JP2017177191A - Stainless steel finished article excellent in corrosion resistance, and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a stainless steel finished article excellent in corrosion resistance, which is prevented from being early rusted even in a waterfront environment affected by sea salt particles, and a method of manufacturing the same.SOLUTION: Polishing marks are provided on a surface of a stainless steel finished article excellent in corrosion resistance. A colored oxide film does not exist on the surface. The average number of surface detects including a cover of a metallic substrate with a maximum length of 5 μm or more on the surface is kept within five per 0.01 mm.SELECTED DRAWING: Figure 2

Description

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

  Stainless steel is widely used in building materials such as roofing materials, wall materials, and building materials because it is excellent in weather resistance, workability, weldability, and the like. In addition, since stainless steel processed products are excellent in design, they are surface-polished and used in many applications such as shape 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 stainless steel processed product, first, polishing removal is performed to remove wrinkles and the like of the processed product before polishing, and then final polishing and gloss polishing are performed. In rough polishing and finish polishing in this polishing operation, dry polishing using a flap wheel, a polishing belt, or the like is performed. Further, after the above process, 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 the polished finish, it may not exhibit the weather resistance inherent to the material and may cause significant bruising. This is one of the factors that eliminate the stability (reliability) of weather resistance. For example, it may occur in a short period of about one month after construction on an outdoor handrail.

  It is considered that the starting point is the oxide film and polishing marks remaining on the polished surface of the processed stainless steel product. The remaining oxide film is a film generated due to heat generation during polishing, and a Cr-deficient layer is formed immediately below the oxide film. For this reason, if the oxide film remains, the firing proceeds from the oxide film and the Cr-deficient layer immediately below the oxide film, and the corrosion resistance tends to deteriorate. In addition, with respect to the polishing marks, which are wrinkles carved on the surface of the processed stainless steel product by polishing, the deeper the recesses in the polishing eyes, the harder the oxide film generated by flap wheel polishing and the like can be removed by buffing. Since the property becomes high and the concave portion of the polished eye becomes a starting point, the wrinkling proceeds and the corrosion resistance tends to deteriorate.

  Patent Documents 1 and 2 propose a stainless steel sheet that can suppress the occurrence of wrinkling in a short period of time and maintain the weather resistance.

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

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

  Moreover, in the manufacturing method of patent document 1, after performing 800 degreeC or more heat processing in a reducing atmosphere, stainless steel is further added to the oxidizing solution containing 0.1 ppm or more ozone and / or 5 mass% or more nitric acid. It is described that it is immersed.

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

  Patent Document 2 discloses that when a stainless steel plate after mechanical polishing is exposed to an air atmosphere, the passive film is not sufficiently regenerated and the corrosion resistance is reduced, so that the stainless steel plate after mechanical polishing is pickled. A surface finishing method for a stainless steel sheet is described. However, performing pickling after mechanical polishing of a stainless steel plate has a problem that the number of steps increases as a manufacturing method.

  In addition, building demand has increased in recent years due to urban redevelopment, etc., and building demand in the waterfront environment has increased. In the 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 seawater. For this reason, 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 excellent in corrosion resistance that does not start early even in a waterfront environment affected by sea salt particles. Moreover, it aims at providing the manufacturing method of the stainless steel processed goods excellent in the 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 stainless steel workpiece. Here, when dry polishing is performed, the surface of the stainless steel workpiece becomes high temperature during polishing and an oxide film is generated, and there is a surface defect along with polishing marks that are engraved by high grinding resistance due to dry polishing. I found out. The surface defect here means that when polishing the surface of the steel workpiece, the abrasive or abrasive paper continuously contacts the surface of the steel workpiece and is polished, so that the metal on the surface is partially peeled off and the substrate It is a defect having a shape that covers a part, and is called “burr” or “cover”. The surface defect includes a portion where the metal is turned up like a strip shape or a bamboo leaf shape, and the maximum length from one end portion of the portion adhered to the substrate to the other end portion of the peeling tip is 5 μm. It is the above defect. 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 the corrosion resistance of the steel processed product.

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

That is, this invention provides the stainless steel processed goods excellent in the corrosion resistance of the following (1)-(6), and its manufacturing method.
(1) The polished surface has a polished surface on the surface of the processed stainless steel product, no colored oxide film is present on the surface, and the average number of surface defects including a metal substrate covering of 5 μm or more on the surface is 0. .01mm is suppressed within five per ^2, good stainless steel workpiece to corrosion.

Since the processed stainless steel product of the present invention has polished eyes on the surface of the processed stainless steel product, it is excellent in design and antiglare properties. In addition, since the colored oxide film does not exist on the surface of the processed stainless steel product, the firing starting from the oxide film and the Cr-deficient layer immediately below the oxide film hardly proceeds, and the corrosion resistance is not easily deteriorated. Furthermore, since the average number of surface defects including the covering of the metal substrate 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 the corrosion resistance is excellent. Stainless steel processed product.

(2) The stainless steel processed product according to (1), wherein the stainless steel processed product is a shaped steel including a flange material and a web material, and a 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), comprising 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), comprising a polishing step of polishing the surface of the processed stainless steel product with a solid abrasive.

(5) Manufacturing of the stainless steel processed product according to (1) or (2), which has 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 processed stainless steel product. Method.

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

  ADVANTAGE OF THE INVENTION According to this invention, even in the waterfront environment which receives the influence of sea salt particle | grains, the stainless steel processed goods excellent in corrosion resistance which do not start early can be provided. Moreover, the manufacturing method of the stainless steel processed goods excellent in the corrosion resistance which does not increase a manufacturing process can be provided.

It is a schematic diagram which shows an example of the stainless steel processed goods of this embodiment. It is an example of the photograph which expanded the surface of the stainless steel plate, (a) The surface where the surface defect was suppressed, and (b) The surface where the surface defect produced. It is a figure which shows an example of the relationship between 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 the surface defect used for a stainless steel processed goods. It is a figure which shows an example of the relationship between 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 in which the surface defect used for stainless steel processed goods was suppressed.

  The form for implementing this invention is demonstrated below. The present invention is not construed as being limited 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 the surface includes a metal substrate covering of 5 μm or more on the surface. Since the average number of defects is suppressed to within 5 per 0.01 mm ² , it is a processed stainless steel product with excellent corrosion resistance.

  The processed stainless steel product is obtained by processing at least one stainless steel material. For example, the processed product may be a processed product composed of a plurality of stainless steel plates, or a processed product configured by welding a plurality of stainless steel plates. There may be.

  FIG. 1 is a schematic diagram showing an example of a processed stainless steel product of the present 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 that are stainless steel plates, and a web material 12 that is a stainless steel plate. It is preferable that the flange material 11a, the flange material 11b, and the web material 12 are welded to each other.

  As a welding method, high-frequency welding or arc welding may be used, but laser welding is preferable. According to laser welding, the damaged area on the surface of the stainless steel plate due to welding can be made as narrow as possible, and a processed product having a required welding strength can be easily manufactured. In particular, as described in Japanese Patent No. 5110642, when a workpiece is formed by laser welding a T-shaped joint portion in which an end portion of a web material is pressed perpendicularly to a flange material, the end portion of the web material is formed. It is preferable that the laser beam is irradiated from only one side so as to hit only the edge of the web material without contacting the surface of the flange material while pressing the flange material and the flange material against each other. The melted 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 spreads to the outer region of the joint portion due to solidification of the melted portion. As a result, the formation of dents at the joint portion is suppressed, the cross-sectional area of the joint portion is enlarged, and the joint strength tends to increase. Thus, in this stainless steel processed product, the joint between the flange material and the web material is preferably a laser welded joint.

In the present invention, the processed stainless steel product has a surface polished for imparting unevenness and gloss to the surface. As a result, the processed stainless steel product has a polished eye and becomes a processed stainless steel product excellent in design and antiglare properties. Polishing eyes are ridges carved on the surface of a stainless steel workpiece by polishing.
The surface polishing of the stainless steel processed product may be performed by polishing the surface of, for example, a stainless steel plate before forming the stainless steel processed product and using the polished stainless steel plate as a stainless steel processed product. Further, surface polishing may be performed after the stainless steel processed product is formed.

  As the surface of the polished surface after polishing becomes deeper, the oxide film produced by flap wheel polishing or the like is more likely to remain, and the recessed portion of the polished surface becomes the starting point. Progresses and the corrosion resistance tends to deteriorate. Therefore, the surface roughness Ra after polishing of the surface of the processed stainless steel product in the present invention 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.

  Conventionally, dry polishing using a flap wheel or the like has been performed as a polishing finish. However, when dry polishing is performed, the surface of the stainless steel processed product becomes high temperature 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 consider that the reason is that the processed stainless steel product of the present invention is due to removal of the oxide film on the surface by polishing with a solid abrasive. Moreover, the generation of an oxide film is further suppressed by attaching a solid abrasive to the polishing flap wheel.

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

  Moreover, when dry polishing is performed using a flap wheel or the like as the polishing finish, the abrasive or polishing paper continuously contacts the surface of the stainless steel workpiece, the surface metal is partially peeled off, A surface defect that is a fogging occurs. The surface defect causes crevice corrosion because a minute gap is generated between the surface base portion of the processed stainless steel product.

  FIG. 2 is an example of a photograph in which the surface of the stainless steel plate is enlarged, (a) a surface in which surface defects are suppressed and (b) a surface in which surface defects are generated. FIG. 2 (a) shows the surface of a stainless steel plate, which has polished eyes but suppresses surface defects. On the other hand, FIG. 2 (b) shows the surface of the stainless steel plate that has been dry-polished, and the surrounding portions 1 to 9 show surface defects in which the metal on the surface is partially peeled and covered with the base portion. As the 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), the present inventors use a solid abrasive during polishing. It is analyzed. Moreover, surface defects are further suppressed by attaching a solid abrasive to the polishing flap wheel. Note that the white horizontal lines in FIG. 2 indicate convex portions formed during polishing, and the concave portions between the white horizontal lines that are convex portions and the adjacent white horizontal lines are polishing eyes.

In the present invention, the surface defect means that the maximum length portion of the defect has a covering of a metal substrate having a size of 5 μm or more. In addition, when the range of 100 μm × 100 μm (0.01 mm ² ) at an arbitrary 10 points on the surface of a stainless steel workpiece polished using an optical microscope is magnified 200 times, the number of surface defects measured 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 preferably 3 or less, more preferably 2 or less per unit area of 100 μm × 100 μm (0.01 mm ² ). In addition, although there is no upper limit in the maximum length part of a surface defect, it is good also considering an upper limit as 50 micrometers as a reference | standard at the time of measuring.

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

  The method for measuring the pitting corrosion potential of stainless steel is based on JIS G 0577 and uses the B method. Method B is a pitting potential measurement method by a kinetic potential method in a 3.5% by 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 To the pitting corrosion potential, that is, the portion where the rate of change in current density (maximum current density / minimum current density) is 10 or more in the potential range of −0.08 to 0.5 V (part B in FIG. 4) unacceptable.

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

  As a composition in the case of using ferritic stainless steel as a raw 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 is lowered. Since it exists in the tendency, 0.02 mass% or less is preferable. Si is an element useful as a deoxidizer and a heat source in the steelmaking process, but when it is contained in a large amount, it tends to harden the steel, so 1.00% by mass or less is preferable. Mn is an element useful as deoxidation in the steelmaking process. However, when it is contained in a large amount, Mn tends to form an austenite phase, and is preferably 2.00% by mass or less, and more preferably 1.00% by mass or less. Although Cr is an element useful for ensuring corrosion resistance, when it is contained in a large amount, it tends to decrease not only the high cost but also the workability, so that it is preferably 17.00 to 30.00% by mass. More preferably, it is 00-24.00 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, it tends to decrease not only the high cost but also the workability. 50 mass% is preferable and 1.00-1.50 mass% is more preferable. Since P reduces corrosion resistance, the smaller one is preferable and 0.040 mass% or less is preferable. Since S reduces corrosion resistance, the smaller one is preferable, and 0.030% by mass or less is preferable. Ni is preferable because it is effective in suppressing the progress of corrosion and effective in improving the toughness of the ferritic stainless steel processed product. However, if it is too much, it causes generation of austenite phase and high cost, so 0.6 mass % Or less is preferable. Ti and Nb preferably contain one or two of these. Ti has a strong affinity with C and N, and is preferable in terms of suppressing intergranular corrosion of ferritic stainless steel processed products. However, since a large amount of Ti tends to deteriorate the surface quality of the steel, 0.05 to 0.5 mass% is preferable. Nb has a strong affinity with C and N, and is preferable in terms of suppressing intergranular corrosion of the ferritic stainless steel processed product. However, since a large amount of Nb tends to inhibit toughness, 0.1 to 0. 6 mass% is preferable. N, if included in a large amount like C, tends to lower the corrosion resistance, so 0.025% by mass or less is preferable. Al is an element effective for refining and casting as a deoxidizer, but when added in excess, it degrades the surface quality and lowers the weldability and low temperature toughness of the steel, so 0.01 to 0.50 mass. % Is preferred. The balance is preferably Fe and inevitable impurities. 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%, 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%, and Nb is 0.10. 0.6% by mass, N is 0.025% by mass or less, Al is 0.15% by mass or less, and the balance is Fe, and the processed stainless steel product of the present invention can also be used.

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

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

(Production method)
The manufacturing method of the processed stainless steel product of the present invention is a manufacturing method including a polishing step of polishing the surface of the processed stainless steel product by wet polishing. Moreover, the manufacturing method of the stainless steel processed goods of this invention is a manufacturing method which has the grinding | polishing process which grind | polishes the surface of a stainless steel processed goods with a solid abrasive | polishing agent. In the manufacturing method of this invention, you may have the grinding | polishing process which grind | polishes the surface of the stainless steel plate which comprises a stainless steel processed goods with a solid abrasive before shaping | molding of a stainless steel processed goods.

  The solid abrasive can be used without particular limitation as long as it contains a fatty acid and 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 preferred.

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

  In the method for producing a processed stainless steel product, in the polishing step, the surface of the processed stainless steel product is preferably polished with a polishing flap wheel, and a solid abrasive is adhered to the polishing flap wheel.

  As described above, when dry polishing with a flap wheel or the like was performed as a polishing finish, the abrasive or polishing paper contacted the stainless steel workpiece surface continuously, and the metal on the surface was partially peeled off and covered the substrate portion. Surface defects such as burrs and fogging occur. In contrast, in the method for producing 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 polishing resistance even when abrasive materials or abrasive paper continuously contact the surface of the stainless steel workpiece, and the metal on the surface is partially peeled off, so that the burrs and fogging that covers the substrate are covered. It becomes easier to suppress the occurrence of surface defects.

  In addition, this invention is not restrict | limited by the said embodiment. For example, after performing wet polishing by attaching a solid abrasive to a polishing flap wheel, buffing using a solid abrasive may be performed. Also, after applying a solid abrasive and performing wet polishing, using a polishing apparatus (air sander) attached with a nonwoven fabric, and manually polishing by a movement that combines eccentric motion and rotational motion, it is also possible to randomly 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 colored oxide films and surface defects.

  Examples of the present invention will be described below. In addition, this invention is not limitedly interpreted by the following examples.

  The stainless steel plate used for the stainless steel processed product was subjected to a decorative polishing finish. The following two types of stainless steel plates 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 (provide polishing eyes).
Line 2 is a line in which four flap wheels (# 240, # 240, # 240, # 400) are lined up so as to polish the longitudinal direction of the steel sheet surface (provide a polishing grain in the longitudinal direction).
Line 3 is a line in which four flap wheels (# 150, # 150, # 150, # 320) are lined up so as to polish the longitudinal direction of the steel sheet surface (provide a polishing grain in the longitudinal direction).
Line 4 comprises three flap wheels (# 320, # 400, # 600) arranged so as to polish the longitudinal direction of the steel sheet surface (providing abrasive grains in the longitudinal direction), and polishing the steel sheet surface (giving abrasive eyes) ) Is a line made up of two cotton buffs (# 400, # 400) arranged side by side.
Here, in line 1 and line 4, a solid abrasive was applied to the flap wheel. On the other hand, no solid abrasive was applied in line 2 and line 3. “# 240” and the like indicate the mesh granularity.

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

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

Example 1
About the steel type 1, it grind | polished by the line 1 (with solid abrasive | polishing agent application | coating).

(Example 2)
About the steel type 1, after grinding | polishing by the line 3 (without solid abrasive | polishing agent application | coating), it grind | polished by the line 4 (with solid abrasive | polishing agent application | coating). Then, using a polishing device (air sander) with a non-woven fabric (# 80) attached, it was possible to polish evenly with random polishing eyes by applying a combination of eccentric motion and rotational motion without applying a solid abrasive. Done by work.

(Comparative Example 1)
About the steel type 1, it grind | polished by the line 2 (no solid abrasive application | coating).

(Comparative Example 2)
About the steel type 2, it grind | polished by the line 2 (no solid abrasive application | coating).

(Reference Example 1)
About the steel type 2, it grind | polished by the line 1 (with solid abrasive | polishing agent application | coating).

(Surface defect)
The polished stainless steel plate surface was magnified 200 times using an optical microscope, and a range of 100 μm × 100 μm (0.01 mm ² ) was observed. When the number of surface defects having a metal substrate covering of 5 μm or more is 5 or less, it is evaluated as “◯” as a state in which the surface defects are suppressed. X "(refer to Table 1).

  As shown in Table 1, the surface of the stainless steel plate of Examples 1 and 2 was in a state in which surface defects were suppressed. On the other hand, the surface of the stainless steel plate of Comparative Examples 1 and 2 was not in a state where surface defects were suppressed. Reference Example 1 was a state in which 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 brownish brown stain-like substance, was present in an area ratio in a 50 μm square. When the area ratio of the remaining oxide film is 3% or more and less than 5%, “O” indicates that there is no colored oxide film, and when the area ratio of the remaining oxide film is less than 3%, “ When the area ratio was 5% or more, it was evaluated as “x” because there was a colored oxide film (see Table 1).

  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 colored oxide film. On the other hand, in Comparative Examples 1 and 2, the area ratio of the oxide film was 15% and 20%, and the surface was a stainless steel plate surface on which a colored oxide film was present. In Reference Example 1, the area ratio of the oxide film was 2%, and there was no colored oxide film.

(Corrosion resistance test)
The stainless steel plates of Examples 1 and 2, Comparative Examples 1 and 2 and Reference Example 1 were subjected to a corrosion resistance test (salt-dry moisture combined cycle test (CCT test)) under the following conditions.
Conditions: (1) Salt spray (35 ° C., 5% NaCl, 15 minutes)
(2) Drying (60 ° C., 30% RH, 60 minutes)
(3) Wet (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 surface area after the test is within 5% of the entire surface of the steel sheet, the corrosion resistance is evaluated as “Good”, and when it is larger than 5% but not larger than 15%, “△” is larger than 15%. Was evaluated as “x” because of its poor corrosion resistance (see Table 1).

  As shown in Table 1, in Examples 1 and 2, the surface was not wrinkled even after the CCT test, indicating that it was excellent in corrosion resistance. On the other hand, in Comparative Examples 1 and 2, wrinkles occurred on the surface after the CCT test, and the corrosion resistance was poor. In Reference Example 1, since the corrosion resistance level of the base material itself was low, the corrosion resistance was Δ. As for the base material corrosion resistance level in the waterfront environment affected by sea salt particles, the pitting corrosion resistance index (PI) is preferably 24 or more.

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

Claims (6)

Has a polishing eye on the surface of the stainless steel processed product,
There is no colored oxide film on the surface,
A processed stainless steel product having excellent corrosion resistance, wherein the average number of surface defects including a metal substrate covering of 5 μm or more on the surface is suppressed to 5 or less per 0.01 mm ² .   The stainless steel processed product according to claim 1, wherein the stainless steel processed product is a shape steel including a flange material and a web material, and a joint portion between the flange material and the web material is a laser welded joint.   The manufacturing method of the stainless steel processed goods of Claim 1 or 2 which has a grinding | polishing process which grind | polishes the surface of the said stainless steel processed goods by wet grinding | polishing.   The manufacturing method of the stainless steel processed goods of Claim 1 or 2 which has the grinding | polishing process of grind | polishing the surface of the said stainless steel processed goods with a solid abrasive | polishing agent.   The manufacturing method of the stainless steel processed goods of Claim 1 or 2 which has the grinding | polishing process of grind | polishing the surface of the stainless steel plate which comprises the said stainless steel processed goods with a solid abrasive before shaping | molding of the said stainless steel processed goods.   The manufacturing method according to claim 3, wherein in the polishing step, the surface of the processed stainless steel product is polished by attaching the solid abrasive to a polishing flap wheel.