WO2014157578A1

WO2014157578A1 - Ferritic stainless steel with excellent surface corrosion resistance after polishing, and process for producing same

Info

Publication number: WO2014157578A1
Application number: PCT/JP2014/059017
Authority: WO
Inventors: 佑一田村; 透松橋; 石丸　詠一朗
Original assignee: 新日鐵住金ステンレス株式会社
Priority date: 2013-03-27
Filing date: 2014-03-27
Publication date: 2014-10-02
Also published as: CN105074035A; KR20150110762A; CN105074035B; KR101663207B1; JP5837258B2; JPWO2014157578A1

Abstract

Provided are a ferritic stainless steel which, even when subjected to rough polishing, is inhibited from decreasing in surface corrosion resistance and a process for producing, through a smaller number of steps, a ferritic stainless steel in which the surface corrosion resistance can be inhibited from decreasing through polishing. The ferritic stainless steel is characterized by containing, in terms of mass%, up to 0.030% C, up to 0.030% N, 0.15-3.0% Si, up to 1.5% Mn, up to 0.04% P, up to 0.01% S, 12-22.5% Cr, up to 0.60% Nb, up to 0.60% Ti, and up to 0.80% Al, having polishing marks so as to result in an arithmetic average surface roughness Ra of 0.45-5.0 μm, and having average Si and Fe concentrations by mass of 5% or greater and 75% or less, respectively, in the portion ranging from the surface to a depth of 10 nm therefrom. The ferritic stainless steel can be produced by temper rolling at a draft of 0.5-5.0%.

Description

Ferritic stainless steel having excellent surface corrosion resistance after polishing and method for producing the same

The present invention relates to a ferritic stainless steel having excellent surface corrosion resistance after polishing and a method for producing the same.

Stainless steel is superior in corrosion resistance compared to ordinary steel, etc., so it may be used with the surface of the base exposed without the use of rust-proof coating for the purpose of effectively using metallic luster as a design. Many. However, in products such as kitchen appliances, home appliances, electronic devices, and appliances that are easily accessible to the public, such as elevators, refrigerators, kitchen sinks, and tableware, unevenness in a certain roughness range is obtained by polishing. In some cases, the anti-glare property and the anti-fingerprint stain resistance are improved by providing a streak pattern having, for example, polished eyes, and the metallic luster of the surface is secured. As a polishing tool, a polishing belt with abrasive grains fixed with an adhesive on the stainless steel plate production line is pressed against the steel plate, or processed with a sponge that is mixed with resin and hardened after product shipment. A method of rubbing a stainless steel product can be exemplified. Or the method of rotating the wheel (flap wheel) which bundled the thing which bundled the abrasive paper which fixed the abrasive grain with the adhesive agent in a ring shape, and pressed on stainless steel etc. is mentioned. Regarding the surface roughness of the polished eyes, JIS G 4305 established by the Japanese Industrial Standards, No. 3, no. The symbols such as 4, # 240, # 320, # 400, and HL define that a predetermined surface roughness can be designated.

Conventionally, when polishing with a polishing belt, a polishing oil is used for the purpose of improving cooling and grindability. In Patent Document 1, the formation of oxides is suppressed by adding an antioxidant to the polishing oil itself at the time of temperature rise due to frictional heat, an agent for preventing oil film breakage, and an agent for improving grindability, thereby preventing corrosion. Is preventing the decline.

Further, Patent Document 2 discloses polishing corresponding to # 400 abrasive grains defined by JIS R 6001 such that the arithmetic average roughness Ra, which is the roughness of the surface, is in the range of 0.23 to 0.31 μm. By specifying a stainless steel product that has eyes and has a surface color tone of Lab and a red value of 1.0 or less, the degree of surface oxidation by polishing is small, and it has good corrosion resistance. Is described.

Patent Document 3 discloses that in stainless steel to which Mo is added, a halogen-containing acid treatment is performed for the purpose of removing the oxide film caused by the dense Mo formed on the surface in the annealing process and improving the polishability. Is doing. However, at this time, since the dissolution is non-uniform and grain boundary erosion also occurs, the Cr addition amount is increased, Cu, Ni is added, and the SiO ₂ oxide film is left, so that the polishing property is excellent. In addition, a method for producing a stainless steel plate having excellent corrosion resistance is described.

Patent Document 4 discloses that after polishing a ferritic stainless steel sheet, the temperature is 1000 ° C. or higher and the time for which the temperature is maintained is 10 seconds or longer in a hydrogen gas atmosphere having a dew point of −40 ° C. or lower, that is, a so-called BA atmosphere. A manufacturing method is described in which the oxide in the oxide film produced by polishing is reduced by continuously heat-treating.

JP 2001-269851 A JP 2004-330394 A Japanese Patent No. 5018257 JP 2010-229488 A

Ferritic stainless steel is liable to cause a decrease in surface corrosion resistance due to polishing burn due to heat generated during polishing. That is, in order to create design properties, when a polishing eye is provided, an oxide containing a large amount of Fe is formed on the polished surface by heat generated by friction between these abrasive grains and the stainless steel substrate. The to oxides Cl such as Fe ^- when an aqueous solution containing adheres, hydroxides such as after dissolving the oxide solution such as Fe, etc. and oxygen chemically reacts with atmospheric Fe (OH) ₂ To form a precipitate. As a result, red rust is generated on the stainless steel surface, resulting in an appearance in which the corrosion resistance of the substrate is lowered.

In the method described in Patent Document 1, when polishing a small stainless steel strip surface roughness, if the polishing resistance increases, only the devising of polishing oil can not be prevented heated, Cl ^- of aqueous solution containing Red rust on the surface caused by adhesion cannot be suppressed.

The range described in Patent Document 2 defines Ra and color tone of the surface, but many products are provided with relatively rough polishing marks such that Ra is 0.45 to 5.0 μm. In this case as well, red rust on the surface caused by adhesion of an aqueous solution containing Cl ⁻ cannot be suppressed.

In the method described in Patent Document 3, the oxide film formed at the time of annealing is intentionally left on the surface of the steel sheet, thereby minimizing the dissolution of the base iron, especially the erosion at the grain boundary, and ensuring the corrosion resistance after polishing. is doing. However, when a relatively rough polishing grain is provided, even if the pickling process after annealing is devised to leave an oxide film during annealing, all the oxide film is removed during polishing. Therefore, since the Fe compound adhering to the surface of the ground iron corrodes, generation of red rust on the surface cannot be suppressed.

In the method described in Patent Document 4, since the BA atmosphere is used, the manufacturing cost increases.

Aqueous solution containing ^- object of the present invention, even when subjected to coarser grinding, Cl ^- red rust suppress ferritic stainless steel on the surface due to the deposition of an aqueous solution containing, and Cl after polishing with fewer steps It is an object to provide a method for producing a ferritic stainless steel having excellent surface corrosion resistance that can suppress red rust on the surface due to adhesion of steel.

In order to solve the above-mentioned problems of the prior art and develop a ferritic stainless steel sheet having excellent surface corrosion resistance after polishing, the inventors have developed the oxide structure formed on the surface after polishing and the oxidation in salt water. We intensively investigated the corrosion resistance of the structure. As a result, it was found that the amount of grinding at the time of polishing can be suppressed and heat generation can be suppressed by adding a small amount of Si and surface hardening of stainless steel by applying a manufacturing method that increases the rolling reduction of temper rolling. In addition, combined with the addition of a small amount of Si and the suppression of heat generation during polishing, it is possible to form an oxide containing a large amount of SiO ₂ on the surface, which causes red rust in salt water. Concentration of Fe on the oxide surface is suppressed, and furthermore, SiO ₂ reduces the thermal conductivity of the surface, thereby suppressing the generation of Fe oxide at the iron-iron interface, and with water containing Cl 2 ⁻ It has been found that the iron oxide is prevented from changing into red rust due to contact. It was also found that the addition of a small amount of Sn hardens the surface of stainless steel in the same way as Si, and contributes to the amount of grinding and the suppression of heat generation during polishing.

That is, the present invention is as follows.
(1) By mass%, C: 0.030% or less, N: 0.030% or less, Si: 0.15-3.0%, Mn: 1.5% or less, P: 0.04% or less, S: 0.01% or less, Cr: 12-22.5%, Nb: 0.60% or less, Ti: 0.60% or less, Al: 0.80% or less, the balance being Fe and inevitable A ferritic stainless steel excellent in surface corrosion resistance after polishing, which is an impurity and has a surface hardness Hv of 175 or more.
(2) By mass%, C: 0.030% or less, N: 0.030% or less, Si: 0.15-3.0%, Mn: 1.5% or less, P: 0.04% or less, S: 0.01% or less, Cr: 12-22.5%, Nb: 0.60% or less, Ti: 0.60% or less, Al: 0.80% or less, the balance being Fe and inevitable When the surface concentration of elements is measured by glow discharge optical emission spectrometry (GD-OES) when the surface of arithmetic mean roughness Ra is given to the steel, which is an impurity, with an arithmetic mean roughness Ra of 0.45 to 5.0 μm. In the depth from the surface to 10 nm, the average mass concentration of the elements excluding C, O and N contains Si of 5% or more and Fe of 75% or less, and the surface brightness L * value is 70 or more. Ferritic stainless steel with excellent surface corrosion resistance after polishing, characterized by
(3) By mass%, C: 0.030% or less, N: 0.030% or less, Si: 0.15-3.0%, Mn: 1.5% or less, P: 0.04% or less, S: 0.01% or less, Cr: 12-22.5%, Nb: 0.60% or less, Ti: 0.60% or less, Al: 0.80% or less, the balance being Fe and inevitable It is made of impurities and has a polished surface with an arithmetic average roughness Ra of 0.45 to 5.0 μm. Further, when the element concentration of the surface is measured by glow discharge optical emission spectrometry (GD-OES) In a depth of 10 nm from the surface, the average mass concentration of the elements excluding C, O and N contains Si of 5% or more and Fe of 75% or less, and the surface brightness L * value is 70 or more. Ferritic stainless steel with excellent surface corrosion resistance after polishing, characterized by its value.
(4) By mass%, C: 0.030% or less, N: 0.030% or less, Si: 0.15-3.0%, Mn: 1.5% or less, P: 0.04% or less, S: 0.01% or less, Cr: 12 to 22.5%, Nb: 0.60% or less, Ti: 0.60% or less, Al: 0.80% or less, and further Sn% : 0.005 to 1.0%, Ni: 0.50% or less, Cu: 1.50% or less, Mo: 3.0% or less, V: 1.0% or less, B: 0.003% or less, Contains one or more of Sb: 0.001 to 0.3%, Ga: 0.0002 to 0.1%, and Ta: 0.50% or less, with the balance being Fe and inevitable impurities, A ferritic stainless steel excellent in surface corrosion resistance after polishing, characterized by having a hardness Hv of 175 or more.
(5) By mass%, C: 0.030% or less, N: 0.030% or less, Si: 0.15-3.0%, Mn: 1.5% or less, P: 0.04% or less, S: 0.01% or less, Cr: 12 to 22.5%, Nb: 0.60% or less, Ti: 0.60% or less, Al: 0.80% or less, and further Sn% : 0.005 to 1.0%, Ni: 0.50% or less, Cu: 1.50% or less, Mo: 3.0% or less, V: 1.0% or less, B: 0.003% or less, Contains one or more of Sb: 0.001 to 0.3%, Ga: 0.0002 to 0.1%, and Ta: 0.50% or less, with the balance being Fe and inevitable impurities, When an abrasive having an arithmetic average roughness Ra of 0.45 to 5.0 μm was applied, the elemental concentration of the surface was measured by glow discharge emission spectrometry (GD-OES). Furthermore, at a depth of 10 nm from the surface, Si contains 5% or more and Fe contains 75% or less at an average mass concentration of the elements excluding C, O and N, and the surface brightness L * value is 70 Ferritic stainless steel with excellent surface corrosion resistance after polishing, characterized by taking the above values.
(6) By mass%, C: 0.030% or less, N: 0.030% or less, Si: 0.15-3.0%, Mn: 1.5% or less, P: 0.04% or less, S: 0.01% or less, Cr: 12 to 22.5%, Nb: 0.60% or less, Ti: 0.60% or less, Al: 0.80% or less, and further Sn% : 0.005 to 1.0%, Ni: 0.50% or less, Cu: 1.50% or less, Mo: 3.0% or less, V: 1.0% or less, B: 0.003% or less, Contains one or more of Sb: 0.001 to 0.3%, Ga: 0.0002 to 0.1%, and Ta: 0.50% or less, with the balance being Fe and inevitable impurities, And having an arithmetic mean roughness Ra of 0.45 to 5.0 μm, and when the surface element concentration is measured by glow discharge optical emission spectrometry (GD-OES) In a depth of 10 nm from the surface, the average mass concentration of the ratio of elements excluding C, O, and N is a value that contains 5% or more of Si and 75% or less of Fe and has a surface brightness L * value of 70 or more Ferritic stainless steel with excellent surface corrosion resistance after polishing.
(7) Further, by mass%, W: 0.50% or less, Co: 0.50% or less, Mg: 0.01% or less, Ca: 0.0030% or less, Zr: 0.30% or less, REM ( (Rare earth element): Ferritic stainless steel excellent in surface corrosion resistance after polishing according to any one of (1) to (6), characterized by containing one or more of 0.20% or less.
(8) A ferritic stainless steel part characterized by using the ferritic stainless steel having excellent surface corrosion resistance after polishing according to any one of (1) to (7).
(9) The ferrite excellent in surface corrosion resistance after polishing according to any one of (1) to (7), wherein temper rolling is performed at a rolling reduction of 0.5% to 5.0% A method for producing stainless steel is proposed.

According to the present invention, it is confirmed from the corrosion resistance test results that a ferritic stainless steel having excellent surface corrosion resistance is obtained even when polishing with a relatively rough roughness is performed. Therefore, the ferritic stainless steel according to the present invention has good surface corrosion resistance in indoor applications that come into contact with chlorine-containing tap water, and the occurrence of red rust is suppressed even after polishing, and the surface aesthetics are improved. Maintained.

In addition, after forming the ferritic stainless steel of the present invention into a predetermined shape according to the purpose, by polishing as described in the present invention, among products such as kitchen appliances, home appliances, electronic devices, and instruments It can be suitably used as a part for exterior and daily necessities that are easy to touch.

It is a graph which shows about the determination by the corrosion resistance evaluation value after a salt spray test in the relationship between the mass concentration of Si contained in the thickness of the surface 10 nm after polishing and the L * value measured with a color difference meter.

Detailed description of the ferritic stainless steel component according to the present invention will be described below. In addition, the description of% about a composition means the mass% unless there is particular notice.

C: 0.030% or less C has an effect of improving strength by suppressing coarsening of grains by combination with hardening or a stabilizing element, but reduces intergranular corrosion resistance and workability of a welded portion. In high-purity ferritic stainless steel, the content must be reduced, so the upper limit was made 0.030%. To reduce excessively deteriorates the refining cost, more desirably, the lower limit is made 0.002% and the upper limit is made 0.020%.

N: 0.030% or less N, like C, reduces intergranular corrosion resistance and workability, so its content must be reduced, so its upper limit was made 0.030%. However, reducing excessively deteriorates the refining cost. More desirably, the lower limit is 0.002% and the upper limit is 0.020%.

Mn: 1.5% or less Mn is an element that may not be contained in the present invention, but is also an element useful as a deoxidizing element. However, if Mn is added excessively, MnS that becomes a starting point of corrosion tends to be generated, so the upper limit was made 1.5%. Since it is used as a deoxidizing element, 0.01% or more is preferable. In order to destabilize the ferrite structure, the lower limit of the content is preferably 0.01% and the upper limit is preferably 0.60%. More desirably, the lower limit is 0.05% and the upper limit is 0.3%.

P: 0.04% or less P not only lowers weldability and workability, but also tends to cause intergranular corrosion, so P needs to be kept low. Therefore, the content is set to 0.04% or less. More preferably, the lower limit is 0.001% and the upper limit is 0.03%.

S: 0.01% or less S needs to be reduced because water-soluble inclusions such as the above-mentioned CaS and MnS, which are the starting points of corrosion, are generated. Therefore, the content is made 0.01% or less. However, excessive reduction leads to cost deterioration. More preferably, the lower limit is 0.0001% and the upper limit is 0.006%.

Cr: 12-22.5%
Cr is the most important element for securing the corrosion resistance of stainless steel, and at least 12% is necessary because it stabilizes the ferrite structure. Cr is concentrated in the oxide film on the surface in the same manner as Si described later, and the generation of red rust after polishing is suppressed by relatively suppressing the concentration of Fe. Increasing Cr improves the corrosion resistance after polishing, but lowers workability and manufacturability, so the upper limit was made 22.5%. Preferably, the lower limit is 13.5% and the upper limit is 21.0%, more preferably the lower limit is 16.0% and the upper limit is 20.0%. More preferably, the lower limit is 16.5% and the upper limit is 18.0%.

Si: 0.15-3.0%
Si is an extremely important element in the present invention, is generally effective in corrosion resistance and oxidation resistance, and is an element added as a deoxidizer. According to the knowledge of the inventors, when 0.15% or more of Si is added to the steel, an oxide film of SiO ₂ is formed on the outermost layer after polishing, and the concentration of Fe oxide is relatively suppressed. Therefore, the occurrence of red rust after polishing is suppressed. In addition, since the metal structure is hardened by adding Si and increasing the rolling reduction of temper rolling, the amount of grinding during polishing can be reduced, and as a result, polishing heat is suppressed and oxide formation is suppressed. However, excessive addition reduces processability and manufacturability. Therefore, the upper limit was made 3.0%. Desirably, the upper limit is less than 2.5%. More desirably, it is 1.5% or less. More desirably, it is 1.0% or less. The lower limit is desirably 0.3% or more, and more desirably 0.4% or more.

Al: 0.80% or less Al is an element that does not need to be contained, but is useful as a deoxidizing element like Si, and also has the effect of controlling the composition of non-metallic inclusions and refining the structure. . However, if it is added excessively, the non-metallic inclusions become coarse, which may be the starting point for product wrinkles. Therefore, the upper limit is set to 0.80%. The lower limit value does not need to be set in particular. However, since it takes time to remove Al, the lower limit value may be 0.01% or more from an economic viewpoint. Desirably, the lower limit is 0.01% and the upper limit is 0.80%. More desirably, the lower limit is 0.03%, and the upper limit is 0.5%.

Ti: 0.60% or less Ti is an important element that generally suppresses intergranular corrosion and improves workability by fixing C and N in a weld zone of ferritic stainless steel. However, excessive addition causes surface flaws during production, so the range was made 0.60% or less. The lower limit may be 0.03% or more. 0.05% or more is desirable, and more desirably 0.08% or more. Desirably, the lower limit is 0.08 and the upper limit is 0.30%. More desirably, the lower limit is 0.08% and the upper limit is 0.20%.

Nb: 0.60% or less Nb is an extremely important element for fixing C and N like Ti, suppressing intergranular corrosion of the welded portion, and improving workability. Moreover, when it precipitates as a carbide | carbonized_material or nitride, it has a function which hardens a metal structure and suppresses the grinding amount at the time of grinding | polishing. However, excessive addition causes a decrease in toughness due to excessive precipitation and decreases workability. Therefore, when added, the content is preferably made 0.60% or less. The lower limit value may be set to 0.03% or more. The lower limit is preferably 0.05%, more preferably 0.08%. A desirable range is to set the lower limit to 0.10% and the upper limit to 0.30%. A more desirable range is to set the lower limit to 0.10% and the upper limit to 0.20%. In addition, as long as one of Ti and Nb is contained, the other may not be contained.

Further, other chemical compositions that can be selectively contained as required in the present invention will be described in detail below.

Sn: 0.005 to 1.0%
Since Sn hardens the metal structure like Si, it can reduce the amount of grinding during polishing, and as a result, is an important element that suppresses polishing heat and suppresses oxide formation. At the same time, it is an important element for suppressing the corrosion rate and improving the flow rust resistance after polishing. Since the effect is manifested at 0.005% or more, the lower limit is set to 0.005%. 0.05% or more is desirable, and further 0.08% or more is desirable. Excessive addition deteriorates manufacturability and cost, so the upper limit was made 1.0%, preferably 0.5%. A more desirable upper limit of Sn is 0.4%. Therefore, the Sn range is to set the lower limit to 0.005% and the upper limit to 1.0%. Desirably, the lower limit is 0.05% and the upper limit is 0.5%. More desirably, the lower limit is 0.08% and the upper limit is 0.4%.

Cu: 1.5% or less Cu is not essential, but may be contained in an amount of 0.01% or more as an inevitable impurity when scrap is used as a raw material. In general, Cu suppresses the corrosion rate, and is added as necessary to improve the flow rust resistance after polishing in the same manner as Sn. It is good to add 0.05% or more. Desirably, it is 0.09% or more, and more desirably 0.15% or more. However, excessive addition deteriorates manufacturability and cost, so the upper limit was made 1.5%. A desirable upper limit is 1.0%. A more desirable upper limit is 0.50%. Therefore, the desirable range of Cu is to set the lower limit to 0.05% and the upper limit to 1.0%, and more preferably to set the lower limit to 0.09% and the upper limit to 0.50%. .

Ni: 0.50% or less Ni is not essential, but if contained, it suppresses the active dissolution rate and is very effective for passivation. However, excessive addition reduces workability and not only destabilizes the ferrite structure but also deteriorates the cost, so it was made 0.50% or less. Desirably, it was made into less than 0.35%. The lower limit is preferably 0.05%. Therefore, the desirable range of Ni is 0.05% or more and less than 0.35%.

Mo: 3.0% or less Mo is effective in repairing the passive film, and is an element that is very effective for improving the corrosion resistance. In particular, Mo is effective in improving the pitting corrosion resistance in combination with Cr. However, when Mo is increased, the corrosion resistance is improved, but the workability is lowered and the cost is increased, so the upper limit is made 3.0%. More desirably, the lower limit is 0.30% and the upper limit is 2.00%.

B: 0.003% or less B is a grain boundary strengthening element effective for improving secondary work brittleness, and can be added as necessary. However, excessive addition causes the solid solution strengthening of ferrite and causes a decrease in ductility. Therefore, the lower limit is made 0.0001%. The upper limit is 0.003%. More desirably, the lower limit is 0.0002% and the upper limit is 0.0020%.

V: 1.0% or less V improves the weather resistance and crevice corrosion resistance, and can suppress the use of Cr and Mo and add V to ensure excellent workability. Can be added. The lower limit is preferably 0.03%. However, excessive addition of V reduces workability and also saturates the effect of improving corrosion resistance, so the upper limit is made 1.0%. More desirably, the lower limit is 0.05% and the upper limit is 0.50%.

Sb: 0.001 to 0.3%
Sb is effective in improving the corrosion resistance, and may be added in an amount of 0.3% by mass or less as necessary. In particular, when adding the amount of Sb from the viewpoint of crevice corrosion, the lower limit of the amount of Sb is set to 0.001% by mass. Furthermore, it is preferable that the amount of Sb is 0.01% by mass or more from the viewpoint of manufacturability and cost. From the viewpoint of cost, the upper limit of the amount of Sb is preferably 0.1% by mass.

Ga: 0.0002 to 0.1%
Ga may be added in an amount of 0.1% by mass or less in order to improve corrosion resistance and suppress hydrogen embrittlement. From the viewpoint of the formation of sulfides and hydrides, the lower limit of Ga content is 0.0002% by mass. Furthermore, the amount of Ga is preferably 0.0020% by mass or more from the viewpoint of manufacturability and cost.

Ta: 0.50% or less Ta is an element that improves high-temperature strength, and can be added as necessary. However, addition of an excessive amount of Ta causes a decrease in normal temperature ductility and a decrease in toughness, so 0.50% by mass is made the upper limit of the Ta amount. In order to achieve both high temperature strength and ductility / toughness, the Ta content is preferably 0.05% by mass or more and 0.5% by mass or less.

W: 0.50% or less W is effective in improving the high-temperature strength, and is added at 0.01% or more as necessary. Further, if added over 0.50%, the solid solution strengthening is too large and the mechanical properties are lowered, so the lower limit is made 0.01% and the upper limit is made 0.50%. Considering the manufacturing cost and hot-rolled sheet toughness, it is desirable that the lower limit is 0.02% and the upper limit is 0.15%.

Co: 0.50% or less Co is effective for improving wear resistance and high-temperature strength, and is added at 0.01% or more as necessary. Moreover, even if added over 0.50%, the effect is saturated, and mechanical properties are deteriorated due to solid solution strengthening. Therefore, the lower limit is set to 0.01% and the upper limit is set to 0.50%. Add in. From the viewpoint of manufacturing cost and stability of high temperature strength, it is desirable to add in a range where the lower limit is 0.05% and the upper limit is 0.20%.

Mg: 0.01% or less Mg is an element effective for refining the solidified structure in the steel making process, and is added in an amount of 0.0003% or more as necessary. Further, even if added over 0.01%, the effect is saturated, and the corrosion resistance due to Mg sulfide or oxide is likely to be lowered. Therefore, the lower limit is set to 0.0003%, and the upper limit is set to 0.00. Add within the range of 01%. In consideration of the fact that the Mg addition in the steelmaking process causes oxidative combustion of Mg and the yield decreases and the cost increases greatly, the lower limit is preferably 0.0005% and the upper limit is preferably 0.0015%.

Ca: 0.0030% or less Ca is an important desulfurization element in the steel making process, and also has a deoxygenating effect, so is added at 0.0003% or more as necessary. Moreover, even if added over 0.0030%, the effect is saturated, and the corrosion resistance is reduced due to Ca granulated material and the workability is deteriorated due to oxide. Therefore, the lower limit is made 0.0003%. The upper limit is added within a range of 0.0030%. Considering manufacturability such as slag treatment, it is desirable that the lower limit is 0.0005% and the upper limit is 0.0015%.

Zr: 0.30% or less Zr is added in an amount of 0.01% or more as necessary in order to form a carbonitride and suppress the formation of Cr carbonitride and improve the corrosion resistance like Nb and Ti. To do. Moreover, even if added over 0.30%, the effect is saturated and the formation of large oxides can cause surface defects. Therefore, the lower limit is set to 0.01% and the upper limit is set to 0.30%. Add within range. Since it is an expensive element compared with Ti and Nb, considering the manufacturing cost, it is desirable that the lower limit is 0.02% and the upper limit is 0.05%.

REM (rare earth element): 0.20% or less REM is effective in improving oxidation resistance, and is added at 0.001% or more as necessary. Moreover, even if added over 0.20%, the effect is saturated, and the corrosion resistance is reduced by the REM granulated material. Therefore, the lower limit is set to 0.001% and the upper limit is added to 0.20%. To do. Considering the workability and manufacturing cost of the product, it is desirable that the lower limit is 0.002% and the upper limit is 0.05%. In addition, REM (rare earth element) refers to a generic name of two elements of scandium (Sc) and yttrium (Y) and 15 elements (lanthanoid) from lanthanum (La) to lutetium (Lu) according to a general definition. It may be added alone or as a mixture.

Other components are not particularly defined in the present embodiment, but in this embodiment, Hf, Bi, etc. may be added in an amount of 0.001 to 0.1% by mass as necessary. Note that the amount of generally harmful elements such as As and Pb and impurity elements is preferably reduced as much as possible.

In the stainless steel plate of the present invention, the arithmetic average roughness Ra of the surface is not particularly limited, but it is desirable that the stainless steel plate has a polishing grain having Ra of 0.45 to 5.0 μm. When Ra is 0.45 μm or more, the method described in Patent Document 2 cannot prevent the corrosion resistance of the steel sheet surface from being lowered, and for the first time in the present invention, it is possible to prevent the corrosion resistance from being degraded by polishing the steel sheet surface.

The polished stainless steel plate of the present invention has a surface layer containing 5% or more of the Si concentration, so-called SiO ₂ rich oxidation, even though the Si composition is 0.15 to 3.0% of the steel plate. It is characterized in that a surface layer of an object is formed. The concentration of Si in the surface layer as described above occurs when the surface is oxidized by heat generation during polishing. Therefore, the lower limit of Ra of the present invention is set to 0.45 μm. On the other hand, since there are almost no examples in which Ra exceeds 5.0 μm in applications such as kitchen appliances, the upper limit of Ra is set to 5.0 μm.

The stainless steel plate of the present invention has an average ratio of elements excluding C, O and N at a depth of 10 nm from the surface when the element concentration on the surface is measured by glow discharge optical emission spectrometry (GD-OES). In terms of mass concentration, Si contains 5% or more and Fe contains 75% or less. Since Si has a high oxygen affinity, it is preferentially oxidized at a high temperature. Therefore, by setting the element concentration on the surface within this range, it is possible to prevent the occurrence of red rust on the surface and prevent the surface aesthetics from being impaired. In addition, the steel component of the present invention, particularly the Si content, is within the scope of the present invention, and Ra is 0 only after temper rolling with a rolling reduction of 0.5% to 5.0% as described below. Even in the case of polishing having a polishing mesh of .45 μm or more, the elemental concentration of the surface can be 5% or more for Si and 75% or less for Fe.

The stainless steel plate of the present invention is characterized in that the surface brightness L * value is 70 or more. This is because when L * is less than 70, the Si concentration in the range from the surface to 10 nm is 5% or less. In the present invention, the lightness L * value means the CIE lightness in the L ^* a ^* b ^* color system defined in JIS Z 8729.

Next, a method for producing a stainless steel plate according to the present invention will be described.

The above-mentioned steel having the proper composition is melted by a known method, and is made into a slab by a known method such as continuous casting. After the slab is reheated to 1100 to 1200 ° C, the finishing temperature is 700 to 900 ° C. Perform hot rolling to obtain a hot-rolled steel strip. Subsequently, this hot-rolled steel strip is annealed at a temperature of 800 to 1100 ° C., pickled, and then cold-rolled to obtain a cold-rolled steel strip having a finished thickness of 6.0 mm or less. If necessary, the cold-rolled steel strip is annealed in a coke oven combustion gas atmosphere, for example, at about 950 ° C. for about 60 seconds, and then subjected to a salt treatment, followed by a dipping treatment in a nitric hydrofluoric acid solution, or Electrolytic treatment in neutral salt.

The surface of the cold-rolled steel strip is hardened by temper rolling at a rolling reduction of 0.5% to 5.0%. Rolling at a rolling reduction of more than 5.0% may lead to the capacity limit of the equipment and the occurrence of surface flaws, so it is necessary to take measures for equipment and surface flaws when applying.

Generally, in stainless steel, during hot rolling or cold rolling, metal crystal grains are refined by rolling and large work hardening occurs, and therefore an annealing process is required. On the other hand, the temper rolling is performed only for the purpose of adjusting the brightness and roughness of the surface, and therefore it is premised that annealing is not performed, and therefore is operated only in a range where work hardening does not occur so much. In normal temper rolling, the rolling reduction is less than 0.5%. In contrast, in the present invention, temper rolling is performed at a rolling reduction larger than that of normal temper rolling, and in the present invention, the Si content is 0.15 at a rolling reduction of 0.5% or more. Combined with -3.0%, the effect of hardening the surface was recognized. The rolling reduction of temper rolling is desirably 1% or more. In consideration of the facility capacity and surface defects, the upper limit is preferably 4%. This curing can suppress heat generation when the surface is polished.

The surface hardening by temper rolling in the present invention varies depending on the hardness (hereinafter referred to as Hv _s value) and the reduction rate of the annealed cold-rolled steel strip before temper rolling. For example, when Hv _s is 170, the hardness after temper rolling (hereinafter referred to as Hv value) when the rolling reduction is 0.5%, 1.0%, 4.0%, 5.0% Becomes 172, 174, 184, 188. As a result of the corrosion resistance evaluation after the application of the polishing eyes shown below, it was found that the Hv value after temper rolling required to sufficiently obtain the corrosion resistance after polishing was 175 or more. It is desirably 180 or more, and more desirably 182 or more. The upper limit of the surface hardness after the temper rolling is not particularly limited, but the upper limit of the Hv value is desirably 195 because the viewpoint of productivity and the effect are saturated.

Next, in order to give a polished surface as a design property to the surface, the product plate of the stainless steel plate or the processed product is polished to have an arithmetic average roughness Ra of 0.45 to 5.0 μm. The size of the abrasive grains adhering to the polishing belt used for polishing becomes finer by use. That is, when the same belt portion is continuously used and the abrasive grains adhering to the belt are worn or dropped, the size of the abrasive grains becomes finer than that in a new state. In general, this is called “blindness”, and the actual count or the particle size number of the polishing belt used increases. Therefore, the count of the polishing belt and the size of the abrasive grains may be finely changed depending on the usage state of the polishing belt so that the surface roughness at the time of finishing is arbitrary Ra within the range of 0.45 to 5.0 μm. .

Furthermore, when the surface element concentration was measured by GD-OES, Si was 5% or more and Fe was 75% or less at an average mass concentration of elements excluding C and O at a depth of 10 nm from the surface. Even if a relatively rough polishing is performed by setting the Si addition amount to 0.3 to 3.0% and performing the temper rolling as specified above to perform surface hardening so that the surface is included. By reducing the amount of grinding sometimes, temperature rise is suppressed, Si is preferentially oxidized, and formation of Fe oxide on the surface is further suppressed. Further, when the amount of grinding is reduced by surface hardening and preferential oxidation of Si occurs, the formation of Fe oxide is suppressed, and the surface brightness L * value takes a value of 70 or more.

The steels of the present invention having the composition shown in Table 2-1 were melted in a vacuum melting furnace and the comparative steels B1 to B19 shown in Table 2-2 were cast to obtain a 30 kg steel ingot, This steel ingot was heated to 1150 ° C. and hot-rolled in a temperature range of 1150 to 900 ° C. to obtain a hot rolled sheet having a thickness of 3 mm. Subsequently, these hot rolled sheets were annealed at 950 ° C., and then cold rolling and annealing were repeated to obtain cold rolled sheets having a sheet thickness of 1.0 mm. Thereafter, in order to remove the scale on the surface, after a salt treatment, an immersion treatment in a nitric hydrofluoric acid solution or an electrolytic treatment in a neutral salt was performed. In order to harden the surface of this cold-rolled sheet, as shown in Table 3, temper rolling was performed at a maximum reduction of 5.0%.

Next, the surface was polished with a polishing belt having an arbitrary abrasive grain size such that the arithmetic average roughness Ra was in the range of 0.45 to 5.0 μm. Ra was measured in accordance with JIS B0601 at a measurement length of 5 mm, a measurement speed of 0.60 mm / s, and a cutoff wavelength of 0.8 mm. Table 3 shows Ra.

The surface of various stainless steels obtained as described above was subjected to brightness measurement, GD-OES analysis, and corrosion resistance evaluation. Various evaluations were performed as follows.

<GD-OES analysis>
The sample was cut into a size of 30 mm × 30 mm, the sputtering diameter was 4 mm, and the sputtering interval was 2.5 msec. In the high-frequency method, each element was analyzed in the depth direction up to 100 nm using GDA-750HP manufactured by Spectrum Analytical GmbH. The Si concentration was calculated by the mass ratio of elements excluding the light elements C, O, and N in the range from the surface to 10 nm.

<Lightness measurement>
According to JIS Z8730, an average value of n times 3 times was calculated using CR-200b manufactured by Konica Minolta, Inc. with a measurement area of 10 mm. The numerical values used the L * a * b * color system, and L * representing CIE brightness was used as an index. When L * was less than 70, the Si concentration in the range from the surface to 10 nm was 5% or less.

<Corrosion resistance test>
The corrosion resistance was evaluated by the salt spray test (SST) defined in JIS Z2371 using the sample after polishing. The condition of the salt spray test was that a 5% by mass sodium chloride aqueous solution was continuously sprayed at a temperature of 35 ° C. for 96 hours.

<Corrosion resistance evaluation>
Corrosion resistance is evaluated based on the degree of rust generation on the surface, and the evaluation results are shown in seven stages A to G. As for the corrosion resistance evaluation result, A is the best, G is the worst result, and stage C is set as the lower limit of acceptance. In the salt spray test, a 5% sodium chloride aqueous solution was continuously sprayed at 35 ° C. for 96 hours. Specific evaluation criteria for corrosion resistance are shown in Table 1.

Table 3 shows the rolling reduction of temper rolling, the surface Ra, the L * value by brightness measurement, the mass concentration of Si and Fe in the thickness range of 10 nm from the surface, and the corrosion resistance evaluation results.

In addition, FIG. 1 shows the determination by the corrosion resistance evaluation value after the salt spray test in the relationship between the mass concentration (mass%) of Si contained in the thickness of 10 nm after polishing and the L * value measured with a color difference meter. A graph is shown.

Tables 2-1 and A1 to A34 in Table 3 are examples of the present invention. These invention examples contain components within the scope of the present invention, and have the surface arithmetic mean roughness Ra, surface Si, Fe concentration, surface brightness L * value specified in the present invention, and as a result, polishing Later, excellent surface corrosion resistance was achieved.

Tables 2-2 and B1 to B19 in Table 3 are comparative examples.

Since B1 and B19 have a small Si addition amount, the Si concentration on the surface is low, and SiO ₂ cannot be sufficiently formed on the surface. Furthermore, since the hardness is small and the polishing amount is increased, heat generation is increased and oxidation is promoted. Therefore, it is inferior in the corrosion resistance evaluation. Since B2 and B4 have a large N addition amount, intergranular corrosion is likely to progress, and inferior in corrosion resistance evaluation. In particular, since the amount of Cr added is small in B2, the concentration of Fe in the oxide film cannot be sufficiently suppressed, and the corrosion resistance is significantly lower than that in B4.

Since B3 has a large amount of C added, intergranular corrosion is likely to proceed as in the case where the amount of N added is large, and inferior in corrosion resistance evaluation. B5, like B2, has a small amount of Cr added, so it cannot sufficiently suppress the concentration of Fe in the oxide film, and the corrosion resistance is inferior. Since B6 or B7 has a large amount of Mn or S added, it becomes easy to generate MnS as a starting point of corrosion, and the corrosion resistance is inferior.

Since B8 or B9 has a large amount of Al or Ti added, non-metallic inclusions are coarsened and surface flaws are observed, which is inappropriate for the present invention. Since B10 or B11, B12, B13, B14, B15, B18 has a large amount of Cr or Nb, V, Cu, Sn, Ni, Si added, the workability and manufacturability are reduced, and the cost is further increased. It is inappropriate for the invention. Moreover, since B17 contains P at P> 0.04%, the workability was lowered and the SST evaluation was also low.

Since B16 has a temper rolling reduction ratio of less than 0.5%, its surface hardness is insufficient and its corrosion resistance is inferior.

The ferritic stainless steel sheet of the present invention is suitable for use in exteriors and daily necessities that are easy to touch among products such as kitchen equipment, home appliances, electronic equipment, and equipment.

Claims

% By mass
C: 0.030% or less, N: 0.030% or less, Si: 0.15-3.0%, Mn: 1.5% or less, P: 0.04% or less, S: 0.01% or less Cr: 12 to 22.5%, Nb: 0.60% or less, Ti: 0.60% or less, Al: 0.80% or less, the balance being Fe and inevitable impurities,
A ferritic stainless steel excellent in surface corrosion resistance after polishing, characterized by having a surface hardness Hv of 175 or more.
% By mass
C: 0.030% or less, N: 0.030% or less, Si: 0.15-3.0%, Mn: 1.5% or less, P: 0.04% or less, S: 0.01% or less Cr: 12 to 22.5%, Nb: 0.60% or less, Ti: 0.60% or less, Al: 0.80% or less, the balance being Fe and inevitable impurities,
When a surface having arithmetic average roughness Ra of 0.45 to 5.0 μm is applied to the surface, when the surface element concentration is measured by glow discharge optical emission spectrometry (GD-OES), the depth from the surface to 10 nm The average mass concentration of the elements excluding C, O, and N includes Si of 5% or more and Fe of 75% or less, and the surface brightness L * value is 70 or more. Ferritic stainless steel with excellent surface corrosion resistance after polishing.
% By mass
C: 0.030% or less, N: 0.030% or less, Si: 0.15-3.0%, Mn: 1.5% or less, P: 0.04% or less, S: 0.01% or less Cr: 12 to 22.5%, Nb: 0.60% or less, Ti: 0.60% or less, Al: 0.80% or less, the balance being Fe and inevitable impurities,
The surface has an arithmetic mean roughness Ra of 0.45 to 5.0 μm,
Further, when the element concentration on the surface was measured by glow discharge emission spectrometry (GD-OES), Si was measured at an average mass concentration of the ratio of elements excluding C, O and N at a depth of 10 nm from the surface. A ferritic stainless steel excellent in surface corrosion resistance after polishing, characterized by having 5% or more and Fe of 75% or less and having a surface brightness L * value of 70 or more.
% By mass
C: 0.030% or less, N: 0.030% or less, Si: 0.15-3.0%, Mn: 1.5% or less, P: 0.04% or less, S: 0.01% or less Cr: 12 to 22.5%, Nb: 0.60% or less, Ti: 0.60% or less, Al: 0.80% or less,
Further, by mass%, Sn: 0.005 to 1.0%, Ni: 0.50% or less, Cu: 1.50% or less, Mo: 3.0% or less, V: 1.0% or less, B: 0.003% or less, Sb: 0.001 to 0.3%, Ga: 0.0002 to 0.1%, and Ta: 0.50% or less,
The balance is Fe and inevitable impurities,
A ferritic stainless steel excellent in surface corrosion resistance after polishing, characterized by having a surface hardness Hv of 175 or more.
% By mass
C: 0.030% or less, N: 0.030% or less, Si: 0.15-3.0%, Mn: 1.5% or less, P: 0.04% or less, S: 0.01% or less Cr: 12 to 22.5%, Nb: 0.60% or less, Ti: 0.60% or less, Al: 0.80% or less,
Further, by mass%, Sn: 0.005 to 1.0%, Ni: 0.50% or less, Cu: 1.50% or less, Mo: 3.0% or less, V: 1.0% or less, B: 0.003% or less, Sb: 0.001 to 0.3%, Ga: 0.0002 to 0.1%, and Ta: 0.50% or less,
The balance is Fe and inevitable impurities,
When a surface having arithmetic average roughness Ra of 0.45 to 5.0 μm is applied to the surface, when the surface element concentration is measured by glow discharge optical emission spectrometry (GD-OES), the depth from the surface to 10 nm The average mass concentration of the elements excluding C, O, and N includes Si of 5% or more and Fe of 75% or less, and the surface brightness L * value is 70 or more. Ferritic stainless steel with excellent surface corrosion resistance after polishing.
% By mass
C: 0.030% or less, N: 0.030% or less, Si: 0.15-3.0%, Mn: 1.5% or less, P: 0.04% or less, S: 0.01% or less Cr: 12 to 22.5%, Nb: 0.60% or less, Ti: 0.60% or less, Al: 0.80% or less,
Further, by mass%, Sn: 0.005 to 1.0%, Ni: 0.50% or less, Cu: 1.50% or less, Mo: 3.0% or less, V: 1.0% or less, B: Contains 0.003% or less, Sb: 0.001 to 0.3%, Ga: 0.0002 to 0.1%, and Ta: 0.50% or less, with the balance being Fe and inevitable Impurities,
The surface has an arithmetic mean roughness Ra of 0.45 to 5.0 μm, and when the element concentration of the surface is measured by glow discharge optical emission spectrometry (GD-OES), the depth from the surface to 10 nm Then, the average mass concentration of the ratio of elements excluding C, O and N is characterized in that Si is 5% or more and Fe is 75% or less, and the surface brightness L * value is 70 or more. Ferritic stainless steel with excellent surface corrosion resistance after polishing.
Further, in mass%, W: 0.50% or less, Co: 0.50% or less, Mg: 0.01% or less, Ca: 0.0030% or less, Zr: 0.30% or less, REM (rare earth element) The ferritic stainless steel excellent in surface corrosion resistance after polishing according to any one of claims 1 to 6, characterized by containing one or more of 0.20% or less.
A ferritic stainless steel part using the ferritic stainless steel having excellent surface corrosion resistance after polishing according to any one of claims 1 to 7.
The method for producing a ferritic stainless steel having excellent surface corrosion resistance after polishing according to any one of claims 1 to 7, wherein the temper rolling is performed at a rolling reduction of 0.5% to 5.0%. .