JP7414615B2 - Austenitic stainless steel sheet for building materials and its manufacturing method - Google Patents

Description

The present invention relates to an austenitic stainless steel sheet for building materials that has excellent corrosion resistance and a method for manufacturing the same.

Austenitic stainless steel plates such as SUS304 and SUS316, and ferritic stainless steel plates such as SUS430 are often used for exterior and interior building materials.

In applications for exterior and interior building materials, corrosion resistance against flying sea salt that adheres to the surface of steel is required when manufacturing building material products from steel plates or during construction of building materials. On the other hand, when stainless steel sheets are used as roofing or wall materials, anti-glare properties are often improved by rolling the steel sheets with dull rolls to give the surface irregularities of several μm. However, in an outdoor usage environment, dust and sea salt particles tend to adhere to the steel plate due to the presence of small irregularities on the surface. In addition, the recesses on the surface of the steel sheet formed by dull rolls have been subjected to heavy processing, which weakens the passive film.On the other hand, concave parts are prone to condensation, so the higher the surface roughness, the more difficult it is to use outdoors. It is known that corrosion resistance is extremely reduced.

Therefore, in Patent Document 1, in order to ensure anti-glare properties, the surface is roughened with a dull roll to make Ra 0.5 μm to 5 μm, and the average inclination angle of the unevenness is set to 4° or more and 11° or less, and furthermore, corrosion resistance is ensured. In order to achieve this, the steel composition satisfies 45≧Cr(%)+4Mo(%)≧28, thereby achieving both corrosion resistance and anti-glare property.

In addition, as shown in Patent Document 2, as a stainless steel sheet having both anti-glare properties and corrosion resistance, rolling with dull rolls is performed to make the surface arithmetic mean roughness Ra of 2.8 μm or more, and Cr+Mo: 24.5% or more. , Ni: 0.1% or more and 25% or less, and Cu: 0.01% or more and 3% or less.

However, in the technology described in Patent Document 1 or Patent Document 2, it is essential to increase the alloying elements in the steel, and a significant increase in cost is unavoidable.

Further, when the surface is roughened by dull rolls as in the case of the stainless steel sheet described in Patent Document 1 or Patent Document 2, adhesion of dust and sea salt particles is unavoidable, which may reduce corrosion resistance. Generally, corrosion resistance and surface roughening are opposed to each other, and the rougher the surface, the worse the corrosion resistance may be.

Patent No. 3287302 Patent No. 3499361

The present invention has been made in view of the above circumstances, and provides an austenitic stainless steel sheet for building materials that has excellent corrosion resistance even when the surface is roughened to ensure anti-glare properties, and a method for manufacturing the same. The task is to

[1] Concave portions and convex portions are provided on the steel plate surface,
The area ratio of the recess is 40 to 60%,
The surface roughness Rz in the center roughness curve of the surface is 3.0 to 10.0 μm,
An austenitic stainless steel sheet for building materials, wherein the maximum diameter of the recess is 500.0 μm or less.
[2] The chemical composition of the steel sheet is in mass%,
C+N: 0.01-0.15%,
Si: 0.1 to 3.0%,
Mn: 5.0% or less,
Cr: 10.0-20.0%,
Ni: 1.0 to 10.0%,
Cu: 0.01 to 3.0%,
Mo: 0.01-3.0%,
and the remainder consists of Fe and impurities,
The austenitic stainless steel sheet for building materials according to [1], wherein the _Md30 value, an index of austenite stability, satisfies the following formula (1).
-10(℃)<Md ₃₀ (℃)<50(℃)...(1)
Md ₃₀ (℃): 497-462(C+N)-9.2Si-8.1Mn-13.7Cr-20(Ni+Cu)-18.5Mo...(2)
However, Md ₃₀ (°C) in formula (1) is determined by formula (2), and C, N, Si, Mn, Cr, Ni, Cu, and Mo in formula (2) are the austenitic stainless steel plate. The content (mass%) of each element in .
[3] After final cold rolling and final annealing of the austenitic stainless steel sheet, shot blasting and pickling are performed,
The shot blasting is characterized in that the average particle diameter of the blasting material is 0.1 to 1.2 mm, the blasting speed is 30 to 100 m/s, and the blasting amount is 30 to 200 kg/ ^m2. The method for producing an austenitic stainless steel sheet for building materials according to [1] or [2].

According to the present invention, it is possible to provide an austenitic stainless steel sheet for building materials that has excellent corrosion resistance even when the surface of the steel sheet is roughened.

FIG. 1 is a diagram showing the uneven form and recesses on the surface of an austenitic stainless steel sheet for building materials according to the present embodiment.

Embodiments of the present invention will be described in detail below.
The austenitic stainless steel sheet for building materials (hereinafter sometimes referred to as austenitic stainless steel sheet) according to the embodiment of the present invention has a surface roughened by shot blasting and pickling after finish cold rolling and continuous annealing. This steel plate is suitable as a building material for roofs, building materials, etc. The austenitic stainless steel sheet of this embodiment is controlled to have a predetermined surface texture by shot blasting and pickling after final cold rolling, and thus becomes a stainless steel sheet whose surface texture is controlled by conventional dull roll rolling. In comparison, a significant improvement in corrosion resistance is expected.
Hereinafter, the austenitic stainless steel plate of this embodiment will be described in detail.

(Surface texture of steel plate)
First, the surface properties of the austenitic stainless steel sheet of this embodiment will be explained. The steel plate surface of the austenitic stainless steel plate of this embodiment is provided with concave portions and convex portions, the area ratio of the concave portions is 40 to 60%, and the surface roughness Rz in the center roughness curve of the surface is 3. 0 to 10.0 μm, and the maximum diameter of the recess is 500.0 μm or less. By having such surface properties, it is possible to ensure desirable anti-glare properties as a building material, and it is also possible to improve corrosion resistance. Hereinafter, the relationship between the surface texture and corrosion resistance of the austenitic stainless steel sheet of this embodiment will be explained.

From the viewpoint of improving the corrosion resistance of stainless steel used outdoors, aqueous solutions containing chloride ions, such as seawater and condensed water, are considered to be severe corrosive environments. When seawater dries, it produces salts such as sodium chloride (NaCl), and when this salt comes into close contact with the steel base, corrosion is further accelerated.

Therefore, as a result of intensive studies by the present inventors, it was found that controlling the surface to have a predetermined unevenness suppresses the adhesion between the generated salt and the steel base material and improves corrosion resistance.

In the austenitic stainless steel sheet according to the present embodiment, the surface quality is defined using three parameters: the area ratio of the recesses, the maximum diameter of the recesses, and the surface roughness Rz, which is an index of the maximum height. was found to be preferable. The arithmetic mean roughness Ra is not appropriate for evaluating the influence of protruding irregularities that can become corrosion starting points, but the maximum height Rz is an index that can appropriately evaluate the relationship with corrosion. I found out. Furthermore, it has been found that a steel plate having a surface roughness Rz within a predetermined range has excellent corrosion resistance when evaluated by surface roughness Rz. The reasons for limiting each parameter will be explained below.

[Area ratio of recesses]
The area ratio of the recesses on the surface of the steel plate is in the range of 40 to 60%. This improves corrosion resistance. When the area ratio of the recesses is less than 40%, salts precipitated from an aqueous solution containing chloride ions are preferentially precipitated in the convex parts and adhere to the steel base, resulting in deterioration of corrosion resistance. On the other hand, when the area ratio of the recesses exceeds 60%, the salt precipitated within the recesses grows, and as a result, the salt adheres to the steel base, reducing corrosion resistance. In addition, the adhesion of salt can be judged by the presence or absence of salt precipitation traces in the dry-wet repeated test described below.

[Surface roughness Rz]
The surface roughness Rz in the center roughness curve is in the range of 3.0 to 10.0 μm. This improves corrosion resistance. If Rz is less than 3.0 μm, the salt and the steel base will adhere to each other, reducing corrosion resistance. Moreover, when Rz exceeds 10.0 μm, dirt tends to adhere to the surface of the steel plate provided with concave portions and convex portions, degrading corrosion resistance. Rz is more preferably in the range of 5.0 to 8.0 μm.

[Maximum diameter of recess]
The maximum diameter of the recess is 500.0 μm or less. This improves corrosion resistance. If the maximum diameter of the recess exceeds 500.0 μm, the salt and the steel base will come into close contact with each other, reducing corrosion resistance.

Rz on the surface of the steel plate is measured by a method according to JIS B 0601:2013. Note that the arithmetic mean roughness Rz is measured three times in a direction perpendicular to the rolling direction, and the average value is calculated and evaluated.

The area ratio of the recesses and the maximum diameter of the recesses on the surface of the steel plate are measured by observing the steel plate surface using a three-dimensional shape measuring machine (manufactured by Keyence: VR-3000) and calculating the area ratio of the recesses. The recess is defined as a place that is circularly recessed and has a height of 0 μm or less based on a height of 0 μm of the evaluation surface measured by a three-dimensional shape measuring device. The area other than the concave portion is defined as a convex portion. Note that a reference plane is set when analyzing a three-dimensional profile obtained using a three-dimensional shape measuring machine. This reference plane is automatically determined by the accompanying analysis software. The reference plane corresponds to the median depth of the entire measurement area. In the present invention, the reference plane is set from the height information of the entire field of view measured at a magnification of 120 times. Furthermore, the maximum diameter of the recess is calculated from the measured three-dimensional profile. Note that the observation of the surface of the steel plate is evaluated using an observation magnification of 120 times.

Next, an example of the chemical components of the austenitic stainless steel sheet of this embodiment will be described, but the austenitic stainless steel sheet of this embodiment is not limited to the chemical components described below.

The austenitic stainless steel sheet of this embodiment has, in mass %, C+N: 0.01 to 0.15%, Si: 0.1 to 3.0%, Mn: 5.0% or less, Cr: 10.0 to 20.0%, Ni: 1.0 to 10.0%, Cu: 0.01 to 3.0%, Mo: 0.01 to 3.0%, and the balance is Fe and impurities, making it austenite. The stability index _Md30 value satisfies the following formula (1).

-10(℃)<Md ₃₀ (℃)<50(℃)...(1)

Md ₃₀ (℃): 497-462(C+N)-9.2Si-8.1Mn-13.7Cr-20(Ni+Cu)-18.5Mo...(2)

However, Md ₃₀ (°C) in formula (1) is determined by formula (2), and C, N, Si, Mn, Cr, Ni, Cu, and Mo in formula (2) are the austenitic stainless steel plate. The content (mass%) of each element in .

[Austenite stability index: Md ₃₀ value (℃)]
Metastable austenitic stainless steel undergoes martensitic transformation through plastic working even at temperatures above the Ms point. The upper limit temperature at which a transformation point occurs during processing is called the Md value. That is, the Md value is an index indicating the stability of austenite. The temperature at which 50% martensite occurs when 30% strain is applied by tensile deformation is called the Md ₃₀ value. The formula (2) above shows the formula for calculating the Md ₃₀ value. By designing the Md ₃₀ value (°C) in the range of -10°C to 50°C in the austenitic stainless steel of this embodiment, the surface unevenness targeted by this embodiment can be more easily secured. It becomes possible.

The deformation-induced martensite dissolves preferentially during pickling, smoothing the surface. In addition, if deformation-induced martensite remains after pickling, it will cause deterioration in corrosion resistance, so it is necessary to remove it by pickling. In other words, it is possible to improve corrosion resistance by controlling the amount of deformation-induced martensite on the surface introduced by shot blasting by Md ₃₀ (°C) and removing it by pickling to obtain a desired unevenness. .

When the Md ₃₀ value is less than -10°C, the austenite stability is high, so that the introduction of deformation-induced martensite during shot blasting is inhibited. When the amount of process-induced martensite is small, roughness caused by shot blasting remains even after pickling, and when the surface roughness Rz exceeds 10.0 μm, dirt tends to adhere to the unevenness, deteriorating corrosion resistance. On the other hand, when the Md ₃₀ value exceeds 50°C, a large amount of deformation-induced martensite is introduced, the diameter of the recess exceeds 500.0 μm, the surface becomes smooth, and the formed salt and base material adhere to each other, reducing corrosion resistance. . Therefore, when the Md ₃₀ value is −10 to 50° C., the corrosion resistance of the austenitic stainless steel sheet of this embodiment can be further improved.

Hereinafter, each chemical component of the austenitic stainless steel sheet of this embodiment will be explained. In addition, in the following description, mass % is expressed as %.

C+N: 0.01~0.15%
C and N are elements effective in stabilizing the austenite phase and suppressing the formation of the δ ferrite phase. On the other hand, these elements increase the 0.2% yield strength of the steel material through solid solution strengthening and reduce workability. Therefore, the total of C content and N content (C+N) is set to 0.15% or less. However, if C+N is less than 0.01%, steel manufacturing costs for reducing C and N will be incurred. Therefore, C+N is set to 0.01% or more. The preferred range of C+N is 0.04 to 0.12%.

Si: 0.1-3.0%
Si is effective as a deoxidizing agent during melting, and in order to obtain this effect, the Si content is set to 0.1% or more. More preferably, it is 0.3% or more. However, if the Si content exceeds 3.0%, the pickling rate will be reduced. Therefore, the Si content is set to 3.0% or less.

Mn: 5.0% or less Mn contributes to preventing brittle fracture during hot working and strengthening the steel. However, since Mn is a strong austenite-forming element, if the Mn content exceeds 5.0%, the amount of deformation-induced martensite generated during shot blasting will decrease, making it impossible to obtain the desired surface roughness. Therefore, the Mn content is set to 5.0% or less. It is preferably 3.0% or less. The Mn content may be 0.01% or more, or 0.1% or more.

Cr:10.0~20.0%
Cr is an alloying element necessary to obtain the corrosion resistance required for stainless steel, and is preferably contained in an amount of 10.0% or more. More preferably, it is 12.0% or more. However, since Cr is a strong ferrite stabilizing element, when the Cr content exceeds 20.0%, ∂ ferrite is generated, and this ∂ ferrite deteriorates the hot workability of the material. Therefore, the Cr content is set to 10.0% or more and 20.0% or less. In practice, in order to control the Md ₃₀ value to -10 to 50°C, it may be less than 17.5%.

Ni: 1.0-10.0%
Ni is an expensive element, and austenitic stainless steel with a Ni content of more than 10.0% causes an increase in raw material costs. Therefore, the Ni content is set to 10.0% or less. However, since Ni is an element necessary for austenitic stainless steel, the Ni content should be 1.0% or more.

Cu: 0.01~3.0%
Cu is an austenite-forming element and is an element that can adjust the stability of the austenite phase. However, when the Cu content exceeds 3.0%, it segregates at grain boundaries during the manufacturing process, and this grain boundary segregation significantly deteriorates hot workability, making manufacturing difficult. Therefore, the Cu content is set to 3.0% or less. It is preferably 2.5% or less. Further, the Cu content is 0.01% or more.

Mo: 0.01~3.0%
Mo is an element that improves the corrosion resistance of materials. However, when the Mo content exceeds 3.0%, the pickling rate decreases, leading to an increase in manufacturing costs. Therefore, the Mo content is set to 3.0% or less. It is desirably 2.5% or less. In practical terms, it may be less than 1.5%. It may be less than 1.2%. Moreover, Mo content shall be 0.01% or more.

The austenitic stainless steel sheet of this embodiment consists of Fe and impurities (including inevitable impurities) in addition to the elements mentioned above. Furthermore, in addition to the elements described above, they can be contained within a range that does not impair the effects of the present invention.

The thickness of the steel plate is not particularly limited, but is preferably in the range of 0.1 mm or more and 10.0 mm or less, for example, for outdoor building material applications such as roofing materials.

Next, a method for manufacturing an austenitic stainless steel sheet according to the present embodiment will be described.

In order to produce austenitic stainless steel sheets with excellent corrosion resistance, the steel sheets after hot rolling are sequentially subjected to annealing, pickling, final cold rolling, and final annealing, and then the steel sheets after final annealing are subjected to shot treatment. It is important to control the surface to desired properties by performing blasting and pickling.

First, using a hot-rolled steel plate as a starting material, it is annealed and pickled to remove relatively coarse deposits such as metal and scale. Hot rolling conditions, annealing conditions, and pickling conditions will be described later.

Next, finish cold rolling is carried out at a sufficient rolling rate to smooth out as much as possible the depressions (drop-off marks) generated by pickling and the depressions caused by grain boundary erosion. Further, by performing finish annealing after finish cold rolling, an original plate of austenitic stainless steel with excellent corrosion resistance is manufactured. Conditions for final cold rolling, final annealing, and pickling will be described later.

Then, in order to control the area ratio of the recesses, Rz, and the maximum diameter of the recesses, the two-phase stainless steel base plate manufactured in this way was shot blasted and pickled under predetermined conditions to improve its corrosion resistance. Manufacture superior austenitic stainless steel sheets. Conditions for shot blasting and pickling will be described later.

In addition, when manufacturing the austenitic stainless steel sheet of this embodiment, it is sufficient to use a hot rolled steel sheet as a starting material, perform at least final cold rolling, then perform final annealing, shot blasting and pickling; The step may be omitted, or the order of the steps may be changed.

An example is procedure (i) in which a hot rolled steel plate is subjected to annealing, pickling, final cold rolling, final annealing, shot blasting, and pickling in this order.

In addition, as another procedure, the steel plate after hot rolling is subjected to the following treatments: annealing, pickling, cold rolling, annealing, pickling, finish cold rolling, finish annealing, shot blasting, and pickling. Procedure (ii) may also be used.

Furthermore, the steel plate after hot rolling is subjected to annealing, pickling, first cold rolling, first annealing, first pickling, second cold rolling, second annealing, second The procedure (iii) may be performed in the order of pickling, final cold rolling, final annealing, shot blasting, and pickling.

Alternatively, the procedure (iv) may be such that the hot-rolled steel sheet is subjected to annealing, pickling, cold rolling, bright annealing, finish cold rolling, finish annealing, shot blasting, and pickling in this order.

Note that in the above steps (i) to (iv), a polishing step or a degreasing step may be added as necessary. Further, after the pickling after shot blasting, skin pass rolling may be performed within a range that does not affect the surface properties. Furthermore, after temper rolling, refining processes such as degreasing, tension leveling, slitting, etc. may be performed within a range that does not affect the surface properties.

Hereinafter, specific conditions in each step will be explained.

Hot-rolled steel sheets are manufactured by melting, casting, and hot rolling stainless steel in the same manner as general austenitic stainless steels are manufactured.

Annealing and pickling of a steel plate after hot rolling are effective treatments for removing coarse foreign matter such as metal and scale attached to the surface of the steel plate.

The conditions for annealing after hot rolling can be selected as appropriate in consideration of the manufacturability and characteristics of the material. Further, the annealing may be performed by either batch annealing or continuous annealing as long as it does not affect the surface properties of the steel sheet, and can be selected depending on the material, for example.

Pickling is performed using a combination of neutral salts and acids such as sulfuric acid, nitric acid, hydrofluoric acid, and hydrochloric acid, and electrolytic pickling may also be performed.

Finish cold rolling is cold rolling performed immediately before final finish annealing. The number of cold rolling passes may be one pass or multiple passes. Furthermore, a plurality of different types of rolling mills, such as a general Sendzimir mill and a mill exclusively for thin plates, may be used in sequence.

The soaking temperature for finish annealing may be the general conditions for finish annealing austenitic stainless steel sheets, and is not particularly limited, but is preferably 1000 to 1100°C. Since recrystallization is stabilized when the soaking temperature during annealing is 1000°C or higher, the soaking temperature during annealing is preferably 1000°C or higher. Further, if the soaking temperature during annealing is set to 1100°C or lower, coarsening of the crystal grain size can be prevented, so the soaking temperature during annealing is preferably set to 1100°C or lower.

The soaking time for final annealing is 0.1 to 1.0 minutes. In order to stabilize recrystallization, the soaking time is preferably 0.2 minutes or more. Further, in order to prevent coarsening of the crystal grain size, the soaking time is preferably set to 0.9 minutes or less.

The average particle diameter of the blast material in the shot blasting process is 0.1 to 1.2 mm, the blast speed is 30 to 100 m/s, and the blast amount is 30 to 200 Kg/m ² . Since the area ratio of the recesses increases with the shot amount, the shot amount is preferably 70 to 120 kg/m ² . Further, since Rz and the maximum diameter of the recess increase proportionally with the projection speed, the projection speed is preferably 50 to 70 m/s. When the average particle diameter, blasting speed, and blasting amount of the blasting material in shot blasting are within the above ranges, oxidized scale on the surface of the stainless steel plate tends to be easily removed. The material of the shot material is preferably hard particles such as iron, alumina, SiC, and ceramics, and any of them may be used.

For pickling after shot blasting, it is preferable to use a mixed acid containing any two of sulfuric acid, nitric acid, hydrofluoric acid, and hydrochloric acid. Preferred concentration ranges for mixed acids are 100 to 300 g/L for sulfuric acid, 20 to 200 g/L for nitric acid, and 10 to 250 g/L for hydrofluoric acid. The temperature of the mixed acid solution is preferably 20°C to 90°C, and electrolytic pickling may be performed.

Through the above steps, the austenitic stainless steel sheet of this embodiment can be manufactured. The austenitic stainless steel sheet of this embodiment has excellent corrosion resistance even when the surface of the steel sheet is roughened to provide antiglare properties.

Hereinafter, the present invention will be explained in more detail with reference to Examples.

[Example 1]
First, as austenitic stainless steels, steel grades A to L having the chemical components shown in Table 1 were melted and continuously cast into slabs. Note that steel types A to H satisfy the preferred chemical composition, and steel types I to L fall outside of the preferred range.

The slab after continuous casting was then hot rolled into a steel plate using a conventional method. Then, using the hot rolled steel plate as a starting material, annealing, pickling, final cold rolling, final annealing, shot blasting, and pickling were performed in this order (step (i) above) to obtain a plate with a thickness of 1.5 mm. A steel plate was obtained after shot blasting and pickling. In addition, for Comparative Example 6, the treatments were performed in the order of annealing, pickling, final cold rolling, final annealing, and shot blasting (the procedure excluding the last pickling from the above procedure (i)), and the plate thickness was 1.5 mm. A steel plate was obtained after shot blasting.

The soaking temperature for final annealing was 1000°C to 1100°C, and the soaking time was 0.3 minutes. Further, shot blasting after final annealing used a shot material with an average particle size of 0.4 mm. The material of the shot material was iron. Other shot blasting conditions were as listed in Table 2. Further, pickling after shot blasting was carried out using a mixed acid of 50 g/L hydrofluoric acid and 120 g/L nitric acid at a liquid temperature of 50°C. In this way, test materials of Inventive Examples 1 to 8 and Comparative Examples 1 to 7 were obtained.

Various measurements regarding corrosion resistance and surface properties were performed using each sample material. Specifically, the area ratio of the recesses on the steel sheet surface, the surface roughness Rz in the center roughness curve on the steel sheet surface, and the maximum diameter of the recesses were measured, and the corrosion resistance was further evaluated.

Rz on the surface of the steel plate was measured by a method according to JIS B 0601:2013 after performing ultrasonic cleaning using acetone on a 50 mm square sample cut out from each test material. The arithmetic mean roughness Rz was measured three times in a direction perpendicular to the rolling direction, and the average value was calculated and evaluated.

The area ratio of the recesses and the maximum diameter of the recesses on the surface of the steel plate were measured using a three-dimensional shape measuring machine (Keyence: The surface of the steel plate was observed using VR-3000), and the area ratio of the recesses was calculated. The concave portion was defined as a place having a height of 0 μm or less and having a circular concave shape based on the height of the evaluation surface of 0 μm measured by a three-dimensional shape measuring device. Note that a reference plane is set when analyzing a three-dimensional profile obtained using a three-dimensional shape measuring machine. This reference plane is automatically determined by the accompanying analysis software. The reference plane corresponds to the median depth of the entire measurement area. In the present invention, the reference plane was set from the height information of the entire field of view measured at a magnification of 120 times. Furthermore, the maximum diameter of the recess was calculated from the measured three-dimensional profile. Note that the observation of the surface of the steel plate was evaluated using an observation magnification of 120 times. FIG. 1 shows an example of a three-dimensional profile.

In the evaluation of corrosion resistance, artificial seawater CCT was performed on samples of L150 mm x W70 cut out from each test material to obtain measurement samples. Artificial seawater CCT is a repeated dry-wet test using Aquamarine (manufactured by Yasu Pharmaceutical Co., Ltd.) in a combined cycle testing machine (Suga Test Machine: CYP-90). Specifically, artificial seawater was sprayed on the test material at an angle of 70° to 75° for 4 hours as a spraying process, then maintained at RH 25% for 2 hours as a drying process, and maintained at RH 95% for 2 hours as a wet process. This is a test in which one cycle consists of This artificial seawater CCT was performed for 12 cycles. The degree of rust generated after the above 12 cycles of CCT was evaluated by evaluating the appearance of the sample using a rating number (RN) based on JIS G 0595:2004. An RN of 6 or more was considered a pass (○), and an RN of 5 or less was judged a fail (x). The adhesion between the precipitated salt and the material surface is evaluated by the presence or absence of traces of the precipitated salt on the rust generated by CCT. If there is no trace, it is evaluated as no adhesion (○), and if there is a trace, it is evaluated as (x). did.

The results of these various measurements are shown in Table 2.

As shown in Table 2, in all of the invention examples 1 to 8, the area ratio of the recess is 40% to 60%, Rz is 3.0 to 10.0 μm, and the diameter of the recess is 500.0 μm or less. Met. Further, in Invention Examples 1 to 8, the Md ₃₀ value, an index of austenite stability, satisfied -10<Md ₃₀ <50. As a result, the corrosion resistance evaluation and adhesion evaluation were good.

Therefore, all of the examples of the present invention that meet the requirements of the present invention can be evaluated as steel plates having surface properties with excellent corrosion resistance suitable for use as building materials, for example.

Claims (3)

Concave and convex portions are provided on the surface of the steel plate,
The area ratio of the recess is 40 to 60%,
The surface roughness Rz in the center roughness curve of the surface is 3.0 to 10.0 μm,
An austenitic stainless steel sheet for building materials, wherein the maximum diameter of the recess is 500.0 μm or less. The chemical composition of the steel plate is in mass%,
C+N: 0.01-0.15%,
Si: 0.1 to 3.0%,
Mn: 5.0% or less,
Cr: 10.0-20.0%,
Ni: 1.0 to 10.0%,
Cu: 0.01 to 3.0%,
Mo: 0.01-3.0%,
and the remainder consists of Fe and impurities,
The austenitic stainless steel sheet for building materials according to claim 1, wherein the _Md30 value, an index of austenite stability, satisfies the following formula (1).
-10(℃)<Md ₃₀ (℃)<50(℃)...(1)
Md ₃₀ (℃): 497-462(C+N)-9.2Si-8.1Mn-13.7Cr-20(Ni+Cu)-18.5Mo...(2)
However, Md ₃₀ (°C) in formula (1) is determined by formula (2), and C, N, Si, Mn, Cr, Ni, Cu, and Mo in formula (2) are the austenitic stainless steel plate. The content (mass%) of each element in . After final cold rolling and final annealing of the austenitic stainless steel sheet, shot blasting and pickling are performed.
The shot blasting is characterized in that the average particle diameter of the blasting material is 0.1 to 1.2 mm, the blasting speed is 30 to 100 m/s, and the blasting amount is 30 to 200 kg/ ^m2. A method for manufacturing an austenitic stainless steel sheet for building materials according to claim 1 or 2.