WO2021241132A1

WO2021241132A1 - Ferrite-based stainless steel material and corrosion resistant member

Info

Publication number: WO2021241132A1
Application number: PCT/JP2021/017109
Authority: WO
Inventors: 明訓河野; 一成森田
Original assignee: 日鉄ステンレス株式会社
Priority date: 2020-05-28
Filing date: 2021-04-28
Publication date: 2021-12-02
Also published as: CN114901848B; CN114901848A; KR20220107255A

Abstract

This ferrite-based stainless steel material has a compositional makeup including, in mass basis, 0.001-0.100% of C, not more than 5.00% of Si, not more than 2.00% of Mn, not more than 0.050% of P, not more than 0.0300% of S, less than 2.00% of Ni, 11.00-30.00% of Cr, not more than 6.00% of Mo, not more than 0.60% of Cu, not more than 0.050% of N, and not more than 3.500% of Al, the remaining portion being Fe and impurities, and has excellent corrosion resistance. The surface of the ferrite-based stainless steel material has an arithmetic mean roughness Ra of 0.10-3.00 μm and a 60-degree specular gloss Gs (60°) of 10-100%.

Description

Ferritic stainless steel and corrosion resistant members

The present invention relates to ferritic stainless steel materials and corrosion resistant members.

Since stainless steel has excellent corrosion resistance and other properties, it is used in a wide range of applications such as automobile parts, building parts, and kitchen utensils.
Stainless steel materials are classified into steel plates, strips, strips, steel bars, steel pipes, etc. according to their shapes. A stainless steel sheet, which is a general stainless steel material, is manufactured by the following process. A hot-rolled steel plate (thick plate material) can be obtained by continuously casting hot metal in which a raw material of stainless steel is melted into a slab and hot-rolling the slab. Further, if necessary, a cold-rolled steel sheet (thin plate material) can be obtained by cold-rolling the hot-rolled steel sheet. In the production of such a stainless steel material, an oxide scale is formed on the surface of the stainless steel material, so that the oxide scale is removed by pickling. Hereinafter, removing the oxide scale formed on the surface of the stainless steel material is referred to as "descale".

However, it may not be possible to sufficiently remove the oxidation scale only by pickling. In particular, in hot rolling, the heating temperature is high and the heating time is long, so that the oxide scale formed on the surface of the stainless steel material is composed of a thick and stable oxide and is difficult to remove.
Therefore, in a general descale process, a method is performed in which mechanical pretreatment such as a scale breaker or shot blast is performed to crack the oxide scale, and then pickling is performed to facilitate removal of the oxide scale. (For example, Patent Documents 1 and 2).

Japanese Unexamined Patent Publication No. 2014-172007 Japanese Unexamined Patent Publication No. 2-145785

However, in the above-mentioned descale process, the surface of the stainless steel material becomes white and loses its luster due to the unevenness of the surface formed by the mechanical pretreatment and the rough surface due to pickling, and the design is deteriorated. In particular, since the ferritic stainless steel material has a thick oxide scale formed on the surface, it is difficult to make cracks by mechanical pretreatment, and uneven pickling is likely to occur. Further, in the case of a stainless steel material having a high content of Si and Al, the _{internal oxide layer containing SiO 2} and Al ₂ O ₃ formed at the interface between the oxide scale and the stainless steel material is chemically stable, so that the oxide scale is formed. It becomes even more difficult to remove.
On the other hand, in order to ensure the design of the stainless steel material, it is conceivable to polish the surface after the above descaling step, but if the surface is polished until it becomes smooth, the amount of grinding increases, the yield decreases, and polishing is performed. Grinding oil (cooling oil) and polishing debris may remain in the eyes and the corrosion resistance may decrease.

The present invention has been made to solve the above problems, and 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. The purpose.

As a result of diligent research to solve the above problems, the present inventors control the composition of the ferrite stainless steel material and adopt a descale process using a laser and a subsequent descale process by pickling. As a result, it was found that the smoothness and glossiness of the surface can be improved without lowering the corrosion resistance. As a result of producing various ferrite stainless steel materials based on this finding and examining them, the arithmetic average roughness Ra and 60 degree mirror surface gloss Gs (60 °) of the surface having a predetermined composition are in a predetermined range. We have found that the ferritic stainless steel material in the above can solve the above-mentioned problems, and have completed the present invention.

That is, in the present invention, C: 0.001 to 0.100%, Si: 5.00% or less, Mn: 2.00% or less, P: 0.050% or less, S: 0.0300 on a mass basis. % Or less, Ni: less than 2.00%, Cr: 11.00 to 30.00%, Mo: 6.00% or less, Cu: 0.60% or less, N: 0.050% or less, Al: 3. It contains less than 500% and has a composition with the balance consisting of Fe and impurities.
A ferrite-based stainless steel material having an arithmetic average roughness Ra of the surface of 0.10 to 3.00 μm and a 60-degree mirror surface gloss Gs (60 °) of 10 to 100%, and having excellent corrosion resistance.

Further, the present invention is a corrosion resistant member containing the above-mentioned ferritic stainless steel material.

According to the present invention, it is possible 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.

It is an SEM photograph of the surface of the stainless steel plate manufactured by carrying out the laser descaling process and the pickling descaling process. 6 is a photomicrograph of the surface of a stainless steel sheet manufactured by performing a pickling descaling step after pretreatment by shot blasting. It is a laser micrograph of the surface of the stainless steel sheet manufactured by performing the pickling descale process after performing the pretreatment by the shot blasting process, and then performing the belt polishing.

Hereinafter, embodiments of the present invention will be specifically described. The present invention is not limited to the following embodiments, and changes, improvements, etc. have been appropriately added to the following embodiments based on the ordinary knowledge of those skilled in the art, without departing from the spirit of the present invention. It should be understood that things also fall within the scope of the present invention.
In addition, in this specification, "%" notation about a component means "mass%" unless otherwise specified.

The ferrite stainless steel material according to the embodiment of the present invention has C: 0.001 to 0.100%, Si: 5.00% or less, Mn: 2.00% or less, P: 0.050% or less, S: 0.0300% or less, Ni: less than 2.00%, Cr: 11.00 to 30.00%, Mo: 6.00% or less, Cu: 0.60% or less, N: 0.050% or less, Al : Contains 3.500% or less, and has a composition in which the balance is composed of Fe and impurities.
Here, the term "stainless steel material" as used herein means a material formed of stainless steel, and the material shape thereof is not particularly limited. Examples of the material shape include a plate shape (including a strip shape), a rod shape, a tubular shape, and the like. Further, various shaped steels having a cross-sectional shape such as T-shaped or I-shaped may be used. Further, the "impurity" is a component mixed with raw materials such as ore and scrap and various factors in the manufacturing process when the stainless steel material is industrially manufactured, and is permissible as long as it does not adversely affect the present invention. Means what is done. For example, the stainless steel material may contain 0.02% or less of О as an impurity. Further, REM (rare earth element) may be contained in a total of 0.1% or less.

Further, the ferrite-based stainless steel material according to the embodiment of the present invention has Ti: 0.001 to 0.500%, Nb: 0.001 to 1.000%, V: 0.001 to 1.000%, W :. It can further contain one or more selected from 0.001 to 1.000%, Zr: 0.001 to 1.000%, and Co: 0.001 to 1.200%.
Further, the ferritic stainless steel material according to the embodiment of the present invention is selected from Ca: 0.0001 to 0.0100%, B: 0.0001 to 0.0080%, and Sn: 0.001 to 0.500%. Can further include one or more species.
Hereinafter, each component will be described in detail.

<C: 0.001 to 0.100%>
If the content of C is too large, it becomes hard and the workability is lowered, and sensitization occurs when it is affected by heat such as welding, and the corrosion resistance of the ferritic stainless steel material is lowered. Therefore, the upper limit of the C content is controlled to 0.100%, preferably 0.060%, more preferably 0.040%, and even more preferably 0.020%. On the other hand, if the content of C is too small, it leads to deterioration of workability and an increase in refining cost. Therefore, the lower limit of the C content 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 high, it will become hard and the workability of the ferritic stainless steel will deteriorate. Therefore, the upper limit of the Si content is controlled to 5.00%.
In particular, in the case of a ferrite stainless steel material having a low content of Si and Al (Si + 2Al is less than 1.20%), the upper limit of the Si content is preferably 1.00%, more preferably 0.80. %, More preferably 0.70%, 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%.
Further, in the case of a ferrite stainless steel material having a high content of Si and Al (Si + 2Al is 1.20% or more), the upper limit of the Si content is preferably 4.00%, more preferably 3.00. %, 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%, still more preferably 1.00, from the viewpoint of ensuring the heat resistance of the ferritic stainless steel material. %, Most preferably 1.50%.

<Mn: 2.00% or less>
Mn is an element that improves the heat resistance of ferritic stainless steel materials. However, if the Mn content is too high, the corrosion resistance of the ferritic stainless steel material will deteriorate. Further, since Mn is an austenite phase (γ phase) forming element, a γ phase (martensite phase at room temperature) is generated at a high temperature, and the processability of the ferritic stainless steel material is also deteriorated. Therefore, the upper limit of the Mn content is controlled to 2.00%, preferably 1.50%, more preferably 1.20%, and even 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 will deteriorate. Therefore, the upper limit of the P content is controlled to 0.050%, preferably 0.035%, more preferably 0.030%, and even 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%, still more preferably 0.003%, still more preferably 0.005%, and most preferably. Is 0.010%.

<S: 0.0300% or less>
If the content of S is too large, the hot workability is lowered, the manufacturability of the ferritic stainless steel material is lowered, and the corrosion resistance is also adversely affected. Therefore, the upper limit of the S content 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 S content 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, since Ni is an austenite phase (γ phase) forming element like Mn, if its content is too large, γ phase (martensite phase at room temperature) is generated at high temperature, and ferritic stainless steel is processed. The sex is reduced. Moreover, since Ni is an expensive element, it also leads to an increase in manufacturing cost. 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. Will be done. 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 to 30.00%>
If the Cr content is too high, the refining cost will increase and the solid solution will be strengthened to harden the ferritic stainless steel material, resulting in a decrease in workability. Therefore, the upper limit of the Cr content is controlled to 30.00%, preferably 24.00%, more preferably 22.00%, and even more preferably 18.00%. On the other hand, if the Cr content is too small, sufficient corrosion resistance cannot be 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 high, the manufacturing cost will increase. Therefore, the upper limit 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 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. Is 0.50%, most preferably 1.00%.

<Cu: 0.60% or less>
Cu is an element that improves the workability of ferritic stainless steel materials. If the Cu content is too high, the corrosion resistance of the ferritic stainless steel material will decrease, and a low melting point phase will be formed during casting, leading to 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%, still more 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, it becomes hard and the processability of the ferritic stainless steel material deteriorates. Therefore, the upper limit of the N content is controlled to 0.050%, preferably 0.040%, more preferably 0.030%, and even 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%, and more preferably 0.010%.

<Al: 3.500% or less>
Al is an element that is added as needed for deoxidation in the refining process and improves corrosion resistance and heat resistance. If the Al content is too high, the amount of inclusions produced increases and the quality deteriorates. Therefore, the upper limit of the Al content is controlled to 3.500%.
In particular, in the case of a ferrite stainless steel material having a low 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. %, 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%.
Further, in the case of a ferrite stainless steel material having a high 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%. %, 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%.

When the ferritic stainless steel material according to the embodiment of the present invention is intended for a material having a low content of Si and Al, Si + 2Al (each element symbol represents the content of each element) is less than 1.20%. It is preferably 1.10% or less, more preferably 1.00% or less, and further 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%.
Further, when the ferritic stainless steel material according to the embodiment of the present invention is intended for a material having a large content of Si and Al, 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, still 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 to 0.500%>
Ti is an element that binds to C and N to improve corrosion resistance and intergranular corrosion resistance, and is added as necessary. From the viewpoint of obtaining the effect of Ti, the lower limit of the Ti content is controlled to 0.001%, preferably 0.005%. On the other hand, if the Ti content is too high, it causes surface defects and causes quality deterioration, and the processability of the ferritic stainless steel material is deteriorated. Therefore, the upper limit of the Ti content is controlled to 0.500%, preferably 0.300%, and more preferably 0.100%.

<Nb: 0.001 to 1.000%>
Like Ti, Nb is an element that binds to C and N to improve corrosion resistance and intergranular corrosion resistance, and is added as necessary. From the viewpoint of obtaining the effect of Nb, the lower limit of the content of Nb is controlled to 0.001%, preferably 0.004%, and more preferably 0.010%. On the other hand, if the content of Nb is too large, the processability of the ferritic stainless steel material will deteriorate. Therefore, the upper limit of the Nb content is controlled to 1.000%, preferably 0.600%, and more preferably 0.060%.

<V: 0.001 to 1.000%>
V is an element that improves corrosion resistance and is added as needed. From the viewpoint of obtaining the effect of V, the lower limit of the content of V is controlled to 0.001%, preferably 0.010%. On the other hand, if the V content is too large, the processability of the ferritic stainless steel material will deteriorate. Therefore, the upper limit of the V content is controlled to 1.000%, preferably 0.200%.

<W: 0.001 to 1.000%>
W is an element that improves high temperature strength and corrosion resistance, and is added as necessary. From the viewpoint of obtaining the effect of W, the lower limit of the content of W is controlled to 0.001%, preferably 0.010%. On the other hand, if the content of W is too large, it becomes hard and the workability is deteriorated, and surface defects are increased, so that the surface quality of the ferritic stainless steel material is deteriorated. Therefore, the upper limit of the W content is controlled to 1.000%, preferably 0.300%.

<Zr: 0.001 to 1.000%>
Zr is an element that binds to C and N to improve oxidation resistance and intergranular corrosion resistance, and is added as necessary. From the viewpoint of obtaining the effect of Zr, the lower limit of the Zr content is controlled to 0.001%, preferably 0.010%. On the other hand, if the Zr content is too large, the processability of the ferritic stainless steel material will deteriorate. Therefore, the upper limit of the Zr content is controlled to 1.000%, preferably 0.200%, and more preferably 0.050%.

<Co: 0.001 to 1.200%>
Co is an element that improves heat resistance and is added as needed. From the viewpoint of obtaining the effect of Co, the lower limit 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 will increase. Therefore, the upper limit of the Co content is controlled to 1.200%, preferably 0.400%.

<Ca: 0.0001 to 0.0100%>
Ca is an element that forms sulfides and reduces the adverse effects of S, and is added as necessary. From the viewpoint of obtaining the effect of Ca, the lower limit of the Ca content is controlled to 0.0001%, preferably 0.0003%. On the other hand, if the Ca content is too high, the amount of inclusions produced increases and the quality deteriorates. Therefore, the upper limit of the Ca content is controlled to 0.0100%, preferably 0.0050%.

<B: 0.0001 to 0.0080%>
B is an element that improves hot workability and is added as needed. From the viewpoint of obtaining the effect of B, the lower limit of the content of B is controlled to 0.0001%, preferably 0.0003%, and more preferably 0.0005%. On the other hand, if the content of B is too large, the corrosion resistance of the ferritic stainless steel material will deteriorate. Therefore, the upper limit of the B content is controlled to 0.0080%, preferably 0.0040%, and more preferably 0.0025%.

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

The ferrite-based stainless steel material according to the embodiment of the present invention has a surface 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. be. 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.
Here, the "arithmetic mean roughness Ra" in the present specification means the arithmetic mean roughness Ra measured in accordance with JIS B0601: 2013.

The ferrite-based stainless steel material according to the embodiment of the present invention has a surface surface gloss of 60 ° Gs (60 °) of 10 to 100%, preferably 13 to 70%, and more preferably 15 to 65%. By controlling the 60-degree mirror surface gloss Gs (60 °) of the surface within such a range, the glossiness of the ferritic stainless steel material can be ensured.
Here, in the present specification, "60 degree mirror surface gloss Gs (60 °)" means 60 degree mirror surface gloss Gs (60 °) measured in accordance with JIS Z8741: 1997.

The ferritic stainless steel material according to the embodiment of the present invention has excellent corrosion resistance. Here, "excellent in corrosion resistance" in the present specification means that the rusting area ratio is 1% or less when 10 cycles of salt spraying, drying and wetting are performed as one cycle in the salt-dry-wet repeat test (CCT). Means that.

The surface of the ferritic stainless steel material according to the embodiment of the present invention preferably satisfies the following (1) and (2).
(1) The root mean square slope RΔq is 35 ° or less, preferably 30 ° or less, and more preferably 25 ° or less. By controlling the root mean square slope RΔq of the surface in such a range, the gloss of the ferritic stainless steel material can be improved. The lower limit of the root mean square slope RΔq is, for example, 3 °.
Here, the “root mean square slope RΔq” in the present specification means the root mean square slope RΔq measured in accordance with JIS B0601: 2013.

(2) The chromanetics index b ^* is 7.00 or less, preferably 6.00 or less, and more preferably 5.00 or less. The chromatics index b ^* is a chromatics index that indicates the chromaticity from blue to yellow in the L ^* a ^* b ^* color space, and is made of stainless steel when a burn (oxide) is formed on the surface by polishing or electrolysis. It is known that steel materials have a yellowish tint. By controlling the chromatic index b ^* within the above range, it is possible to obtain a ferritic stainless steel material having good corrosion resistance in which an oxide that is a starting point of corrosion does not exist. The lower limit of the chromatics index b ^* is, for example, 2.00.
Here, the “ ^{chromanetics index b *} ^{” as used herein means the CIE-L *} a ^* b ^* chromanetics index b in the color space used in the CIEDE2000 color difference formula measured in accordance with JIS Z8781-6: 2017. ^* Means.

The surface of the ferritic stainless steel material according to the embodiment of the present invention may further satisfy the following (3).
(3) The aspect ratio Str of the 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 in such a range, it is possible to obtain a ferritic stainless steel material having a good appearance without streaks. The upper limit of the aspect ratio Str of the texture is 1 from the definition, but is, for example, about 0.95.
Here, the “texture aspect ratio Str” as used herein means the texture aspect ratio Str measured in accordance with JIS B0661-2: 2018.

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 3 mm or more.

The ferrite-based stainless steel material according to the embodiment of the present invention is used by melting stainless steel having the above composition, and as a descaling step, a descaling step using a laser (hereinafter referred to as “laser descaling”) and an acid. It can be produced by using a method known in the art, except that the step of descaling by washing (hereinafter referred to as “pickling descaling”) is adopted. Specifically, stainless steel having the above composition is melted and forged or cast to produce steel pieces. After that, the steel pieces may be hot-rolled, and then a laser descaling step and then a pickling descaling step may be carried out. Annealing may be appropriately performed before the laser descaling step.

The laser descaling step is a step of evaporating and removing the oxide scale by irradiating the oxide scale formed on the surface of the ferritic stainless steel material with a laser beam.
Various conditions of the laser descaling process may be adjusted in consideration of the following items according to the apparatus to be used.

(Type of laser)
A continuous wave laser is preferable because the heat input is too large and the base material (ferritic stainless steel material) is likely to melt.
(wavelength)
In general, the reflectance of a substance to light has a wavelength dependence, and if a wavelength having a low reflectance is selected, heat input increases and transpiration is likely to occur. Therefore, the oxidation scale can be selectively transpired and removed by selecting a wavelength having a high reflectance of the base material and a low reflectance of the oxide.
(pulse width)
If the pulse width is short, ablation occurs before the heat input by the laser is transmitted to the surroundings, so that the ablation threshold becomes small. However, the pulse width is mainly determined by the performance of the oscillator, and a device capable of oscillating with a short pulse width is expensive. Therefore, it is preferable to select a short pulse width within the specification range of the laser descale equipment.
(Oscillation frequency)
The shorter the pulse width, the higher the oscillation frequency, and the higher the oscillation frequency, the smaller the gap between the pulses when scanning can be made. Therefore, it is preferable to select a high oscillation frequency within the specification range of the laser descale equipment.

(Scan frequency)
The higher the scan frequency, the faster the line processing speed, but if it is too high, gaps between pulses will occur and the descale rate will decrease. Therefore, it is preferable to increase the scan frequency within a range in which the descale rate can be maintained.
(Laser beam diameter)
The larger the value, the wider the irradiation range, that is, the range that can be descaled by one pulse, and the descale efficiency is improved, but the energy density (fluence) of one pulse is lowered. It is preferable to increase the beam diameter within a range in which the fluence capable of transpiration removal of the scale is maintained.
(Fruence)
Oxidation scale can be evaporated and removed by irradiating a laser beam with fluence exceeding the ablation threshold of the oxides constituting the scale, but if the fluence is set too high, not only the scale but also the base metal is evaporated and removed. Material damage will increase. Therefore, the fluence may be adjusted in consideration of the descale rate and the damage to the base metal.

The pickling descaling step is a step of immersing the ferritic stainless steel material that has undergone the laser descaling step in a pickling bath to wash off the oxide scale that could not be completely removed by the laser descaling step. The pickling solution used in the pickling bath is not particularly limited, but includes one component such as _{nitric acid (HNO 3} ), sulfuric acid (H ₂ SO ₄ ), hydrofluoric acid (HF), and ferric chloride (FeCl _3). A solution containing the above can be used. A typical pickling solution is a mixture of nitric acid and hydrofluoric acid.

Here, as a reference showing the difference in surface condition, (1) the surface of the stainless steel plate manufactured by performing the laser descaling step and the pickling descaling step, and (2) pickling after performing the pretreatment by the shot blasting treatment. SEM photograph of the surface of the stainless steel plate manufactured by performing the descaling process and (3) the surface of the stainless steel plate manufactured by performing the pickling descaling process after pretreatment by shot blasting and then belt polishing. Alternatively, laser micrographs are shown in FIGS. 1, 2 and 3, respectively.
FIG. 1 is an SEM photograph of (a) 100 times and (b) 1000 times the surface of the above (1). As shown in FIG. 1, this stainless steel sheet has a surface structure having many smooth portions, although pulse marks due to a pulse laser are seen on the surface. Therefore, it is possible to control the surface roughness parameter (arithmetic mean roughness Ra, etc.), 60 degree mirror surface gloss Gs (60 °, etc.) within the above range.

FIG. 2 is a laser micrograph (50 times) of the surface of the above (2). As shown in FIG. 2, this stainless steel sheet has a rough surface structure in which impact marks due to shot blasting treatment and dissolution marks due to pickling are mixed. Therefore, the arithmetic mean roughness Ra and the root mean square slope RΔq tend to be large, and the 60-degree mirror surface gloss Gs (60 °) tends to be small.
FIG. 3 is a laser micrograph (50 times) of the surface of the above (3). As shown in FIG. 3, this stainless steel sheet has a surface structure having a streak pattern by belt polishing. Therefore, the aspect ratio Str of the texture tends to be small.

The ferrite-based stainless steel material according to the embodiment of the present invention having the above-mentioned characteristics is excellent in corrosion resistance, and therefore can be used as a corrosion-resistant member. In particular, this ferritic stainless steel material has a smooth and glossy surface and is excellent in designability, and is therefore suitable for use in corrosion-resistant members that require designability.

Hereinafter, the contents of the present invention will be described in detail with reference to examples, but the present invention is not limited to these.

30 kg of stainless steel having the composition of steel grades A to J shown in Table 1 (the balance is Fe and impurities) is melted by vacuum melting, forged into a steel piece having a thickness of 30 mm, and then heated at 1230 ° C. for 2 hours. , Hot-rolled to a thickness of 3 mm to obtain a hot-rolled steel sheet (ferrite-based stainless steel sheet). The hot-rolled steel sheet was cut into 50 mm (rolling direction) × 50 mm (width direction) by cutting, and used in each of the following Examples and Comparative Examples.

(Example 1)
A laser descaling step and a pickling descaling step were sequentially carried out on the hot-rolled steel sheet having the composition of steel type A.
The laser descaling step was performed using a commercially available device (LaserClear 50A manufactured by IHI Corporation). A hot-rolled steel sheet is installed on the movable stage of this device, and while moving at 0.2 m / min along the rolling direction, it is scanned from above the hot-rolled steel sheet at a constant speed in the plate width direction and irradiated with a pulse laser once. bottom. The scan width per scan was 25 mm. The irradiation conditions of the pulse laser were as follows.
Wavelength: 1085 nm
Pulse width: 100ns
Oscillation frequency: 120kHz
Scan frequency: 100Hz
Laser beam diameter: 90 μm
Fluence: 6J / cm ²
For pickling descale, an aqueous solution of hydrofluoric acid containing 30 g / L of hydrofluoric acid and 60 g / L of nitric acid is kept at 60 ° C. in a constant temperature bath, the hot-rolled steel sheet is immersed for 90 seconds, and then immediately washed with running water and air-dried. I went by that.

(Examples 2 to 5)
The same procedure as in Example 1 was carried out except that a hot-rolled steel sheet having the composition of the steel type shown in Table 2 was used and the fluence of the pulse laser in the laser descaling step was set to 7 J / cm ^2.

(Example 6)
After using a hot-rolled steel sheet having the composition of steel type F, and holding a hydrofluoric acid aqueous solution containing 45 g / L of hydrofluoric acid and 145 g / L of nitric acid at 50 ° C. in a constant temperature bath, the hot-rolled steel sheet was immersed for 230 seconds. The same procedure as in Example 1 was carried out except that the pickling descale was immediately washed with running water and naturally dried.

(Examples 7 to 10)
The same procedure as in Example 6 was carried out except that a hot-rolled steel sheet having the composition of the steel type shown in Table 2 was used and the fluence of the pulse laser in the laser descaling step was set to 7 J / cm ^2.

(Comparative Example 1)
A hot-rolled steel sheet having the composition of steel type A is subjected to bending and unbending treatment with a bending radius of 50 mm by a scale breaker, and pretreatment by shot blasting using steel shot (SB-5), and then acid. A washing descale process was carried out.
The pickling descaling step was carried out as follows. First, an aqueous solution of hydrofluoric acid containing 50 g / L of hydrofluoric acid and 150 g / L of nitric acid was kept at 50 ° C. in a constant temperature bath, the hot-rolled steel sheet was immersed for 240 seconds, and then immediately washed with running water and air-dried. Next, an aqueous solution of hydrofluoric acid containing 30 g / L of hydrofluoric acid and 60 g / L of nitric acid was kept at 60 ° C. in a constant temperature bath, the hot-rolled steel sheet was immersed for 90 seconds, and then immediately washed with running water and air-dried.

(Comparative Example 2)
The hot-rolled steel sheet after the pickling descaling step obtained in Comparative Example 1 was subjected to belt polishing using SiC abrasive paper (count # 400) and water-soluble grinding oil. The grinding depth was 20 μm from the surface.

(Comparative Example 3)
The same procedure as in Comparative Example 1 was carried out except that a hot-rolled steel sheet having a composition of steel type F was used.

(Comparative Example 4)
The hot-rolled steel sheet obtained in Comparative Example 3 after the pickling descaling step was subjected to belt polishing using SiC abrasive paper (count # 400) and water-soluble grinding oil. The grinding depth was 20 μm from the surface.

The following evaluations were performed on the hot-rolled steel sheets obtained in the above Examples and Comparative Examples.

(Measurement of surface roughness)
Arithmetic mean roughness Ra and root mean square root of the surface of the above hot-rolled steel plate subjected to the descale process using a contact-type surface roughness meter (Surfcom 2800 manufactured by Tokyo Precision Co., Ltd.) in accordance with JIS B0601: 2013. The slope RΔq was measured. In the measurement of the arithmetic mean roughness Ra, the reference length was set to 4 mm.
Similarly, on the surface of the above-mentioned hot-rolled steel sheet subjected to the descaling step, the aspect ratio Str of the texture was measured using a 3D measuring laser microscope (LEXT OLS4100 manufactured by Olympus Corporation) in accordance with JIS B0681-2: 2018. .. The observation magnification at the time of measurement was 50 times, and the measurement range was 3 mm × 3 mm.
The arithmetic mean roughness Ra, the root mean square slope RΔq, and the aspect ratio Str of the texture were measured at five points excluding the range from the end to 5 mm, and the average value was used as the evaluation result. The distance between the measurement positions was 5 mm or more.

(Gloss measurement)
For the surface of the above hot-rolled steel sheet that has undergone the descale process, 60 degree mirror gloss Gs (60 °) was measured using a gloss meter (PG-1M manufactured by Nippon Denshoku Industries Co., Ltd.) in accordance with JIS Z8741: 1997. It was measured. The 60-degree mirror gloss Gs (60 °) was measured at 5 points excluding the range from the end to 5 mm, and the average value was used as the evaluation result. The distance between the measurement positions was 5 mm or more.

(Chromanetic index b ^* )
^{The chromanetics index b *} was measured on the surface of the hot-rolled steel sheet subjected to the descaling step using a spectrophotometer (CM-700d manufactured by Konica Minolta Co., Ltd.) in accordance with JIS Z 8722: 2009. The geometric conditions of the measurement were c (di: 8 °), the measurement diameter was 8 mmφ, the field of view was 10 °, and the D65 illuminant was used as the illumination light source. Measurements were performed at 5 points excluding the range from the end to 5 mm, and the average value was used as the evaluation result.

(Corrosion resistance test)
The corrosion resistance test was carried out by a repeated salt-dry-wet test in which salt spraying, drying and wetting were repeated. In the salt-dry-wet repeat test, the hot-rolled steel sheet subjected to the descale step was sprayed with a 5% NaCl aqueous solution (15 minutes at 35 ° C), dried (relative humidity 30%, temperature 60 ° C for 1 hour), and Wetting (relative humidity 95%, temperature 50 ° C. for 3 hours) was taken as one cycle for 10 cycles. Then, the hot-rolled steel sheet was washed with water and dried, and the rusted area ratio of the hot-rolled steel sheet was calculated.
The rusting area ratio was calculated by the following procedure. The surface of the hot-rolled steel sheet after the repeated salt-dry-wet test was photographed, and the ratio of the area of the rusted portion in the central 25 mm × 25 mm range excluding the end face was determined. The area of the rusted portion was obtained by binarizing the photograph of the surface of the hot-rolled steel sheet by image analysis, calculating the area per pixel, and then counting the number of pixels of the rusted portion. The rusting area ratio was calculated by the following formula.
Rust area ratio (%) = Area of rusting part (mm ² ) / Area of the entire observation part (625 mm ² ) x 100
In this evaluation, those having a rusting area ratio of 1% or less were evaluated as "○" (good corrosion resistance), and those having a rust area ratio of more than 1% were evaluated as "x" (poor corrosion resistance).
The results of each of the above evaluations are shown in Table 2.

As shown in Table 2, the hot-rolled steel sheets of Examples 1 to 10 have a surface arithmetic average roughness Ra of 0.10 to 3.00 μm and a 60-degree mirror gloss Gs (60 °) of 10 to 100%. It was confirmed that it was in the range and had a smooth and glossy surface. In addition, the hot-rolled steel sheets of Examples 1 to 10 had good corrosion resistance.
On the other hand, in the hot-rolled steel sheets of Comparative Examples 1 and 3, one or both of the arithmetic mean roughness Ra and the 60-degree mirror surface gloss Gs (60 °) of the surface is out of the above range, and the surface is rough and has no gloss. Had. Further, the hot-rolled steel sheets of Comparative Examples 2 and 4 were polished after the pickling descaling step, so that the corrosion resistance was not sufficient.

As can be seen from the above results, according to the present invention, it is possible 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.

Claims

Based on mass, C: 0.001 to 0.100%, Si: 5.00% or less, Mn: 2.00% or less, P: 0.050% or less, S: 0.0300% or less, Ni: 2 Includes less than .00%, Cr: 11.00 to 30.00%, Mo: 6.00% or less, Cu: 0.60% or less, N: 0.050% or less, Al: 3.500% or less. The balance has a composition consisting of Fe and impurities.
A ferrite stainless steel material having an arithmetic average roughness Ra of 0.10 to 3.00 μm and a 60 degree mirror gloss Gs (60 °) of 10 to 100%, and having excellent corrosion resistance.
The ferrite-based stainless steel material according to claim 1, wherein the surface of the ferrite-based stainless steel material satisfies the following (1) and (2).
(1) The root mean square slope RΔq is 35 ° or less.
(2) The chromanetics index b * is 7.00 or less.
The ferrite-based 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.
The ferrite-based 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 on a mass basis.
On a mass basis, Ti: 0.001 to 0.500%, Nb: 0.001 to 1.000%, V: 0.001 to 1.000%, W: 0.001 to 1.000%, Zr: The ferrite-based stainless steel material according to any one of claims 1 to 4, further comprising one or more selected from 0.001 to 1.000% and Co: 0.001 to 1.200%.
Claim 1 further comprises one or more selected from Ca: 0.0001 to 0.0100%, B: 0.0001 to 0.0080%, Sn: 0.001 to 0.500% on a mass basis. The ferrite-based stainless steel material according to any one of 5 to 5.
The ferrite-based stainless steel material according to any one of claims 1 to 6, wherein in the salt-dry-wet repeat test, the rusting area ratio after 10 cycles of salt spraying, drying and wetting as one cycle is 1% or less. ..
Corrosion resistant member containing the ferrite stainless steel material according to any one of claims 1 to 7.