CN107964632B

CN107964632B - Ferritic stainless steel sheet having excellent formability

Info

Publication number: CN107964632B
Application number: CN201711384153.0A
Authority: CN
Inventors: 寒川孝; 太田裕树
Original assignee: JFE Steel Corp
Current assignee: JFE Steel Corp
Priority date: 2012-09-24
Filing date: 2013-09-06
Publication date: 2021-01-22
Anticipated expiration: 2033-09-06
Also published as: KR101718757B1; CN104619874A; JP2014205917A; TWI513831B; JP5614516B2; CN107964632A; JP5850090B2; TW201420780A; KR20150038601A; CN104619874B; JPWO2014045542A1; MY160968A; WO2014045542A1

Abstract

The present invention provides a ferritic stainless steel sheet having excellent formability satisfying deep drawability and wrinkle resistance. The ferritic stainless steel sheet contains, in mass%, C: 0.010-0.070%, Si: 1.00% or less, Mn: 1.00% or less, P: 0.040% or less, S: 0.010% or less, Al: 0.150% or less, Cr: 14.00-20.00%, Ni: 1.00% or less, N: 0.010 to 0.060%, further comprising: 0.005-0.100%, B: 0.0001-0.0050% and V/B of 10 or more, the balance being Fe and unavoidable impurities.

Description

Ferritic stainless steel sheet having excellent formability

This application is a divisional application of patent application 201380046801.5 (application date: 2013, 9/6, entitled ferritic stainless steel sheet with excellent formability).

Technical Field

The present invention relates to a ferritic stainless steel sheet suitable for applications such as kitchen appliances for buildings, household appliances, electric appliances, and automobile parts, and particularly to a ferritic stainless steel sheet having excellent formability satisfying deep drawability and crease resistance (ridging resistance). The steel sheet in the present invention includes a steel strip, a steel sheet, and a foil.

Background

Ferritic stainless steel is widely used in various industrial fields including household products and automobile parts as a material having excellent corrosion resistance. The ferritic stainless steel is less expensive than austenitic stainless steel containing a large amount of Ni. However, the steel sheet is generally poor in workability, and when subjected to molding, for example, surface defects called wrinkles are likely to occur, and thus the steel sheet is not suitable for applications in which strong working such as deep drawing is performed. In addition, ferritic stainless steel has a problem that in-plane anisotropy (Δ r) of plastic strain ratio (r value) is also large, and uneven deformation is likely to occur in deep drawing. Therefore, in order to further expand the range of application of ferritic stainless steel sheets, it is required to increase the r value, which is an index of deep drawability, reduce the in-plane anisotropy (Δ r) of the plastic strain ratio, and further improve the wrinkle resistance.

In response to such a demand, for example, patent document 1 discloses a ferritic stainless steel having excellent workability, which contains C: 0.03 to 0.08%, Si: 0.4% or less, Mn: 0.5% or less, P: 0.03% or less, S: 0.008 or less, Ni: 0.3% or less, Cr: 15-20%, Al: nx 2-0.2% or less, N: 0.01% or less, and the balance of Fe and inevitable impurities. Patent document 2 discloses a heat-resistant ferritic stainless steel having excellent press formability, which contains Cr: 11.0 to 20.0%, Si: 1.5% or less, Mn: 1.5% or less, C% + N%: 0.02 to 0.06%, Zr: 0.2 to 0.6%, and 10 (C% + N%) + -0.15% Zr%, the balance being substantially Fe. Patent document 3 discloses a ferritic stainless steel sheet having excellent formability, which is characterized by containing, in mass%, C: 0.02 to 0.06%, Si: 1.0% or less, Mn: 1.0% or less, P: 0.05% or less, S: 0.01% or less, Al: 0.005% or less, Ti: 0.005% or less, Cr: 11-30% or less, Ni: 0.7% or less, and N is contained so as to satisfy 0.06 ≦ (C + N) ≦ 0.12 and 1 ≦ N/C in relation to the C content, and further satisfy 1.5X 10-³≤(V×N)≤1.5×10-²The embodiment (1) contains V, and the balance is Fe and inevitable impurities. Further, patent document 4 discloses a ferritic stainless steel having excellent corrosion resistance, which is calculated by weight%And contains C: 0.02% or less, Si: 1.0% or less, Mn: 2.0% or less, Cr: 11-35%, Ni: 0.5%, N: 0.03% or less, V: 0.5 to 5.0%, the balance consisting of iron and incidental impurities.

Patent document

Patent document 1: japanese patent laid-open publication No. S52-24913

Patent document 2: japanese laid-open patent publication No. Sho 54-112319

Patent document 3: japanese patent No. 3584881

Patent document 4: japanese laid-open patent publication No. 59-193250

Disclosure of Invention

However, the technique described in patent document 1 assumes a low N, and therefore has a problem that the cost in the steel making process is inevitably increased.

In addition, in the technique described in patent document 2, since a large amount of Zr is added, the amount of inclusions in the steel increases, and the occurrence of surface defects caused by the increase is unavoidable.

In addition, in the technique described in patent document 3, the purpose is to improve the elongation and r-value and to improve the wrinkle resistance as an index of the moldability. However, no consideration is given to the reduction of the in-plane anisotropy (Δ r), and there is a problem in moldability.

In addition, in the technique described in patent document 4, the addition of V significantly improves the corrosion resistance, particularly the stress corrosion cracking resistance. However, the moldability is not considered at all, and there is a problem in the moldability.

Thus, the following problems have not been solved in the prior art: when severe deep drawing is performed, wrinkles occur, which increases the polishing load, or tends to cause uneven deformation.

In view of the above circumstances, an object of the present invention is to provide a ferritic stainless steel sheet having excellent formability satisfying deep drawability and wrinkle resistance.

The present inventors have conducted various studies to achieve the above-described object, and as a result, have found that a ferritic stainless steel sheet excellent in formability can be obtained by controlling precipitates such as carbides and nitrides in steel so as to make the crystal grain size fine, improve deep drawability, and suppress wrinkles by setting the V/B to 10 or more and setting the content of V, B to an optimum range, and that sharpening (sensitization) of the steel sheet surface can be suppressed even when the final annealing temperature is changed in actual operation by setting the V/B to 20 or more, thereby completing the present invention. The gist of the present invention is as follows.

(1) A ferritic stainless steel sheet characterized by containing, in mass%, C: 0.010-0.070%, Si: 1.00% or less, Mn: 1.00% or less, P: 0.040% or less, S: 0.010% or less, Al: 0.150% or less, Cr: 14.00-20.00%, Ni: 1.00% or less, N: 0.010 to 0.060%, further comprising: 0.005-0.100%, B: 0.0001-0.0050% and V/B of 10 or more, the balance being Fe and unavoidable impurities.

(2) The ferritic stainless steel sheet according to (1), characterized in that the ratio of Si: 0.05-0.28%, Mn: 0.05 to 0.92 percent.

(3) The ferritic stainless steel sheet according to (1) or (2), which contains V and B so as to satisfy V/B.gtoreq.20.

In the present invention, a ferritic stainless steel sheet having excellent formability is a ferritic stainless steel sheet satisfying an elongation (El) of 30% or more, an r value of 1.3 or more, and Δ r of 0.3 or less.

According to the present invention, a ferritic stainless steel sheet having excellent formability satisfying deep drawability and wrinkle resistance can be obtained.

Drawings

FIG. 1 is a graph showing the relationship between the mechanical properties of a cold-rolled annealed sheet and V/B, FIG. 1(a) is a graph showing the relationship between elongation (El) and V/B, FIG. 1(B) is a graph showing the relationship between r-value and V/B, FIG. 1(c) is a graph showing the relationship between Δ r and V/B, and FIG. 1(d) is a graph showing the relationship between corrugation height and V/B.

Fig. 2 is a graph showing the relationship of the content of V, B for ensuring the sharpening property of the cold rolled and annealed sheet.

Detailed Description

Hereinafter, embodiments for carrying out the present invention will be described in detail. The term "% representing the amount of a component" means "mass% unless otherwise specified.

First, the reasons for limiting the composition of the ferritic stainless steel sheet of the present invention will be described.

C：0.010～0.070％

C is solid-dissolved in steel, contributes to stabilization of an austenite phase during hot rolling, and is bonded to Cr to precipitate as Cr carbide or Cr carbonitride in grains, grain boundaries, and the like. However, if C is less than 0.010%, the composition consisting of V (C, N), VC and V cannot be obtained₄C₃Such as fine precipitation of carbonitrides and carbides. In addition, since the austenite fraction in hot rolling is reduced, the occurrence of wrinkles becomes remarkable in a cold-rolled steel sheet as a product sheet, and the formability is deteriorated. On the other hand, if C is more than 0.070%, the amount of Cr carbide and Cr carbonitride increases excessively, the steel sheet hardens, formability decreases, and a Cr-free layer (Cr removal layer) which becomes a rust starting point, coarse precipitates, and inclusions increase. Therefore, C is set to 0.010% to 0.070%. More preferably 0.020 to 0.040%.

Si: 1.00% or less

Si is a useful element as a deacidification agent for steel. In order to obtain this effect, 0.05% or more is preferable. However, if it exceeds 1.00%, the ductility is lowered and the moldability is lowered. Therefore, Si is 1.00% or less. More preferably 0.05 to 0.50% or less. If Si is 0.28% or less, pickling property becomes good, so that pickling property is 0.05% to 0.28% when pickling property is required.

Mn: 1.00% or less

Mn bonds with S present in the steel to form MnS, decreasing corrosion resistance. Therefore, Mn is 1.00% or less. More preferably 0.80% or less. On the other hand, the Mn content is preferably 0.05% or more because the refining cost increases when the Mn content is lowered more than necessary. Particularly, from the viewpoint of the requirement for high corrosion resistance and the refining cost, it is more preferably 0.05 to 0.60%. When Mn is 0.92% or less, pickling properties become good, and therefore, pickling properties are required to be 0.05% to 0.92%.

P: less than 0.040%

P is an element harmful to corrosion resistance, and therefore is preferably reduced as much as possible. On the other hand, if it exceeds 0.040%, the workability is deteriorated due to solid-solution strengthening. Therefore, P is 0.040% or less. More preferably 0.030% or less.

S: 0.010% or less

S forms sulfides in the steel. When Mn is contained, Mn is bonded to Mn to form MnS. MnS is stretched by hot rolling or the like, and exists as precipitates (inclusions) in ferrite grain boundaries or the like. Such sulfide-based precipitates (inclusions) reduce the elongation, and particularly greatly affect the crack generation in bending, and therefore S is preferably reduced as much as possible and allowed to fall within 0.010%. It is preferably 0.005% or less.

Cr：14.00～20.00％

Cr is an element that enhances the solid solution strength of steel and contributes to the improvement of corrosion resistance, and is an essential element for stainless steel sheets. However, if Cr is less than 14.00%, corrosion resistance as stainless steel is insufficient. On the other hand, if Cr exceeds 20.00%, toughness decreases, and the steel is excessively hardened and elongation significantly decreases. Therefore, Cr is 14.00 to 20.00%. Further, from the viewpoint of corrosion resistance and manufacturability, 16.00 to 18.00% is preferable.

Al: less than 0.150%

Al is a useful element as a deacidification agent for steel. In order to obtain this effect, 0.001% or more is preferable. However, the excessive addition is 0.150% or less because the increase of Al-based inclusions causes surface defects. More preferably 0.100% or less. More preferably 0.010% or less.

Ni: 1.00% or less

Ni has the effect of reducing crevice corrosion. In order to obtain this effect, 0.05% or more is preferable. However, these elements are expensive elements, and even if the content exceeds 1.00%, these effects are saturated, and conversely, the hot workability is lowered. Therefore, Ni is 1.00% or less. More preferably 0.05 to 0.40%.

N：0.010～0.060％

N is solid-dissolved in steel similarly to C, contributes to stabilization of an austenite phase during hot rolling, and is bonded to Cr to precipitate as Cr nitrides or Cr carbonitrides in grains, grain boundaries, and the like. In addition, the V bond, which is important in the present invention, forms nitrides and carbonitrides, thereby refining the crystal grains of the final product and contributing to an increase in the r value. If N is less than 0.010%, the proportion of austenite phase in hot rolling decreases, and therefore the occurrence of wrinkles in the cold-rolled steel sheet as a final product becomes significant, and the formability deteriorates. On the other hand, if the content exceeds 0.060%, the Cr nitride content or Cr carbonitride content is excessively increased, and the steel sheet is hardened, resulting in a decrease in elongation. Therefore, N is 0.010 to 0.060%. More preferably 0.020 to 0.050%.

V: 0.005-0.100%, B: 0.0001-0.0050% and V/B of 10 or more

V and B are elements extremely important in the present invention. V and N are bonded to form nitrides and carbonitrides such as VN and V (C, N), and the effect of suppressing the coarsening of crystal grains of the hot-rolled annealed sheet is obtained. B has an effect of assisting grain growth inhibition by thickening at ferrite grain boundaries to delay grain boundary migration (grain boundary migration). The grain size of the hot-rolled annealed sheet is made finer by the combined effect of these V and B. As a result, it is considered that the area of the grain boundary, which is the preferential nucleation site of the {111} recrystallized grains after cold rolling annealing, is increased and the {111} oriented recrystallized grains are increased, thereby increasing the r-value. Further, the present inventors have considered that the ratio of the amount of V to the amount of B affects the ferrite grain size and the ferrite grain boundary area, and therefore, in order to maximize the r value improving effect, the optimization of the contents of V and B is studied.

A steel containing C as a component composition, which is obtained by melting a steel slab, heating the steel slab to 1170 ℃, and then hot rolling the steel slab at a final temperature of 830 ℃, thereby producing a hot-rolled sheet: 0.04%, Si: 0.40%, Mn: 0.80%, P: 0.030%, S: 0.004%, Al: 0.002%, Cr: 16.20%, Ni: 0.10%, N: 0.060% and V and B were added while varying the amount of V and the amount of B. These hot-rolled sheets were annealed at 860 ℃ for 8hr, then pickled, and then subjected to cold rolling at a total reduction of 86% to prepare cold-rolled sheets. Then, these cold-rolled sheets were subjected to finish annealing at 820 ℃ for 30sec in the air and then pickled to produce cold-rolled and annealed sheets having a thickness of 0.7 mm. The elongation, r-value,. DELTA.r, and ridging height (ridging height) were determined for the obtained cold-rolled and annealed sheet. The V/B is shown in FIG. 1 as a function of the mechanical properties (elongation, r-value,. DELTA.r, corrugation height) of the cold-rolled annealed sheets. As is clear from FIG. 1, El, r-value,. DELTA.r and creping height are all satisfied by satisfying that V content is 0.005% or more, B content is 0.0001% or more and V/B is 10 or more.

In the present invention, V is 0.005-0.1%, B is 0.0001-0.0050%, and V/B is not less than 10. If V and B are added in excess amounts exceeding 0.1% and 0.0050%, respectively, the effect of suppressing the grain refinement and growth during annealing and the effect of improving the formability are saturated, but the material is solidified, the ductility is reduced, and the formability is deteriorated. In order to secure high ductility, it is more preferable that V be 0.005 to 0.03% or less and B be 0.0001 to 0.0020%. Further, if the V/B ratio is less than 10, B and N are bonded to precipitate as nitrides, whereby the effect of B thickening at grain boundaries to suppress grain growth is reduced, and therefore it is considered that the improvement of the r value becomes insufficient.

In actual operation, the final annealing temperature is not always constant, and changes in the heating time and the reaching temperature cannot be avoided. When a ferritic stainless steel sheet to which no stabilizing element such as Ti or Nb fixed to C, N is added is annealed at a high temperature, it may be susceptible to sharpening during cooling, and grain boundaries may be eroded during subsequent pickling, thereby deteriorating the surface quality. Therefore, the fact that sensitization does not occur in a wide temperature range is extremely important in obtaining stable quality in actual operation.

Therefore, the inventors of the present invention have studied the relationship between the sharpening property and V/B. A steel containing C as a component composition, which is obtained by melting a steel slab, heating the steel slab to 1170 ℃, and then hot rolling the steel slab at a final temperature of 830 ℃, thereby producing a hot-rolled sheet: 0.04%, Si: 0.40%, Mn: 0.80%, P: 0.030%, S: 0.004%, Al: 0.002%, Cr: 16.20%, Ni: 0.10%, N: 0.060%, V and B were added while varying the amounts of V and B. These hot-rolled sheets were annealed at 860 ℃ for 8hr, then pickled, and then subjected to cold rolling at a total reduction of 86% to prepare cold-rolled sheets. Then, these cold-rolled sheets were subjected to finish annealing at 900 ℃ for 30sec in the air and then pickled to produce cold-rolled annealed pickled sheets having a thickness of 0.7 mm. The surface of the cold-rolled and annealed pickled sheet thus obtained was observed with a scanning electron microscope for grain boundaries in a 500. mu. m.times.500. mu.m region, and the presence or absence of grain boundary erosion (intergranular corrosion) was examined to evaluate the surface quality. The results are shown in FIG. 2. The evaluation was "good" when no corrosion occurred and "x" when corrosion occurred.

As is clear from FIG. 2, by adding V and B so that the addition amounts satisfy V/B.gtoreq.20, the sensitization of grain boundaries can be suppressed even by annealing at 900 ℃. This is considered to be because C, N in the V-set steel suppresses precipitation of Cr carbonitride at the grain boundaries generated in cooling after the final annealing even when the final annealing temperature reaches a high temperature of 900 ℃. On the other hand, if V/B is less than 20, B bonds with N and precipitates as nitrides, whereby the amount of V carbonitride precipitates decreases, as a result of which the amount of Cr carbonitride precipitates increases and the grain boundary sharpening progresses. In order to secure high ductility, it is more preferable that V be 0.005 to 0.03% and B be 0.0001 to 0.0020%.

The balance other than the above chemical components is Fe and inevitable impurities. As inevitable impurities, for example, Nb: 0.05% or less, Ti: 0.05% or less, Co: 0.5% or less, W: 0.01% or less, Zr: 0.01% or less, Ta: 0.01% or less, Mg: 0.0050% or less, Ca: 0.0020% or less, and the like.

Next, a method for producing the ferritic stainless steel of the present invention will be described. Molten steel having the above composition is melted in a conventionally known converter or electric furnace, further refined by Vacuum degassing (RH), VOD (Vacuum Oxygen Decarburization), AOD (Argon Oxygen Decarburization) or the like, and then cast into a billet (slab or the like) preferably by a continuous casting method. Subsequently, the rolled stock is heated and hot-rolled, thereby producing a hot-rolled sheet. The slab heating temperature for hot rolling is preferably in the temperature range of 1050 to 1250 ℃, and the final temperature for hot rolling is preferably 800 to 900 ℃ from the viewpoint of manufacturability. The hot-rolled sheet may be subjected to hot-rolled sheet annealing as necessary for the purpose of improving workability in the subsequent process. When the hot rolled sheet is annealed, it is preferable to perform box annealing (batch annealing) at 700 to 900 ℃ for 2 hours or more or perform continuous annealing at 900 to 1100 ℃ for a short time. The hot-rolled sheet may be subjected to a descaling treatment to be directly produced into a product, or may be produced into a cold-rolled billet. A hot-rolled sheet of the blank for cold rolling is subjected to cold rolling with a cold rolling reduction of 30% or more to produce a cold-rolled sheet. The cold rolling reduction is preferably 50-95%. In addition, in order to further impart workability to the cold-rolled sheet, final annealing at 600 ℃ or higher, preferably 700 to 900 ℃ may be performed. Further, the cold rolling and annealing may be repeated 2 times. Further, when gloss (gloss) is required, skin pass rolling or the like may be performed. The finish rolling treatment of the cold-rolled sheet may be carried out by 2D, 2B, BA and various kinds of grinding as specified in Japanese Industrial Standard (JIS) G4305.

Example 1

Molten steel having the composition shown in table 1 was melted by 2-time refining in a converter and VOD, and a slab was produced by a continuous casting method. These slabs were heated to 1170 ℃ and then hot-rolled at a final temperature of 830 ℃ to produce hot-rolled sheets. These hot-rolled sheets were annealed at 860 ℃ for 8hr, then pickled, and then subjected to cold rolling at a total reduction of 86% to prepare cold-rolled sheets. Next, the coke oven gas was burned at an air ratio of 1.3, and finish annealing was performed at 820 ℃ for 30sec for cold rolled sheets of steels Nos. 1 to 18 and steels Nos. 24 to 32 in the burned atmosphere. Then, pickling was performed to obtain a cold-rolled annealed pickled plate having a thickness of 0.7 mm. The acid washing was performed at 80 ℃ and 20 mass% of Na₂SO₄In 3 times of 5A/dm ²10 seconds after electrolysis, the electrolysis was performed 2 times at 10A/dm in 5 mass% nitric acid at 60 degrees²X 5 seconds of electrolysis. Each sample was washed with acid to completely remove the oxide film.

TABLE 1

The elongation, r value and Δ r were determined for the obtained cold-rolled annealed pickled sheet, and the formability was evaluated. Further, the wrinkle height was determined, and the wrinkle resistance was evaluated.

Further, the coke oven gas was burned at an air ratio of 1.3, and cold rolled sheets of steels Nos. 19 to 23 and 33 to 36 were subjected to final annealing at 900 ℃ for 30sec in this combustion atmosphere, and then pickled under the same conditions as described above to prepare cold annealed pickled sheets having a sheet thickness of 0.7 mm. Each sample was washed with acid to completely remove the oxide film. The cold-rolled and annealed pickled sheet thus obtained was evaluated for formability and wrinkle resistance. The elongation, r-value,. DELTA.r, and wrinkle height were measured as follows.

(1) Elongation percentage

A test piece of JIS13 No. B was sampled from each direction of the cold-rolled and annealed pickled sheet [ rolling direction (L direction), rolling direction (C direction), and direction at 45 ℃ to the rolling direction (D direction) ]. Tensile tests were carried out using these tensile test pieces, and the elongation in each direction was measured. The average value of the elongation was obtained from the following equation using the elongation values in each direction. An El of 30% or more was evaluated as passed.

E1＝(ElL+2×ElD+ElC)/4

Here, ElL, ElD, and ElC represent the elongation in the L direction, D direction, and C direction, respectively.

(2) r value

A test piece of JIS13 No. B was sampled from each direction of the cold-rolled and annealed pickled sheet [ rolling direction (L direction), rolling direction (C direction), and direction at 45 ℃ to the rolling direction (D direction) ]. R values (Lankford values) in respective directions were measured from the ratio of the width strain (width strain) and the sheet thickness strain (thickness strain) when a uniaxial pre-strain of 15% was applied to these test pieces, and the r values and Δ r were obtained from the following equations. The r value was 1.3 or more and Δ r was 0.3 or less, and the evaluation was judged as pass.

r＝(rL+2×rD+rC)/4

Δr＝(rL-2×rD+rC)/2

Here, rL, rD, and rC represent r values in the L direction, D direction, and C direction, respectively.

(3) Height of corrugation

Tensile test pieces of JIS5 were collected from the cold-rolled annealed pickled sheet in the rolling direction. The surface of each of these test pieces was polished with #600, and after applying a prestrain of uniaxial tension (20%) to the test pieces, the undulation height of the surface of the central portion of the test pieces was measured using a coarseness gauge. The height of the waviness is an unevenness caused by the occurrence of wrinkles. According to the height of the undulation, according to A: 5 μm or less, B: greater than 5 μm and 10 μm or less, C: greater than 10 μm and 20 μm or less, D: the wrinkle resistance was evaluated at 4 stages of more than 20 μm. The lower the height of the undulations, the more beautiful the molded article becomes. The A evaluation that the height of the undulations was 5.0 μm or less was regarded as a pass.

The results are shown in Table 2.

TABLE 2

[ Table 2]

In all of the invention examples, the evaluation A showed an elongation of 30% or more, an r value of 1.3 or more, a Δ r of 0.3 or less, and a height of waviness of 5.0 μm or less, and had good moldability and wrinkle resistance. In contrast, in the comparative example, any of the elongation, r value, Δ r, and wrinkle height was not satisfied.

Example 2

The pickling properties in the electrolytic method (electrolytic method) of nitric acid and hydrochloric acid (mixed acid of nitric acid and hydrochloric acid) having weaker pickling ability and higher productivity than the pickling method of example 1 were evaluated for invention examples 5 to 11 and 19 to 36 of example 1 having good moldability and wrinkle resistance. Cold-rolled sheets of 0.7mm in thickness of steels Nos. 5 to 11 and 19 to 36 produced in example 1 were subjected to a weak reducing atmosphere (H)₂：5vol％，N₂: 95 vol%, dew point (dew point) -40 deg.C, at 820 deg.CAnnealing for 30sec to obtain a cold-rolled annealed sheet. The cold-rolled and annealed sheet was electrolyzed at a temperature of 50 ℃ in a solution containing 10 mass% nitric acid and 1.0 mass% hydrochloric acid, and the presence or absence of oxide film residue was visually observed to evaluate pickling properties.

Will pass through at 10A/dm²The oxide film was completely removed by 2 times of electrolysis for 2 seconds, and the evaluation was excellent, and the oxide film was removed by 10A/dm²2 times of electrolysis for 2 seconds and 2 times of 10A/dm without completely removing the oxide film²The case where the oxide film could be completely removed by 4 seconds of electrolysis was evaluated as good, and 10A/dm was performed 2 times²The case where the oxide film could not be completely removed by electrolysis for 4 seconds was evaluated as X (defective). Excellent and good were acceptable.

The results are shown in Table 3.

TABLE 3

[ Table 3]

Steel Nos. 5 to 10, 19 to 26 and 30 to 34, which have Si of 0.28% or less and Mn of 0.92% or less, are excellent in formability and wrinkle resistance, and are particularly excellent in pickling property. The production can be carried out by adopting a general pickling method and a high-productivity nitric acid and hydrochloric acid electrolysis method.

Example 3

The steels Nos. 19 to 23 and 33 to 36 of example 1 were evaluated for sharpness in consideration of the fact that the range of the final annealing temperature was changed in the actual operation.

The method for evaluating the sharpening was carried out by annealing the cold-rolled sheet having a thickness of 0.7mm prepared in example 1 at 900 ℃ for 30sec under the same conditions as in example 1 under Na₂SO₄Nitric acid pickling is carried out after electrolysis. The surface of the cold-rolled and annealed pickled plate was observed for grain boundaries in a 500. mu. m.times.500. mu.m region by using a scanning electron microscope, and the presence or absence of grain boundary erosion was examined to evaluate the surface quality. No sharpening was evaluated when no erosion occurred in the grain boundary, and sharpening was evaluated when erosion occurred. The results are shown in Table 4.

TABLE 4

[ Table 4]

Steel No.	Acute evaluation	Remarks for note
			19	Has the effect of sharpening	Examples of the invention
20	Has the effect of sharpening	Examples of the invention
			21	No sharpening	Examples of the invention
22	No sharpening	Examples of the invention
			23	No sharpening	Examples of the invention
33	No sharpening	Examples of the invention
			34	No sharpening	Examples of the invention
35	No sharpening	Examples of the invention
			36	No sharpening	Examples of the invention

From the results in Table 4, it is clear that steels Nos. 21 to 23 and 33 to 36 having a V/B of 20 or more are excellent not only in formability and ridging resistance but also in resistance to sharpening without occurrence of grain boundary erosion.

Industrial applicability

According to the present invention, a ferritic stainless steel sheet satisfying deep drawability and wrinkle resistance and having excellent formability can be produced by optimizing the composition of the components, particularly the V, B content, and industrially significant effects can be obtained. Further, by setting the content of V, B to an optimum range, a ferritic stainless steel sheet having improved sharpening resistance and excellent surface quality as well as excellent formability can be stably produced.

Claims

1. A ferritic stainless steel sheet characterized by containing, in mass%, C: 0.010-0.070%, Si: 1.00% or less, Mn: 1.00% or less, P: 0.040% or less, S: 0.010% or less, Al: 0.150% or less, Cr: 14.00-20.00%, Ni: 1.00% or less, N: 0.035 to 0.060%, and further comprises a V: 0.005-0.029%, B: 0.0001-0.0050% and V/B of 10 or more, the balance being Fe and unavoidable impurities.

2. The ferritic stainless steel sheet according to claim 1, characterized in that, in mass%, Si: 0.05-0.28%, Mn: 0.05 to 0.92 percent.

3. The ferritic stainless steel sheet according to claim 1 or 2, characterized by containing V and B so as to satisfy V/B.gtoreq.20.