JP6685160B2 - Stainless steel plate with excellent corrosion resistance - Google Patents

Description

  The present invention relates to a stainless steel plate having excellent corrosion resistance.

  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. Further, since the stainless steel plate is excellent in design, it is used after being surface-polished.

  In general and industrial polishing of this stainless steel sheet, first, in order to remove flaws and the like of the steel sheet before polishing, flaw 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. Further, 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 raw 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 plate after polishing. The remaining oxide film is a film formed 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. In addition, even with respect to the polishing marks that are scratches on the surface of the stainless steel plate due to polishing, the deeper the recesses of the polishing marks, the more difficult the oxide film generated by flap wheel polishing or the like is to be removed by buff polishing, and it may remain. Since the height becomes higher and the recessed portion becomes the starting point of rusting, rusting proceeds and corrosion resistance is likely to deteriorate.

  Patent Documents 1 to 3 propose a stainless steel sheet and a manufacturing method thereof for the purpose of suppressing rusting in a short period of time and maintaining weather resistance.

JP, 2002-3938, A JP, 2003-25209, A JP, 5-263278, A

Patent Document 1 is characterized in that a stainless steel plate containing 16 mass% or more of Cr is polished and then 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 stainless steel plate obtained by a method for producing a stainless steel polishing finish having excellent weather resistance is described.
In addition, in the manufacturing method of Patent Document 1, after performing heat treatment at 800 ° C. or higher in a reducing atmosphere, stainless steel is added to an oxidizing solution containing 0.1 ppm or higher ozone and / or 5 mass% or higher nitric acid. A stainless steel plate obtained by immersion is described.

  Patent Document 2 discloses a method for solving the problems such as an increase in the number of batch processing steps in the method for treating polishing burn by dipping in an acid solution, and a problem in that mechanical polishing requires a lot of man-hours to completely remove polishing burn. Disclosed is a stainless steel obtained by a polishing method in which an abrasive having an oxide of a rare earth element as a main component is applied to the polishing tool when polishing the above with an elastic polishing tool.

  In Patent Document 3, 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 stainless steel sheet obtained by the surface finishing method is described.

  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, there is an increasing need for building members having higher corrosion resistance. In addition, there is a need for a building member that has excellent anti-glare properties in addition to high corrosion resistance. On the other hand, the above Patent Documents 1 to 3 do not describe or suggest any stainless steel sheet having both corrosion resistance and antiglare property against sea salt particles.

  It is an object of the present invention to solve the above problems and to provide a stainless steel sheet having excellent corrosion resistance and antiglare property, which does not rust early even in a waterfront environment affected by sea salt particles. .

  The present inventors have studied a polishing method and a polishing surface of a stainless steel plate in order to solve the above problems. Here, when dry polishing is performed, the surface of the stainless steel plate becomes high in temperature during polishing, an oxide film is generated, and a surface defect is generated along with a polishing eye that is a flaw carved by high grinding resistance due to dry polishing. I found it. The term "surface defect" used here means that when polishing the steel plate surface, the abrasive or polishing paper continuously contacts the steel plate surface, and the metal on the surface is partially peeled off. It is called. 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 substrate 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 plate, corrosion is likely to occur, which causes a reduction in corrosion resistance of the steel plate.

  The present inventors have studied a stainless steel sheet having excellent corrosion resistance and anti-glare property, which does not rust early in a waterfront environment affected by sea salt particles, and found the present invention.

That is, the present invention provides the following stainless steel sheets having excellent corrosion resistance (1) to (2).
(1) Having a unidirectional longitudinal grain on the surface of a ferritic stainless steel plate, a pitting potential of 0.6 V or more, a 60-degree gloss of 75 or less, and a composition of C: 0.020 mass. % Or less, Si: 0.40 mass% or less, Mn: 0.40 mass% or less, Cr: 25.00-32.00 mass%, Mo: 1.00-4.00 mass%, P: 0.030. % Or less, S: 0.020% by mass or less, Ni: 0.50% by mass or less, N: 0.020% by mass or less, the balance being Fe and unavoidable impurities, and the pitting corrosion resistance index (PI = PI = Cr mass% + 3Mo mass%) is 30 or more, and is a stainless steel plate having excellent corrosion resistance.

  The stainless steel sheet of the present invention has a colored oxide film on the surface of the stainless steel sheet and has a predetermined composition even if surface defects are present, and has a high pitting corrosion resistance (PI) of 30 or more. Therefore, it is a stainless steel sheet having excellent corrosion resistance with a pitting potential of 0.6 V or more, in which rusting originating from the oxide film and the Cr-deficient layer immediately below it is suppressed. Further, since the ferritic stainless steel sheet has a grain in one longitudinal direction on the surface, the design is excellent, and the 60-degree gloss is 75 or less, so the anti-glare property is also excellent.

(2) Further, one or more of Nb: 0.1 to 1.0% by mass, Ti: 0.05 to 0.3% by mass, and Al: 0.01 to 0.5% by mass. Including the stainless steel plate according to (1).

  According to the present invention, it is possible to provide a stainless steel sheet that is excellent in corrosion resistance and antiglare property and does not rust early even in a waterfront environment affected by sea salt particles.

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 graph which shows an example of the measurement result of the pitting corrosion potential of the stainless steel plate which has a surface defect. It is a graph which shows an example of the measurement result of the pitting corrosion potential of the stainless steel plate in which the surface defect was suppressed. It is the photograph which expanded the surface of the stainless steel plate of this invention. 3 is a graph showing the measurement results of pitting potential of Example 1.

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

(Stainless steel plate)
INDUSTRIAL APPLICABILITY The stainless steel sheet of the present invention has a unidirectional longitudinal grain on the surface of a ferritic stainless steel sheet, has a pitting potential of 0.6 V or more, a 60 degree glossiness of 75 or less, and a composition of C: 0.020 mass% or less, Si: 0.40 mass% or less, Mn: 0.40 mass% or less, Cr: 25.00-32.00 mass%, Mo: 1.00-4.00 mass%, P : 0.030 mass% or less, S: 0.020 mass% or less, Ni: 0.50 mass% or less, N: 0.020 mass% or less, the balance consisting of Fe and inevitable impurities, and pitting corrosion resistance It is a stainless steel plate having an index (PI = Cr mass% + 3Mo mass%) of 30 or more and excellent in corrosion resistance.

  In the present invention, the stainless steel sheet has a surface that has been subjected to polishing and finishing in order to impart unevenness and gloss to the surface. As a result, the stainless steel plate has a polished eye and becomes a stainless steel plate having excellent design and antiglare properties. The grind is a flaw carved on the surface of a stainless steel plate by grinding. In the present invention, the polishing stitches include polishing stitches in one longitudinal direction. A stainless steel plate having a longitudinal grain in one direction has excellent antiglare properties. When dry polishing with a flap wheel or the like is performed as polishing finish in one direction in the longitudinal direction, the surface of the stainless steel plate becomes high temperature, and a colored oxide film is formed. Further, the polishing grain of the surface after polishing, the deeper the concave portion of the polishing eye, the higher the possibility that the oxide film generated by the flap wheel polishing or the like will remain, and the concave portion of the polishing eye becomes the rust starting point, Corrosion is likely to deteriorate due to the progress of rusting. In the present invention, the presence of a colored oxide film means that when any 10 points on the surface of the stainless steel plate are observed with an optical microscope at a magnification of 400 times, the oxide film, which is a colored stain-like substance, has a size of 50 μm square. The area ratio is 10% or more. Here, the coloring is not limited to a particular color, and may be any color that can be visually distinguished from the metallic base material or metallic luster of the stainless steel plate. A typical color for coloring is dark brown.

Also, when dry polishing with a flap wheel etc. is performed as polishing finish, abrasives and polishing papers continuously contact the stainless steel plate surface, the metal on the surface is partially peeled off and it is a burr or a cover that covers the base part. Surface defects occur. The surface defect causes a crevice corrosion because a minute gap is generated between the surface base material portion of the stainless steel plate. FIG. 1 is 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. The surface of the stainless steel plate of FIG. 1 (a) has a polishing grain, but surface defects are suppressed. On the other hand, the surface of the stainless steel plate of FIG. 1 (b) is dry-polished, and the enclosing portions 1 to 9 indicate surface defects in which the surface metal is partially peeled off and the base portion is covered. In the present invention, the surface defect has a maximum length of 5 μm or more from one end of the portion bonded to the base material to the other end of the peeling tip. 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 plate polished using an optical microscope is magnified 200 times and observed, the average number of surface defects measured is The case of 6 or more is regarded as the state where the surface defects in the present invention are not suppressed. There is no upper limit on the maximum length portion of the surface defect, but the upper limit may be 50 μm as a standard for measurement.

  From the technical common sense of those skilled in the art, in order to suppress the progress of rusting and the deterioration of corrosion resistance, there is no oxide film having the above-mentioned coloring on the surface of the polished stainless steel plate, as shown in FIG. Since it is preferable that there are no surface defects such as burrs and fogging, it has been used pickling treatment to remove the oxide film. However, in the stainless steel sheet of the present invention, an oxide film having coloring may be present, surface defects may not be suppressed, and the progress of rusting and deterioration of corrosion resistance may be caused without performing pickling treatment. It is a steel plate that can be suppressed.

  The composition of the stainless steel sheet of the present invention is C: 0.020 mass% or less, Si: 0.40 mass% or less, Mn: 0.40 mass% or less, Cr: 25.00-32.00 mass%, Mo. : 1.00 to 4.00 mass%, P: 0.030 mass% or less, S: 0.020 mass% or less, Ni: 0.50 mass% or less, N: 0.020 mass% or less, and the balance Is Fe and inevitable impurities, and has a pitting corrosion resistance index (PI = Cr mass% + 3Mo mass%) of 30 or more. The ferritic stainless steel sheet of the present invention having the above composition and having a pitting corrosion resistance index (PI) of 30 or more has a high pitting potential of 0.6 V or more and is excellent in corrosion resistance, and thus has a low pitting resistance index of 19 In the waterfront environment in which SUS304 is affected by sea salt particles, rusting occurs early, whereas rusting can be suppressed. Further, even if there is a colored oxide film or surface defect caused by polishing, rusting can be suppressed.

  The stainless steel sheet of the present invention further comprises one or more of Nb: 0.1 to 1.0% by mass, Ti: 0.05 to 0.3% by mass, and Al: 0.01 to 0.5% by mass. It is preferable to include two or more kinds. Corrosion resistance tends to be further improved by containing a predetermined amount of Nb, Ti and / or Al.

The reasons for limiting the components of the stainless steel plate will be described below.
C is an element useful for obtaining the strength of steel, but if it is contained in a large amount, it tends to lower the corrosion resistance. The content of C is preferably 0.015 mass% or less, more preferably 0.010 mass% or less.

  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. The Si content is preferably 0.35% by mass or less, and more preferably 0.30% by mass or less.

  Mn is an element useful as deoxidation in the steelmaking process, but if it is contained in a large amount, it tends to form an austenite phase. The Mn content is preferably 0.35% by mass or less, and more preferably 0.30% by 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 decrease. 25.00-31.50 mass% is preferable, and, as for content of Cr, 25.00-31.00 mass% is more preferable.

  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. The Mo content is preferably 1.50 to 4.00 mass%, more preferably 1.80 to 3.80 mass%.

  P tends to reduce the corrosion resistance. 0.025 mass% or less is preferable and, as for content of P, 0.020 mass% or less is more preferable.

  S tends to reduce the corrosion resistance. 0.015 mass% or less is preferable and, as for content of S, 0.010 mass% or less is more preferable.

  Ni is preferable in that it is effective in suppressing the progress of corrosion and effective in improving the toughness of the ferritic stainless steel sheet, but if it is too large, it causes the formation of an austenite phase and increases the cost. The Ni content is preferably 0.45 mass% or less, more preferably 0.40 mass% or less.

  When N is contained in a large amount like C, the corrosion resistance tends to decrease. The content of N is preferably 0.015 mass% or less, more preferably 0.010 mass% or less.

  Nb is preferable because it has a strong affinity with C and N and suppresses the intergranular corrosion of the ferritic stainless steel sheet, but the inclusion of a large amount of Nb tends to hinder the toughness. The content of Nb is more preferably 0.1 to 0.9% by mass, further preferably 0.1 to 0.8% by mass.

  Ti is preferable because it has a strong affinity with C and N and suppresses the intergranular corrosion of the ferritic stainless steel sheet, but the inclusion of a large amount of Ti tends to deteriorate the surface quality of the steel. The content of Ti is more preferably 0.05 to 0.25% by mass, further preferably 0.05 to 0.2% by mass.

  Al is an element effective for refining and casting as a deoxidizing agent, but if added in excess, it deteriorates the surface quality and reduces the weldability and low temperature toughness of steel. The content of Al is more preferably 0.01 to 0.45% by mass, further preferably 0.01 to 0.4% by mass.

  2 and 3 are diagrams showing surface defects and pitting potentials, and FIG. 2 is a graph showing measurement results of pitting potentials of stainless steel plates having surface defects. FIG. 3 is a graph showing the measurement results of the pitting potential of the stainless steel plate in which the surface defects are suppressed. The stainless steel plates of FIGS. 2 and 3 are stainless steel plates having a pitting corrosion resistance index (PI) of about 24, which is lower than the pitting corrosion resistance index (PI) of the present invention. As shown in FIG. 2, the pitting potential of a stainless steel plate having surface defects is a low value of about 0.3V. Further, as shown in FIG. 3, the pitting corrosion potential of the stainless steel plate with suppressed surface defects is a low value of about 0.5V. On the other hand, the stainless steel sheet of the present invention has a high pitting potential of 0.6 V or more and is excellent in corrosion resistance. Therefore, even if a colored oxide film or a surface defect is present, the progress of rusting and the deterioration of corrosion resistance can be suppressed. The pitting potential is more preferably 0.65 V or higher, and further preferably 0.7 V or higher.

  The pitting corrosion potential measurement method for stainless steel is based on 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 speed is 20 mV / min.

  The surface roughness Ra of the surface of the stainless steel sheet according to the present invention is preferably 0.1 to 1.0 μm, and more preferably 0.2 to 0.5 μm. When the surface roughness Ra is less than 0.1 μm, the antiglare property is inferior, and further, polishing residue is difficult to be maintained and the designability tends to be difficult to be secured.

  Regarding the glossiness of the surface of the stainless steel plate in the present invention, the 60-degree glossiness is preferably 75 or less. It is more preferably 60 or less. The glossiness is measured according to JIS Z 8741, and can be measured by, for example, a gloss meter. Specifically, when measuring the glossiness, a light beam having a specified opening angle is made incident on the sample surface at a specified incident angle, and a light beam having a specified opening angle reflected in the reflection direction is measured by a light receiver. The 60 degree glossiness is the glossiness when the specified incident angle is 60 degrees. When the 60 degree glossiness is 75 or less, the surface of the stainless steel plate has a preferable antiglare property.

  The manufactured stainless steel plate was used for decorative polishing. The following two types of stainless steel sheets were used. The composition (% by mass) and dimensions are as follows.

Steel type 1 (SUS447J1) Cr: 30%, Mo: 2%, Ti: 0.15%, Nb: 0.15%, Al: 0.09%, balance Fe
Steel type 2 (SUS445J1) Cr: 22%, Mo: 1.05%, Ti: 0.2%, Nb: 0.2%, Al: 0.09%, balance Fe
Steel type 3 (SUS304) Cr: 18%, Ni: 8%, Si: 0.6%, Mn: 0.8%, balance Fe
Dimensions: board thickness 1.5 mm x width 200 mm x length 1000 mm.

  Polishing was performed in a line in which four flap wheels (# 80, # 80, # 80, # 150) were aligned so as to polish the longitudinal direction of the steel plate surface (give a polishing grain in the longitudinal direction), and dry polishing was performed. . Note that “# 80” and the like indicate mesh grain size.

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

  After polishing, only some of the stainless steel plates were pickled as shown in Table 1 (Comparative Example 3, Reference Example 1). No pickling treatment was performed on Examples 1 to 3 and Comparative Examples 1 and 2.

(Surface defect)
Using an optical microscope, the range of 100 μm × 100 μm on the surface of the stainless steel sheets of Examples 1 to 3 and Comparative Examples 1 to 3 and Reference Example 1 was magnified 200 times and observed, and the number of surface defects was measured (Table. 1).

(Oxide film)
The surface of each of the stainless steel sheets of Examples 1 to 3 and Comparative Examples 1 to 3 and Reference Example 1 was observed with an optical microscope at a magnification of 400 times, and the extent to which the oxide film that was a dark brown stain-like substance was 50 μm square in terms of area ratio It was calculated whether it exists. When the area ratio of the residual oxide film is less than 10%, it is evaluated as "none" because there is no colored oxide film, and when the area ratio is 10% or more, there is an oxidized film that has coloring "Yes". Was evaluated (see Table 1).

(Pit corrosion potential)
The pitting corrosion potentials of the stainless steel sheets of Examples 1 to 3 and Comparative Examples 1 to 3 and Reference Example 1 were measured. Specifically, based on JIS G 0577, the B method (3.5% (mass fraction) sodium chloride aqueous solution test method) was used, and the potentiodynamic method in a 3.5 mass% sodium chloride aqueous solution was used. The pH of the aqueous sodium chloride solution was 7, and the temperature was 30 ° C. The potential sweep rate was 20 mV / min (see Table 1).

(Polishing residue)
In order to evaluate the polishing residue, the surface roughness Ra of the stainless steel plates of Examples 1 to 3 and Comparative Examples 1 to 3 and Reference Example 1 was measured, and when Ra ≧ 0.1 μm, the polishing residue remained. Because of its excellent design, it was rated as "○". On the other hand, in the case of Ra <0.1 μm, the number of remaining polishing marks was small and the design was not excellent, so it was evaluated as “x”. The surface roughness Ra was measured according to JIS B 0601 and a contact type surface roughness meter was used (see Table 1).

(Glossiness)
Based on JIS Z 8741, the 60-degree glossiness of the stainless steel plate surface of Examples 1-3, Comparative Examples 1-3, and Reference Example 1 was measured using the gloss meter. The case where the 60 degree glossiness was 75 or less was evaluated as “◯”, and the case where it was greater than 75 was evaluated as “x” (see Table 1).

(Corrosion resistance test)
A corrosion resistance test (salt-dry wet-composite cycle test (CCT test)) was performed on the stainless steel sheets of Examples 1 to 3 and Comparative Examples 1 to 3 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 was within 5% of the entire surface of the steel sheet, the corrosion resistance was good and was evaluated as “◯”. When the rust area was more than 5%, the corrosion resistance was poor and was evaluated as “x” (Table 1 reference).

  As shown in Table 1, the stainless steel sheet of Example 1 had polishing eyes on the surface of the stainless steel sheet, had many surface defects (see FIG. 4), and had an oxide film with coloring on the surface. However, pitting corrosion did not occur even at a potential of 1.0 V (see FIG. 5). Also, regarding the stainless steel sheets of Examples 2 and 3, as in Example 1, no pitting corrosion occurred even at a potential of 1.0V. Moreover, as shown in Table 1, the stainless steel sheets of Examples 1 to 3 were also excellent in corrosion resistance in the CCT test.

1-9 ... surface defect 20 ... stainless steel plate of Example 1

Claims (2)

Having a longitudinal unidirectional polishing on the surface of the ferritic stainless steel plate,
The pitting potential is 0.6 V or higher,
60 degree gloss is 75 or less,
When an arbitrary 10 points on the surface are observed with an optical microscope at a magnification of 400 times, the area ratio of the colored oxide film is 10% or more in a 50 μm square ,
When the area of 100 μm × 100 μm at any 10 points on the surface was magnified 200 times using an optical microscope and observed, the metal on the surface was partially peeled off and the substrate portion was covered with a size of 5 μm or more. Has an average number of surface defects of 6 or more,
The composition is C: 0.020 mass% or less, Si: 0.40 mass% or less, Mn: 0.40 mass% or less, Cr: 25.00-32.00 mass%, Mo: 1.00-4. 00% by mass, P: 0.030% by mass or less, S: 0.020% by mass or less, Ni: 0.50% by mass or less, N: 0.020% by mass or less, and the balance from Fe and inevitable impurities. The stainless steel plate having excellent corrosion resistance, having a pitting corrosion resistance index (PI = Cr mass% + 3Mo mass%) of 30 or more. Further, one or more of Nb: 0.1 to 1.0% by mass, Ti: 0.05 to 0.3% by mass, and Al: 0.01 to 0.5% by mass are included. Item 1. A stainless steel plate according to item 1.