CN114901848B

CN114901848B - Ferritic stainless steel material and corrosion resistant member

Info

Publication number: CN114901848B
Application number: CN202180007523.7A
Authority: CN
Inventors: 河野明训; 森田一成
Original assignee: Nippon Steel and Sumikin Stainless Steel Corp
Current assignee: Nippon Steel Stainless Steel Corp
Priority date: 2020-05-28
Filing date: 2021-04-28
Publication date: 2023-09-19
Anticipated expiration: 2041-04-28
Also published as: KR20220107255A; WO2021241132A1; CN114901848A

Abstract

A ferritic stainless steel material excellent in corrosion resistance, which has the following composition: comprises the following components in mass basis: 0.001 to 0.100 percent of Si: less than 5.00%, mn: less than 2.00%, P: less than 0.050%, S: less than 0.0300%, ni: less than 2.00%, cr: 11.00-30.00%, mo: less than 6.00%, cu: less than 0.60%, N: less than 0.050%, al: less than 3.500%, and the balance of Fe and impurities. The surface of the ferritic stainless steel has an arithmetic average roughness Ra of 0.10-3.00 mu m and a specular gloss Gs (60 DEG) of 10-100%.

Description

Ferritic stainless steel material and corrosion resistant member

Technical Field

The present invention relates to a ferritic stainless steel material and a corrosion resistant member.

Background

Stainless steel materials are used in a wide variety of applications such as automotive parts, architectural parts, and kitchen appliances because of their excellent corrosion resistance and other properties.

Stainless steel is classified into steel plates, steel bars, steel strips, bar steels, steel pipes, and the like according to shape. A stainless steel sheet, which is a general stainless steel material, is manufactured by the following steps. A hot-rolled steel sheet (thick sheet) is obtained by continuously casting a molten iron obtained by melting a raw material of stainless steel to form a slab and hot-rolling the slab. Further, if necessary, a cold-rolled steel sheet (sheet material) can be obtained by cold-rolling a hot-rolled steel sheet. In the production of such a stainless steel material, oxide scale is formed on the surface of the stainless steel material, and therefore, the oxide scale is removed by pickling. Hereinafter, the removal of scale formed on the surface of stainless steel is referred to as "descaling".

However, the scale may not be sufficiently removed only by acid washing. In particular, since the hot rolling is performed at a high heating temperature and for a long period of time, the oxide scale formed on the surface of the stainless steel material is composed of thick and stable oxide, and is difficult to remove.

Then, in a general descaling process, the following method is performed: after cracks are introduced into the scale by mechanical pretreatment using a scale remover, shot blasting, or the like, the scale is easily removed by pickling (for example, patent documents 1 and 2).

Prior art literature

Patent literature

Patent document 1: japanese patent application laid-open No. 2014-172077

Patent document 2: japanese patent laid-open No. 2-145785

Disclosure of Invention

Problems to be solved by the invention

However, in the descaling step described above, the surface of the stainless steel material becomes white and loses gloss due to the surface roughness formed in the mechanical pretreatment and the surface roughness caused by the pickling, and the design property of the pattern is lowered. In particular, since the ferrite stainless steel has a thick oxide scale formed on the surface, cracks are less likely to be induced in the mechanical pretreatment, and uneven pickling is likely to occur. In addition, inIn the case of stainless steel materials containing a large amount of Si or Al, siO is contained in the interface between the scale and the stainless steel material ₂ 、Al ₂ O ₃ Is chemically stable and thus becomes more difficult to remove the scale.

On the other hand, in order to secure the design property of the stainless steel, it is considered to polish the surface after the descaling step, but if the surface is polished to be smooth, the amount of the polishing becomes large, the yield is lowered, and the polishing oil (cooling oil) and the polishing dust remain in the polishing mark, and the corrosion resistance is lowered.

The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a ferritic stainless steel material having a smooth and glossy surface and excellent corrosion resistance, and a corrosion resistant member using the same.

Means for solving the problems

The inventors of the present invention have conducted intensive studies to solve the above-described problems, and as a result, have obtained the following knowledge: by controlling the composition of the ferritic stainless steel material and employing the descaling step using a laser and the subsequent descaling step using an acid wash, the smoothness and gloss of the surface can be improved without deteriorating the corrosion resistance. Based on this knowledge, various ferritic stainless steel materials were produced and studied, and as a result, it was found that: the present invention has been accomplished in view of the above problems, and it is an object of the present invention to provide a ferritic stainless steel material having a predetermined composition and having a surface with an arithmetic average roughness Ra and a specular gloss Gs (60 °) of 60 degrees within predetermined ranges.

That is, the present invention is a ferritic stainless steel material having excellent corrosion resistance, which has the following composition: comprises the following components in mass basis: 0.001 to 0.100 percent of Si: less than 5.00%, mn: less than 2.00%, P: less than 0.050%, S: less than 0.0300%, ni: less than 2.00%, cr: 11.00-30.00%, mo: less than 6.00%, cu: less than 0.60%, N: less than 0.050%, al: less than 3.500%, the balance being Fe and impurities,

the surface has an arithmetic average roughness Ra of 0.10-3.00 mu m and a specular gloss Gs (60 DEG) of 60 DEG of 10-100%.

The present invention also provides a corrosion resistant member comprising the above ferritic stainless steel material.

Effects of the invention

According to the present invention, a ferritic stainless steel material having a smooth and glossy surface and excellent corrosion resistance and a corrosion resistant member using the same can be provided.

Drawings

Fig. 1 is an SEM photograph of the surface of a stainless steel sheet manufactured by performing a laser descaling process and an acid descaling process.

Fig. 2 is a laser microscopic photograph of the surface of a stainless steel sheet manufactured by performing an acid pickling descaling step after performing a pretreatment by shot blasting.

Fig. 3 is a laser microscopic photograph of the surface of a stainless steel sheet manufactured by performing a pickling descaling step after performing a pretreatment by shot blasting, followed by belt polishing.

Detailed Description

Hereinafter, embodiments of the present invention will be described in detail. It should be understood that: the present invention is not limited to the following embodiments, and modifications and the like of the following embodiments are also included in the scope of the present invention, based on the general knowledge of those skilled in the art, without departing from the spirit of the present invention.

In the present specification, "%" expression of a component means "% by mass" unless otherwise specified.

The ferritic stainless steel material according to the embodiment of the present invention has the following composition: comprising C:0.001 to 0.100 percent of Si: less than 5.00%, mn: less than 2.00%, P: less than 0.050%, S: less than 0.0300%, ni: less than 2.00%, cr: 11.00-30.00%, mo: less than 6.00%, cu: less than 0.60%, N: less than 0.050%, al: less than 3.500%, and the balance of Fe and impurities.

In the present specification, "stainless steel" refers to a material made of stainless steel, and the shape thereof is not particularly limited. Examples of the material form include a plate (including a band), a rod, and a tube. The cross-sectional shape may be various types of steel such as T-shape and I-shape. The term "impurities" refers to components that are mixed in by various factors of the production process of raw materials such as ores and scraps in the industrial production of stainless steel, and are allowed in a range that does not adversely affect the present invention. For example, stainless steel may contain not more than 0.02% of an organic impurity. In addition, REM (rare earth element) may be contained in an amount of 0.1% or less in total.

In addition, the ferritic stainless steel material of the embodiment of the present invention may further include a metal selected from the group consisting of Ti:0.001 to 0.500 percent of Nb:0.001 to 1.000 percent, V:0.001 to 1.000 percent, W:0.001 to 1.000 percent of Zr:0.001 to 1.000 percent of Co:0.001 to 1.200% of at least 1 kind.

Further, the ferritic stainless steel material according to the embodiment of the present invention may further include a material selected from the group consisting of Ca: 0.0001-0.0100%, B:0.0001 to 0.0080 percent of Sn:0.001 to 0.500% of more than 1 kind.

The components are described in detail below.

<C：0.001～0.100％>

If the content of C is too large, not only the hardness becomes low and the workability is lowered, but also sensitization occurs when the steel is subjected to heat influence such as welding, and the corrosion resistance of the ferritic stainless steel is lowered. Therefore, the upper limit of the content of C is controlled to 0.100%, preferably 0.060%, more preferably 0.040%, and still more preferably 0.020%. On the other hand, if the content of C is too small, deterioration of workability and increase of refining cost are caused. Therefore, the lower limit of the content of C is controlled to 0.001%, preferably 0.002%, more preferably 0.005%, and even more preferably 0.010%.

< Si:5.00% or less ]

If the Si content is too large, hardening occurs, and the workability of the ferritic stainless steel decreases. Therefore, the upper limit value of the Si content is controlled to 5.00%.

In particular, in the case of a ferritic stainless steel material having a small content of Si and Al (si+2al is less than 1.20%), the upper limit of the content of Si is preferably 1.00%, more preferably 0.80%, still more preferably 0.70%, and most preferably 0.60%. On the other hand, the lower limit of the Si content is not particularly limited, but is preferably 0.01%, more preferably 0.05%, and even more preferably 0.10%.

In the case of a ferritic stainless steel material having a large content of Si and Al (si+2al is 1.20% or more), the upper limit of the content of Si is preferably 4.00%, more preferably 3.00%, and even more preferably 2.50%. On the other hand, the lower limit of the Si content is not particularly limited, but is preferably 0.20%, more preferably 0.40%, even more preferably 1.00%, and most preferably 1.50% from the viewpoint of securing heat resistance of the ferritic stainless steel.

< Mn:2.00% or less ]

Mn is an element for improving heat resistance of a ferritic stainless steel material. However, if the Mn content is too large, the corrosion resistance of the ferritic stainless steel decreases. Further, mn is an austenite phase (γ phase) forming element, and therefore, γ phase (martensite phase at room temperature) is formed at a high temperature, and workability of the ferritic stainless steel decreases. Therefore, the upper limit value of the Mn content is controlled to 2.00%, preferably 1.50%, more preferably 1.20%, and still more preferably 1.00%. On the other hand, the lower limit of the Mn content is not particularly limited, but is preferably 0.01%, more preferably 0.05%, and even more preferably 0.10%.

< P:0.050% or less

If the content of P is too large, the corrosion resistance and workability of the ferritic stainless steel material are lowered. Therefore, the upper limit value of the P content is controlled to 0.050%, preferably 0.035%, more preferably 0.030%, and still more preferably 0.020%. On the other hand, the lower limit of the content of P is not particularly limited, but is preferably 0.001%, more preferably 0.002%, further preferably 0.003%, still further preferably 0.005%, and most preferably 0.010%.

< S:0.0300% or less

If the content of S is too large, hot workability is lowered, and thus the manufacturability of the ferritic stainless steel is lowered, and corrosion resistance is adversely affected. Therefore, the upper limit value of the content of S is controlled to 0.0300%, preferably 0.0100%, more preferably 0.0050%, and even more preferably 0.0010%. On the other hand, the lower limit of the content of S is not particularly limited, but is preferably 0.0001%, more preferably 0.0002%, and even more preferably 0.0003%.

< Ni: less than 2.00%

Ni is an element that improves the corrosion resistance of ferritic stainless steel materials. However, ni is an austenite phase (γ phase) forming element like Mn, and therefore if the content thereof is excessive, γ phase (martensite phase at room temperature) is generated at high temperature, and workability of the ferritic stainless steel decreases. Further, ni is an expensive element, and thus, the manufacturing cost increases. Therefore, the Ni content is controlled to be less than 2.00%, preferably 1.00% or less, more preferably 0.70% or less, still more preferably 0.50% or less, and most preferably 0.35% or less. On the other hand, the lower limit of the Ni content is not particularly limited, but is preferably 0.01%, more preferably 0.03%, and even more preferably 0.05%.

<Cr：11.00～30.00％>

If the Cr content is too large, the refining cost increases, hardening occurs by solid solution strengthening, and the workability of the ferritic stainless steel decreases. Therefore, the upper limit of the Cr content is controlled to 30.00%, preferably 24.00%, more preferably 22.00%, and still more preferably 18.00%. On the other hand, if the Cr content is too small, the corrosion resistance cannot be sufficiently obtained. Therefore, the lower limit of the Cr content is controlled to 11.00%, preferably 13.00%, more preferably 14.00%, and even more preferably 15.00%.

< Mo:6.00% or less ]

Mo is an element that improves the corrosion resistance of ferritic stainless steel materials. Since Mo is expensive, if the content of Mo is too large, the manufacturing cost increases. Therefore, the upper limit value of the Mo content is controlled to 6.00%, preferably 5.00%, more preferably 3.00%, further preferably 2.00%, and most preferably 1.00%. On the other hand, the lower limit value of the Mo content is not particularly limited, but is preferably 0.01%, more preferably 0.03%, still more preferably 0.05%, still more preferably 0.10%, particularly preferably 0.50%, and most preferably 1.00%.

< Cu:0.60% or less ]

Cu is an element that improves workability of a ferritic stainless steel material. If the Cu content is too large, the corrosion resistance of the ferritic stainless steel decreases, and a low-melting phase is formed at the time of casting, resulting in a decrease in hot workability. Therefore, the upper limit of the Cu content is controlled to 0.60%, preferably 0.40%, more preferably 0.20%, and even more preferably 0.10%. On the other hand, the lower limit of the Cu content is not particularly limited, but is preferably 0.01%, more preferably 0.02%, further preferably 0.03%, and most preferably 0.04%.

< N:0.050% or less

N is an element that improves corrosion resistance. If the content of N is too large, hardening occurs, and workability of the ferritic stainless steel decreases. Therefore, the upper limit value of the N content is controlled to 0.050%, preferably 0.040%, more preferably 0.030%, and still more preferably 0.020%. On the other hand, the lower limit of the content of N is not particularly limited, but is preferably controlled to 0.001%, preferably 0.005%, more preferably 0.010%.

< Al:3.500% or less ]

Al is an element that is added as needed to improve corrosion resistance and heat resistance in order to deoxidize in the refining step. If the content of Al is too large, the amount of inclusions produced increases, and the quality is lowered. Therefore, the upper limit value of the Al content is controlled to 3.500%.

In particular, in the case of a ferritic stainless steel material having a small content of Si and Al (si+2al is less than 1.20%), the upper limit of the content of Al is preferably 0.400%, more preferably 0.100%, and still more preferably 0.050%. On the other hand, the lower limit of the Al content is not particularly limited, but is preferably 0.001%, more preferably 0.005%.

In the case of a ferritic stainless steel material having a large content of Si and Al (si+2al is 1.20% or more), the upper limit of the Al content is preferably 3.000%, more preferably 2.000%, and even more preferably 1.500%. On the other hand, the lower limit of the Al content is not particularly limited, but is preferably 0.001%, more preferably 0.010%, and even more preferably 0.100%.

In the case of the ferritic stainless steel according to the embodiment of the present invention, si+2al (each element symbol represents the content of each element) is less than 1.20%, preferably 1.10% or less, more preferably 1.00% or less, and even more preferably 0.90% or less. The lower limit of si+2al is not particularly limited, but is preferably 0.01%, more preferably 0.05%, and even more preferably 0.10%.

In the case of the ferritic stainless steel according to the embodiment of the present invention, si+2al (each element symbol represents the content of each element) is 1.20% or more, preferably 1.30% or more, more preferably 1.50% or more, and even more preferably 2.00% or more. The upper limit of si+2al is not particularly limited, but is preferably 10.00%, more preferably 8.00%, and even more preferably 7.00%.

<Ti：0.001～0.500％>

Ti is an element that is bonded to C, N to improve corrosion resistance and intergranular corrosion resistance, and is added as necessary. The lower limit of the Ti content is controlled to 0.001%, preferably 0.005% from the viewpoint of obtaining the effect by Ti. On the other hand, if the Ti content is too high, it causes surface defects, which results in a decrease in quality, and a decrease in workability of the ferritic stainless steel. Therefore, the upper limit value of the Ti content is controlled to 0.500%, preferably 0.300%, more preferably 0.100%.

<Nb：0.001～1.000％>

Nb is an element that improves corrosion resistance and intergranular corrosion resistance by being bonded to C, N, similarly to Ti, and is added as necessary. From the viewpoint of obtaining the effect by Nb, the lower limit value of the Nb content is controlled to 0.001%, preferably 0.004%, more preferably 0.010%. On the other hand, if the Nb content is too large, the workability of the ferritic stainless steel decreases. Therefore, the upper limit value of the Nb content is controlled to 1.000%, preferably 0.600%, more preferably 0.060%.

<V：0.001～1.000％>

V is an element for improving corrosion resistance, and is added as necessary. From the viewpoint of obtaining the effect by V, the lower limit value of the V content is controlled to 0.001%, preferably 0.010%. On the other hand, if the V content is too large, workability of the ferritic stainless steel decreases. Therefore, the upper limit value of the content of V is controlled to 1.000%, preferably 0.200%.

<W：0.001～1.000％>

W is an element for improving high temperature strength and corrosion resistance, and is added as necessary. From the viewpoint of obtaining the effect by W, the lower limit value of the W content is controlled to 0.001%, preferably 0.010%. On the other hand, if the content of W is too large, hardening occurs to decrease workability, and surface defects increase to decrease the surface quality of the ferritic stainless steel material. Therefore, the upper limit value of the content of W is controlled to 1.000%, preferably 0.300%.

<Zr：0.001～1.000％>

Zr is an element that improves oxidation resistance and intergranular corrosion resistance by bonding with C, N, and is added as necessary. From the viewpoint of obtaining the effect by Zr, the lower limit value of Zr content is controlled to 0.001%, preferably 0.010%. On the other hand, if the Zr content is too large, the workability of the ferritic stainless steel decreases. Accordingly, the upper limit value of the Zr content is controlled to 1.000%, preferably 0.200%, more preferably 0.050%.

<Co：0.001～1.200％>

Co is an element for improving heat resistance, and is added as needed. From the viewpoint of obtaining the effect by Co, the lower limit value of the Co content is controlled to 0.001%, preferably 0.010%. On the other hand, since Co is expensive, if the content of Co is too large, the manufacturing cost increases. Therefore, the upper limit of the Co content is controlled to 1.200%, preferably 0.400%.

<Ca：0.0001～0.0100％>

Ca is an element that forms sulfide to reduce the adverse effect of S, and is added as needed. From the viewpoint of obtaining the effect by Ca, the lower limit value of the Ca content is controlled to 0.0001%, preferably 0.0003%. On the other hand, if the content of Ca is too large, the amount of inclusions produced increases, and the quality is lowered. Therefore, the upper limit of the Ca content is controlled to 0.0100%, preferably 0.0050%.

<B：0.0001～0.0080％>

B is an element for improving hot workability, and is added as needed. From the viewpoint of obtaining the effect by B, the lower limit value of the B content is controlled to 0.0001%, preferably 0.0003%, more preferably 0.0005%. On the other hand, if the content of B is too large, the corrosion resistance of the ferritic stainless steel decreases. Therefore, the upper limit of the content of B is controlled to 0.0080%, preferably 0.0040%, more preferably 0.0025%.

<Sn：0.001～0.500％>

Sn is an element that improves corrosion resistance and high temperature strength, and is added as needed. From the viewpoint of obtaining the effect due to Sn, the lower limit value of the Sn content is controlled to 0.001%, preferably 0.002%. On the other hand, if the Sn content is too large, a low melting point phase is formed and the hot workability of the ferritic stainless steel decreases. Therefore, the upper limit value of the Sn content is controlled to 0.500%, preferably 0.100%, more preferably 0.050%.

The surface of the ferritic stainless steel material according to the embodiment of the present invention has an arithmetic average roughness Ra of 0.10 to 3.00 μm, preferably 0.50 to 2.00 μm, and more preferably 1.00 to 1.90 μm. By controlling the arithmetic average roughness Ra of the surface within such a range, the smoothness of the ferritic stainless steel material can be ensured.

In the present specification, the term "arithmetic average roughness Ra" means a roughness obtained according to JIS B0601:2013, and an arithmetic average roughness Ra measured.

The surface of the ferritic stainless steel material according to the embodiment of the present invention has a specular gloss Gs (60 °) of 10 to 100%, preferably 13 to 70%, and more preferably 15 to 65% at 60 degrees. By controlling the 60-degree specular gloss Gs (60 °) of the surface within such a range, the glossiness of the ferritic stainless steel material can be ensured.

In the present specification, "60-degree specular gloss Gs (60 °)" means that according to JIS Z8741:1997, 60 degrees specular gloss Gs (60 °).

The ferritic stainless steel material according to the embodiment of the present invention has excellent corrosion resistance. In the present specification, "excellent corrosion resistance" means that the rust area ratio is 1% or less when brine is sprayed, dried, and humidified for 10 cycles as 1 cycle in a salt dry-wet repeat test (CCT).

The ferritic stainless steel material according to the embodiment of the present invention preferably has the following (1) and (2) on the surface.

(1) The root mean square inclination rΔq is 35 ° or less, preferably 30 ° or less, and more preferably 25 ° or less. By controlling the root mean square inclination rΔq of the surface within such a range, the gloss of the ferritic stainless steel material can be improved. The lower limit value of the root mean square inclination rΔq is, for example, 3 °.

In the present specification, "root mean square inclination rΔq" means that according to JIS B0601:2013, and a root mean square inclination rΔq measured by 2013.

(2) The chromaticity index b is 7.00 or less, preferably 6.00 or less, and more preferably 5.00 or less. It is known that: the chromaticity index b is a chromaticity index indicating a hue from blue to yellow in the color space of L x a x b, and when a burn (oxide) is formed on the surface by grinding or electrolysis, the stainless steel material becomes a yellowish color. By controlling the chromaticity index b in the above-described range, a ferritic stainless steel material having excellent corrosion resistance without the presence of oxides that act as starting points of corrosion can be obtained. The lower limit value of the chromaticity index b is, for example, 2.00.

In the present specification, the term "chromaticity index b" means a value according to JIS Z8781-6:2017, and the CIE-L a b color space used in the CIE de2000 color difference formula.

The ferritic stainless steel material according to the embodiment of the present invention may further have the following (3) on the surface.

(3) The aspect ratio Str of the texture (texture) is 0.50 or more, preferably 0.60 or more, and more preferably 0.70 or more. By controlling the aspect ratio Str of the texture within such a range, a ferritic stainless steel material having a good appearance without a streak pattern can be obtained. The upper limit value of the aspect ratio Str of the texture is defined as 1, but is, for example, about 0.95.

In the present specification, the term "aspect ratio of texture Str" means a texture according to JIS B0681-2:2018, aspect ratio Str of the texture measured.

The thickness (plate thickness) of the ferritic stainless steel material according to the embodiment of the present invention is not particularly limited, but is preferably 3mm or more.

The ferritic stainless steel material according to the embodiment of the present invention can be produced by using a method known in the art, in addition to the steps of melting the stainless steel having the above-described composition and using a laser descaling (hereinafter, referred to as "laser descaling") step and an acid pickling descaling (hereinafter, referred to as "acid pickling descaling") step as the descaling step. Specifically, stainless steel having the above composition is melted, and a billet is manufactured by forging or casting. Thereafter, the slab is hot rolled, then subjected to a laser descaling step, and then subjected to an acid pickling descaling step. The annealing may be performed before the laser descaling step.

The laser descaling process comprises the following steps: the scale formed on the surface of the ferritic stainless steel material is irradiated with laser light, whereby the scale is vaporized and removed.

The various conditions of the laser descaling process may be adjusted in consideration of the following matters according to the apparatus used.

(kind of laser)

In the case of continuous wave laser, the heat input is excessive and melting of the base material (ferritic stainless steel material) is likely to occur, so that pulse laser is preferable.

(wavelength)

In general, a substance has a wavelength dependence on the reflectance of light, and if a wavelength having a low reflectance is selected, the heat input increases, and evaporation is likely to occur. Therefore, by selecting a wavelength at which the reflectance of the base material is high and the reflectance of the oxide is low, the oxide scale can be selectively removed by evaporation.

(pulse width)

If the pulse width is short, ablation occurs before the heat input with the laser is transferred to the surroundings, and thus the ablation threshold becomes small. However, since the pulse width is mainly determined by the performance of the oscillator, and the device capable of oscillating with a short pulse width is expensive, it is preferable to select a short pulse width within the specification range of the laser descaling device.

(oscillation frequency)

Since the shorter the pulse width is, the higher the oscillation frequency is, and the more the oscillation frequency is, the smaller the gap between pulses at the time of scanning can be, the higher the oscillation frequency is preferably selected within the specification range of the laser descaling device.

(scanning frequency)

The higher the scanning frequency, the faster the processing speed of the production line becomes, but if it is too high, gaps between pulses are generated and the descaling rate decreases. Therefore, the scanning frequency is preferably increased within a range in which the descaling rate can be maintained.

(Beam diameter of laser)

The larger the beam diameter of the laser light, the wider the irradiation range, that is, the range in which the descaling can be performed by one pulse, the better the descaling efficiency, but the lower the energy density (flux) of one pulse. The beam diameter is preferably increased within a range where the flux capable of removing the oxide scale by evaporation is maintained.

(flux)

The scale can be removed by irradiation with a laser beam having a fluence exceeding the ablation threshold of the oxide constituting the scale, but if the fluence is too high, not only the scale but also the base material is removed by evaporation, and hence the base material damage becomes large. Therefore, the flux may be adjusted in consideration of the descaling rate and the base material damage.

The pickling and descaling step is the following steps: the ferrite stainless steel material subjected to the laser descaling step is immersed in an acid bath, whereby the scale that has not been completely removed in the laser descaling step is washed away. The pickling solution used for the pickling bath is not particularly limited, and may be any pickling solution containing nitric acid (HNO ₃ ) Sulfuric acid (H) ₂ SO ₄ ) Hydrofluoric acid (HF), ferric chloride (FeCl) ₃ ) And 1 or more of the components. A typical pickling solution is a mixture of nitric acid and hydrofluoric acid.

Here, as different references showing the surface states, SEM photographs or laser microscope photographs of the surfaces of the following stainless steel plates are shown in fig. 1, 2, and 3, respectively: the method comprises (1) a surface of a stainless steel sheet produced by performing a laser descaling step and an acid descaling step, (2) a surface of a stainless steel sheet produced by performing an acid descaling step after performing a pretreatment by shot blasting, and (3) a surface of a stainless steel sheet produced by performing an acid descaling step after performing a pretreatment by shot blasting and then performing belt grinding.

FIG. 1 is a SEM photograph of the surface of (1) at (a) 100 times and (b) 1000 times. As shown in fig. 1, the stainless steel sheet has a surface structure with many smooth portions, although pulse marks generated by a pulse laser are observed on the surface. Therefore, it becomes possible to control the surface roughness parameter (arithmetic average roughness Ra, etc.), 60-degree specular gloss Gs (60 °), etc. within the above-described range.

FIG. 2 is a laser microscopic photograph (50 times) of the surface of the above-mentioned (2). As shown in fig. 2, the stainless steel sheet has a rough surface structure in which a scratch generated by shot peening and a dissolution mark generated by pickling are mixed. Thus, there is a tendency that: the arithmetic average roughness Ra and the root mean square inclination rΔq become larger, and the 60-degree specular gloss Gs (60 °) becomes smaller.

FIG. 3 is a laser micrograph (50 times) of the surface of the above (3). As shown in fig. 3, the stainless steel sheet has a surface structure having a streak pattern generated by belt grinding. Therefore, the aspect ratio Str of the texture tends to be small.

The ferritic stainless steel material according to the embodiment of the present invention having the above-described characteristics is excellent in corrosion resistance, and therefore can be used as a corrosion resistant member. In particular, since the ferritic stainless steel material has a smooth and glossy surface and is excellent in design property, the ferritic stainless steel material is suitable for corrosion resistant members requiring design property.

Examples

The following examples are given to illustrate the present invention in detail, but the present invention is not limited to these examples.

30kg of stainless steel having the compositions of steel grades A to J shown in Table 1 (the balance being Fe and impurities) was melted by vacuum melting, forged into a billet having a thickness of 30mm, and then heated at 1230℃for 2 hours, and hot-rolled into a hot-rolled steel sheet (ferritic stainless steel sheet) having a thickness of 3mm was obtained. The hot-rolled steel sheet was cut into 50mm (rolling direction) ×50mm (width direction) by cutting, and used in the following examples and comparative examples.

TABLE 1

Example 1

The hot-rolled steel sheet having the composition of steel grade a was subjected to a laser descaling step and an acid pickling descaling step in this order.

The laser descaling step was performed using a commercially available apparatus (LaserClear 50A, manufactured by IHI inspection and measurement, inc.). The hot-rolled steel sheet was set on a movable stage of the apparatus, and was moved at 0.2 m/min in the rolling direction, and simultaneously scanned at a constant speed in the sheet width direction from above the hot-rolled steel sheet, and irradiated with 1 pulse laser. The scan width at each time was set to 25mm. The irradiation conditions of the pulse laser were set as follows.

Wavelength: 1085nm

Pulse width: 100ns

Oscillation frequency: 120kHz

Scanning frequency: 100Hz

Beam diameter of laser: 90 μm

Flux: 6J/cm ²

The pickling and descaling are performed in the following manner: an aqueous hydrofluoric acid/nitric acid solution containing 30g/L hydrofluoric acid and 60g/L nitric acid was kept at 60℃in a constant temperature bath, and after immersing the hot-rolled steel sheet for 90 seconds, immediately water-washed with running water and naturally dried.

Examples 2 to 5

Except that a hot rolled steel sheet having the composition of the steel grade shown in Table 2 was used, the flux of the pulse laser in the laser descaling step was set to 7J/cm ² The procedure was the same as in example 1, except that the catalyst was used.

Example 6

The procedure was as in example 1, except for the following: using a hot-rolled steel sheet having a composition of steel grade F; and pickling to remove scale by maintaining an aqueous hydrofluoric acid nitric acid solution containing 45g/L hydrofluoric acid and 145g/L nitric acid at 50 ℃ in a constant temperature bath, immersing the hot rolled steel sheet for 230 seconds, immediately washing with running water, and naturally drying.

Examples 7 to 10

Except that a hot rolled steel sheet having the composition of the steel grade shown in Table 2 was used, the flux of the pulse laser in the laser descaling step was set to 7J/cm ² The procedure was the same as in example 6, except that the catalyst was used.

Comparative example 1

A hot-rolled steel sheet having the composition of steel grade A was subjected to bending and bending recovery treatment with a bending radius of 50mm by a scale remover and pretreatment by shot blasting treatment using shot (SB-5), and then subjected to an acid pickling descaling step.

The pickling descaling step is performed as follows. First, an aqueous hydrofluoric acid/nitric acid solution containing 50g/L hydrofluoric acid and 150g/L nitric acid was kept at 50℃in a constant temperature bath, and after immersing a hot-rolled steel sheet for 240 seconds, immediately after immersing the steel sheet, the steel sheet was washed with running water and naturally dried. Then, an aqueous hydrofluoric acid/nitric acid solution containing 30g/L hydrofluoric acid and 60g/L nitric acid was kept at 60℃in a constant temperature bath, and after immersing the hot-rolled steel sheet for 90 seconds, immediately after immersing the steel sheet therein, the steel sheet was washed with running water and naturally dried.

Comparative example 2

The hot-rolled steel sheet after the pickling and descaling step obtained in comparative example 1 was subjected to belt polishing using SiC polishing paper (particle size # 400) and a water-soluble polishing oil. The grinding depth was set to a depth of 20 μm from the surface.

Comparative example 3

The same procedure as in comparative example 1 was conducted except that a hot-rolled steel sheet having the composition of steel grade F was used.

Comparative example 4

The hot-rolled steel sheet after the pickling and descaling step obtained in comparative example 3 was subjected to belt polishing using SiC polishing paper (particle size # 400) and a water-soluble polishing oil. The grinding depth was set to a depth of 20 μm from the surface.

The hot rolled steel sheets obtained in the examples and comparative examples were evaluated as follows.

(measurement of surface roughness)

The surface of the hot-rolled steel sheet subjected to the descaling step was subjected to the descaling step according to JIS B0601:2013, the arithmetic average roughness Ra and the root mean square inclination rΔq were measured using a contact surface roughness meter (SURFCOM 2800 manufactured by tokyo precision corporation). In the measurement of the arithmetic average roughness Ra, the reference length was set to 4mm.

Similarly, the surface of the hot rolled steel sheet subjected to the descaling step was subjected to JIS B0681-2:2018, and measuring aspect ratio Str of the texture using a 3D measurement laser microscope (LEXT OLS4100, olympus corporation). The observation magnification at the time of measurement was set to 50 times, and the measurement range was set to 3mm×3mm.

The arithmetic average roughness Ra, the root mean square inclination rΔq, and the aspect ratio Str of the texture were measured at 5 sites other than the range from the end to 5mm, and the average value thereof was used as the evaluation result. The measurement positions are separated by 5mm or more.

(determination of gloss)

The surface of the hot-rolled steel sheet subjected to the descaling step was subjected to the descaling step according to JIS Z8741:1997, 60-degree specular gloss Gs (60 °) was measured using a gloss meter (PG-1M manufactured by Nippon Denshoku industries Co., ltd.). The specular gloss Gs (60 °) at 60 degrees was measured at 5 locations other than the range from the end to 5mm, and the average value was used as the evaluation result. The measurement positions are separated by 5mm or more.

(chromaticity index b:)

The surface of the hot-rolled steel sheet subjected to the descaling step was subjected to JIS Z8722:2009, chromaticity index b was measured using a spectrocolorimeter (CM-700 d, KONICAMINOLTA corporation). The geometry of the measurement was set to c (di: 8 °), the measurement diameter was set to 8mm phi, the field of view was set to 10 °, and a D65 illuminant was used as the illumination light source. The measurement was performed at 5 sites other than the range from the end to 5mm, and the average value was used as the evaluation result.

(Corrosion resistance test)

The corrosion resistance test was performed by repeating the salt spray, dry and wet salt dry and wet repeated tests. The salt dry-wet repeat test is as follows: the hot rolled steel sheet subjected to the descaling step was subjected to 10 cycles of spraying (15 minutes at 35 ℃) of a 5% aqueous NaCl solution, drying (1 hour at a relative humidity of 30% and a temperature of 60 ℃) and wetting (3 hours at a relative humidity of 95% and a temperature of 50 ℃) as 1 cycle. Thereafter, the hot-rolled steel sheet was washed with water and dried, and the rust area ratio of the hot-rolled steel sheet was calculated.

The rust area ratio was calculated by the following procedure. The surface of the hot-rolled steel sheet after the salt dry-wet repeat test was photographed, and the ratio of the area of the rust portion in the range of 25mm×25mm in the center except the end face was determined. The area of the rust portion was determined as follows: the photograph of the surface of the hot-rolled steel sheet was subjected to 2-valued analysis, and after calculating the area of each 1 pixel, the number of pixels of the rusted portion was counted. The rust area ratio was calculated by the following equation.

Rust area ratio (%) =area of rust portion (mm) ² ) Area of the entire observation portion (625 mm) ² )×100

In this evaluation, the rust area ratio was set to be "o" (good corrosion resistance) for 1% or less, and to be "x" (poor corrosion resistance) for more than 1%.

The evaluation results are shown in table 2.

TABLE 2

As shown in table 2, it was confirmed that: the hot-rolled steel sheets of examples 1 to 10 had smooth and glossy surfaces with an arithmetic average roughness Ra of 0.10 to 3.00 μm and a specular gloss Gs (60 DEG) of 60 degrees in the range of 10 to 100%. The hot-rolled steel sheets of examples 1 to 10 also have good corrosion resistance.

In contrast, the hot-rolled steel sheets of comparative examples 1 and 3 had rough and matt surfaces outside the above range of either or both of the arithmetic average roughness Ra and the 60-degree specular gloss Gs (60 °). Further, the hot rolled steel sheets of comparative examples 2 and 4 have insufficient corrosion resistance because they are polished after the pickling descaling step.

As is clear from the above results, according to the present invention, a ferritic stainless steel material having a smooth and glossy surface and excellent corrosion resistance and a corrosion resistant member using the same can be provided.

Claims

1. A ferritic stainless steel material excellent in corrosion resistance, which has the following composition: comprises the following components in mass basis: 0.001 to 0.100 percent of Si: less than 5.00%, mn: less than 2.00%, P: less than 0.050%, S: less than 0.0300%, ni: less than 2.00%, cr: 11.00-30.00%, mo: less than 6.00%, cu: less than 0.60%, N: less than 0.050%, al: less than 3.500%, the balance being Fe and impurities,

the arithmetic average roughness Ra of the surface is 0.10-3.00 mu m, the specular gloss Gs (60 DEG) of 60 DEG is 10-100%,

the surface of the ferritic stainless steel material satisfies the following (2),

(2) The chromaticity index b is 7.00 or less.

2. The ferritic stainless steel product according to claim 1, wherein the surface of the ferritic stainless steel product satisfies the following (1),

(1) The root mean square inclination RΔq is 35 DEG or less.

3. The ferritic stainless steel material according to claim 1 or 2, wherein Si is 1.00% or less, al is 0.400% or less, and si+2al is less than 1.20% on a mass basis.

4. The ferritic stainless steel material according to claim 1 or 2, wherein Si is 0.20 to 5.00% and si+2al is 1.20% or more by mass.

5. The ferritic stainless steel according to any one of claims 1 to 4, further comprising, on a mass basis, a metal selected from the group consisting of Ti:0.001 to 0.500 percent of Nb:0.001 to 1.000 percent, V:0.001 to 1.000 percent, W:0.001 to 1.000 percent of Zr:0.001 to 1.000 percent of Co:0.001 to 1.200% of at least 1 kind.

6. The ferritic stainless steel according to any one of claims 1 to 5, further comprising, on a mass basis, a metal selected from the group consisting of Ca: 0.0001-0.0100%, B:0.0001 to 0.0080 percent of Sn:0.001 to 0.500% of more than 1 kind.

7. The ferritic stainless steel material according to any one of claims 1 to 6, wherein a rust area ratio after 10 cycles of spraying, drying and wetting brine as 1 cycle in a salt dry-wet repeat test is 1% or less.

8. A corrosion resistant member comprising the ferritic stainless steel material according to any one of claims 1 to 7.