reduce the material cost, a low Cr ferritic stainless steel having a Cr content lower than that of the conventional 16 to 18 mass% Cr ferritic stainless steel is required. . There is also a need for a ferritic stainless steel sheet that can be further reduced in the polishing process of ridging that leads to an increase in manufacturing cost, that is, more excellent in ridging resistance than in the past.

For the above problems, for example, in Patent Document 1, C: 0.02 to 0.06%, Si: 1.0% or less, Mn: 1.0% or less, P: 0.05 by mass% % Or less, S: 0.01% or less, Al: 0.005% or less, Ti: 0.005% or less, Cr: 11 to 30%, Ni: 0.7% or less and 0.06 ≦ C + N) ≦ 0.12, 1 ≦ N / C and 1.5 × 10 ⁻³ ≦ (V × N) ≦ 1.5 × 10 ⁻² (C, N and V each represent mass% of each element) A ferritic stainless steel sheet excellent in formability characterized by satisfying the above is disclosed.

  Further, Patent Document 2 is a ferritic stainless steel sheet containing 0.15% or less of C and 13 to 25% Cr, and the hot-rolled sheet of this steel is 930 to 990 ° C. in which austenite and ferrite phase coexist. In the range of 10 minutes or less, the structure is made a dual phase structure of a martensitic phase and a ferritic phase, then cold rolling is performed, and the cold rolled sheet is annealed in a range of 750 to 860 ° C. A method of producing a ferritic stainless steel sheet excellent in ridging resistance and processability, which is characterized by the characteristics, is disclosed.

  Further, in Patent Document 3, C: 0.005 to 0.035%, Si: 0.25 to less than 0.40%, Mn: 0.05 to 0.35%, P: 0.040 by mass%. % Or less, S: 0.01% or less, Cr: 15.5 to 18.0%, Al: 0.001 to 0.10%, N: 0.01 to 0.06%, Si and Mn Discloses a ferritic stainless steel characterized in that 29.5 × Si−50 × Mn + 6 ≧ 0, and the balance consists of Fe and unavoidable impurities.

  Moreover, in patent document 4, C: 0.01-0.03%, Si: 0.02-0.30%, Mn: 0.45-1.0%, P: 0.05% by mass%. The following contains S: 0.01% or less, Al: 0.01 to 0.20%, N: 0.01 to 0.06%, Cr: 16.0 to 18.0%, and the balance is Fe and Cold stainless steel characterized by having a composition comprising unavoidable impurities, and a microstructure having an area ratio of ferrite phase in the entire structure of 80 to 97% and an average particle diameter of ferrite phase of 5 to 20 μm. Rolled steel sheets are disclosed.

Patent No. 3584881 Japanese Patent Publication No. 47-1878 Patent No. 5904310 Unexamined-Japanese-Patent No. 2010-95742

  The present inventors produced a plurality of steel plates in the range of 10.0% to 15.5% of Cr content by the method described in Patent Documents 1 to 3, and were resistant to the method described later. The ridging property was evaluated. As a result, in any steel plate, the predetermined ridging resistance described later was not obtained.

  Further, the present inventors prepare a ferritic stainless steel plate in which only the Cr content is changed within a range of 10.0 to 15.5% based on the method described in Patent Document 4, and will be described later. The ridging resistance was evaluated by the method. However, in any of the steels, the predetermined ridging resistance described later could not be obtained.

  As described above, in the inventions described in Patent Documents 1 to 4, the ridging resistance is not sufficient, and it is necessary to further improve the ridging resistance.

  The present invention has been developed in view of the above-mentioned present situation, and an object of the present invention is to provide a ferritic stainless steel sheet excellent in corrosion resistance and further excellent in ridging resistance, and a method of manufacturing the same. In particular, it is an object of the present invention to provide the above-described steel plate and manufacturing method with respect to a low Cr ferritic stainless steel for which a conventional method of reducing ridging resistance has not been sufficiently studied.

  In addition, "excellent corrosion resistance" means that the weir area ratio measured by the measuring method described below is 40% or less. More preferably, it is 30% or less.

  The corrosion test is carried out in accordance with JASO M 609-91. The test piece is polished to No. 600 with emery paper, washed with a neutral detergent and subjected to ultrasonic degreasing for 5 minutes in ethanol. After that, one cycle is salt spray (5 mass% NaCl aqueous solution, 35 ° C) 2h → dry (60 ° C, relative humidity 40%) 4h → wet (50 ° C, relative humidity 95% or more) 2h, and three cycles of corrosion test Conduct. After the test, the appearance of the corroded surface is photographed, and the area ratio of the area of 30 mm × 30 mm at the center of the steel plate is calculated by image analysis from the obtained photograph.

  In addition, "excellent ridging resistance" means that the ridging height measured by the measuring method described below is 1.5 micrometers or less.

  First, the inventors examined a method for evaluating the ridging resistance shown next, assuming a household cooking appliance that is required to have a further resistance to the ridging compared to the conventional method. Various ferritic stainless steel plates and austenitic stainless steel plates including the present invention are deep drawn and formed into a pan shape having a diameter of 14 cm and a height of 6 cm, and thereafter, for ferritic stainless steel, ridging generated on the side surface of the pan is removed by polishing Conducted a verification. Furthermore, separately, the steel plate was subjected to a tensile test, and the shape of the ridging developed was compared with the shape of the ridging recognized in the above-mentioned verification to comprehensively study the method of evaluating the ridging resistance. As a result, in the case of a ferritic stainless steel sheet having a ridging height of 1.5 μm or less in the method described below, it is confirmed that the time required for the polishing process for removing the ridging can be reduced and the manufacturing cost of the product can be reduced. did.

  In order to measure the ridging height, first, JIS No. 5 tensile test specimens are taken parallel to the rolling direction. Next, the surface of the collected test piece is wet-polished using # 1000 emery paper, and then a 20% tensile strain is applied. Next, the surface shape is measured with a laser displacement meter in the direction perpendicular to the rolling direction on the polished surface of the parallel part of the test piece. The measurement length is 16 mm per line, and the height is measured in 0.05 mm steps. For this reason, the number of height data per line is 321 points including the start point and the end point. Moreover, the space | interval of each line is 1 mm, and a total of 51 lines are measured. The shape data of each line obtained are smoothed and undulated using a Hanning window function type FIR (Finite Impulse Response) band pass filter with a high cut filter wavelength of 0.8 mm and a low cut filter wavelength of 8 mm. . Thereafter, based on the shape data of each processed line, data of 2 mm at both ends of each line, that is, data of 80 points in total are eliminated. After that, first, the arithmetic mean waviness Wa of each line is determined, and then Wa obtained in each line is averaged for all 51 lines to obtain a ridging height.

  The present inventors comprehensively examined the above problems in order to obtain a ferritic stainless steel sheet having excellent ridging resistance. As a result, the following findings were obtained.

  If a ferritic stainless steel sheet having a specific component composition is manufactured by a specific method, a ferritic stainless steel sheet having excellent ridging resistance can be obtained. First, as a raw material, stainless steel having a component composition capable of making the austenite phase fraction 80% or more at high temperature is used. After heating a steel slab having this composition to a temperature of 1000 ° C. or more and “a structure having an austenite phase area ratio of 80% or more”, all hot rolling is performed “austenite phase area ratio is 80% or more Temperature range having a texture, and then, it is cooled to a temperature of 600.degree. Moreover, the hot rolled sheet which has a structure | tissue whose area ratio of a martensitic phase is 80% or more is obtained by this hot rolling. Thereafter, the hot-rolled sheet is cold-rolled to form a cold-rolled sheet. Then, annealing which hold | maintains the cold rolled sheet in the temperature range of 720-800 degreeC for 5 second or more is performed, and it is set as a cold rolled annealed sheet.

  The mechanism is considered to be as follows. The ridging produced when processing a ferritic stainless steel sheet is caused by colonies (crystal grain groups having similar crystal orientations).

  A part of this colony originates in the texture which the ferrite grain which exists in the steel slab used as the material for hot rolling forms in a hot rolling process. Even if the rolled ferrite grains are transformed to the austenite phase during hot rolling, they will form colonies in the structure of the cold rolled annealed sheet to be manufactured thereafter.

  Moreover, a part of this colony originates in the texture which the ferrite grain contained in the material for cold rolling forms in a cold rolling and a cold rolling sheet annealing process.

  Among the colony formation mechanisms described above, the former can be suppressed by sufficiently reducing the number of ferrite grains subjected to hot rolling by rolling in a state where the austenite phase of 80% or more is included in the hot rolling step. . In the latter, by performing rolling in a state where a martensitic phase of 80% or more is included in the cold rolling step, the number of ferrite grains subjected to cold rolling can be sufficiently reduced. By combining and implementing these both methods, it becomes possible to fully suppress the ridging of a ferritic stainless steel plate.

  The present invention is based on the above findings, and the gist configuration is as follows.

  [1] Mass%, C: 0.001 to 0.040%, Si: 0.05 to 0.30%, Mn: 0.05 to 1.00%, P: 0.040% or less, S: Less than 0.030%, Al: 0.001 to 0.300%, Cr: 10.5 to 14.5%, Ni: 0.01 to 1.00% and N: 0.001 to 0.100% A ferritic stainless steel sheet which contains a residual portion of Fe and unavoidable impurities, and which has a ridging height of 1.5 μm or less on the surface of the steel sheet to which a tensile strain of 20% is imparted in the rolling direction.

  [2] Furthermore, Co: 0.01 to 0.50%, Cu: 0.01 to 0.80%, Mo: 0.01 to 0.50% and W: 0.01 to 0% by mass. The ferritic stainless steel sheet according to [1], which contains one or more selected from 50%.

  [3] Furthermore, in mass%, Ti: 0.01 to 0.10%, V: 0.01 to 0.10%, Zr: 0.01 to 0.10%, Nb: 0.01 to 0. 10%, B: 0.0003 to 0.0030%, Mg: 0.0005 to 0.0100%, Ca: 0.0003 to 0.0030%, Y: 0.01 to 0.20% and REM (rare earth Metal): The ferritic stainless steel sheet according to [1] or [2], which contains one or more selected from 0.001 to 0.100%.

  [4] Furthermore, it contains one or two selected from Sn: 0.001 to 0.500% and Sb: 0.001 to 0.500% by mass% [1] to [3] The ferritic stainless steel sheet according to any one of the above.

  [5] The method for producing a ferritic stainless steel sheet according to any one of [1] to [4], wherein the temperature of the steel slab is 1000 ° C. or more and the area ratio of the austenite phase is 80% or more. After heating, all hot rolling is performed in a temperature range having a structure in which the area ratio of the austenite phase is 80% or more, and then, the hot rolling is performed after cooling to a temperature of 600 ° C. or less. A hot rolling step of forming a hot rolled sheet having a structure having an area ratio of a martensite phase of 80% or more; a cold rolling step of cold rolling the hot rolled sheet to form a cold rolled sheet; The annealing process which hold | maintains a rolled sheet in the temperature range of 720-800 degreeC for 5 second or more, The manufacturing method of the ferritic stainless steel plate which has.

  According to the present invention, it is possible to provide a ferritic stainless steel sheet which is excellent in corrosion resistance and further excellent in ridging resistance.

  Hereinafter, embodiments of the present invention will be described. The present invention is not limited to the following embodiments.

  First, the reason why the component composition is limited to the above range in the present invention will be described. In addition, about% which shows the component of a steel plate, unless otherwise indicated, it means mass%.

C: 0.001 to 0.040%
C is an element that promotes the formation of the austenite phase during hot rolling and improves the ridging resistance. These effects are obtained by setting the C content to 0.001% or more. However, if the C content exceeds 0.040%, the precipitation and coarsening of Cr carbides are promoted, and the Cr carbides become the starting point of corrosion and the corrosion resistance is lowered. Therefore, the C content is set to 0.001 to 0.040%. Preferably, the C content is 0.010 to 0.035%. More preferably, the C content is 0.015 to 0.030%.

Si: 0.05 to 0.30%
Si is an element useful as a deoxidizer. This effect is obtained by setting the Si content to 0.05% or more. However, if the Si content exceeds 0.30%, the steel hardens and the formability decreases. Furthermore, the formation of the austenite phase during hot rolling is suppressed, and the ridging resistance is reduced. Therefore, the Si content is made 0.05 to 0.30%. Preferably, the Si content is 0.05 to 0.25%. More preferably, the Si content is 0.07% to 0.20%.

Mn: 0.05 to 1.00%
Mn has a deoxidizing effect. Furthermore, Mn is an element that promotes the formation of the austenite phase during hot rolling and improves the ridging resistance. These effects are obtained by setting the Mn content to 0.05% or more. However, if the Mn content exceeds 1.00%, precipitation and coarsening of MnS are promoted, and this MnS becomes a starting point of heat generation and corrosion resistance is lowered. Therefore, the Mn content is made 0.05 to 1.00%. Preferably, the Mn content is 0.20 to 0.95%. More preferably, the Mn content is 0.30 to 0.90%.

P: 0.040% or less P is an element that reduces the corrosion resistance. In addition, P segregates at grain boundaries to lower the hot workability. Therefore, the P content is desirably as low as possible, and should be 0.040% or less. Preferably, the P content is 0.030% or less.

S: 0.030% or less S forms precipitates MnS with Mn. This MnS becomes the starting point of the pit and causes the deterioration of the corrosion resistance. Therefore, the lower the S content, the better, and the content is made 0.030% or less. Preferably, the S content is 0.020% or less. More preferably, the S content is 0.008% or less.

Al: 0.001 to 0.300%
Al is an element useful as a deoxidizer. This effect is obtained by setting the Al content to 0.001% or more. However, if the Al content exceeds 0.300%, the steel hardens and the formability decreases. Furthermore, the formation of the austenite phase during hot rolling is suppressed, and the ridging resistance is reduced. Therefore, the Al content is set to 0.001 to 0.300%. Preferably, the Al content is 0.002 to 0.200%. More preferably, the Al content is 0.002 to 0.008%.

Cr: 10.5 to 14.5%
Cr is an element that forms a passive film on the surface to enhance corrosion resistance. If the Cr content is less than 10.5%, sufficient corrosion resistance can not be obtained. On the other hand, when the Cr content exceeds 14.5%, the austenitic phase is not sufficiently formed in the steel during hot rolling, and the ridging resistance is reduced. Therefore, the Cr content is made 10.5 to 14.5%. Preferably, the Cr content is in the range of 11.5-14.0%. More preferably, the Cr content is 12.0-13.5%.

Ni: 0.01 to 1.00%
Ni is an element that promotes the formation of the austenite phase during hot rolling and improves the ridging resistance. Furthermore, Ni is an element that reduces the corrosion rate and enhances the corrosion resistance when the steel corrodes. These effects are obtained when the Ni content is 0.01% or more. On the other hand, if it exceeds 1.00%, a large amount of austenite phase will be generated in the steel in the cold rolled sheet annealing step. When this austenite phase is transformed into a martensitic phase in the cooling process after annealing, the formability of the cold rolled annealed sheet is reduced. Furthermore, the material cost is high. Therefore, the Ni content is 0.01 to 1.00%. Preferably, the Ni content is 0.05 to 1.00%. More preferably, the Ni content is 0.10 to 0.50%.

N: 0.001 to 0.100%
N is an element that promotes the formation of the austenite phase during hot rolling and improves the ridging resistance. This effect is obtained by setting the N content to 0.001% or more. However, if the N content exceeds 0.100%, precipitation and coarsening of Cr nitride are promoted, and this Cr nitride becomes a starting point of heat generation and corrosion resistance decreases. Therefore, the N content is set to 0.001 to 0.100%. Preferably, the N content is 0.005 to 0.080%. More preferably, the N content is 0.010 to 0.050%.

  In the present invention, in addition to the above-described basic components, elements described below can be appropriately contained as optional components. In addition, when the following arbitrary components are included by less than the following lower limit, in order not to impair the effect of this invention, the arbitrary components contained by less than a lower limit shall be contained as an unavoidable impurity.

  Furthermore, Co: 0.01 to 0.50%, Cu: 0.01 to 0.80%, Mo: 0.01 to 0.50% and W: 0.01 to 0.50% by mass% One or more selected from them can be contained as an optional component.

Co: 0.01 to 0.50%
Co is an element that improves the crevice corrosion resistance of stainless steel. On the other hand, when it contains excessive Co, processability will fall. Therefore, when Co is contained, it is preferable to make Co content into 0.01 to 0.50%. More preferably, the Co content is 0.01 to 0.30%. More preferably, the Co content is 0.01 to 0.10%.

Cu: 0.01 to 0.80%
Cu is an element that strengthens the passive film and improves the corrosion resistance. Furthermore, it is an element that promotes the formation of the austenite phase during hot rolling and improves the ridging resistance. On the other hand, when it contains Cu excessively, while a workability will fall, (epsilon) -Cu will precipitate easily and corrosion resistance will fall. Therefore, when it contains Cu, it is preferable to make Cu content into 0.01 to 0.80%. More preferably, the Cu content is 0.15 to 0.60%. More preferably, the Cu content is 0.40 to 0.45%.

Mo: 0.01 to 0.50%
Mo has the effect of improving the crevice corrosion resistance of stainless steel. On the other hand, when Mo is contained excessively, the formation of the austenitic phase during hot rolling is suppressed, and the ridging resistance is reduced. Therefore, when it contains Mo, it is preferable to make Mo content into 0.01 to 0.50%. More preferably, the Mo content is 0.05 to 0.25%.

W: 0.01 to 0.50%
W is an element that improves the crevice corrosion resistance of stainless steel. On the other hand, when W is contained excessively, processability will fall. Therefore, when it contains W, it is preferable to make W content into 0.01 to 0.50%. More preferably, the W content is 0.03 to 0.30%. More preferably, the W content is 0.05 to 0.10%.

  Furthermore, in mass%, Ti: 0.01 to 0.10%, V: 0.01 to 0.10%, Zr: 0.01 to 0.10%, Nb: 0.01 to 0.10%, B: 0.0003 to 0.0030%, Mg: 0.0005 to 0.0100%, Ca: 0.0003 to 0.0030%, Y: 0.01 to 0.20% and REM (rare earth metal): One or more selected from 0.001 to 0.100% can be contained as an optional component.

Ti: 0.01 to 0.10%
Ti is an element having high affinity to C and N, and precipitates as carbides or nitrides during hot rolling to reduce solid solution C and solid solution N in the matrix, and processability after cold-rolled sheet annealing Have the effect of improving On the other hand, when Ti is contained excessively, the formation of the austenitic phase during hot rolling is suppressed, and the ridging resistance is reduced. Therefore, when it contains Ti, it is preferable to make Ti content into 0.01 to 0.10%. More preferably, the Ti content is 0.02 to 0.08%.

V: 0.01 to 0.10%
V is an element having a high affinity to C and N, and precipitates as carbides or nitrides during hot rolling to reduce solid solution C and solid solution N in the matrix, and processability after cold-rolled sheet annealing Have the effect of improving On the other hand, when V is contained excessively, the formation of the austenite phase during hot rolling is suppressed, and the ridging resistance is reduced. Therefore, when it contains V, it is preferable to make V content into 0.01 to 0.10%. More preferably, the V content is 0.02 to 0.08%.

Zr: 0.01 to 0.10%
Zr is an element having a high affinity to C and N, and precipitates as carbides or nitrides during hot rolling to reduce solid solution C and solid solution N in the matrix, and processability after cold-rolled sheet annealing Have the effect of improving On the other hand, if the content of Zr is excessive, the formation of austenite phase during hot rolling is suppressed, and the ridging resistance is reduced. Therefore, when it contains Zr, it is preferable to make Zr content into 0.01 to 0.10%. More preferably, the Zr content is 0.02 to 0.08%.

Nb: 0.01 to 0.10%
Nb is an element having a high affinity to C and N, and precipitates as carbides or nitrides during hot rolling to reduce solid solution C and solid solution N in the matrix, and processability after cold-rolled sheet annealing Have the effect of improving On the other hand, when Nb is excessively contained, the formation of the austenite phase during hot rolling is suppressed, and the ridging resistance is reduced. Therefore, when Nb is contained, the Nb content is preferably 0.01 to 0.10%. More preferably, the Nb content is 0.02 to 0.08%.

B: 0.0003 to 0.0030%
B is an element effective to prevent low temperature secondary processing embrittlement. On the other hand, when it contains excessive B, hot workability will fall. Therefore, when it contains B, it is preferable to make B content into 0.0003-0.0030%. More preferably, B content is 0.0005 to 0.0020%.

Mg: 0.0005 to 0.0100%
Mg forms Mg oxide with Al in molten steel and acts as a deoxidizer. On the other hand, if the Mg content is excessive, the toughness of the steel is reduced and the productivity is reduced. Therefore, when it contains Mg, it is preferable to make Mg content into 0.0005 to 0.0100%. More preferably, the Mg content is 0.0005 to 0.0050%. More preferably, the Mg content is 0.0010 to 0.0030%.

Ca: 0.0003 to 0.0030%
Ca is an element that improves the hot workability. On the other hand, when the content of Ca is excessive, the toughness of the steel is lowered and the productivity is lowered, and furthermore, the corrosion resistance is lowered by the precipitation of CaS. Therefore, when it contains Ca, it is preferable to make Ca content into 0.0003-0.0030%. More preferably, the Ca content is 0.0010 to 0.0020%.

Y: 0.01 to 0.20%
Y is an element that reduces the decrease in viscosity of molten steel and improves the degree of cleanliness. On the other hand, when Y is contained excessively, the effect is saturated and the processability is further reduced. Therefore, when it contains Y, it is preferable to make Y content into 0.01 to 0.20%. More preferably, the Y content is 0.01 to 0.10%.

REM (rare earth metal): 0.001 to 0.100%
REM (rare earth metal: an element with an atomic number of 57 to 71 such as La, Ce, Nd) is an element that improves high-temperature oxidation resistance. On the other hand, if the content of REM is excessive, the effect is saturated, and further, surface defects occur during hot rolling, which lowers productivity. Therefore, when REM is contained, it is preferable to make REM content into 0.001 to 0.100%. More preferably, the REM content is 0.005 to 0.050%.

  Furthermore, one or two selected from Sn: 0.001 to 0.500% and Sb: 0.001 to 0.500% by mass can be contained as an optional component.

Sn: 0.001 to 0.500%
Sn is effective in improving the ridging resistance by promoting the formation of deformation bands during rolling. On the other hand, if the content of Sn is excessive, the effect is saturated and the formability is further reduced. Therefore, when it contains Sn, it is preferable to make Sn content into 0.001 to 0.500%. More preferably, the Sn content is 0.003 to 0.200%.

Sb: 0.001 to 0.500%
Sb is effective for improving the ridging resistance by promoting the formation of deformation bands during rolling. On the other hand, if Sb is excessively contained, the effect is saturated and the formability is further reduced. Therefore, when Sb is contained, it is preferable to make Sb content into 0.001 to 0.500%. More preferably, the Sb content is 0.003 to 0.200%.

  Next, the suitable manufacturing method of the ferritic stainless steel plate of this invention is demonstrated.

  The steel having the above-described composition is melted by a known method such as a converter, an electric furnace, a vacuum melting furnace or the like, and made into a steel material (steel slab) by a continuous casting method or an ingot-slump method. The steel slab is then subjected to hot rolling under the following conditions. First, the steel slab is heated to a temperature having a structure in which the area ratio of the austenitic phase is not less than 80 ° C. and not less than 1000 ° C. Thereafter, hot rolling is started, and finish rolling, which is the final rolling, is finished before the temperature of the steel sheet is lowered to a temperature at which the area ratio of the austenitic phase is less than 80%. That is, all rolling is performed in a temperature range having a structure in which the area ratio of austenite phase is 80% or more. After the finish rolling, the steel plate is cooled to 600 ° C. or less, and then the steel plate is wound up.

Slab heating temperature: Temperature having a structure in which the area ratio of austenitic phase is at least 1000 ° C. and 80% or more The surface temperature of the steel plate is roughened by the hot rolling if the heating temperature of the steel slab is less than 1000 ° C. descend. In addition, when the heating temperature of the steel slab is a temperature having a structure in which the area ratio of the austenite phase is less than 80%, many ferrite grains are rolled during hot rolling. The ferrite grains thus rolled are transformed to an austenite phase during hot rolling, for example, and even if they are transformed to a martensitic phase as the hot rolled sheet cools, the structure of a cold rolled annealed sheet produced thereafter It results in the formation of colonies, which reduces the resistance to ridging. Therefore, the slab heating temperature is set to a temperature having a structure in which the area ratio of the austenite phase is 80% or more and 1000 ° C. or more. The heating time is preferably 10 minutes to 24 hours.

Hot rolling temperature: Temperature having a structure in which the area ratio of austenite phase is 80% or more Hot rolling temperature is a temperature having a structure in which the area ratio of austenite phase is less than 80% Of the ferrite grains of the Therefore, the hot rolling temperature is a temperature having a structure in which the area ratio of the austenite phase is 80% or more. Specifically, the slab heating temperature is set as described above, and the temperature of the steel plate immediately after finish rolling, that is, the finish rolling end temperature, is set to a temperature having a structure in which the area ratio of austenite phase is 80% or more. Just do it.

Winding temperature: 600 ° C. or less After slab heating and rolling under the conditions described above, the steel plate is cooled to 600 ° C. or less and then wound, the austenitic phase contained in the steel plate after finish rolling is the component system of the present invention In, almost all of them transform to martensitic phase. As a result, the structure of the hot-rolled sheet contains a martensite phase of 80% or more in area ratio, and a hot-rolled sheet suitable as a material for cold rolling described later can be obtained. However, if the steel plate is rolled up to 600 ° C. or less without being cooled, a part of the austenite phase contained in the steel plate is transformed to the ferrite phase during cooling after winding up, which will be described later for cold rolling It becomes a hot-rolled board which is not suitable as a material.

  When the austenite phase area ratio at each temperature of the steel material is not known, it can be determined by the following method.

  First, steel slabs are taken from the steel slab, and the steel slabs are held at each temperature for 1 hour in the range of 700 to 1300 ° C., and then water-cooled. At this time, in the high temperature state, in the component system of the present invention, one or both of the ferrite phase and the austenite phase are contained in the structure of the steel. When water cooling from a high temperature state, in the component system of the present invention, the ferrite phase is cooled as it is in the ferrite phase, but the austenite phase transforms to the martensite phase during cooling. That is, the area ratio of the martensitic phase contained in the structure of the steel sheet after cooling is the area ratio of the austenite phase at each temperature in the high temperature state, and the area ratio of the ferrite phase contained in the structure of the steel sheet after cooling It becomes the area ratio of the ferrite phase in each temperature in a high temperature state. The area ratio of each phase contained in the structure of the steel slab after cooling is determined by the following method.

A steel piece which has been held in a high temperature state obtained by water cooling is cut out and a cross section is observed. In order to observe, the specimen for tissue observation is collected, the cross section is mirror-polished and corroded (etched) with Murakami's reagent (8 mass% KOH-8 mass% [K ₃ Fe (CN) ₆ ] aqueous solution) Take 10 fields of view at a magnification of 400x using an optical microscope. In addition, corrosion is sufficiently performed so that the ferrite phase and the martensite phase can be clearly judged in the structure photograph obtained by the optical microscope observation. The obtained structure photograph is binarized by image analysis to distinguish and separate a martensite phase and a ferrite phase, and the area ratio of the ferrite phase is measured. Here, as the threshold value at the time of binarization, the tissue photograph and the binarized image are compared, and both set appropriate values. When shading (brightness and darkness unevenness) is present in the tissue photograph, it is preferable to carry out shading correction processing before binarization. The measurement results are averaged over all 10 fields of view, and the calculated value is taken as the area ratio of the ferrite phase. In addition, inclusions are disregarded and it calculates. Let the value which deducted the area ratio of a ferrite phase from 100% be the austenite phase area ratio in each temperature.

  For example, when the steel material is held at 840 ° C. for 1 hour and the area ratio of the martensitic phase and the ferrite phase contained in the water-cooled structure is 72% and 28%, respectively, 840 ° C. The temperature is such a temperature that the area ratio of the austenite phase is 72%, and the area ratio of the ferrite phase is 28%.

  Further, the temperature having a structure in which the area ratio of the austenite phase is 80% or more is the temperature within the range in which the area ratio is 80% or more as a result of determining the area ratio of the austenite phase at each temperature by the above method It is. For example, when a steel material is held at each temperature for 1 hour and the area ratio of the martensitic phase contained in the water-cooled structure is measured, the area ratio is 80% or more at 860 ° C. or more and 1040 ° C. or less When the area ratio is less than 80% at the temperature of 1, the temperature having a structure in which the area ratio of the austenite phase is 80% or more is a temperature within the range of 860 ° C. or more and 1040 ° C. or less.

  C, Mn, Ni, N, etc. when the component composition is such that the temperature range in which the area ratio of the austenitic phase is 80% or more is narrow or not and hot rolling can not be performed under the conditions described above By increasing the content of elements that increase the stability of the austenite phase represented by the above, or decreasing the content of elements that decrease the stability of the austenite phase represented by Si, Al, and Cr. It can adjust to the component composition which can perform hot rolling on conditions of (1).

  In the hot rolling process, from slab heating to finish rolling, conditions are adjusted so that the above-described hot rolling conditions are satisfied based on the austenitic phase area ratio at each temperature obtained by the above-described structure observation method. You can do it.

  The hot-rolled sheet thus produced contains 80% or more of the martensitic phase in area ratio. This hot rolled sheet is pickled to obtain a cold rolling material, and then cold rolling is performed, and cold rolled sheet annealing is performed in a continuous annealing line and held for at least 5 seconds in a range of 720 ° C. to 800 ° C. , Obtain cold rolled annealed sheet. After cold-rolled sheet annealing, pickling is performed in a pickling line to remove scale. The cold-rolled sheet from which the scale has been removed may be subjected to skin pass rolling or polishing. In particular, skin pass rolling is preferably applied at an elongation of 0.3 to 2.0% for shape correction and removal of elongation at yield point. Note that some or all of the above-described steps may be repeatedly performed.

Structure of material for cold rolling: area ratio of martensite phase is 80% or more When material for cold rolling does not contain 80% or more of martensite phase in area ratio, area ratio of remaining ferrite phase is high As a result, a large amount of ferrite grains are to be rolled by cold rolling. The rolled ferrite grains form colonies in the structure of a cold rolled annealed sheet to be produced thereafter, which reduces the ridging resistance. In addition, the area ratio of the martensitic phase of the material for cold rolling may be determined by extracting the specimen for observing the structure from the material for cold rolling, mirror-polishing the cross section in the rolling direction, and using the above-mentioned structure observation method .

Cold rolled sheet annealing: maintained at a temperature range of 720 to 800 ° C. for 5 seconds or more If the cold rolled sheet annealing temperature is less than 720 ° C., the martensitic phase contained in the cold rolled sheet does not sufficiently transform to a ferrite phase, The ferrite phase does not recrystallize sufficiently, so that sufficient formability can not be obtained for a cold rolled annealed sheet. When the cold-rolled sheet annealing temperature exceeds 800 ° C., a large amount of austenite phase is formed in the steel, and the austenitic phase is transformed into a martensitic phase in the cooling process after annealing to form a cold-rolled annealed sheet Sufficient formability can not be obtained.

  If the cold-rolled sheet annealing time is less than 5 seconds, the martensitic phase contained in the cold-rolled sheet does not sufficiently transform to the ferrite phase, and the ferrite phase does not sufficiently recrystallize, which is sufficient for the cold-rolled annealed sheet Formability can not be obtained.

  The ferritic stainless steel plate defined in the present invention is a steel plate in which the area ratio of the ferrite phase is recognized to be 90% or more using the above-described structure observation method, and such a structure can be obtained by cold-rolled sheet annealing. Good. This is because the area ratio of the ferrite phase contained in the structure of the cold rolled annealed sheet is less than 90%, that is, the area ratio of the martensitic phase contained in the structure of the cold rolled annealed sheet exceeds 10%. Is hardened and the formability is reduced.

  Table 1 No. A ferritic stainless steel having the component compositions shown in 1-1 to 1-3 (the balance being Fe and unavoidable impurities) was melted into a 100 kg steel ingot.

Thereafter, 1 kg of steel slab was taken from the bottom portion of the steel slab and held in the range of 700 ° C. to 1300 ° C. at each temperature of 20 ° C. for 1 hour, and then water cooled. The obtained annealed billet was cut out and cross-sectional observation was performed. For observation, a specimen for texture observation is collected, and the cross section in the rolling direction is mirror-polished, corroded (etched) with Murakami's reagent (8 mass% KOH-8 mass% [K ₃ Fe (CN) ₆ ] aqueous solution), It implemented by imaging | photography 10 fields of vision by magnification 400x using a microscope. The obtained structure photograph was binarized by image analysis to distinguish and separate the martensite phase and the ferrite phase, and the area ratio of the martensite phase was measured. The measurement results were averaged over all 10 fields of view, and the calculated value was taken as the area ratio of the martensitic phase. In addition, inclusions were disregarded and calculated. The value of the area ratio of the obtained martensitic phase was made into the austenite phase area ratio in each temperature. In this result, the maximum temperature and the minimum temperature at which the austenite phase area ratio was 80% or more were respectively defined as the γ phase area ratio 80% or more upper limit temperature and the lower limit temperature.

  Of the steel slabs, the remaining portion from which the steel pieces are collected is divided into five, heated to each slab heating temperature shown in Table 1 and held for 1 hour, and then hot rolling is started 10 seconds after taking out from the heating furnace, A hot-rolled sheet having a thickness of 4.0 mm was obtained. In hot rolling, the temperature immediately after the final pass was measured and used as the finish rolling temperature. In addition, all the hot rolling was performed at the temperature between the heating temperature and the finish rolling end temperature. After finish rolling, the hot-rolled sheet was sprayed with water to cool the hot-rolled sheet to each winding temperature. Thereafter, the hot-rolled sheet was held for 1 hour in an electric furnace having an Ar atmosphere held at each winding temperature, and then subjected to a furnace cooling process (winding process). This process simulates the temperature history of the hot-rolled sheet when the hot-rolled sheet is wound at each winding temperature in an actual production line. The respective heating temperatures, finish rolling temperatures and winding temperatures are shown in Table 1.

  After the temperature of the hot-rolled sheet was lowered to room temperature, grinding was performed on both the front and back sides to remove the scale, and a material for cold rolling was obtained. A test piece for structure observation was cut out from the material for cold rolling, cross-sectional observation was performed by the method described above, and the structure of the material for cold rolling was investigated. Those having an area ratio of 80% or more of the martensitic phase were evaluated as “○”, and those having less than 80% were evaluated as “▲”.

  The material for cold rolling was then cold-rolled to form a cold-rolled plate with a plate thickness of 1.0 mm. The obtained cold rolled sheet was annealed at each temperature shown in Table 1 for each time to obtain a cold rolled annealed sheet.

Then, cross-sectional observation of the obtained cold-rolled annealing board was performed. For observation, a specimen for texture observation is collected, and the cross section in the rolling direction is mirror-polished, corroded (etched) with Murakami's reagent (8 mass% KOH-8 mass% [K ₃ Fe (CN) ₆ ] aqueous solution), It implemented by imaging | photography 10 fields of vision by magnification 400x using a microscope. The obtained structure photograph was binarized by image analysis to distinguish and separate the martensite phase and the ferrite phase, and the area ratio of the ferrite phase was measured. The measurement results were averaged over all 10 fields of view, and the calculated value was taken as the area ratio of the ferrite phase. In addition, inclusions were disregarded and calculated. As a result, it was confirmed that the area ratio of the ferrite phase of the obtained cold rolled annealed sheet was 90% or more.

  The remaining portion of the obtained cold rolled annealed sheet from which the above-described test piece for structure observation was collected was pickled by a usual method and subjected to skin pass rolling at 0.8%.

  The cold rolled annealed pickling sheet obtained under the above-mentioned production conditions was subjected to the evaluation shown below.

<Corrosion resistance>
The cold-rolled annealed plate pickling plate was cut into a length of 80 mm × a width of 60 mm by shearing. After cutting out, it was polished to No. 600 with emery abrasive paper, washed with a neutral detergent, and then ultrasonic degreased for 5 minutes in ethanol. The corrosion test was implemented based on JASO M609-91 with respect to the obtained steel plate, and corrosion resistance was evaluated. The test piece was placed in the test apparatus at an inclination of 60 ° with its length direction vertical after covering the end and back with vinyl tape. Three cycles were carried out with one cycle being salt spray (5% by mass aqueous NaCl solution, 35 ° C.) 2 h → dry (60 ° C., relative humidity 40%) 4 h → wet (50 ° C., relative humidity 95% or more) 2 h. After the test, the appearance of the corroded surface was photographed, and the area ratio of wrinkles was calculated by image analysis from the obtained photograph for a 30 mm × 30 mm area centered on the steel plate. “銹” (pass: excellent) when the area rate was 30% or less, “□” (pass) when it was more than 30% to 40% or less It was evaluated as "▲" (failed).

<Riding resistance>
Furthermore, the No. 5 test piece specified in JIS Z 2241 is collected so that the rolling direction is the longitudinal direction of the test piece, and the surface is wet-polished using # 1000 emery paper, and then the tensile test is performed according to the same standard. And a tensile strain of 20% was applied. Thereafter, the surface shape was measured using a laser displacement meter in the direction perpendicular to the rolling direction on the polished surface at the center of the parallel portion of the test piece. The measurement length was 16 mm per line, and the height was measured while shifting the position by 0.05 mm. Therefore, the number of height data per line is 321 points including the start point and the end point. In addition, a total of 51 lines were measured with an interval of 1 mm between the lines. The shape data of each line obtained are smoothed and undulated using an Hanning window function type FIR (Finite Impulse Response) band pass filter with a high cut filter wavelength of 0.8 mm and a low cut filter wavelength of 8 mm. The Thereafter, based on the shape data of each processed line, data of 2 mm at both ends of each line, that is, data of 80 points in total was excluded. After that, first, the arithmetic mean waviness Wa of each line was determined, and then the Wa obtained in each line was averaged for all 51 lines to obtain the ridging height. The case where the ridging height is 1.5 μm or less is “o” (pass), and the case where it is more than 1.5 μm is “▲” (fail).

  The obtained results are shown in Table 1. After heating to a temperature having a structure in which the composition of the steel is within the range of the present invention, and the slab heating temperature is 1000 ° C. or more and the area ratio of austenite phase is 80% or more, all rolling is austenite phase Hot rolling is performed in a temperature range having a structure having an area ratio of 80% or more, and thereafter cooled to a temperature of 600 ° C. or less, and then, winding processing is performed, and the area ratio of the martensitic phase is 80%. A hot-rolled sheet having the above-described structure, cold-rolling the hot-rolled sheet, and a cold-rolled sheet, and further annealing for holding the cold-rolled sheet in the temperature range of 720 to 800 ° C for 5 seconds or more The ferritic stainless steels obtained by carrying out the test, that is, the invention steels, all have an evaluation of corrosion resistance of “o” or “□”, and an evaluation of ridging resistance of “o”, which is excellent in corrosion resistance and Riji It was found to be excellent in grayed property.

  Production method No. Comparative examples 1-1-1-3, 1-2-3, and 1-3-3 have a low finish rolling temperature in hot rolling, and roll a large amount of ferrite grains in hot rolling and cold rolling. It was inferior to ridging resistance because it became.

  Production method No. 1-1-4, 1-2-4, and 1-3-4 are high in slab heating temperature in hot rolling, and rolling large amounts of ferrite grains in hot rolling and cold rolling. It was inferior to ridging resistance because it became.

  Production method No. In Comparative Examples 1-1-5, 1-2-5, and 1-3-5, the coiling temperature is high, and a large amount of ferrite particles are rolled in cold rolling, so that the ridging resistance is improved. It was inferior.

  In addition, the Cr content of No. In Nos. 1-2 and 1-3, the Cr content is outside the preferable range. It has excellent corrosion resistance compared to 1-1.

  Table 2 No. A cold-rolled, annealed and pickled sheet, which is a ferritic stainless steel sheet having the component compositions (the balance is Fe and unavoidable impurities) shown in 2-1 to 2-21, was manufactured under the manufacturing conditions shown in Table 2.

  Each γ phase area ratio 80% or more upper limit temperature and lower limit temperature, slab heating temperature of hot rolling, each finish rolling finishing temperature, each manufacturing condition of winding temperature, and each of the structure of the material for cold rolling The evaluation results are shown in Table 2.

  After confirming that the area ratio of the ferrite phase of the obtained cold rolled annealed pickled sheet is 90% or more in all, it was subjected to each test shown in Example 1 to evaluate the corrosion resistance and the ridging resistance. . The obtained results are shown in Table 2.

  The invention steels were all evaluated as "o" for corrosion resistance evaluation, "o" for evaluation of ridging resistance, and were found to be excellent in corrosion resistance as well as being excellent in ridging resistance.

  Test No. Since the content of Cr is lower than the component range of this invention, the comparative example of 2-17 was inferior to corrosion resistance.

  Test No. The comparative examples 2 to 18 and 2 to 19 were inferior in corrosion resistance because the contents of C and N were respectively higher than the component range of the present invention.

  Test No. In the comparative examples 2-20 and 2-21, the content of Si and Cr is respectively higher than the component range of the present invention, so that the austenitic phase is not sufficiently formed in the steel during hot rolling, and hot rolling and Since a large amount of ferrite grains were to be rolled in cold rolling, the ridging resistance was inferior.

  The ferritic stainless steel sheet of the present invention is excellent in corrosion resistance and resistance to ridging, and therefore, it is suitable for household cooking appliances, parts for household appliances, parts for office supplies, parts for automobile interiors, piping for automobile exhaust, building materials It can be suitably used for applications such as

Claims (5)

In mass%,
C: 0.001 to 0.040%,
Si: 0.05 to 0.30%,
Mn: 0.05 to 1.00%,
P: 0.040% or less,
S: 0.030% or less,
Al: 0.001 to 0.300%,
Cr: 10.5 to 14.5%,
Ni: 0.01 to 1.00%
And N: 0.001 to 0.100%, the balance being Fe and unavoidable impurities,
A ferritic stainless steel sheet having a ridging height of 1.5 μm or less on the surface of a steel sheet to which a tensile strain of 20% is applied in the rolling direction. Furthermore, in mass%,
Co: 0.01 to 0.50%,
Cu: 0.01 to 0.80%,
Mo: 0.01 to 0.50%
The ferritic stainless steel sheet according to claim 1, containing one or more selected from W and 0.01 to 0.50%. Furthermore, in mass%,
Ti: 0.01 to 0.10%,
V: 0.01 to 0.10%,
Zr: 0.01 to 0.10%,
Nb: 0.01 to 0.10%,
B: 0.0003 to 0.0030%,
Mg: 0.0005 to 0.0100%,
Ca: 0.0003 to 0.0030%,
Y: 0.01 to 0.20%
And REM (rare earth metal): One or two or more selected from 0.001 to 0.100%. The ferritic stainless steel sheet according to claim 1 or 2. Furthermore, in mass%,
Sn: 0.001 to 0.500%
The ferritic stainless steel sheet according to any one of claims 1 to 3, containing one or two selected from 0.001 to 0.500% of Sb. It is a manufacturing method of the ferritic stainless steel plate in any one of Claims 1-4,
After heating the steel slab to a temperature that has a structure with an area ratio of at least 1000 ° C. and an austenitic phase of at least 80%, all hot rolling is performed to a temperature range having an organization with an area ratio of austenitic phase of at least 80% And hot rolling is carried out after cooling to a temperature of 600 ° C. or less, and hot rolling is performed to form a hot-rolled sheet having a structure in which the area ratio of martensitic phase is 80% or more;
A cold rolling step of cold rolling the hot rolled sheet into a cold rolled sheet;
An annealing step of holding the cold rolled sheet in a temperature range of 720 to 800 ° C. for 5 seconds or more;