JP5505555B1 - Ferritic stainless steel sheet - Google Patents

Abstract

【Task】
A ferritic stainless steel sheet having excellent formability and corrosion resistance is provided.
[Solution]
In mass%, C: 0.003-0.013%, Si: 0.01-0.95%, Mn: 0.01-0.40%, P: 0.020-0.040%, S: 0.010% or less, Al: 0.01 to 0.45%, Cr: 14.5 to 21.5%, Ni: 0.01 to 0.60%, N: 0.005 to 0.012% V: 0.010-0.040%, B: 0.0001-0.0010% is contained in the range which satisfies V / B> = 15.0, and also Ti: 0.20-0 .40% or Nb: 0.40 to 0.60%, or Ti and Nb in a range satisfying the total amount of Ti and Nb: 0.40 to 0.70%, A ferritic stainless steel sheet characterized in that the balance consists of Fe and inevitable impurities.
[Selection figure] None

Description

  The present invention relates to a ferritic stainless steel sheet that can be preferably applied to various uses such as automobile parts, household goods, kitchen appliances, electrical appliances, etc., and is excellent in formability and corrosion resistance.

  Ferritic stainless steel is widely used as a material having excellent corrosion resistance in various fields including automobile parts and household goods. In general, this ferritic stainless steel is cheaper than austenitic stainless steel containing a large amount of Ni, but is inferior in formability. For example, ferritic stainless steel has a problem that irregularities called earrings occur at the edge of a molded member when deep drawing is performed. For this reason, ferritic stainless steel that has both corrosion resistance and formability such as deep drawing is required.

  As a technique for improving the formability of ferritic stainless steel, for example, in Patent Document 1, C: 0.03 mass% or less, Si: 2.0 mass% or less, Mn: 0.8 mass% or less, S : 0.03 mass% or less, Cr: 6 to 25 mass%, N: 0.03 mass% or less, Al: 0.3 mass% or less, Ti: 0.4 mass% or less, V: 0.02 to 0 .4% by mass, B: 0.0002 to 0.0050% by mass in a range satisfying the formulas: Ti / 48> N / 14 + C / 12, V / B> 10, the balance being Fe and inevitable impurities A ferritic stainless hot-rolled steel sheet characterized by comprising: This ferritic stainless steel hot-rolled steel sheet is said to have excellent skin resistance after forming and high temperature fatigue properties.

  In Patent Document 2, C: 0.03 to 0.08 mass%, Si: 1.0 mass% or less, Mn: 1.0 mass% or less, P: 0.05 mass% or less, S: 0 .015 mass% or less, Al: 0.10 mass% or less, N: 0.02 mass% or less, Cr: 5 to 60 mass%, Ti: 4 × (C content + N content) to 0.5 It contains that mass%, Nb: 0.003 to 0.020 mass%, B: 0.0002 to 0.005 mass%, the balance is made of Fe and inevitable impurities, and Δr is 0.3 or less. A featured chromium steel sheet is disclosed. This chromium steel sheet is said to be excellent in deep drawability and secondary work brittleness resistance.

Japanese Patent Laid-Open No. 09-3606 Japanese Patent Laid-Open No. 08-20843

  However, the techniques described in the above patent documents have the following problems. In the technique described in Patent Document 1, the in-plane anisotropy (hereinafter simply referred to as Δr) of the plastic strain ratio (hereinafter simply referred to as r value) is not sufficiently improved. As a result, the technique described in Patent Document 1 has a problem that earrings are generated at the edge of the molded member when deep drawing is performed. In addition, in the technique described in Patent Document 1, the influence on the corrosion resistance due to the addition of B has not been studied, and the corrosion resistance of the ferritic stainless steel hot rolled steel sheet may be lowered. On the other hand, in the technique disclosed in Patent Document 2, although the r value and Δr are improved, the influence on the corrosion resistance by adding B has not been studied, and the corrosion resistance of the chromium steel sheet may be lowered. is there.

  As described above, by the techniques described in Patent Documents 1 and 2 described above, it is not possible to obtain a ferritic stainless steel excellent in both formability such as deep drawing and corrosion resistance.

  An object of the present invention is to solve the above-described problems of the prior art and to provide a ferritic stainless steel sheet having excellent formability and corrosion resistance.

  The present inventors have made various studies in order to achieve the above-described problems. As a result, a ferritic stainless steel sheet having both formability such as deep drawing and corrosion resistance can be obtained by adjusting the V content and B content to appropriate ranges and adjusting V / B to 15.0 or more. As a result, the present invention has been completed.

  Hereinafter, the experimental results on which the present invention is based will be described. “%” Representing the content of the component means “mass%”.

(Experiment 1)
(0.009 to 0.012)% C [C content in Table 1 means in the range of 0.009 to 0.012 mass%. The same applies hereinafter. ], (0.08-0.12)% Si, (0.19-0.23)% Mn, (0.033-0.037)% P, (0.001-0.002)% S, (17.2 to 17.5)% Cr, (0.02 to 0.03)% Al, (0.009 to 0.012)% N, (0.08 to 0.12)% Ni, (0 .25 to 0.27)% Ti, (0.010 to 0.016)% V, and (0.0002 to 0.0010)% B, changing the V / B ratio with the balance being Fe and inevitable impurities Stainless steel made of was melted in a 50 kg small vacuum melting furnace. These steel ingots were heated to 1100 ° C. and then hot rolled to form 4.0 mm hot rolled sheets. Next, the hot-rolled sheet was annealed at 930 ° C. × 60 sec, then shot blasted, pickled with a mixed acid of hydrofluoric acid and nitric acid, and cold rolled into a cold-rolled sheet having a thickness of 0.7 mm. . The obtained cold-rolled sheet was subjected to finish annealing at 880 ° C. × 40 sec to obtain a cold-rolled annealed sheet. A test piece of 60 mm × 80 mm was cut out from the obtained cold-rolled annealed plate, the surface was polished with # 600 count, and corrosion resistance was evaluated by a combined cycle corrosion test. The combined cycle corrosion test is based on JASO M 609-91, salt spray (5% NaCl, 35 ° C., 2 h) → dry (60 ° C., relative humidity 20-30%) → wet (50 ° C., 2 h, relative humidity) 30 cycles of corrosion test with 1 cycle of ≧ 95%) were performed. In the combined cycle corrosion test, an area ratio of 20% or more was determined to be unacceptable and less than 20% was determined to be acceptable. The obtained results are shown in Table 1. From Table 1, it can be seen that the corrosion resistance is improved by setting the V / B ratio to 15.0 or more.

(Experiment 2)
(0.009 to 0.012)% C, (0.82 to 0.89)% Si, (0.35 to 0.40)% Mn, (0.024 to 0.027)% shown in Table 2 P, (0.001-0.003)% S, (14.5-14.9)% Cr, (0.01-0.02)% Al, (0.009-0.012)% N, (0.15-0.20)% Ni, (0.40-0.43)% Nb, (0.011-0.017)% V, (0.0002-0.0010)% B, V The stainless steel consisting of Fe and inevitable impurities was melted in a 50 kg small vacuum melting furnace while changing the / B ratio. These steel ingots were heated to 1100 ° C. and then hot rolled to form 4.0 mm hot rolled sheets. Next, the hot-rolled sheet was annealed at 1020 ° C. × 60 sec, then shot blasted, pickled with a mixed acid of hydrofluoric acid and nitric acid, and cold rolled into a cold-rolled sheet having a thickness of 0.7 mm. . The obtained cold-rolled sheet was subjected to finish annealing at 980 ° C. × 40 sec to obtain a cold-rolled annealed sheet. A test piece of 60 mm × 80 mm was cut out from the obtained cold-rolled annealed plate, the surface was polished with # 600 count, and corrosion resistance was evaluated by a combined cycle corrosion test. In the combined cycle corrosion test, the above corrosion test cycle was performed 30 times. In the combined cycle corrosion test, an area ratio of 20% or more was determined to be unacceptable and less than 20% was determined to be acceptable. The obtained results are shown in Table 2. From Table 2, it can be seen that the corrosion resistance is improved by setting the V / B ratio to 15.0 or more.

When the V / B ratio in Experiment 1 and Experiment 2 is less than 15.0, it is presumed that Cr ₂ B precipitates at the grain boundary, the Cr concentration in the vicinity of the grain boundary decreases, and the corrosion resistance decreases due to sensitization. Moreover, such a sensitization phenomenon can be suppressed by controlling the V / B ratio to 15.0 or more.

  Next, the influence of the V / B ratio on the moldability (elongation, r value, Δr) was examined.

  (0.009 to 0.011)% C, (0.08 to 0.13)% Si, (0.19 to 0.22)% Mn, (0.035 to 0.038)% P, (0 0.001 to 0.003)% S, (17.2 to 17.5)% Cr, (0.02 to 0.03)% Al, (0.007 to 0.011)% N, (0.11 -0.13)% Ni, (0.26-0.30)% Ti, (0.010-0.024)% V, (0.0002-0.0009)% B, the V / B ratio is The steel with the balance being Fe and inevitable impurities is melted in a 50 kg small vacuum melting furnace, the slab is heated to 1100 ° C., and then hot-rolling to a finishing temperature of 850 ° C. is performed. A hot-rolled sheet having a thickness of 0.0 mm was used. These hot-rolled sheets were subjected to hot-rolled sheet annealing at 930 ° C. × 60 sec, then pickled, and then cold-rolled to obtain cold-rolled sheets having a thickness of 0.7 mm. Further, these cold-rolled plates were subjected to finish annealing at 880 ° C. × 40 sec, and then pickled to obtain cold-rolled annealed pickled plates. About the obtained cold-rolled annealed pickling board, the tension test (JIS Z 2201) was done and elongation, r value, and (DELTA) r were calculated | required. Regarding the molding processability, an elongation of 30.0% or more, an r value of 1.50 or more, and Δr of 0.30 or less were determined to be acceptable. Moreover, the surface of the test piece cut out from the cold rolled annealed pickling plate was polished with # 600 count, and the corrosion resistance was evaluated by a combined cycle corrosion test. In the combined cycle corrosion test, the above corrosion test cycle was performed 30 times. In the combined cycle corrosion test, an area ratio of 20% or more was determined to be unacceptable and less than 20% was determined to be acceptable.

  FIG. 1 shows the relationship between V / B, cold-rolled annealed pickling plate forming processability (elongation, r value, Δr) and corrosion resistance evaluation results. From FIG. 1, it was found that by satisfying V / B ≧ 15.0, all of El, r value, Δr, and corrosion resistance evaluation satisfy the determination criteria. In particular, it was found that r value and Δr were excellent when V / B ≧ 30.0.

  More specifically, the present invention provides the following.

  (1) By mass%, C: 0.003 to 0.013%, Si: 0.01 to 0.95%, Mn: 0.01 to 0.40%, P: 0.020 to 0.040% , S: 0.010% or less, Al: 0.01-0.45%, Cr: 14.5-21.5%, Ni: 0.01-0.60%, N: 0.005-0. 012%, V: 0.010-0.040%, B: 0.0001-0.0010%, ratio of V content to B content (V / B) ≧ 15.0 When it is contained within a range satisfying Ti: 0.20% or more and 0.40% or less and Ti% + Nb% ≦ 0.70, Ti is contained or Ti and Nb are contained, and Nb : 0.40% or more and 0.60% or less, Nb contained within a range satisfying Ti% + Nb% ≦ 0.70, or a small amount when Nb and Ti are contained Ferritic stainless steel sheet, characterized in that consisting of also satisfying one, balance Fe and unavoidable impurities.

  (2) The ferritic stainless steel sheet according to (1), wherein V / B ≧ 30.0 is satisfied.

  (3) By mass%, and further containing one or two of Cu: 0.01 to 1.40% and Mo: 0.01 to 1.62% (1) or (2 ) Ferritic stainless steel sheet.

  (4) By mass%, Zr: 0.01-0.20%, REM: 0.001-1.00%, W: 0.01-0.20%, Co: 0.01-0. (1) to (3) characterized by containing one or more selected from 20%, Mg: 0.0001 to 0.0010%, Ca: 0.0003 to 0.0030% The ferritic stainless steel sheet according to any one of the above.

  The ferritic stainless steel sheet of the present invention has excellent moldability (formability) and excellent corrosion resistance. Specifically, the ferritic stainless steel sheet of the present invention has a formability satisfying an elongation of 30.0% or more, an r value of 1.50 or more, and Δr of 0.30 or less, and was polished by # 600. In the combined cycle corrosion test (30 cycles) based on JASO M 609-91 on the surface of the steel sheet, the steel sheet has corrosion resistance satisfying a cracking area ratio of less than 20%.

It is a graph which shows the relationship between V / B and the moldability (elongation, r value, Δr), corrosion resistance (spreading area ratio), and V / B of a cold-rolled annealed sheet. (B) is a graph showing the relationship between the r value and V / B, (c) is a graph showing the relationship between Δr and V / B, and (d) is the ratio of the glazing area in the corrosion resistance test. It is a graph which shows the relationship with V / B.

  Hereinafter, embodiments of the present invention will be described.

  First, the reasons for limiting the components of the ferritic stainless steel sheet of the present invention will be described. “%” Representing the content of the component means “mass%”.

C: 0.003 to 0.013%
The lower the C content, the better from the viewpoint of corrosion resistance and moldability. However, it is necessary to perform refining for a long time in order to make the C content less than 0.003%. From the viewpoint of securing desired productivity, the lower limit of the C content is 0.003%. On the other hand, when the content of C exceeds 0.013%, the formability and corrosion resistance of the ferritic stainless steel sheet are significantly lowered. Therefore, the C content is in the range of 0.003 to 0.013%. More preferably, it is 0.004 to 0.011%.

Si: 0.01-0.95%
Si is an element useful as a deoxidizer for steel. In order to obtain this effect, the Si content is 0.01% or more. However, if the Si content exceeds 0.95%, the rolling load increases in the hot rolling process, and a scale is very easily generated. Moreover, in the annealing process, the pickling property is lowered due to the formation of a scale in which Si is concentrated on the surface layer of the steel sheet. For this reason, it is not preferable that the Si content exceeds 0.95% because surface defects increase or manufacturing costs increase. Therefore, the Si content is in the range of 0.01 to 0.95%. More preferably, it is 0.05 to 0.50%. In particular, when the Ti content to be described later is 0.25% or more, the pickling property is significantly reduced by Si. In this case, the preferable range of the Si content is 0.05 to 0.20%. It is.

Mn: 0.01-0.40%
Mn combines with S present in the steel to form MnS and lowers the corrosion resistance. Therefore, the Mn content is set to 0.40% or less. On the other hand, if the content of Mn is decreased more than necessary, the refining cost increases. For this reason, the Mn content is preferably 0.01% or more. In addition, in order to implement | achieve especially high corrosion resistance, suppressing refining cost, the preferable range of content of Mn is 0.05 to 0.35%.

P: 0.020-0.040%
P is an element inevitably contained in steel. Since P is an element harmful to corrosion resistance and moldability, the P content is preferably low. In particular, if the P content exceeds 0.040%, the formability of the steel sheet decreases due to solid solution strengthening. For this reason, content of P is 0.040% or less. On the other hand, in order to make the P content less than 0.020%, it is necessary to perform refining over time, and making the P content less than 0.020% is not preferable in production. Therefore, the P content is in the range of 0.020 to 0.040%. Preferably, it is 0.025 to 0.035% of range.

S: 0.010% or less S combines with Mn to form MnS. MnS expands by hot rolling or the like and exists as precipitates (inclusions) at ferrite grain boundaries and the like. Such sulfide-based precipitates (inclusions) reduce the elongation of the steel sheet, and sometimes cause cracks in the steel sheet during bending of the steel sheet. For this reason, it is desirable to reduce the S content as much as possible, and the allowable S content is up to 0.010%. A preferable S content is 0.005% or less.

Al: 0.01 to 0.45%
Al is an element useful as a deoxidizer for steel. In order to obtain this effect, the Al content needs to be 0.01% or more. However, if the Al content is excessively large, an increase in Al-based inclusions causes surface defects. Accordingly, the range of Al content is set to 0.01 to 0.45%. Moreover, the preferable range of content of Al is 0.01 to 0.10%. A more preferable range is 0.02 to 0.04%.

Cr: 14.5-21.5%
Cr is an element that contributes to improving corrosion resistance, and is an element included as an essential element in a stainless steel plate. However, if the Cr content is less than 14.5%, a steel sheet having sufficient corrosion resistance cannot be obtained. On the other hand, if the Cr content exceeds 21.5%, in addition to the toughness of the steel sheet being lowered, the steel is too hard and the elongation of the steel sheet is also significantly reduced. Therefore, the range of Cr content is 14.5 to 21.5%. Furthermore, from the viewpoint of corrosion resistance and manufacturability, the preferable range of the Cr content is 16.0 to 21.5%.

Ni: 0.01-0.60%
Ni has an effect of reducing crevice corrosion. In order to obtain this effect, the Ni content must be 0.01% or more. However, in addition to Ni being an expensive element, even if Ni exceeds 0.60%, the above effect is saturated and the hot workability is reduced. Therefore, the range of Ni content is set to 0.01 to 0.60%. Moreover, the preferable range of Ni content is 0.10 to 0.40%.

N: 0.005 to 0.012%
N combines with V to form nitrides or carbonitrides, refines the crystal grains of the final product plate, and contributes to the improvement of the r-value characteristics. However, if the N content is less than 0.005%, the effect of refining crystal grains due to fine precipitation of V (C, N) carbonitride cannot be obtained. On the other hand, when the N content exceeds 0.012%, the Cr nitride amount or the Cr carbonitride amount increases, the steel plate becomes hard and the elongation decreases. Therefore, the range of N content is set to 0.005 to 0.012%. Moreover, the preferable range of N content is 0.006 to 0.010%.

V: 0.010-0.040%, B: 0.0001-0.0010%, V / B: 15.0 or more V and B are extremely important elements in the present invention. V is combined with N to form nitrides and carbonitrides such as VN and V (C, N), and has an effect of suppressing coarsening of crystal grains of the hot-rolled annealing plate. Further, B has an effect of assisting the grain growth suppression by concentrating on the ferrite grain boundary and delaying the grain boundary movement. Due to the combined effect of V and B, the crystal grains of the hot-rolled annealing plate are refined. As a result, the area of the grain boundary, which is the preferential nucleation site of {111} recrystallized orientation grains after cold rolling annealing, increases the {111} orientation, thereby improving the r value. It is considered that the Δr value decreases.

If the V content is less than 0.010%, the effect of refining crystal grains due to fine precipitation of VN or V (C, N) cannot be obtained. When the B content is less than 0.0001%, there is no effect of suppressing grain growth. When the V content exceeds 0.040% or the B content exceeds 0.0010%, the effect of refinement of crystal grains during growth and suppression of growth and improvement of moldability are only saturated. On the contrary, the material is hardened, the ductility is lowered, and the formability of the steel sheet is deteriorated. Therefore, the range of the V content is 0.010 to 0.040%, and the range of the B content is 0.0001 to 0.0010%. The content ratio of V and B (V / B) affects the balance between the ferrite crystal grain size and the ferrite grain interfacial area and the precipitation behavior of Cr ₂ B at the grain boundaries, and affects the moldability and corrosion resistance. it is conceivable that. As described in Tables 1 and 2 and FIG. 1, when the V / B ratio is less than 15.0, B combines with Cr and precipitates as Cr ₂ B at the grain boundary. As a result, the effect of suppressing grain growth is reduced, and the r value is insufficiently improved. Furthermore, the Cr concentration in the vicinity of the grain boundary decreases, and the corrosion resistance of the steel sheet deteriorates. Therefore, (V / B) is set to 15.0 or more. In addition, from a viewpoint of ensuring high moldability, the preferable range of V / B is 30.0 or more.

Ti: 0.20% or more and 0.40% or less, Ti in a range satisfying Ti% + Nb% ≦ 0.70, or Ti and Nb, and Nb: 0.40% or more and 0.60 % Or less, when Nb is contained in a range satisfying Ti% + Nb% ≦ 0.70, or Nb and Ti are contained Ti and Nb are both solid solution C and N are fixed as a compound to fix the corrosion resistance of the steel sheet. And has the effect of improving moldability. For this reason, it is necessary to use either Ti or Nb alone or to use both Ti and Nb. Specifically, in order to acquire the said effect, it is necessary to contain Ti: 0.20% or more or Nb: 0.40% or more. Preferably, it contains Ti: 0.25% or more, or Nb: 0.45% or more. On the other hand, when the Ti content, the Nb content, and the total amount of Ti and Nb are too large, it is not preferable because the surface quality is lowered and the productivity is lowered due to the increase in the recrystallization temperature. Therefore, the Ti amount is 0.40% or less, the Nb amount is 0.60% or less, and Ti% + Nb% ≦ 0.70 (in the present invention, all of Ti amount, Nb amount, Ti% + Nb% Must be less than or equal to the upper limit). Preferably, the Ti content is 0.35% or less, the Nb content is 0.55% or less, and Ti% + Nb% ≦ 0.65.

  As described above, the ferritic stainless steel sheet of the present invention contains the essential components, with the balance being Fe and inevitable impurities. The ferritic stainless steel sheet of the present invention further includes one or more selected from one or two of Cu and Mo, Zr, REM, W, Co, Mg, and Ca, if necessary. You may contain in the following range.

Cu: 0.01 to 1.40%
Cu is an element that improves the corrosion resistance. Specifically, Cu is an element that is particularly effective for improving the corrosion resistance when the steel sheet is in an aqueous solution or when weakly acidic water droplets adhere to the steel sheet. This effect is obtained by containing 0.01% or more of Cu, and increases as the Cu content increases. However, when the Cu content exceeds 1.40%, the hot workability deteriorates and Cu-derived oxide called red scale is generated on the hot-rolled slab during hot rolling, resulting in surface defects. Therefore, it is not preferable. Furthermore, if the Cu content exceeds 1.40%, descaling after annealing becomes difficult, which is not preferable for production. Therefore, when it contains Cu, it is preferable that the range of the content is 0.01 to 1.40%. Moreover, the more preferable range of Cu content is 0.10 to 1.00%, and the most preferable range is 0.30 to 0.50%.

Mo: 0.01 to 1.62%
Mo is an element that significantly improves the corrosion resistance of the stainless steel plate. This effect is obtained by adding 0.01% or more of Mo to the steel sheet, and the effect improves as the Mo content increases. However, if the Mo content exceeds 1.62%, the hot workability deteriorates and surface defects frequently occur during hot rolling. Moreover, since Mo is an expensive element, an increase in the Mo content increases the manufacturing cost. Therefore, when it contains Mo, it is preferable to make the range of the content into 0.01 to 1.62%. The range of more preferable content is 0.30 to 1.62%, and most preferably 0.40 to 1.20%. Especially in Ti-containing steels where hot-rolled sheet toughness decreases, addition of Mo further reduces toughness, making it difficult to obtain good hot-rolled sheet annealing, so when containing Ti 0.15% or more It is preferable to make the Mo content 0.30 to 1.40%. More preferably, it is 0.40 to 1.00% of range.

  Then, the said component in the case of including the 1 type (s) or 2 or more types chosen from Zr, REM, W, Co, Mg, Ca is demonstrated.

Zr: 0.01-0.20%
Zr binds to C and N and has the effect of suppressing sensitization. This effect is obtained when the Zr content is 0.01% or more. On the other hand, if the content of Zr exceeds 0.20%, the workability of the steel sheet decreases. Further, since Zr is an expensive element, an increase in the Zr content increases the manufacturing cost. Therefore, when it contains Zr, it is preferable to make the content range into 0.01 to 0.20%.

REM: 0.001 to 0.100%
REM has the effect of improving oxidation resistance. This effect is obtained by containing REM 0.001% or more. On the other hand, if REM is contained in an amount exceeding 0.100%, hot rollability is lowered and surface defects frequently occur, which is not preferable. Therefore, when it contains, it is preferable to make the range of content of REM 0.001 to 0.100%, More preferably, it is 0.001 to 0.050%.

W: 0.01-0.20%
W has the effect of improving the corrosion resistance like Mo. This effect is obtained when the W content is 0.01% or more. On the other hand, when the amount of W exceeds 0.20%, the strength increases, and the productivity decreases due to an increase in rolling load or the like. Therefore, the range of the W content is preferably 0.01 to 0.20%, and more preferably 0.01 to 0.10%.

Co: 0.01-0.20%
Co, like Mo, has the effect of improving the corrosion resistance. This effect is obtained when the Co content is 0.01% or more. On the other hand, if an amount of Co exceeding 0.20% is contained, moldability is lowered. Therefore, the content range of Co is preferably 0.01 to 0.20%, and more preferably 0.01 to 0.10%.

Mg: 0.0001 to 0.0010%
Mg is an element that improves the equiaxed crystal ratio of the slab and is effective in improving formability and toughness. This effect is obtained when the Mg content is 0.0001% or more. On the other hand, if the Mg content exceeds 0.0010%, Mg-based inclusions increase and the surface properties are deteriorated. Therefore, the content range of Mg is preferably 0.0001 to 0.0010%, and more preferably 0.0002 to 0.0004%.

Ca: 0.0003 to 0.0030%
Ca is an effective component for preventing nozzle clogging due to precipitation of Ti-based inclusions that are likely to occur during continuous casting. The effect is obtained when the Ca content is 0.0003% or more. However, when the Ca content exceeds 0.0030%, the corrosion resistance decreases due to the generation of CaS. Therefore, the preferable range of the content of Ca is 0.0003 to 0.0030%, more preferably 0.0005 to 0.0020%, and most preferably 0.0005 to 0.0015%. .

  Below, the manufacturing method of the ferritic stainless steel of this invention is demonstrated. In addition, the manufacturing method of the ferritic stainless steel of this invention is not limited to the following embodiment. The molten steel having the above composition is melted in a generally known converter or electric furnace, further refined by vacuum degassing (RH), VOD, AOD, etc., and then preferably cast by a continuous casting method to obtain a rolled material (slab Etc.). Next, the rolled material is heated and hot rolled to obtain a hot rolled sheet. The slab heating temperature for hot rolling is preferably in the temperature range of 1050 ° C. to 1250 ° C., and the finishing temperature for hot rolling is preferably 750 to 900 ° C. from the viewpoint of manufacturability. A hot-rolled sheet can perform hot-rolled sheet annealing as needed. When hot-rolled sheet annealing is performed, it is preferable to perform short-term continuous annealing in a temperature range of 850 to 1150 ° C. In addition, a hot-rolled sheet can be descaled and used as a product as it is, or can be used as a material for cold rolling. The hot-rolled sheet of the material for cold rolling is subjected to cold rolling at a cold rolling reduction ratio of 30% or more to obtain a cold-rolled sheet. The cold rolling reduction ratio is preferably 50 to 95%. Moreover, in order to provide further formability of the cold-rolled sheet, recrystallization annealing (finish annealing) at 800 to 1100 ° C. can be performed. Moreover, you may perform cold rolling-annealing twice or more. Furthermore, when glossiness is required, skin pass (rolling) or the like may be performed. The finish of the cold-rolled sheet can be 2D, 2B, BA, and various types of polishing specified by the Japan industrial Standard (JIS) G4305.

  In addition, the steel plate as used in this invention shall contain a steel strip and foil material.

[Example 1]
Molten steel having the composition shown in Table 3 (the balance being Fe) was melted by a converter and secondary refining (VOD), and a slab was formed by a continuous casting method. After these slabs were heated to 1120 ° C., hot rolling was performed at a finishing temperature of 800 ° C. to obtain hot rolled sheets having a thickness of 4.0 mm. These hot-rolled sheets were subjected to hot-rolled sheet annealing at 940 ° C. × 60 sec, and then pickled and cold-rolled to obtain cold-rolled sheets. Next, these cold-rolled plates were subjected to finish annealing at 900 ° C. × 40 sec, and then pickled to obtain cold-rolled annealed pickled plates having a thickness of 0.7 mm. About the obtained cold-rolled annealing pickling board, forming processability and corrosion resistance evaluation were performed.
[Evaluation]
The evaluation methods for molding processability and corrosion resistance are shown below.

(1) Elongation A JIS No. 13 B specimen was collected from each direction [rolling direction (L direction), rolling perpendicular direction (C direction), and 45 ° direction (D direction)] from the cold-rolled annealed pickled sheet. Using these tensile test pieces, a tensile test (JIS Z 2201) was performed, and the elongation in each direction was measured. Using the elongation value in each direction, the average value of elongation (El) was obtained from the following equation. El passed 30.0% or more.
El = (ElL + 2 × ElD + ElC) / 4
Here, ElL, ElD, and ElC represent elongations in the L direction, the D direction, and the C direction, respectively.

(2) r value JIS No. 13 B test specimens were collected from each direction [rolling direction (L direction), rolling perpendicular direction (C direction) and 45 ° direction (D direction)] from the cold-rolled annealed pickled sheet. . From these specimens, the r value (Rankford value) in each direction was measured from the ratio of the width strain and the plate thickness strain when uniaxial tensile pre-strain of 15% was applied. Δr was determined. An r value of 1.50 or more and Δr of 0.30 or less were accepted.
r = (rL + 2 × rD + rC) / 4
Δr = (rL−2 × rD + rC) / 2
Here, rL, rD, and rC represent r values in the L direction, the D direction, and the C direction, respectively.

(3) Corrosion resistance A test piece of 60 mm x 80 mm was cut out from the obtained cold-rolled annealed plate, the surface was polished with # 600 count, a test piece for corrosion resistance evaluation was produced, and corrosion resistance evaluation was performed by a combined cycle corrosion test. In the combined cycle corrosion test, the above-described corrosion test cycle was performed 30 times, and an area ratio of 20% or more was rejected, and less than 20% was determined to be acceptable.

[Example 2]
Molten steel having the composition shown in Table 4 was melted by a converter and secondary refining (VOD) to obtain a slab by a continuous casting method. After these slabs were heated to 1120 ° C., hot rolling was performed at a finishing temperature of 800 ° C. to obtain hot rolled sheets having a thickness of 4.0 mm. These hot-rolled sheets were subjected to hot-rolled sheet annealing at 1020 ° C. × 60 sec, followed by pickling and cold rolling to obtain cold-rolled sheets. Subsequently, these cold-rolled plates were subjected to finish annealing at 1000 ° C. × 40 sec, and then pickled to obtain cold-rolled annealed pickled plates having a thickness of 0.7 mm. About the obtained cold-rolled annealing pickling board, forming processability and corrosion resistance evaluation were performed. The evaluation method is as follows.

  A similar evaluation was performed in the same manner as in Example 1.

  The results obtained in Example 1 are shown in Table 5, and the results obtained in Example 2 are shown in Table 6.

  In any of the invention examples, excellent moldability with an elongation of 30.0% or more, an r value of 1.50 or more, and an Δr of 0.30 or less, and an area ratio of less than 20% in a 30-cycle combined cycle corrosion test It has excellent corrosion resistance. In contrast, the comparative example did not satisfy any of elongation, r value, Δr, and corrosion resistance.

  Further, since it has excellent moldability with an elongation of 30.0% or more, an r value of 1.50 or more, and Δr of 0.30 or less, deep drawing can be performed without any problem.

  According to the present invention, a ferritic stainless steel sheet excellent in forming processability and corrosion resistance can be produced by optimizing the component composition, particularly the V and B contents, and there is a remarkable industrial effect.

Claims (2)

In mass%, C: 0.003-0.013%, Si: 0.01-0.95%, Mn: 0.01-0.40%, P: 0.020-0.040%, S: 0.010% or less, Al: 0.01 to 0.45%, Cr: 14.5 to 21.5%, Ni: 0.01 to 0.60%, N: 0.005 to 0.012%, Mo: contains 0.01 to 1.62%,
V: 0.010-0.040%, B: 0.0001-0.0010% are contained in the range which satisfies ratio (V / B)> = 30.0 of V content and B content. ,
Further, when Ti is contained or Ti and Nb are contained within a range satisfying Ti: 0.20% or more and 0.40% or less and Ti% + Nb% ≦ 0.70, and Nb: 0.40% or more and 0 .. 60% or less, satisfying at least one of Nb and Ti containing Nb and Ti within a range satisfying Ti% + Nb% ≦ 0.70, the balance being made of Fe and inevitable impurities Ferritic stainless steel sheet.   % By mass, REM: 0.001 to 0.100%, W: 0.01 to 0.20%, Co: 0.01 to 0.20%, Mg: 0.0001 to 0.0010%, The ferritic stainless steel sheet according to any one of claims 1 to 3, comprising one or more selected from Ca: 0.0003 to 0.0030%.

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