KR102067154B1 - Ferritic Stainless Steel Sheet - Google Patents

Abstract

Provided is a ferritic stainless steel sheet excellent in corrosion resistance that simultaneously reduces surface defects and improves toughness. In mass%, C: 0.020% or less, Si: 0.05-0.40%, Mn: 0.05-1.00%, P: 0.040% or less, S: 0.030% or less, Al: 0.001-0.15%, Cr: 20.0-23.0%, Ni: 0.01% to 0.80%, Cu: 0.30% to 0.80%, Ti: 0.10% to 0.50%, Nb: 0.010% to 0.150%, Zr: 0.005% to 0.150%, and N: 0.020% or less, and the following formula (1) Satisfactory, and the balance is made of a ferritic stainless steel sheet, characterized in that the balance is made of Fe and unavoidable impurities. Zr ≤ Nb ≤ Ti (1) (In addition, Zr, Nb and Ti in the formula (1) means content (mass%) of each component)

Description

Ferritic Stainless Steel Sheet

The present invention relates to a ferritic stainless steel sheet excellent in corrosion resistance, low surface defects and excellent in toughness.

Ferritic stainless steel sheet is inexpensive and has excellent cost stability compared to austenitic stainless steel sheet because it does not contain a large amount of Ni. In addition, ferritic stainless steel sheets are used for various applications such as building materials, transportation equipment, home appliances, and kitchen appliances because of their excellent rust resistance.

Among ferritic stainless steel sheets, SUS443J1 (JIS G 4305) contains austenite by containing 20.0 to 23.0 mass% of Cr, 0.3 to 0.8 mass% of Cu, and a sufficient amount of stabilizing elements (Ti, Nb and Zr). Since it has the excellent corrosion resistance equivalent to SUS304 (JIS G 4305, 18 mass% Cr-8 mass% Ni) which is a system stainless steel, it is especially applied to the severe use of a corrosive environment.

Common among SUS443J1 is SUS443J1 which mainly contains Ti as a stabilizing element. By containing Ti, this steel promotes the development of texture and is excellent in workability. In addition, even when cold-rolled sheet annealing at a low temperature is sufficiently softened compared with the one containing Nb, the cold rolled sheet annealing acid washing line common to common steel can be passed through to manufacture and the productivity is good. . However, in the Ti-containing SUS443J1, streaks (surface defects) may be produced on the surface that impairs aesthetics. It is known that the string shape is due to the coarse TiN produced on the surface during casting. In addition, Ti-containing SUS443J1 also has a problem of low toughness. This is because coarse TiN which is a preferential starting point of destruction is generated.

Patent document 1 and patent document 2 have description about the prevention of the surface defect and the toughness improvement of Ti containing ferritic stainless steel.

Patent Document 1 discloses a method for producing a Ti-added ferritic stainless steel that is excellent in roping resistance and has good surface properties. In Patent Document 1, by controlling the solidification temperature, the casting temperature, and the TiN precipitation temperature of the steel so as to have a specific relationship, the precipitation of TiN at the injection time of molten steel is controlled to prevent the surface defects of the cold rolled annealing plate. .

Patent Literature 2 discloses a ferritic stainless steel sheet having excellent toughness and good corrosion resistance, and excellent in productivity and economy, and a method for producing the same. In patent document 2, the nitride in steel exists in the form of ZrN, and the toughness of a hot rolled annealing plate and a cold rolled annealing plate is improved.

Japanese Patent Application Laid-Open No. Hei1-118341 Japanese Laid-Open Patent Publication No. 2011-214060

In recent years, with the diversification of household telephone products, in addition to excellent corrosion resistance, there is a demand for a ferritic stainless steel sheet which simultaneously achieves both a reduction in surface shape and excellent toughness.

However, in the method disclosed in Patent Document 1, since TiN is deliberately precipitated in order to obtain an effect of improving the equiaxial crystal ratio of the slab, sufficient toughness improvement effect and surface defect reduction effect are not obtained. Moreover, in the method shown by patent document 2, generation | generation of TiN in steel cannot fully be suppressed, and sufficient toughness improvement effect and the surface defect reduction effect are not acquired.

The present invention provides a ferritic stainless steel sheet excellent in corrosion resistance, which simultaneously realizes reduction of surface defects and improvement of toughness, and is further softened by cold rolling annealing at a temperature equivalent to that of conventional Ti-containing SUS443J1. For the purpose of

The inventors carried out a comprehensive examination to realize the reduction of the surface defects and the improvement of the toughness at the same time with respect to the above problem. As a result, by appropriately adding an appropriate amount of Zr and Nb to Ti-containing SUS443J1, the precipitation form of TiN, which causes a decrease in toughness, is changed without increasing the cold-rolled sheet annealing temperature, and the toughness of Ti-containing SUS443J1 is increased. I found it possible to improve. In addition, this effect makes it possible to finely disperse and precipitate Ti-based inclusions, and found that it is possible to reduce the surface defects of the steel sheet due to TiN.

Specifically, with respect to the stabilizing elements (Ti, Nb and Zr) of the ferritic stainless steel sheet of SUS443J1, the main components thereof are 0.10 to 0.50% by mass of Ti, and 0.010 to 0.150 mass of Nb having a Ti content or less. By containing in the range of% and making Zr of Nb content or less into 0.005 to 0.150 mass% in range, it fully softens by cold-rolled sheet annealing at the temperature equivalent to the case where only the composition of a stabilizing element is Ti. It has also been found that it is possible to simultaneously achieve reduction of surface defects and realization of high toughness. It is assumed that his mechanism is as follows.

By complexly containing Nb and Zr in the steel, the composite carbonitride of Ti, Zr and Nb, which is smaller in size than TiN produced in a ferritic stainless steel of Ti-only addition system, ((Ti, Zr, Nb) (C And N)) are dispersed and precipitated, thereby improving toughness and reducing surface defects.

This invention is based on said recognition, The summary structure is as follows.

[1] In mass%, C: 0.020% or less, Si: 0.05-0.40%, Mn: 0.05-1.00%, P: 0.040% or less, S: 0.030% or less, Al: 0.001-0.15%, Cr: 20.0- 23.0%, Ni: 0.01% to 0.80%, Cu: 0.30% to 0.80%, Ti: 0.10% to 0.50%, Nb: 0.010% to 0.150%, Zr: 0.005% to 0.150%, and N: 0.020% or less. 1) The ferritic stainless steel sheet, wherein the formula is satisfied and the balance is made of Fe and unavoidable impurities.

Zr≤Nb≤Ti (1)

(In addition, Zr, Nb, and Ti in Formula (1) mean content (mass%) of each component.)

[2] Furthermore, in mass%, it contains 1 type (s) or 2 or more types chosen from Co: 0.01-0.50%, Mo: 0.01-0.30%, and W: 0.01-0.50%, To [1] characterized by the above-mentioned. The ferritic stainless steel sheet described.

[3] Further, in mass%, V: 0.01-0.50%, B: 0.0003-0.0030%, Mg: 0.0005-0.0100%, Ca: 0.0003-0.0030%, Y: 0.001-0.20%, and REM (rare earth metal) : 1 type (s) or 2 or more types chosen from 0.001 to 0.10%, The ferritic stainless steel plate as described in [1] or [2] characterized by the above-mentioned.

[4] The ferrite according to any one of [1] to [3], further comprising, in mass%, one or two kinds selected from Sn: 0.001 to 0.50% and Sb: 0.001 to 0.50%. Based stainless steel plate.

According to this invention, the ferritic stainless steel plate which is excellent in corrosion resistance, few surface defects, and excellent in toughness is obtained.

In addition, since the composition of the stabilizing element is sufficiently softened by cold rolling annealing at a temperature equivalent to that of only Ti, the productivity of the ferritic stainless steel sheet is high.

1 is a diagram showing the effect of Ti and Nb content on the amount of toughness and surface defects under the condition of Zr ≦ Nb.
FIG. 2 is a diagram showing the effect of the content of Nb and Zr on the amount of toughness and surface defects under the condition of Nb ≦ Ti.

(Form to carry out invention)

EMBODIMENT OF THE INVENTION Hereinafter, embodiment of this invention is described. In addition, this invention is not limited to the following embodiment.

The component composition of the ferritic stainless steel sheet of the present invention is, by mass%, C: 0.020% or less, Si: 0.05-0.40%, Mn: 0.05-1.00%, P: 0.040% or less, S: 0.030% or less, Al: 0.001 to 0.15%, Cr: 20.0 to 23.0%, Ni: 0.01 to 0.80%, Cu: 0.30 to 0.80%, Ti: 0.10 to 0.50%, Nb: 0.010 to 0.150%, Zr: 0.005 to 0.150%, and N: It contains 0.020% or less, satisfy | fills following formula (1), and remainder consists of Fe and an unavoidable impurity.

Zr≤Nb≤Ti (1)

In addition, Zr, Nb, and Ti in Formula (1) mean content (mass%) of each component.

The component composition may further contain, in mass%, one or two or more selected from Co: 0.01 to 0.50%, Mo: 0.01 to 0.30%, and W: 0.01 to 0.50%.

In addition, the said component composition is further in mass%, V: 0.01-0.50%, B: 0.0003-0.0030%, Mg: 0.0005-0.0100%, Ca: 0.0003-0.0030%, Y: 0.001-0.20%, and REM (Rare earth metal): You may contain 1 type (s) or 2 or more types chosen from 0.001 to 0.10%.

In addition, the said component composition may contain 1 type or 2 types selected from Sn: 0.001-0.50% and Sb: 0.001-0.50% further by mass%.

Hereinafter, each component is demonstrated. "%" Which means content of a component means the mass% unless there is particular notice.

C: 0.020% or less

C is an effective element for increasing the strength of steel. The effect is obtained by making C content into 0.001% or more. However, when C content exceeds 0.020%, corrosion resistance and workability will fall remarkably. Therefore, C content is made into 0.020% or less. Moreover, it is preferable to make C content into 0.015% or less. More preferably, it is 0.010% or less.

Si: 0.05-0.40%

Si is an element useful as a deoxidizer. This effect is obtained by making Si content into 0.05% or more. However, when Si content exceeds 0.40%, steel will harden and workability will fall. Moreover, when Si content exceeds 0.40%, generation | occurrence | production of the scale of the slab phase surface which has a lubricating effect at the time of hot rolling is suppressed, and surface defect is enlarged. Therefore, Si content is limited to 0.05 to 0.40% of range. More preferably, it is 0.05 to 0.25% of range. The lower limit of the Si content is more preferably 0.08% or more. The upper limit of the Si content is more preferably 0.15% or less.

Mn: 0.05 to 1.00%

Mn has a deoxidizing action. This effect is obtained by making Mn content 0.05% or more. On the other hand, when Mn content exceeds 1.00%, precipitation and coarsening of MnS are accelerated | stimulated and corrosion resistance falls. Therefore, Mn content is limited to 0.05 to 1.00% of range. More preferably, Mn content is 0.10% or more with respect to a minimum, More preferably, it is 0.15% or more. More preferably, Mn content is less than 0.30% with respect to an upper limit, More preferably, it is 0.25% or less.

P: 0.040% or less

P is an element which reduces corrosion resistance. In addition, hot workability deteriorates because P segregates at grain boundaries. Therefore, as low as possible, the P content is preferably as low as 0.040% or less. Preferably it is 0.030% or less.

S: 0.030% or less

S forms Mn and precipitate MnS. The interface between the MnS and the stainless steel base material becomes the starting point of the etch pit, which lowers the corrosion resistance. Therefore, the lower the S content is, the more preferable it is at most 0.030%. Preferably it is 0.020% or less.

Al: 0.001 to 0.15%

Al is an effective element for deoxidation. This effect is obtained at Al content of 0.001% or more. On the other hand, when Al content exceeds 0.15%, generation | occurrence | production of the scale of the slab phase surface which has a lubricating effect at the time of hot rolling is suppressed, and surface defects increase. Therefore, Al content is limited to 0.001 to 0.15% of range. Preferable Al content is 0.005% or more with respect to a minimum, More preferably, it is 0.01% or more. Preferable Al content is 0.10% or less with respect to an upper limit, More preferably, it is 0.05% or less.

Cr: 20.0 to 23.0%

Cr is an element which forms a passive film on the surface and improves corrosion resistance. If the Cr content is less than 20.0%, sufficient corrosion resistance cannot be obtained. On the other hand, when Cr content exceeds 23.0%, toughness will fall easily by the influence of (sigma) phase and 475 degreeC brittleness. Therefore, Cr content is made into 20.0 to 23.0%. Preferable Cr content is 20.5% or more with respect to a minimum. Cr content with respect to an upper limit is 22.0% or less, More preferably, it is 21.5% or less.

Ni: 0.01% to 0.80%

Ni is an element which suppresses the anode reaction by acid and enables passivation maintenance even at a lower pH. In other words, Ni enhances the effect of crevice corrosion resistance, significantly inhibits the progress of corrosion in the active dissolved state, and improves the corrosion resistance. This effect is obtained at 0.01% or more of Ni content. On the other hand, when Ni content exceeds 0.80%, steel will harden and its workability will fall. Therefore, Ni content is limited to 0.01 to 0.80% of range. Ni content with respect to a minimum is 0.05% or more, More preferably, it is 0.10% or more. Ni content with respect to an upper limit is 0.40% or less, More preferably, it is 0.25% or less.

Cu: 0.30 to 0.80%

Cu is an element which strengthens a passivation film and improves corrosion resistance. On the other hand, when Cu is added excessively, (epsilon) -Cu will become easy to precipitate and corrosion resistance will fall. Therefore, Cu content is made into 0.30 to 0.80%. Cu content with respect to a minimum is 0.35% or more, More preferably, it is 0.40% or more. Cu content with respect to an upper limit is 0.60% or less, More preferably, it is 0.45% or less.

Ti: 0.10 to 0.50%

Ti is an element which fixes C and N, prevents sensitization by Cr carbonitride, and improves corrosion resistance. However, TiN produced by the addition of Ti causes a decrease in toughness. As described later, in the present invention, the above-mentioned toughness reduction is suppressed by the composite effect of Nb and Zr. Corrosion resistance improvement effect by Ti is obtained when Ti content is 0.10% or more. On the other hand, when Ti content exceeds 0.50%, a stainless steel plate will harden and workability will fall. Moreover, when Ti content exceeds 0.50%, it will become difficult to control the precipitation form of Ti type interference | inclusion also by addition of Nb or Zr, and surface quality will fall. Therefore, Ti content is taken as 0.1 to 0.50% of range. Preferable Ti content is 0.15% or more with respect to a minimum, More preferably, it is 0.18% or more. Preferable Ti content with respect to an upper limit is 0.35% or less, More preferably, it is 0.26% or less.

Nb: 0.010 to 0.150%

Nb, like Ti, is an element that fixes C and N to prevent sensitization by Cr carbonitride and improves corrosion resistance. Moreover, Nb improves toughness by the composite effect with Zr mentioned later, and suppresses generation of surface defects. The effect is obtained at 0.010% or more of Nb content. On the other hand, when Nb content exceeds 0.150%, a stainless steel plate will harden and workability will fall. Moreover, when Nb content exceeds 0.150%, rise of recrystallization temperature will arise and manufacturability will fall. Therefore, Nb content is taken as 0.010 to 0.150% of range. The lower limit of the Nb content is preferably 0.030% or more, and more preferably 0.070% or more. Preferable Nb content with respect to an upper limit is less than 0.100%, More preferably, it is 0.090% or less.

Zr: 0.005 to 0.150%

Zr, like Ti, is an element that fixes C and N to prevent sensitization by Cr carbonitride and improves corrosion resistance. Moreover, Zr improves toughness by the composite effect with Nb mentioned later, and suppresses generation of surface defects. In order to acquire these effects, containing of 0.005% or more of Zr is required. On the other hand, when Zr content exceeds 0.150%, Zr type interference | inclusion precipitates on the surface and causes an increase of surface defect. Therefore, Zr content is limited to 0.005 to 0.150% of range. Preferable Zr content is 0.010% or more with respect to a minimum, More preferably, it is 0.030% or more. Zr content with respect to an upper limit is less than 0.100%, More preferably, it is 0.080% or less.

In the present invention, by adding Nb and Zr in combination to SUS443J1 containing only Ti as the stabilizing element, the composition is sufficiently softened by cold-rolled sheet annealing at a temperature equivalent to the case where the stabilizing element has only Ti, and further surface defects. While suppressing the occurrence of, it has been found that the toughness can be improved. Specifically, the stabilizing elements (Ti, Nb and Zr) of SUS443J1 are 0.10 to 0.50% of Ti, 0.010 to 0.150% of Nb, and 0.005 to 0.150% of Zr under the restriction of the following formula (1). By setting it as the component composition to contain, it was discovered that it can soften sufficiently by cold-rolled sheet annealing at the temperature equivalent to the case where only the stabilization element is Ti, and can simultaneously achieve the generation | occurrence | production reduction of surface defects and realization of high toughness. It is estimated that the mechanism is based on the following.

By complexly containing Nb and Zr in the steel, the composite carbonitride of Ti, Zr and Nb, which is smaller in size than TiN produced in a ferritic stainless steel of Ti-only addition system, ((Ti, Zr, Nb) (C , N)) is dispersed and precipitated, and it is thought that the improvement of toughness and the reduction of surface defect generation are realized. In order to fully generate said ((Ti, Zr, Nb) (C, N)), it is necessary to satisfy following formula (1).

Zr≤Nb≤Ti (1)

In addition, Zr, Nb, and Ti in Formula (1) mean content (mass%) of each component.

The relation between Ti and Nb is preferably Ti≥1.5Nb, more preferably Ti≥2Nb. The relationship between Nb and Zr is preferably Nb ≧ 1.3 Zr, more preferably Nb ≧ 1.5 Zr.

N: 0.020% or less

N is an element unavoidably mixed in steel. However, when N content exceeds 0.020%, corrosion resistance and workability will fall remarkably. Therefore, N content is made into 0.020% or less. More preferably, it is 0.015% or less.

As mentioned above, although the basic component was demonstrated, in addition to the above, in this invention, the element described below can be contained suitably.

Co: 0.01% to 0.50%

Co is an element which improves the inter electrode corrosion resistance of stainless steel. This effect is acquired at 0.01% or more of Co content. However, when the content exceeds 0.50%, the effect is saturated, and workability further decreases. Therefore, when Co is added, Co content is made into 0.01 to 0.50%. Preferable Co content is 0.02% or more with respect to a minimum, More preferably, it is 0.03% or more. Preferable Co content is 0.30% or less with respect to an upper limit, More preferably, it is 0.10% or less.

Mo: 0.01% to 0.30%

Mo has the effect of improving the inter electrode corrosion resistance of stainless steel. The effect is obtained with Mo content of 0.01% or more. However, when Mo content exceeds 0.30%, the effect is saturated, and further coarse intermetallic compound is produced and toughness falls. Therefore, Mo is made into 0.01 to 0.30% when Mo is added. Preferable Mo content is 0.02% or more with respect to a minimum, More preferably, it is 0.03% or more. Preferable Mo content is 0.20% or less with respect to an upper limit, More preferably, it is 0.10% or less.

W: 0.01% to 0.50%

W is an element which improves the inter electrode corrosion resistance of stainless steel. The effect is obtained in W content of 0.01% or more. However, when the content exceeds 0.50%, the effect is saturated, and workability further decreases. Therefore, when adding W, W content shall be 0.01 to 0.50%. Preferable W content is 0.02% or more with respect to a minimum, More preferably, it is 0.03% or more. Preferable W content is 0.30% or less with respect to an upper limit, More preferably, it is 0.10% or less.

V: 0.01 to 0.50%

V is an element which improves the interelectrode corrosion resistance of stainless steel. This effect is obtained in V content of 0.01% or more. However, when the content exceeds 0.50%, the effect is saturated, and workability further decreases. Therefore, when adding V, V content is made into 0.01 to 0.50%. More preferably, it is 0.01 to 0.30% of range. More preferably, it is 0.01 to 0.10% of range.

B: 0.0003 to 0.0030%

B is an element which improves hot workability and secondary workability, and it is effective to add B to Ti-added steel. This effect is obtained when B content is 0.0003% or more. On the other hand, when B content exceeds 0.0030%, toughness will fall. Therefore, when adding B, B content shall be 0.0003 to 0.0030% of range. B content with respect to a minimum is 0.0015% or more. B content with respect to an upper limit is 0.0025% or less.

Mg: 0.0005-0.0100%

Mg forms Mg oxide with Al in molten steel and acts as a deoxidizer. This effect is obtained when Mg content is 0.0005% or more. On the other hand, when Mg content exceeds 0.0100%, toughness of steel will fall and manufacturability will fall. Therefore, when adding Mg, Mg content is restrict | limited to 0.0005 to 0.0100% of range. Mg content preferable with respect to a minimum is 0.0010% or more. Mg content with respect to an upper limit is 0.0050% or less, More preferably, it is 0.0030% or less.

Ca: 0.0003 to 0.0030%

Ca is an element which improves hot workability. This effect is obtained when Ca content is 0.0003% or more. On the other hand, when Ca content exceeds 0.0030%, the toughness of steel will fall. Moreover, corrosion resistance also falls by precipitation of CaS. Therefore, when Ca is added, Ca content is limited to 0.0003% to 0.0030% of range. Preferable Ca content is 0.001% or more with respect to a minimum. Ca content preferable with respect to an upper limit is 0.002% or less.

Y: 0.001-0.20%

Y is an element that reduces the decrease in viscosity of molten steel and improves cleanliness. This effect is obtained at Y content of 0.001% or more. On the other hand, when Y content exceeds 0.20%, the effect will be saturated, and also workability will fall. Therefore, when adding Y, Y content is limited to 0.001 to 0.20% of range. More preferably, it is 0.001 to 0.10% of range.

REM (rare earth metal): 0.001 to 0.10%

REM (rare earth metal: elements having atomic numbers 57 to 71 such as La, Ce, and Nd) is an element that improves high temperature oxidation resistance. This effect is obtained when REM content is 0.001% or more. On the other hand, when REM content exceeds 0.10%, the effect is not only saturated but surface defect arises at the time of hot rolling. Therefore, when adding REM, REM content is limited to 0.001 to 0.10% of range. Preferable REM content with respect to a minimum is 0.005% or more. The REM content preferable with respect to an upper limit is 0.05% or less.

Sn: 0.001-0.50%

Sn is effective for improving ridging by promoting the generation of deformation zones during rolling. This effect is obtained when Sn content is 0.001% or more. However, when the content of Sn exceeds 0.50%, not only the effect is saturated but also the workability is further lowered. Therefore, the content is made into 0.001 to 0.50% when Sn is added. Sn content with respect to a minimum is 0.003% or more. Preferable Sn content is 0.20% or less with respect to an upper limit.

Sb: 0.001 to 0.50%

Sb is effective for improving the ridging by promoting the generation of strain bands during rolling. This effect is obtained when content of Sb is 0.001% or more. However, when the content of Sb exceeds 0.50%, not only the effect is saturated but also the workability is further lowered. Therefore, the content is made into 0.001 to 0.50% when Sb is added. Preferable Sb content is 0.003% or more with respect to a minimum, and preferable Sb content is 0.20% or less with respect to an upper limit.

Remainder other than the above components is Fe and an unavoidable impurity. Representative examples of the unavoidable impurities mentioned herein include H, O (oxygen), Zn, Ga, Ge, As, Ag, In, Hf, Ta, Re, Os, Ir, Pt, Au, Pb and the like. Among these elements, H and O (oxygen) can be contained in 0.05% or less of range. About other elements, it can contain in 0.3% or less of range.

Next, the suitable manufacturing method of the ferritic stainless steel plate of this invention is demonstrated. The steel of the above-mentioned component composition is melted by well-known methods, such as a converter, an electric furnace, and a vacuum melting furnace, and is made into a steel raw material (slab) by the continuous casting method or the ingot casting-slabbing method. . After heating this steel raw material at 1000 degreeC-1200 degreeC, it hot-rolls so that a finishing temperature may be 2.0 mm-5.0 mm in the conditions of 700 degreeC-1000 degreeC. The hot rolled sheet thus produced is annealed at a temperature of 800 ° C to 1100 ° C to perform acid washing, followed by cold rolling, and cold rolled sheet annealing at a temperature of 700 ° C to 1000 ° C. After cold-rolled sheet annealing, acid washing is performed to remove scale. You may perform skin pass rolling on the cold rolled sheet from which the scale was removed.

In addition, this invention is not only limited to said cold rolled sheet products, but is also effective as a hot rolled sheet product.

Example

Table 1 (Table 1-1 and Table 1-2 together as Table 1), Table 2 (Table 2-1 and Table 2-2 together as Table 2), Table 3 (Table 3-1 and Table 3) The ferritic stainless steel having the composition shown in Table 3 together with -2 was dissolved in 100 kg steel ingot and then heated to a temperature of 1200 ° C. to hot roll to obtain a hot rolled sheet having a plate thickness of 4.0 mm. Thereafter, after annealing at 1100 ° C. and acid washing in a conventional method, cold rolling to a plate thickness of 2.0 mm and annealing at 900 ° C. and acid washing in a conventional method were performed.

About the obtained cold-rolled annealing board, pitting potential measurement (JIS G 0577) was performed and corrosion resistance was evaluated. "(Circle)" (passed) and the thing below 290 kV were evaluated as "(circle)" (failed) that the formula potential was 290 kV (vs. SCE) or more.

Moreover, about the obtained cold-rolled annealing board, the test piece (JIS B 7722V notch) was extract | collected in the rolling direction, the Charpy impact test was done, and the toughness of the steel plate was evaluated. "(Circle)" (passed) and the thing below 200 J / cm <2> evaluated that the Charpy impact value in 25 degreeC was 200 J / cm <2> or more as "(circle)" (failure).

Furthermore, the surface of the cold rolled annealing plate was observed, and the quantity of surface defects was evaluated by measuring the density of the stripe shape of the surface. Ten steel sheets of each composition were produced, and the number of stripe shapes in which the length in the L direction exceeded 10 mm was measured for an area of 200 mm in width x 200 mm in length at the center of the surface of each steel plate, and the average number thereof. The thing which was more than 1 evaluated "(circle)" and the thing more than 1 was evaluated as "▲" (failure).

Furthermore, using the cold rolled steel sheet before performing annealing, also in the 20s annealing at 880 degreeC, it evaluated whether it softened enough. Evaluation is based on the hardness (a) of the steel sheet as it is cold rolled, the hardness (b) of the steel sheet subjected to annealing at 20 ° C. at 880 ° C., and the hardness of the steel sheet subjected to annealing at 20 ° C. at 1000 ° C. as an indicator when sufficiently softened ( c) was compared and evaluated. For evaluation, three steel sheets 15 mm in length and 20 mm in width were cut out, and after the annealing was performed for each of the test pieces for measuring b and c, the steel sheets were cut into sizes of 15 mm in length and 10 mm in width. And Vickers hardness measured from the cross section was used. When the annealing is carried out, the hardness of the steel sheet changes from a to c, but 90% or more of the soft nitriding is achieved by annealing at 20 s at 880 ° C, that is, c + 0.1 x (a-c) ≥ b Was evaluated as "(circle)" (pass). Moreover, what was not was evaluated by "▲" (failure).

The obtained results are shown in Tables 1, 2, and 3. Inventive steel has all of the evaluation of formula potential measurement, evaluation of Charpy impact value, evaluation of surface defects, evaluation of soft nitriding temperature, all of which are "(circle)", good corrosion resistance and toughness, few surface defects, and also problems in manufacturability. You can see that there is no.

In the comparative example of test No. 34, since Cr content is lower than the range of this invention, corrosion resistance is inferior.

Since the Cr content is higher than the range of this invention, the comparative example of test No. 35 is inferior in toughness.

In the comparative example of test No. 36, since Ni content is lower than the range of this invention, corrosion resistance is inferior.

In the comparative example of test No. 37, since Ti content is lower than the range of this invention, corrosion resistance is inferior.

In the comparative example of test No. 38, since Ti content is higher than the range of this invention, it is inferior in toughness and has many surface defects.

In the comparative example of test No. 39, since Nb content is lower than the range of this invention, it is inferior in toughness and has many surface defects.

In the comparative example of test No. 40, since Nb content is higher than the range of this invention, soft-nitriding temperature is high and it is inferior to manufacturability.

Since the Zr content is lower than the range of this invention, the comparative example of test No. 41 is inferior in toughness and has many surface defects.

Since the Zr content is higher than the range of this invention, the comparative example of test No. 42 is inferior in toughness and has many surface defects.

In the comparative example of test No. 57, since both Nb content and Zr content are lower than the range of this invention, it is inferior in toughness and has many surface defects.

In Comparative Example No. 58, since the Ti content and the Zr content were lower than the range of the present invention, and the Nb content was higher than the range of the present invention, the toughness was poor, the surface defects were high, and the soft nitriding temperature was high. This is inferior.

In addition, the comparative example of the test Nos. 43-54, 67, 68 is demonstrated below using FIG. 1 and FIG.

Table 1-1

Table 1-2

Table 2-1

Table 2-2

Table 3-1

Table 3-2

Fig. 1 shows the results of the Charpy impact value for the results of the examples of the present invention and the results of the comparative examples (Nos. 43 to 48) in which the composition is within the scope of the present invention and satisfies Nb≥Zr and does not satisfy Ti≥Nb. About evaluation and evaluation of a surface defect, Ti content was taken to the horizontal axis and Nb content was taken to the graph and put together in the graph. In addition, all evaluations of a Charpy impact value pass the evaluation of a surface defect, and all the steel plates shown in the drawing pass, and evaluation of a surface defect also fails a test of the result of a Charpy impact value. As shown in FIG. 1, it is necessary to satisfy Ti≥Nb in order to simultaneously achieve excellent toughness and reduction of surface defects within the composition range of the present invention.

2 shows the results of the examples of the present invention and the results of the comparative examples (Nos. 49 to 54, 67 and 68) in which the composition is within the scope of the present invention and meets Ti≥Nb and does not satisfy Nb≥Zr. About evaluation of Charpy impact value and evaluation of surface defect, Nb content was taken on the horizontal axis and Zr content was taken on the vertical axis, and was put together in the graph. As shown in FIG. 2, in order to simultaneously achieve excellent toughness and reduction of surface defects within the composition range of the present invention, it is necessary to satisfy Nb ≧ Zr. 1 and 2, it is necessary to satisfy both Ti≥Nb and Nb≥Zr, that is, Zr≤Nb≤Ti in order to simultaneously achieve excellent toughness and reduction of surface defects within the composition range of the present invention. Able to know.

In Comparative Examples Nos. 55 and 56, the composition was within the scope of the present invention, and did not satisfy both Ti≥Nb and Nb≥Zr, and both the results of the Charpy impact value and the evaluation of the surface defects failed. .

(Industrial availability)

Since the ferritic stainless steel sheet of the present invention has excellent toughness and few surface defects, the interior of the elevator, as well as interiors, duct hoods, muffler cutters, lockers, parts for home appliances, office parts, and automobiles Corrosion resistance is required mainly for interior parts, exhaust pipes for automobiles, building materials, cover of drainage grooves, containers for maritime transport, materials, kitchen appliances, interior and exterior materials of construction, automobile parts, escalators, railroad cars, and electrical case casings. In addition to the member, it is suitable as a member requiring toughness and design.

Claims (5)

In mass%, C: 0.001% or more and 0.020% or less, Si: 0.05% or more and 0.12% or less, Mn: 0.05 to 1.00%, P: 0.040% or less, S: 0.030% or less, Al: 0.001 to 0.15%, Cr: 20.0 to 23.0%, Ni: 0.01 to 0.80%, Cu: 0.30 to 0.80%, Ti: 0.10 to 0.50%, Nb: 0.010 to 0.150%, Zr: 0.005 to 0.150%, and N: 0.020% or less, and The ferritic stainless steel sheet which satisfy | fills following formula (1), and remainder consists of Fe and an unavoidable impurity.
Zr≤Nb≤Ti (1)
(In addition, Zr, Nb, and Ti in Formula (1) mean content (mass%) of each component.) The method of claim 1,
Furthermore, the ferritic stainless steel sheet which contains 1 type (s) or 2 or more types selected from Co: 0.01 to 0.50%, Mo: 0.01 to 0.30%, and W: 0.01 to 0.50% by mass%. The method according to claim 1 or 2,
Furthermore, in mass%, V: 0.01-0.50%, B: 0.0003-0.0030%, Mg: 0.0005-0.0100%, Ca: 0.0003-0.0030%, Y: 0.001-0.20%, and REM (rare earth metal): 0.001-- 1 type (s) or 2 or more types chosen from 0.10%, The ferritic stainless steel plate characterized by the above-mentioned. The method according to claim 1 or 2,
Furthermore, the ferritic stainless steel sheet characterized by containing 1 type or 2 types selected from Sn: 0.001-0.50% and Sb: 0.001-0.50% by mass%. The method of claim 3,
Furthermore, the ferritic stainless steel sheet characterized by containing 1 type or 2 types selected from Sn: 0.001-0.50% and Sb: 0.001-0.50% by mass%.

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