CN114761597A

CN114761597A - Austenitic stainless steel

Info

Publication number: CN114761597A
Application number: CN202180006823.3A
Authority: CN
Inventors: 吉见敏彦; 平出信彦
Original assignee: Nippon Steel and Sumikin Stainless Steel Corp
Current assignee: Nippon Steel Stainless Steel Corp
Priority date: 2020-03-30
Filing date: 2021-03-16
Publication date: 2022-07-15
Also published as: TWI762248B; WO2021200106A1; US20230076254A1; KR20220088921A; EP4130322A1; TW202138589A; AU2021245528B2; JP7301218B2; AU2021245528A1; JPWO2021200106A1

Abstract

The present invention provides an austenitic stainless steel, which contains, in mass%, C: 0.100% or less, Si: 3.00% or less, Mn: 0.01% or more and 5.00% or less, P: 0.100% or less, S: 0.0050% or less, Ni: 7.00% or more and 38.00% or less, Cr: 17.00% or more and 28.00% or less, Mo: 10.00% or less, N: more than 0.100% and 0.400% or less, the remainder comprising Fe and impurities; the difference in brightness Δ L on the steel sheet surface is 5 or less.

Description

Austenitic stainless steel

Technical Field

The present invention relates to an austenitic stainless steel.

The present application claims priority based on Japanese patent application No. 2020-.

Background

Stainless steel has been used in various applications as a representative corrosion resistant material, but recently, steel grades having high weather resistance have been developed, and the use thereof in building materials such as roofs and exterior materials has been increasing. In these exterior building material applications, not only is it required that rust and perforation due to corrosion not occur, but also the appearance after construction is required to be beautiful.

As a stainless steel sheet having improved appearance, for example, patent document 1 discloses a stainless steel sheet having both antiglare properties and corrosion resistance, characterized in that: which contains C in weight percent: 0.10% or less, Si: 1.0% or less, Mn: 1.0% or less, P: 0.09% or less, S: 0.01% or less, Cr: 20% to 40% inclusive, Mo: 0.5% to 6.0%, Cr + Mo: more than 24.5%, N: 0.1% or less, Nb: 0.01% or more and 0.8% or less, Ti: 0.01% or more and 0.8% or less, Al: 0.008% or more and 1.0% or less, and further contains Ni: 0.1% or more and 25% or less, Cu: 0.01% to 3% inclusive, and the balance of Fe and inevitable impurities, and a surface roughness of 1.0 [ mu ] m or more in terms of arithmetic average roughness (Ra).

Further, patent document 2 discloses a pickling agent for stainless steel, which contains 10 to 200g/L of sulfuric acid or 5 to 150g/L of hydrochloric acid as a main component, 1 to 40g/L of each of 1 or 2 or more selected from hydrofluoric acid, fluorosilicic acid and sodium fluoride, and 5 to 40g/L of Fe³⁺Adding a thickening agent into an ionic nitric acid-free aqueous solution, and preparing into slurry. Patent document 2 discloses an acid pickling agent further containing 5 to 15g/L of hydrogen peroxide and 5 to 10g/L of sodium persulfate in terms of a concentration of 35%, or both of them, in addition to the above.

The stainless steel disclosed in patent document 1 has relatively high corrosion resistance. However, in a humid environment containing chlorides such as seawater, rust may be generated and the beautiful appearance may be impaired, and there is room for improvement.

On the other hand, austenitic stainless steel containing a large amount of Cr, Mo, and N is superior in corrosion resistance to other austenitic stainless steels. However, in the production of a super austenitic stainless steel, in a conventional pickling process which is finally performed, there is a case where elution of the surface of a steel sheet varies due to segregation of components. Specifically, the portions eluted by pickling are white, and therefore the portions not eluted are glossy, and the appearance of the super austenitic stainless steel is sometimes uneven. Even in the technique described in patent document 2, it is difficult to elute the entire surface of the superaustenitic stainless steel, and the appearance may be uneven. Thus, when used for exterior building materials requiring a beautiful appearance, the super austenitic stainless steel still has room for improvement.

Documents of the prior art

Patent literature

Patent document 1: japanese laid-open patent publication No. 9-228002

Patent document 2: japanese laid-open patent publication No. 2005-29828

Disclosure of Invention

Problems to be solved by the invention

The present invention has been made in view of the above problems, and an object of the present invention is to provide an austenitic stainless steel having a beautiful appearance.

Means for solving the problems

The present inventors have made various studies on the pickling conditions under which the appearance unevenness does not occur, and as a result, have obtained the following findings: even in the case of super austenitic stainless steel having component segregation, if cleaning is performed with a predetermined acidic solution having oxidizing power, the appearance unevenness due to the component segregation can be suppressed.

The gist of the present invention completed based on the above-described findings is as follows.

[1] An austenitic stainless steel, comprising, in mass%:

c: less than 0.100 percent,

Si: less than 3.00 percent,

Mn: 0.01% to 5.00%,

P: less than 0.100 percent,

S: less than 0.0050%,

Ni: 7.00% to 38.00%,

Cr: 17.00% to 28.00%,

Mo: less than 10.00 percent,

N: more than 0.100% and not more than 0.400%,

the remainder comprising Fe and impurities;

The difference in brightness Δ L between the steel sheet surfaces is 5 or less.

[2] The austenitic stainless steel according to [1], wherein 1 or 2 or more elements selected from the following elements are contained in mass% in place of part of Fe:

cu: less than 3.00 percent,

W: 2.00% or less, and

v: 1.00% or less.

[3] The austenitic stainless steel according to the above [1] or [2], wherein 1 or 2 or more elements selected from the following elements are contained in mass% in place of a part of Fe:

al: 0.001% to 0.3%,

Ca: 0.001% to 0.3%,

B: 0.0001% to 0.1%,

Ti: 0.001% to 0.40%,

Nb: 0.001% to 0.40%,

Sn: 0.001% to 0.5%,

Zr: 0.001% to 0.5%,

Co: 0.001% to 0.5%,

Mg: 0.001% to 0.5%,

Hf: 0.001% to 0.5%,

REM: 0.001% to 0.5%,

Ta: 0.001% to 0.5%,

Ga: 0.001% or more and 0.5% or less, and

sb: 0.001% or more and 0.5% or less.

ADVANTAGEOUS EFFECTS OF INVENTION

According to an aspect of the present invention, an austenitic stainless steel having a beautiful appearance can be provided.

Detailed Description

Hereinafter, preferred embodiments of the present invention will be described in detail. The description is made in the following order.

< Austenitic stainless Steel >

< method for producing austenitic stainless Steel >

< Austenitic stainless Steel >

The austenitic stainless steel according to the present embodiment contains, in mass%, C: 0.100% or less, Si: 3.00% or less, Mn: 0.01% or more and 5.00% or less, P: 0.100% or less, S: 0.0050% or less, Ni: 7.00% or more and 38.00% or less, Cr: 17.00% or more and 28.00% or less, Mo: 10.00% or less, N: more than 0.100% and 0.400% or less, the remainder comprising Fe and impurities; the difference in brightness Δ L on the steel sheet surface is 5 or less.

The austenitic stainless steel according to the present embodiment will be described in detail below. The term "component" means "mass%.

C: less than 0.100%

C is an element inevitably contained in stainless steel, and contributes to stabilization of the austenite phase and improvement of high-temperature strength. If the C content is excessive, the weld solidification cracking resistance is lowered and the corrosion resistance accompanying the precipitation of Cr-based carbide is lowered. Therefore, the C content is set to 0.100% or less. The C content is preferably 0.06% or less, more preferably 0.04% or less. On the other hand, the lower limit of the C content is not particularly limited, but is preferably 0.005% or more.

Si: 3.00% or less

Si is an effective element for stabilizing the austenite phase. However, if the Si content is excessive, the precipitation of the σ phase is promoted. Therefore, the Si content is set to 3.00% or less. The Si content is preferably 1.00% or less, more preferably 0.80% or less. On the other hand, the lower limit is not particularly limited, but the Si content is preferably 0.01% or more in order to obtain the effect of stabilizing the austenite phase of Si. The Si content is more preferably 0.10% or more.

Mn: 0.01% to 5.00%

Mn is an effective element for stabilizing the austenite phase. In order to obtain the above effects of Mn, the Mn content is set to 0.01% or more. The Mn content is preferably 0.20% or more, more preferably 0.4% or more. On the other hand, if the Mn content is excessive, the corrosion resistance is lowered. Therefore, the Mn content is set to 5.00% or less. The Mn content is preferably 2.00% or less, more preferably 1.50% or less.

P: less than 0.100%

P may be contained in stainless steel as an impurity. P is an element that degrades hot workability, and is preferably reduced as much as possible. Therefore, the P content is set to 0.100% or less. The P content is preferably 0.080% or less, more preferably 0.050% or less. The lower limit is not particularly limited, but the P content is preferably 0.005% or more from the viewpoint of cost.

S: 0.0050% or less

S is an element which is segregated at austenite grain boundaries during hot working, weakens the bonding strength of the grain boundaries, and induces cracking during hot working. Therefore, it is preferable to reduce the S content as much as possible. Therefore, the S content is set to 0.0050% or less. The S content is preferably 0.0020% or less, and more preferably 0.0010% or less. On the other hand, the lower limit is not particularly set, but an extreme reduction in the S content leads to an increase in the steel making cost. Therefore, the S content is preferably 0.0001% or more. The S content is more preferably 0.0002% or more.

Ni: 7.00% or more and 38.00% or less

Ni is an important element for stabilizing the austenite phase. In order to obtain the above effects of Ni, the Ni content is set to 7.00% or more. The Ni content is preferably 16.00% or more, and more preferably 18.00% or more. On the other hand, excessive Ni content increases material cost, and thus the economic efficiency is deteriorated. Therefore, the Ni content is set to 38.00% or less. The Ni content is preferably 30.00% or less, more preferably 25.00% or less.

Cr: 17.00% or more and 28.00% or less

Cr is an element very important for improving the corrosion resistance of austenitic stainless steel. Cr is also an element contributing to an increase in strength of austenitic stainless steel. Therefore, the Cr content is set to 17.00% or more. The Cr content is preferably 18.00% or more, and more preferably 19.00% or more. On the other hand, if Cr is contained excessively, σ -compatability is likely to precipitate. Therefore, the Cr content is set to 28.00% or less. The Cr content is preferably 25.00% or less, more preferably 22.00% or less.

Mo: less than 10.00%

Mo is an important element for improving the corrosion resistance of austenitic stainless steel. Further, Mo is also an element contributing to an increase in strength. However, if Mo is contained excessively, σ -phase is likely to precipitate. Therefore, the Mo content is set to 10.00% or less. The Mo content is preferably 8.00% or less, more preferably 7.00% or less. On the other hand, although the lower limit is not particularly set, the Mo content is preferably 3.00% or more in order to stably obtain the corrosion resistance improving effect and the strength increasing effect of Mo. The Mo content is more preferably 5.00% or more, further preferably more than 5.00%, and most preferably 6.00% or more.

N: more than 0.100% and not more than 0.400%

N is an element very important for improving the corrosion resistance of austenitic stainless steel. In addition, N has an effect as an austenite stabilizing element. In order to obtain the above effects, the content of N is set to more than 0.100%. The N content is preferably 0.120% or more, and more preferably 0.150% or more. On the other hand, if N is excessively contained, the intergranular corrosion resistance and the workability are deteriorated. Therefore, the N content is set to 0.400% or less. The N content is preferably 0.300% or less, more preferably 0.250% or less.

In the austenitic stainless steel according to the present embodiment, the balance of the elements other than the above elements is Fe and impurities. However, other elements than the above elements may be contained within a range that does not impair the effects of the present embodiment. The impurities mentioned here are components that are mixed by various factors such as raw materials such as ores and scraps, and production processes when the austenitic stainless steel according to the present embodiment is industrially produced, and mean components that can be tolerated within a range that does not adversely affect the present embodiment.

The austenitic stainless steel according to the present embodiment preferably contains, in place of part of Fe, one or more elements selected from Cu: 3.00% or less, W: 2.00% or less and V: 1.00% or less, or 2 or more. Since these elements may not be contained, the lower limit of the content of these elements is 0%.

Cu: 3.00% or less

Cu is an effective element for stabilizing the austenite phase. However, excessive Cu content may reduce the strength of the austenite phase and impair hot workability. Therefore, the Cu content is preferably 3.00% or less. The Cu content is more preferably 2.00% or less. On the other hand, the lower limit is not particularly limited, but the Cu content is preferably 0.10% or more in order to stably obtain the austenite phase stabilization effect of Cu. The Cu content is more preferably 0.50% or more.

W: 2.00% or less

W has the effect of improving corrosion resistance by forming carbonitrides. However, even if W is contained in a large amount, the effect of corrosion resistance is saturated. Therefore, the W content is preferably 2.00% or less. The W content is more preferably 1.00% or less. On the other hand, in order to stably obtain the above-mentioned effect of W, the W content is preferably 0.01% or more. The W content is more preferably 0.05% or more.

V: 1.00% or less

V has the effect of improving corrosion resistance by forming carbonitrides. However, even if V is contained in a large amount, the effect of corrosion resistance is saturated. Therefore, the V content is preferably 1.00% or less. The V content is more preferably 0.50% or less. On the other hand, in order to stably obtain the above-mentioned effects of V, the V content is preferably 0.05% or more. The V content is more preferably 0.10% or more.

In addition, the austenitic stainless steel according to the present embodiment preferably contains, in place of a part of Fe, a component selected from the group consisting of Al: 0.001% or more and 0.3% or less, Ca: 0.001% or more and 0.3% or less, B: 0.0001% or more and 0.1% or less, Ti: 0.001% or more and 0.40% or less, Nb: 0.001% or more and 0.40% or less, Sn: 0.001% or more and 0.5% or less, Zr: 0.001% or more and 0.5% or less, Co: 0.001% or more and 0.5% or less, Mg: 0.001% or more and 0.5% or less, Hf: 0.001% or more and 0.5% or less, REM: 0.001% or more and 0.5% or less, Ta: 0.001% or more and 0.5% or less, Ga: 0.001% or more and 0.5% or less and Sb: 0.001% to 0.5% of 1 or 2 or more. Since these elements may not be contained, the lower limit of the content of these elements is 0%.

Al: 0.001% or more and 0.3% or less

Al is an element having a deoxidizing effect. In order to stably obtain the deoxidation effect of Al, the Al content is preferably 0.001% or more. The Al content is more preferably 0.01% or more. On the other hand, if Al is contained in a large amount, a large amount of nonmetallic inclusions may be produced, which may deteriorate workability and toughness. Therefore, the Al content is preferably 0.3% or less. The Al content is more preferably 0.30% or less, and still more preferably 0.10% or less.

Ca: 0.001% or more and 0.3% or less

Ca is an element effective for deoxidation and improvement of hot workability. In order to stably obtain the above-mentioned effect of Ca, the Ca content is preferably 0.001% or more. The Ca content is more preferably 0.002% or more. On the other hand, if Ca is present excessively, the hot workability is rather deteriorated. Therefore, the Ca content is preferably 0.3% or less. The Ca content is more preferably 0.30% or less, and still more preferably 0.01% or less.

B: 0.0001% or more and 0.1% or less

B is an element for improving hot workability. In order to stably obtain the effect of improving the hot workability of B, the content of B is preferably 0.0001% or more. The content of B is more preferably 0.0002% or more. On the other hand, if B is present excessively, the hot workability is rather deteriorated. Therefore, the B content is preferably 0.1% or less. The B content is more preferably 0.10% or less, and still more preferably 0.001% or less.

Ti: 0.001% or more and 0.40% or less

Ti is an element that forms carbonitride to improve corrosion resistance. Therefore, the Ti content is preferably 0.001% or more. The Ti content is more preferably 0.005% or more. On the other hand, if Ti is contained excessively, the effect is saturated. Therefore, the Ti content is preferably 0.40% or less. The Ti content is more preferably 0.10% or less.

Nb: 0.001% or more and 0.40% or less

Nb is an element that forms carbonitrides to improve corrosion resistance. Therefore, the Nb content is preferably 0.001% or more. The Nb content is more preferably 0.002% or more. On the other hand, if Nb is excessively contained, the effect is saturated. Therefore, the Nb content is preferably 0.40% or less. The Ti content is more preferably 0.10% or less.

Sn: 0.001% or more and 0.5% or less

Sn is an effective element for improving oxidation resistance. In order to stably obtain the effect of improving the oxidation resistance of Sn, the Sn content is preferably 0.001% or more. The Sn content is more preferably 0.01% or more. On the other hand, if Sn is contained excessively, hot workability may be degraded. Therefore, the Sn content is preferably 0.5% or less. The Sn content is more preferably 0.50% or less, and still more preferably 0.10% or less.

Zr: 0.001% or more and 0.5% or less

Zr is an element for improving strength. In order to stably obtain the strength-improving effect of Zr, the Zr content is preferably 0.001% or more. The Zr content is more preferably 0.01% or more. On the other hand, if Zr is present excessively, toughness may be reduced. Therefore, the Zr content is preferably 0.5% or less. The Zr content is more preferably 0.50% or less, and still more preferably 0.10% or less.

Co: 0.001% or more and 0.5% or less

Co is an effective element for improving corrosion resistance. In order to stably obtain the above-mentioned effects of Co, the Co content is preferably 0.001% or more. The content of Co is more preferably 0.01% or more. On the other hand, if Co is present in excess, hardening may occur, and therefore the Co content is preferably 0.5% or less. The Co content is more preferably 0.50% or less, and still more preferably 0.10% or less.

Mg: 0.001% or more and 0.5% or less

Mg is an element effective for deoxidation and improvement of hot workability. In order to stably obtain the above-mentioned effects of Mg, the Mg content is preferably 0.001% or more. The Mg content is more preferably 0.01% or more. On the other hand, excessive Mg content causes a significant increase in manufacturing cost. Therefore, the Mg content is preferably 0.5% or less. The Mg content is more preferably 0.50% or less, and still more preferably 0.10% or less.

Hf: 0.001% or more and 0.5% or less

Hf is an element for improving corrosion resistance. In order to stably obtain the above-mentioned effect of Hf, it is preferable that the Hf content is 0.001% or more. The Hf content is more preferably 0.01% or more. On the other hand, if Hf is excessively contained, workability may be deteriorated. Therefore, the Hf content is preferably 0.5% or less. The Hf content is more preferably 0.50% or less, and still more preferably 0.10% or less.

REM: 0.001% or more and 0.5% or less

REM (rare earth element) is an effective element for deoxidation, improvement of hot workability and corrosion resistance. In order to stably obtain the above-mentioned effects of REM, the REM content is preferably 0.001% or more. The REM content is more preferably 0.01% or more. On the other hand, excessive inclusion of REM causes a significant increase in manufacturing cost. Therefore, the REM content is preferably 0.5% or less. The REM content is more preferably 0.50% or less, and still more preferably 0.10% or less.

REM is two elements of Sc and Y and 15 elements (lanthanoid) from La to Lu, and REM is 1 or more selected from the above elements. When 2 or more elements are contained as REM, the REM content refers to the total amount of the contained elements.

Ta: 0.001% or more and 0.5% or less

Ta forms carbonitride, improving corrosion resistance. In order to stably obtain the above-described effects of Ta, the Ta content is preferably 0.001% or more. The Ta content is more preferably 0.01% or more. On the other hand, even if Ta is excessively contained, the above effect is saturated. Therefore, the Ta content is preferably 0.5% or less. The Ta content is more preferably 0.50% or less, and still more preferably 0.10% or less.

Ga: 0.001% or more and 0.5% or less

Ga is an element contributing to improvement of corrosion resistance and workability. In order to stably obtain the above-mentioned effects of Ga, the Ga content is preferably 0.001% or more. The Ga content is more preferably 0.01% or more. On the other hand, if the Ga content exceeds 0.5%, the above effects are saturated, resulting in only an increase in cost. Therefore, the Ga content is preferably 0.5% or less. The Ga content is more preferably 0.50% or less, and still more preferably 0.10% or less.

Sb: 0.001% or more and 0.5% or less

Sb is an effective element for improving oxidation resistance. In order to stably obtain the oxidation resistance-improving effect of Sb, the Sb content is preferably 0.001% or more. The Sb content is more preferably 0.01% or more. On the other hand, if Sb is contained excessively, hot workability may be degraded. Therefore, the Sb content is preferably 0.5% or less. The Sb content is more preferably 0.50% or less, and still more preferably 0.10% or less.

[ surface Properties ]

The austenitic stainless steel according to the present embodiment has a brightness difference Δ L of 5 or less.

The luminance difference Δ L means a luminance difference in accordance with JIS Z8730: 2009, the difference between the maximum value and the minimum value of the luminance L. For example, when the austenitic stainless steel is plate-shaped, the luminance difference Δ L is a difference between the maximum value and the minimum value of the measured luminance (L value) when the luminance L is continuously measured in the plate width direction orthogonal to the rolling direction. When a part of the sheet width is removed by slitting or the like in order to obtain a target building material, the measurement region of the luminance L is set to a portion excluding the portion to be removed.

The luminance difference Δ L was obtained by equally dividing the rolling direction length into 10 parts, and calculating the luminance difference Δ L' in the sheet width direction at the center position in the rolling direction of each of the 10 segments, and the largest value of the luminance differences Δ L was defined as the luminance difference Δ L.

When the austenitic stainless steel is in the shape of a rod or a tube, the axial length is equally divided into 10 parts, and the brightness L is continuously measured along the circumference at the axial center position of the 10 segments to calculate the brightness difference Δ L'. Then, the largest value among the calculated luminance differences Δ L' is taken as the luminance difference Δ L.

If the luminance difference Δ L is 5 or less, the exterior building material using the same will not be problematic because the appearance unevenness will not be seen or will be very slight. On the other hand, when the luminance difference Δ L exceeds 5, it is very difficult to stably prevent the occurrence of the appearance unevenness even if various finishing treatments such as temper rolling, matte rolling (dull rolling), embossing rolling, and polishing are performed.

The austenitic stainless steel according to the present embodiment may have various shapes such as a thin plate, a thick plate, a wire, and a rod.

The austenitic stainless steel according to the present embodiment is explained so far. The method for producing the austenitic stainless steel sheet according to the present embodiment is not particularly limited, and can be produced, for example, by the following method. Hereinafter, an example of a method for producing the austenitic stainless steel according to the present embodiment will be described.

< method for producing austenitic stainless Steel >

The method for producing an austenitic stainless steel according to the present embodiment includes a steel-making step, a hot-rolling step, an annealing step after hot-rolling, a pickling step of a hot-rolled sheet, a cold-rolling step, an annealing step after cold-rolling, and a final pickling step. The production conditions for the steps other than the final pickling step are not particularly limited, and a known method can be used.

[ Final Pickling Process ]

In the final pickling step, the stainless steel material is immersed in the pickling solution for 10 seconds or more. The pickling solution contains 10-200 g/L sulfuric acid and 5-150 g/L hydrochloric acid, 1 or 2 or more selected from 40g/L hydrofluoric acid, 40g/L fluorosilicic acid and 40g/L sodium fluoride, and ozone with dissolved ozone concentration of 0.5-2.0 mg/L, wherein the total amount of the hydrofluoric acid, the hydrofluoric acid and the sodium fluoride is 1g/L or more, and the balance is water.

The pickling solution contains either or both of sulfuric acid having a concentration of 10 to 200g/L and hydrochloric acid having a concentration of 5 to 150 g/L.

When the pickling solution contains sulfuric acid, if the sulfuric acid concentration is less than 10g/L, it takes a long time to remove the scale on the surface of the stainless steel material. Therefore, when the pickling solution contains sulfuric acid, the sulfuric acid concentration is 10g/L or more. The sulfuric acid concentration is preferably 20g/L or more, more preferably 50g/L or more. On the other hand, if the sulfuric acid concentration exceeds 200g/L, the corrosion by the acid becomes severe, and the surface properties of the stainless steel after pickling deteriorate. Therefore, when the pickling solution contains sulfuric acid, the sulfuric acid concentration is 200g/L or less. The sulfuric acid concentration is preferably 150g/L or less, more preferably 100g/L or less.

When the pickling solution contains hydrochloric acid, if the hydrochloric acid concentration is less than 5g/L, it takes a long time to remove the scale on the surface of the stainless steel material. Therefore, when the pickling solution contains hydrochloric acid, the hydrochloric acid concentration is 5g/L or more. The concentration of hydrochloric acid is preferably 10g/L or more, more preferably 50g/L or more. On the other hand, if the hydrochloric acid concentration exceeds 150g/L, the corrosion by the acid becomes severe, and the surface properties of the stainless steel after pickling deteriorate. Therefore, when the pickling solution contains hydrochloric acid, the hydrochloric acid concentration is 150g/L or less. The concentration of hydrochloric acid is preferably 120g/L or less, more preferably 100g/L or less.

The acid cleaning solution contains 1 or 2 or more selected from hydrofluoric acid having a concentration of 40g/L or less, fluorosilicic acid having a concentration of 40g/L or less, and sodium fluoride having a concentration of 40g/L or less so that the total amount of F is 1g/L or more.

If the concentration of hydrofluoric acid, fluorosilicic acid, or sodium fluoride contained in the pickling solution is less than 1g/L in terms of F in total, it takes a long time to remove the scale on the surface of the stainless steel material. Therefore, when 1 or 2 or more compounds selected from hydrofluoric acid, fluorosilicic acid and sodium fluoride are contained, the concentration of the contained compounds is 1g/L or more in terms of F in total. These concentrations are preferably 5g/L or more, more preferably 10g/L or more in terms of F in total.

On the other hand, if the concentration of hydrofluoric acid, fluorosilicic acid, or sodium fluoride contained in the pickling solution exceeds 40g/L, the effect of removing scale is saturated, leading to an increase in production cost. Therefore, the concentration of hydrofluoric acid, fluorosilicic acid, or sodium fluoride contained in the pickling solution is 40g/L or less, respectively. These concentrations are preferably 30g/L or less, more preferably 20g/L or less.

The pickling solution contains ozone having a dissolved ozone concentration of 0.5 to 2.0 mg/L. Ozone is an oxidizing agent, and uniformly whitens the surface of the pickled austenitic stainless steel. If the dissolved ozone concentration is less than 0.5mg/L, the surface of the austenitic stainless steel after pickling is not uniformly whitened. Therefore, the dissolved ozone concentration is 0.5mg/L or more. The dissolved ozone concentration is preferably 0.8mg/L or more, and more preferably 1.0mg/L or more. On the other hand, if the dissolved ozone concentration exceeds 2.0mg/L, the effect of whitening is saturated. Therefore, the dissolved ozone concentration is 2.0mg/L or less. The dissolved ozone concentration is preferably 1.8mg/L or less, more preferably 1.5mg/L or less.

The method for adjusting the dissolved ozone concentration in the acid washing solution is not particularly limited, and for example, the dissolved ozone concentration may be adjusted by introducing ozone gas into the acid washing solution from below. The dissolved ozone concentration can be measured, for example, using a commercially available dissolved ozone meter.

The immersion time in the pickling solution is 10 seconds or more. If the pickling time is less than 10 seconds, the surface of the austenitic stainless steel after pickling is not uniformly whitened. When the pickling time is excessively long, the pickling solution deteriorates due to dissolution of steel components, and therefore the pickling time is preferably 60 seconds or less, more preferably 20 seconds or less.

Further, nitric acid can also be used as the oxidizing agent in the pickling solution, but when pickling is performed using nitric acid, nitrogen oxides are sometimes generated. Additional equipment and processing is required to treat the nitrogen oxides. Therefore, it is preferable that the pickling solution does not contain a nitric acid solution.

The austenitic stainless steel obtained through the final pickling step has a difference Δ L in brightness of 5 or less, and is beautiful with no variation in appearance. Further, the austenitic stainless steel obtained through the final pickling process has high corrosion resistance because of having the above chemical components.

An example of the method for producing an austenitic stainless steel according to the present embodiment is described above.

Examples

Hereinafter, embodiments of the present invention will be specifically described with reference to examples. The following embodiments are merely examples of the present invention, and the present invention is not limited to the following examples.

First, stainless steel having chemical compositions shown in tables 1A to 1C was melted in a vacuum induction melting furnace, and cast into a cast slab. Then, each cast slab was uniformly heated to 1200 ℃, followed by hot forging and hot rolling, thereby obtaining a hot-rolled sheet of 6 mm. The hot-rolled sheet was annealed and pickled, and then cold-rolled to obtain a cold-rolled sheet having a length of 1m in the rolling direction, a length of 200mm in the width direction, and a thickness of 1 mm. The cold-rolled sheet was subjected to a final pickling step under the conditions shown in tables 1D to 1F, thereby obtaining a stainless steel sheet.

The luminance difference Δ L was calculated as follows. The rolling direction length of the produced stainless steel sheet was equally divided into 10 parts, and the brightness difference Δ L 'in the sheet width direction was calculated at the rolling direction center position of each of the 10 segments, and the maximum value of the calculated brightness differences Δ L' was defined as the brightness difference Δ L. The luminance L required for calculating the luminance difference Δ L is calculated in accordance with JIS Z8730: 2009 was performed. The measurement interval of the luminance L was set to 10 mm.

Further, the appearance evaluation was performed by the following method. The surface of the stainless steel sheet was masked so as to expose 50mm square, and whether or not streaky unevenness was observed at the 50mm square was visually observed. The score 1 was set when unevenness was visible, and the score 0 was set when unevenness was not visible. The above evaluation was performed on 10 places on the surface of the stainless steel sheet, and the evaluation was performed in the total (0 to 10) of the scores. If the total score is 3 or less, the evaluation is very beautiful in practice.

Production conditions and evaluation results are shown in tables 1D to 1F.

The chemical composition of each of the obtained steel sheets was substantially the same as the chemical composition of the raw material of each of the stainless steels. Further, as shown in tables 1D to 1F, the stainless steel sheets according to the present embodiment (inventive examples) were beautiful in appearance.

Although the preferred embodiments of the present invention have been described in detail above, the present invention is not limited to such examples. It is obvious that a person having a basic knowledge in the technical field to which the present invention pertains can conceive various modifications and alterations within the scope of the technical elements described in the claims, and these should be understood as falling within the technical scope of the present invention.

Industrial applicability

The austenitic stainless steel of the present embodiment is suitably used for building materials such as roofs and exterior decorations which require a beautiful appearance.

Claims

1. An austenitic stainless steel, comprising, in mass%:

c: less than 0.100 percent,

Si: less than 3.00 percent,

Mn: 0.01% to 5.00%,

P: less than 0.100 percent,

S: less than 0.0050%,

Ni: 7.00% to 38.00%,

Cr: 17.00% or more and 28.00% or less,

Mo: less than 10.00 percent,

N: more than 0.100% and not more than 0.400%,

the rest part comprises Fe and impurities;

the difference in brightness Δ L on the steel sheet surface is 5 or less.

2. The austenitic stainless steel according to claim 1, wherein 1 or 2 or more elements selected from the following elements are contained in mass% in place of a part of Fe:

cu: less than 3.00 percent,

W: 2.00% or less, and

v: 1.00% or less.

3. The austenitic stainless steel according to claim 1 or 2, wherein 1 or 2 or more elements selected from the following elements are contained in mass% in place of a part of Fe:

al: 0.001% to 0.3%,

Ca: 0.001% to 0.3%,

B: 0.0001% to 0.1%,

Ti: 0.001% to 0.40%,

Nb: 0.001% to 0.40%,

Sn: 0.001% to 0.5%,

Zr: 0.001% to 0.5%,

Co: 0.001% to 0.5%,

Mg: 0.001% to 0.5%,

Hf: 0.001% to 0.5%,

REM: 0.001% to 0.5%,

Ta: 0.001% to 0.5%,

Ga: 0.001% or more and 0.5% or less, and

sb: 0.001% or more and 0.5% or less.