JP6722489B2 - Stainless steel processed product excellent in corrosion resistance and method for manufacturing the same - Google Patents

Description

The present invention relates to a processed stainless steel product having excellent corrosion resistance and a method for manufacturing the same.

Since stainless steel has excellent weather resistance, workability, weldability, etc., it is widely used for building materials such as roofing materials, wall materials, and building materials. In addition, processed stainless steel products are also excellent in design, so they are surface-polished and used in many applications such as shaped steel such as H-shaped steel and T-shaped steel, building pillars and outer wall materials, handrails and fence members. Used in.

In general and industrial polishing of this processed stainless steel product, first, in order to remove the scratches and the like of the processed product before polishing, scratch removal polishing is performed, and then finish polishing and gloss polishing are performed. In the rough polishing and finish polishing in this polishing operation, dry polishing using a flap wheel, a polishing belt, or the like is performed. Furthermore, after the above steps, wet polishing by buffing may be performed to obtain a desired surface.

Conventionally, stainless steel has excellent weather resistance as a material, but depending on the state of polishing finish, the weather resistance originally possessed by the material may not be exhibited and marked rusting may occur. It is one of the factors that lose the stability (reliability) of weather resistance. For example, there is a case where rust is rusted in a short period of about one month after construction on an outdoor handrail or the like.

With regard to rusting, it is considered that the starting point is the oxide film or polishing marks remaining on the surface of the stainless steel product after polishing. The remaining oxide film is a film generated due to heat generated during polishing, and a Cr-deficient layer is formed immediately below the oxide film. For this reason, if the oxide film remains, rusting proceeds from the oxide film and the Cr-deficient layer immediately thereunder as a starting point, and corrosion resistance is likely to deteriorate. Also, with regard to the polishing marks that are scratches on the surface of the stainless steel processed product due to polishing, the deeper the recesses of the polishing marks, the more difficult the oxide film generated by flap wheel polishing, etc., to be removed by buff polishing and remain. Since the corrosion resistance becomes high and the concave portion of the polishing eye becomes the starting point of rusting, rusting proceeds and corrosion resistance is likely to deteriorate.

Patent Documents 1 and 2 propose a stainless steel plate capable of suppressing rusting in a short period of time and maintaining weather resistance.

JP, 2002-3938, A Japanese Patent Laid-Open No. 5-263278

Patent Document 1 is characterized in that after polishing a stainless steel plate containing 16 mass% or more of Cr, it is heat-treated at a temperature of 800° C. or higher in a reducing atmosphere having a hydrogen concentration of 75 vol% or higher and a dew point of −40° C. or lower. A method for producing a stainless steel abrasive finish having excellent weather resistance is described.

Further, in the manufacturing method of Patent Document 1, after performing heat treatment at 800° C. or higher in a reducing atmosphere, stainless steel is further added to an oxidizing solution containing 0.1 ppm or higher ozone and/or 5 mass% or higher nitric acid. Immersion is described.

However, performing the heat treatment at 800° C. or higher and the immersion treatment in the oxidizing solution after polishing the stainless steel plate is expected to increase the number of steps as a manufacturing method.

In Patent Document 2, when the stainless steel sheet after mechanical polishing is exposed to the air atmosphere, the stainless steel sheet after mechanical polishing is subjected to pickling treatment in order to suppress deterioration of corrosion resistance due to insufficient regeneration of the passive film. A method for finishing the surface of a stainless steel sheet is described. However, performing pickling treatment after mechanical polishing of a stainless steel plate has a problem that the number of steps is increased as a manufacturing method.

Further, in recent years, the demand for buildings has increased along with urban redevelopment, etc., and the demand for buildings in the waterfront environment has increased. In a waterfront environment, there is a problem that a building member is easily affected by sea salt particles, which are a kind of aerosol particles contained in the atmosphere and are fine particles composed of salt derived from sea water. Therefore, the need for highly corrosion-resistant building members is increasing.

An object of the present invention is to solve the above-mentioned problems and to provide a processed stainless steel product having excellent corrosion resistance, which does not rust early even in a waterfront environment affected by sea salt particles. Moreover, it aims at providing the manufacturing method of the stainless steel processed product excellent in corrosion resistance which does not increase a manufacturing process.

In order to solve the above problems, the present inventors have studied a polishing method and a polished surface of a processed stainless steel product. Here, when dry polishing is performed, the surface of the stainless steel workpiece becomes high temperature during polishing, an oxide film is generated, and surface defects are generated along with the polishing marks which are marks carved by the high grinding resistance of dry polishing. I found out. The term "surface defect" as used herein means that when the surface of a steel product is polished, an abrasive or a polishing paper is continuously brought into contact with the surface of the steel product to be polished, whereby the metal on the surface is partially peeled off and the base metal is removed. It is a defect that has a form covered on a portion, and is called a "burr" or a "cover". Surface defects include a metal-like part that is turned up like a strip or a bamboo leaf, and the maximum length from one end of the part that adheres to the base material to the other end of the peeling tip is 5 μm. These are the above defects. Since the surface defect forms a minute gap with the surface base portion of the stainless steel processed product, crevice corrosion is likely to occur, which causes a reduction in corrosion resistance of the steel processed product.

The present inventors have found a processed stainless steel product having excellent corrosion resistance and a method for producing the same, based on the analysis results.

That is, the present invention provides the following stainless steel processed products excellent in corrosion resistance and a method for producing the same, which are described below.
(1) The surface of the processed stainless steel product has polishing eyes, the colored oxide film does not exist on the surface, and the average number of surface defects including the covering of the metal base of 5 μm or more on the surface is 0. A processed stainless steel product with excellent corrosion resistance that is suppressed to 5 or less per 0.01 mm ² .

Since the processed stainless steel product of the present invention has polishing eyes on the surface of the processed stainless steel product, it has excellent design and antiglare properties. In addition, since the colored oxide film does not exist on the surface of the processed stainless steel product, rusting starting from the oxide film and the Cr-deficient layer immediately thereunder does not easily proceed, and corrosion resistance does not easily deteriorate. Furthermore, since the average number of surface defects including the metal base covering of 5 μm or more on the surface of the processed stainless steel product is suppressed to 5 or less per 0.01 mm ² , crevice corrosion is suppressed and corrosion resistance is excellent. It becomes a stainless steel processed product.

(2) The processed stainless steel product according to (1), wherein the processed stainless steel product is a shaped steel having a flange material and a web material, and the joint between the flange material and the web material is a laser welded joint.

(3) The method for producing a processed stainless steel product according to (1) or (2), which has a polishing step of polishing the surface of the processed stainless steel product by wet polishing.

(4) The method for producing a processed stainless steel product according to (1) or (2), including a polishing step of polishing the surface of the processed stainless steel product with a solid abrasive.

(5) Manufacture of the processed stainless steel product according to (1) or (2), which comprises a polishing step of polishing the surface of the stainless steel plate constituting the processed stainless steel product with a solid abrasive before forming the processed stainless steel product. Method.

(6) The manufacturing method according to any one of (3) to (5), wherein in the polishing step, a solid abrasive is attached to a polishing flap wheel to polish the surface of the processed stainless steel product.

According to the present invention, it is possible to provide a processed stainless steel product which is excellent in corrosion resistance and does not rust early even in a waterfront environment affected by sea salt particles. Further, it is possible to provide a method for manufacturing a processed stainless steel product having excellent corrosion resistance, which does not increase the number of manufacturing steps.

It is a schematic diagram which shows an example of the stainless processed product of this embodiment. It is an example of the photograph which expanded the surface of a stainless steel plate, and is the surface where (a) surface defect was suppressed and the surface where (b) surface defect occurred. It is a figure which shows an example of a surface defect and a current density change, and is a graph which shows the current density change in the pitting corrosion potential measurement of the stainless steel plate which has a surface defect used for a stainless steel processed product. It is a figure which shows an example of the relationship of a surface defect and a current density change, and is a graph which shows the current density change in the pitting corrosion potential measurement of the stainless steel plate used for the stainless steel processed product in which the surface defect was suppressed.

Modes for carrying out the present invention will be described below. The present invention is not limitedly interpreted by the embodiment.

(Stainless steel processed product)
The processed stainless steel product of the present invention has a polished surface on the surface of the processed stainless steel product, a colored oxide film does not exist on the surface, and a surface including a covering of a metal base of 5 μm or more on the surface. Since the average number of defects is suppressed to 5 or less per 0.01 mm ² , it is a processed stainless steel product having excellent corrosion resistance.

The processed stainless steel product is a product obtained by processing at least one stainless steel material, and may be, for example, a processed product composed of a plurality of stainless steel plates, or a processed product formed by welding a plurality of stainless steel plates. It may be.

FIG. 1 is a schematic view showing an example of a processed stainless steel product of this embodiment. As shown in FIG. 1, the processed stainless steel product 10 is an H-shaped steel including a flange material 11 a and a flange material 11 b which are stainless steel plates, and a web material 12 which is a stainless steel plate. The flange material 11a, the flange material 11b, and the web material 12 are preferably welded to each other.

The welding method may be high frequency welding or arc welding, but laser welding is preferable. According to the laser welding, the damaged region on the surface of the stainless steel plate due to the welding can be made as narrow as possible, and the processed product having the required welding strength can be easily manufactured. In particular, as described in Japanese Patent No. 5110642, when a T-shaped joint part in which the end portion of the web material is vertically pressed against the flange material is laser-welded to form a processed product, the end portion of the web material is formed. It is preferable to irradiate the laser light from only one side so as to hit only the end portion of the web material without pressing the surface of the flange material to the joint portion of the end portions of the web material while pressing the above and the flange material with each other. The molten portion in which the joint portion is melted by the irradiation of the laser light is pushed out from the joint portion, and the joining metal is spread to the outer region of the joint portion due to the solidification of the molten portion. This tends to suppress the formation of depressions in the joint portion, expand the cross-sectional area of the joint portion, and increase the joint strength. As described above, in the processed stainless steel product, the joint portion between the flange member and the web member is preferably a laser welded joint.

In the present invention, the processed stainless steel product has a surface that has been subjected to a polishing finish in order to impart irregularities and gloss to the surface. As a result, the processed stainless steel product is a processed stainless steel product having polishing marks and excellent in design and antiglare properties. Abrasive marks are flaws carved on the surface of a stainless steel workpiece by polishing.
The surface polishing of the processed stainless steel product may be performed, for example, by performing surface polishing on a stainless steel plate before the forming of the processed stainless steel product and using the polished stainless steel plate as a processed stainless steel product. Further, surface polishing may be performed after forming the stainless steel processed product.

The deeper the concave portion of the surface after polishing, the higher the possibility that the oxide film generated by flap wheel polishing etc. will remain, and the concave portion of the polished eye will serve as the starting point for rusting. And the corrosion resistance is likely to deteriorate. Therefore, the surface roughness Ra of the surface of the processed stainless steel product in the present invention after polishing is preferably 0.1 to 1.0 μm, and more preferably 0.2 to 0.5 μm. The surface roughness after polishing is measured according to JIS B 0601, and can be measured by, for example, a contact type surface roughness meter.

As a polishing finish, dry polishing with a flap wheel or the like has been conventionally performed, but when dry polishing is performed, the surface of a stainless steel processed product becomes hot and an oxide film is formed. On the other hand, the processed stainless steel product of the present invention is characterized in that a colored oxide film does not exist on the surface. The present inventors believe that the reason for this is that the processed stainless steel product of the present invention is that the oxide film on the surface is removed by polishing with a solid abrasive. Further, by attaching the solid abrasive to the polishing flap wheel, generation of an oxide film is further suppressed.

In the present invention, the presence of a colored oxide film means that when any 10 points on the surface of a stainless steel processed product are observed with an optical microscope at a magnification of 400 times, an oxide film that is a colored stain-like substance is present. An area ratio of 5% or more exists in a 50 μm square. Here, the coloring is not limited to a particular color, and may be any color as long as it can be visually distinguished from the metallic base material or metallic luster of the processed stainless steel product. A typical color for coloring is dark brown.

In addition, when dry polishing with a flap wheel etc. is performed as polishing finish, abrasives and polishing papers continuously contact the surface of the stainless steel processed product, the metal on the surface is partially peeled off and burrs on the base part are removed. Surface defects that are fogging occur. The surface defects cause crevice corrosion because minute gaps are formed between the surface base material portion of the stainless steel processed product.

FIG. 2 is an example of an enlarged photograph of the surface of a stainless steel plate, and shows (a) a surface with suppressed surface defects and (b) a surface with surface defects. FIG. 2(a) shows the surface of a stainless steel plate, which has polishing eyes, but surface defects are suppressed. On the other hand, FIG. 2B shows the surface of a stainless steel plate that has been dry-polished. Enclosed portions 1 to 9 show surface defects in which the metal on the surface is partially peeled off and the base portion is covered. The inventors of the present invention use a solid abrasive during polishing as a reason why the surface defects of the stainless steel plate used in the processed stainless steel product of the present invention are suppressed after polishing as shown in FIG. 2(a). Is analyzed. Further, by attaching the solid abrasive to the polishing flap wheel, surface defects are further suppressed. The white horizontal line in FIG. 2 indicates a convex portion formed during polishing, and the concave portion between the white horizontal line which is a convex portion and the adjacent white horizontal line is a polishing eye.

In the present invention, the surface defect is one in which the maximum length portion of the defect has a covering with a metal base having a size of 5 μm or more. In addition, when the range of 100 μm×100 μm (0.01 mm ² ) at any 10 points on the surface of the stainless steel workpiece polished using an optical microscope is magnified 200 times and observed, When the average is 5 or less, the surface defects in the present invention are suppressed. The number of surface defects on the surface of the polished stainless steel workpiece is more preferably 3 or less, still more preferably 2 or less, per unit area of 100 μm×100 μm (0.01 mm ² ). Although there is no upper limit on the maximum length of the surface defect, the upper limit may be set to 50 μm as a standard for measurement.

3 and 4 are diagrams showing an example of the relationship between surface defects and changes in current density, and FIGS. 3 and 4 show changes in current density in pitting potential measurement of a stainless steel plate used for a stainless steel processed product. It is a graph.

The pitting corrosion potential of stainless steel is measured according to JIS G 0577, and the B method is used. Method B is a pitting potential measuring method by a potentiodynamic method in a 3.5 mass% sodium chloride aqueous solution. The pH of the aqueous sodium chloride solution is 7 and the temperature is 30°C. The potential sweep rate is 20 mV/min.

As shown in FIG. 4, in the case of stainless steel plate having a surface which surface defects is suppressed, the current density changes in pitting potential measurement, change in the value of current density at a potential of less than the pitting potential is small, self-potential From the pit to the pitting potential, that is, the portion where the rate of change in current density (maximum current density/minimum current density) in the potential range of −0.08 to 0.5 V (B portion in FIG. 4) is 10 or more is unacceptable.

On the other hand, as shown in FIG. 3, in the case of a stainless steel sheet having surface defects, the change in the current density in the pitting potential measurement shows a large change in the value of the current density at a potential lower than the pitting potential, and the pitting potential changes from the natural potential. Until that time, that is, there are 10 or more portions where the rate of change of the current density exceeds 10 in the range of the potential of −0.03 to 0.35 V (portion A in FIG. 3). This large change in current density is due to the occurrence of corrosion. Therefore, the present inventors presume that the presence of crevice corrosion caused by the presence of surface defects is indicated. Therefore, in the present invention, in the change of the current density in the pitting potential measurement, there are 10 portions where the rate of change of the current density (maximum current density/minimum current density) in the range from the spontaneous potential to the pitting potential is 10 or more. It is preferably less than 5 and more preferably 5 or less.

As for the composition when ferritic stainless steel is used as the material of the processed stainless steel product of the present invention, for example, C is an element useful for obtaining the strength of steel, but if it is contained in a large amount, the corrosion resistance decreases. Since there is a tendency, 0.02 mass% or less is preferable. Si is an element useful as a deoxidizing agent and a heat source in the steel making process, but if contained in a large amount, Si tends to harden the steel, so Si is preferably 1.00 mass% or less. Mn is an element useful as deoxidation in the steelmaking process, but since it tends to form an austenite phase when it is contained in a large amount, it is preferably 2.00 mass% or less, more preferably 1.00 mass% or less. Cr is an element useful for ensuring corrosion resistance, but if it is contained in a large amount, not only high cost but also workability tends to be lowered, so 17.0 to 30.00 mass% is preferable, and 20. More preferably, it is from 00 to 24.00 mass %. Mo is an element useful for improving the corrosion resistance of stainless steel in the presence of Cr, but if it is included in a large amount, not only high cost but also workability tends to decrease, so 1.00 to 2. 50 mass% is preferable, and 1.00 to 1.50 mass% is more preferable. Since P reduces the corrosion resistance, it is preferable that the content of P is small, and 0.040 mass% or less is preferable. Since S reduces the corrosion resistance, it is preferable that the content of S is small, and 0.030 mass% or less is preferable. Ni is preferable because it has an effect of suppressing the progress of corrosion and is effective in improving the toughness of a ferritic stainless steel processed product, but if it is too much, it causes the formation of an austenite phase and the cost is high. % Or less is preferable. Ti and Nb preferably contain one or two of these. Ti is preferable in that it has a strong affinity with C and N and suppresses intergranular corrosion of a ferritic stainless steel processed product, but if a large amount of Ti is contained, the surface quality of the steel tends to be deteriorated. 0.5 mass% is preferable. Nb is preferable because it has a strong affinity with C and N and suppresses intergranular corrosion of a ferritic stainless steel processed product, but a large amount of Nb tends to impair toughness, so 0.1 to 0. 6 mass% is preferable. Since N tends to lower the corrosion resistance when it is contained in a large amount like C, 0.025 mass% or less is preferable. Al is an element effective for refining and casting as a deoxidizing agent, but if added excessively, it deteriorates the surface quality and also reduces the weldability and low temperature toughness of steel, so 0.01 to 0.50 mass. % Is preferred. The balance is preferably Fe and inevitable impurities. Further, for example, C is 0.02 mass% or less, Si is 0.40 mass% or less, Mn is 0.40 mass% or less, Cr is 21.00 to 23.00 mass%, and Mo is 1.00 to 1 .50 mass%, P is 0.040 mass% or less, S is 0.030 mass% or less, Ni is 0.60 mass% or less, Ti is 0.05 to 0.5 mass%, Nb is 0.10 to 10. It is also possible to use 0.6 mass%, N is 0.025 mass% or less, Al is 0.15 mass% or less, and the balance is Fe as the processed stainless steel product of the present invention.

The material for the processed stainless steel product of the present invention preferably has a pitting corrosion resistance index (PI) of 20 or more. PI is given by the following equation (1).
PI=Cr+3Mo Formula (1)

The processed stainless steel product of the present invention having a pitting corrosion resistance index (PI) of 20 or more has excellent corrosion resistance. For this reason, SUS304, which has a low pitting corrosion resistance index of 19, rusts early in a waterfront environment affected by sea salt particles, whereas the stainless steel processed product of the present invention suppresses rusting. it can. From the viewpoint of corrosion resistance, the pitting corrosion resistance index (PI) is more preferably 24 or more, further preferably 30 or more.

(Production method)
The method for producing a processed stainless steel product of the present invention is a production method having a polishing step of polishing the surface of the processed stainless steel product by wet polishing. Further, the method for producing a processed stainless steel product of the present invention is a production method having a polishing step of polishing the surface of the processed stainless steel product with a solid abrasive. The manufacturing method of the present invention may include a polishing step of polishing the surface of the stainless steel plate constituting the stainless steel processed product with a solid abrasive before forming the stainless steel processed product.

The solid abrasive may be used without particular limitation as long as it contains a fatty acid and a mineral oil.

The solid abrasive preferably contains an oxide such as SiO ₂ , Al ₂ O ₃ , or CrO ₂ . The content of oxides such as SiO ₂ , Al ₂ O ₃ , and CrO ₂ is preferably 50 to 80% by mass, more preferably 55 to 75% by mass, and 60 to 70% by mass. Is particularly preferable.

As the fatty acid, it is preferable to use stearic acid, myristic acid, or the like. As the mineral oil and fat, it is preferable to use palmitic acid or the like.

In the method for producing a processed stainless steel product of the present invention, in the polishing step, it is preferable that the surface of the processed stainless steel product be polished with a polishing flap wheel and a solid abrasive be attached to the polishing flap wheel.

As described above, when dry polishing was performed with a flap wheel or the like as the polishing finish, the stainless steel processed product surface was continuously contacted with the abrasive or the abrasive paper, and the metal on the surface was partially peeled off and the base material was covered. Surface defects such as burrs and fogging occur. On the other hand, in the method for manufacturing a processed stainless steel product of the present invention, it is preferable to perform wet polishing by attaching a solid abrasive to the polishing flap wheel. This makes it possible to reduce the abrasion resistance even when the abrasive material or the abrasive paper is continuously in contact with the surface of the stainless steel product, the metal on the surface is partially peeled off, and the burrs and coverings on the substrate are covered. It becomes easier to suppress the occurrence of surface defects.

The present invention is not limited to the above embodiment. For example, buffing using a solid abrasive may be performed after performing wet polishing by attaching a solid abrasive to the polishing flap wheel. Alternatively, after applying a solid abrasive and performing wet polishing, using a polishing device (air sander) equipped with a non-woven fabric to manually perform polishing with a combined motion of eccentric motion and rotary motion, random It is possible to manufacture a processed stainless steel product having a polished eye on the surface of the processed stainless steel product and suppressing a colored oxide film and surface defects.

Examples of the present invention will be described below. The present invention is not limitedly interpreted by the following examples.

The stainless steel plate used for the processed stainless steel product was subjected to decorative polishing finish. The following two types of stainless steel sheets were used. The composition (mass %) and dimensions are as follows.

Steel type 1 (SUS445J1) Cr: 22%, Mo: 1.05%, Ti: 0.2%, Nb: 0.2%, Al: 0.09%, balance Fe
Steel type 2 (SUS304) Cr: 18%, Ni: 8%, Si: 0.6%, Mn: 0.8%, balance Fe
Dimensions: thickness 1.5 mm x width 200 mm x length 1000 mm.

Polishing was performed on lines 1 to 4 as follows. The polishing conditions are as follows.

Line 1 is a line in which five flap wheels (#240, #240, #240, #400, #600) are lined up so as to polish the surface of the steel sheet (give a polishing eye).
Line 2 is a line in which four flap wheels (#240, #240, #240, #400) are arranged so as to polish the longitudinal direction of the steel sheet surface (give a polishing grain in the longitudinal direction).
The line 3 is a line in which four flap wheels (#150, #150, #150, #320) are arranged so as to polish the longitudinal direction of the steel plate surface (give a polishing grain in the longitudinal direction).
Line 4 includes three flap wheels (#320, #400, #600) arranged so as to polish the longitudinal direction of the steel plate surface (give longitudinal grain), and grind the steel plate surface (give abrasive grain). ) Is a line consisting of two cotton buffs (#400, #400) arranged side by side.
Here, in line 1 and line 4, the solid abrasive was applied to the flap wheel. On the other hand, in lines 2 and 3, the solid abrasive was not applied. Note that “#240” and the like indicate mesh grain size.

(Polishing conditions)
Line speed: 1.8m/min
Wheel speed: 1500rpm
Wheel diameter: 400mm

(Solid abrasive)
The solid abrasive had a SiO ₂ content of 75% by mass, a fatty acid content of stearic acid of 16% by mass, and a mineral oil content of palmitic acid of 3.8% by mass. ..

(Example 1)
The steel type 1 was polished in line 1 (with a solid abrasive applied).

(Example 2)
Steel type 1 was polished in line 3 (without solid abrasive coating) and then in line 4 (with solid abrasive coating). After that, using a polishing machine (air sander) with a non-woven fabric (#80) attached, you can use a polishing machine that does not apply a solid polishing agent, and use a motion that combines eccentric motion and rotary motion to achieve random polishing and uniform polishing. Done in work.

(Comparative Example 1)
The steel type 1 was polished in line 2 (without applying a solid abrasive).

(Comparative example 2)
The steel type 2 was polished in line 2 (without applying a solid abrasive).

(Reference example 1)
The steel type 2 was polished in line 1 (with the solid abrasive applied).

(Surface defect)
The surface of the polished stainless steel plate was magnified 200 times using an optical microscope, and an area of 100 μm×100 μm (0.01 mm ² ) was observed. When the number of surface defects having a metal base covering of 5 μm or more is 5 or less, the surface defects are evaluated as “○”, and when the number is more than 5, the surface defects are suppressed as “ It was evaluated as "X" (see Table 1).

As shown in Table 1, the stainless steel plate surfaces of Examples 1 and 2 were in a state where surface defects were suppressed. On the other hand, the surface defects of the stainless steel sheets of Comparative Examples 1 and 2 were not suppressed. In Reference Example 1, the surface defects were suppressed.

(Oxide film)
The surface of the stainless steel plate was observed with an optical microscope at a magnification of 400 times, and it was calculated how much the oxide film, which is a dark brown stain-like substance, was present in an area ratio of 50 μm square. When the area ratio of the residual oxide film is 3% or more and less than 5%, it is determined that there is no colored oxide film, and "○" is given. When the area ratio of the residual oxide film is less than 3%, it is " ⊚”, and when the area ratio was 5% or more, it was evaluated as “x” (see Table 1) because the colored oxide film was present.

As shown in Table 1, in Example 1, the area ratio of the oxide film was 1% or less, and in Example 2, the area ratio of the oxide film was 3%, and there was no oxide film having coloring. On the other hand, in Comparative Examples 1 and 2, the area ratio of the oxide film was 15% and 20%, and the surface of the stainless steel plate had the oxide film with coloring. In Reference Example 1, the area ratio of the oxide film was 2%, and there was no oxide film having coloring.

(Corrosion resistance test)
A corrosion resistance test (salt-dry-wet combined cycle test (CCT test)) was performed on the stainless steel sheets of Examples 1 and 2 and Comparative Examples 1 and 2 and Reference Example 1 under the following conditions.
Conditions: (1) Salt spray (35°C, 5% NaCl, 15 minutes)
(2) Drying (60°C, 30%RH, 60 minutes)
(3) Wetness (50°C, 95%RH, 3 hours)
The above conditions (1) to (3) were set as one cycle, and 30 cycles were repeated.
Evaluation: When the rusting area after the test is within 5% of the entire surface of the steel sheet, the corrosion resistance is considered to be good, and is evaluated as "○". Was evaluated as "x" because of poor corrosion resistance (see Table 1).

As shown in Table 1, in Examples 1 and 2, no rusting occurred on the surface even after the CCT test, and it was shown that the corrosion resistance was excellent. On the other hand, in Comparative Examples 1 and 2, rusting was generated on the surface after the CCT test, and the corrosion resistance was poor. In Reference Example 1, since the base material itself had a low corrosion resistance level, the corrosion resistance was Δ. The corrosion resistance level of the base material in a waterfront environment affected by sea salt particles preferably has a pitting corrosion resistance index (PI) of 24 or more.

1-9... Surface defect A, B... Current density change region

Claims (6)

It has a polished eye for anti-glare property on the surface of stainless steel processed product,
When observing any 10 points on the surface with an optical microscope at a magnification of 400 times, the area ratio of the colored oxide film is less than 5% in 50 μm square ,
When an area of 100 μm×100 μm at any 10 points on the surface is magnified 200 times using an optical microscope and observed , the average number of surface defects including the covering of the metal base of 5 μm or more on the surface is 0. A processed stainless steel product with excellent corrosion resistance, with 5 or less per 0.01 mm ² . The processed stainless steel product according to claim 1, wherein the processed stainless steel product is a shaped steel having a flange member and a web member, and a joint portion between the flange member and the web member is a laser welded joint. The method for producing a processed stainless steel product according to claim 1 or 2, further comprising a polishing step of polishing the surface of the processed stainless steel product by wet polishing. The method for manufacturing a processed stainless steel product according to claim 1, further comprising a polishing step of polishing the surface of the processed stainless steel product with a solid abrasive. The method for producing a processed stainless steel product according to claim 1, further comprising a polishing step of polishing the surface of the stainless steel plate constituting the processed stainless steel product with a solid abrasive before forming the processed stainless steel product. The manufacturing method according to claim 4 or 5 , wherein in the polishing step, the surface of the stainless steel processed product is polished by adhering the solid abrasive to a polishing flap wheel.