JP4378853B2 - Stainless steel for civil engineering and building structures with excellent fatigue characteristics and paint film adhesion - Google Patents

Description

【００５２】
作製した各種ステンレス鋼板は、板面における残留圧縮応力を測定し、次いで、触針法（JIS B 0601）によって表面粗さを測定するとともに、疲労試験を行って疲労強度を測定した。
【００５３】
前記残留圧縮応力の測定は、Ｘ線回折要論（著者B.D.CULLITY 、松村源太郎訳、アグネ（株）、昭和46年、第９版、ｐ435 −458 ）に準拠した一般的なＸ線回折法（条件：θ−２θ法、CoＫα線使用、電圧46ｋＶ、電流150 ｍＡ、理学電機（株）社製のRINT1500のＸ線回折装置を使用）によって、板面から行った。ただし、この場合、サンプルの調整には十分注意が必要である。すなわち、Ｘ線回折法を用いる場合、表面の凹凸がＸ線の反射に大きな影響を及ぼすので、表面の凹凸を除去しなくてはいけない。ここでは細心の注意を払い、鋼板の表層をまずはメカニカルに細かなエメリー紙（♯800 〜1200）で丁寧に削り取り、その後、５％過塩素酸酢酸（10℃）を用いて表層を電解研磨して、メカニカルな研磨による歪みを除去してから測定に用いた。
【００５４】
表面粗さの測定は、JIS B 0601に準拠した触触法により行った。
【００５５】
疲労強度の測定は、JIS Z 2273に準拠することによって行った。尚、ここで測定した疲労強度は、10⁶ 回に対する疲労強度を意味する。
【００５６】
また、上記各種ステンレス鋼板の塗膜密着性を評価するため、アルカリ洗浄脱脂後、水洗するとともに乾燥させ、さらにCr付着量が30〜35mg／ｍ² となるようにクロメート処理を行った後、ウレタン変性エポキシ樹脂に酸化チタン、防錆顔料等を含有した塗料にさらに平均粒径３μｍのリン化鉄粉末を不揮発分比で30％程度含有した塗料（商品名：ウエルカラーＰ）を用い、乾燥目付け量が17.5mg／ｍ² となるように、280 ℃で60秒の加熱塗装条件で加熱塗装を行うことによって、塗装鋼板を製造した。その後、各塗装鋼板は、その表面にクロスカットを入れてから５mass％塩酸（28℃）に96時間浸漬した後に水洗・乾燥した後、セロテープで剥離試験を行った。そして、塗膜密着性の評価は、クロスカット部で剥離した塗装の最大幅（mm）を測定し、この測定値によって行った。尚、この発明では、塗膜剥離幅が５mm以上の場合に塗膜密着性を不合格とした。
【００５７】
上記した方法で測定した、鋼板表層の残留応力（MPa ）、鋼板の表面粗さ（μｍ）、疲労強度（MPa ）及び塗膜密着性（剥離幅：mm）の結果を表２に示す。尚、表 2中の残留応力の数値は、正の値が残留圧縮応力、負の値が残留引張り応力であることを意味する。
【００５８】
【表２】

【００５９】
表２に示す結果から、発明例はいずれも、大きな疲労強度を有するとともに、塗膜密着性に優れているのがわかる。
また、同一の鋼No. 内で比べた場合には、残留圧縮応力が大きい鋼板の方が小さい鋼板よりも疲労強度が大きいことがわかる。尚、同一の鋼No. 内で疲労強度の低いものについては表２中にアンダーラインを付して比較例とした。さらに、表面粗さが0.2 μｍ未満である鋼板は、塗膜の剥離幅が大きく、塗膜密着性が劣ることがわかる。
【００６０】
【発明の効果】
この発明によれば、鋼組成の適正化を図った上で、鋼板表面の算術平均粗さRaと鋼板表層の残留圧縮応力の適正化を図ることによって、疲労特性と塗膜密着性に優れた土木・建築構造用ステンレス鋼の提供が可能になった。
【図面の簡単な説明】
【図１】 鋼板表層に残留圧縮応力を導入した場合と導入しない場合のＳ−Ｎ線図である。[0001]
[Industrial application fields]
The present invention relates to a stainless steel for civil engineering and building structures having excellent fatigue properties and coating film adhesion.
[0002]
[Prior art]
Conventionally, ordinary steels such as SS400, high-strength steels such as SM490, and materials obtained by painting or plating these steels have been used as civil engineering and building construction materials.
However, in recent years, with the diversification of design, utilization of various materials has begun to be studied.
[0003]
Among them, stainless steel having excellent corrosion resistance and design properties requires very little maintenance cost for firing, and can be said to be an extremely attractive material from the viewpoint of life cycle cost (LCC).
[0004]
In particular, buildings constructed in the coastal area have problems such as short life and increased maintenance costs for controlling corrosion. We also have weldability and corrosion resistance in promoting waterfront development. In particular, the role of stainless steel as a corrosion-resistant functional material for civil engineering and building structures having excellent initial rust resistance is greatly expected.
[0005]
Stainless steels are ferritic stainless steel represented by SUS430, martensitic stainless steel represented by SUS410 steel, austenitic stainless steel represented by SUS304, and duplex stainless steel represented by SUS329 steel. It is roughly classified into precipitation hardened stainless steel represented by steel and SUS630.
[0006]
Among these various stainless steels, what has been studied as a material for civil engineering and building structures has been the most used, including material strength, corrosion resistance, ease of welding, weld toughness and versatility. Austenitic stainless steel.
[0007]
Austenitic stainless steel has properties that sufficiently satisfy properties required for civil engineering and building materials such as strength, corrosion resistance, fire resistance, and weld toughness.
[0008]
However, this austenitic stainless steel
1) Because it contains a large amount of alloying elements such as Ni and Cr, it is much more expensive than ordinary steel.
2) causing stress corrosion cracking,
3) Since the coefficient of thermal expansion is larger than that of ordinary steel and the thermal conductivity is relatively small, distortion caused by the thermal effect during welding is likely to accumulate, making it difficult to apply to members that require precision. thing,
For this reason, it is difficult to apply to general-purpose structural materials in which ordinary steel or a material coated or plated is used, and there is a problem that the application range is limited.
[0009]
For this reason, recently, the application of low Cr content alloy steel with a Cr content of 15 mass% or less and its coated steel sheet to civil engineering and building steel as an alternative to ordinary steel that has been plated or painted has been studied.
[0010]
Here, when stainless steel is used for civil engineering and building structural materials, fatigue characteristics and coating film adhesion are also important selection factors.
[0011]
For example, Japanese Patent Application Laid-Open No. 6-235100 has proposed a method for producing stainless steel for resin coating in which anodic electrolysis is performed after bright annealing.
[0012]
However, in stainless steel for civil engineering and building structures, a technique for effectively improving both the fatigue characteristics and the coating film adhesion has not been clarified so far.
[0013]
[Problems to be solved by the invention]
An object of the present invention is to provide a stainless steel for civil engineering and building structures that solves the above-described problems in the prior art and effectively improves both fatigue properties and coating film adhesion.
[0014]
[Means for Solving the Problems]
The inventors have found that it is useful to improve the surface of a stainless steel plate by means of shot blasting, brushes, dull rolls, etc. as means for achieving the above-mentioned problems, and by performing this surface modification, stainless steel can be used. When the unevenness (roughness) and residual stress on the surface of the steel plate or steel strip were changed variously, as long as both the surface roughness and the residual stress on the surface layer were properly controlled after setting the steel composition appropriately, It has been found that both fatigue characteristics and coating film adhesion can be effectively improved without changing the heat treatment conditions, and the present invention has been completed.
[0015]
That is, the gist configuration of the present invention is as follows.
1. Cr: Exceeding 8 mass%, less than 15 mass% C: Exceeding 0.0025 mass%, less than 0.03 mass% N: Exceeding 0.0025 mass%, less than 0.03 mass% S: Less than 0.03 mass%
Mn: More than 0.5 mass%, less than 3.0 mass%
Al: Less than 0.5 mass% P: Less than 0.04 mass%
Si: contains more than 0.1 mass% and less than 2.0 mass%, the balance is the composition of Fe and inevitable impurities, and the arithmetic average roughness (Ra) of the surface is 0.2 to 50 μm, and the surface layer is 0.01 Stainless steel for civil engineering and building structures with excellent fatigue characteristics and coating film adhesion characterized by introducing strain that generates residual compressive stress of ~ 50MPa.
[0016]
2. In 1 above,
Cu: less than 3.0 mass%,
Mo: less than 3.0 mass% and
Ni: Stainless steel for civil engineering and building structures with excellent fatigue properties and coating film adhesion characterized by a composition containing one or more selected from less than 3.0 mass%.
[0017]
3. In 1 or 2 above,
Co: 0.01 mass% or more, less than 0.5 mass%,
V: 0.01 mass% or more, less than 0.5 mass%, and W: 0.001 mass% or more, less than 0.05 mass%, a fatigue property and a coating film characterized by containing one or more kinds selected from Stainless steel for civil engineering and building structures with excellent adhesion.
[0018]
4). A stainless steel for civil engineering and building structures excellent in fatigue characteristics and coating film adhesion, characterized in that the composition further contains B: 0.0002 to 0.002 mass% in the above 1, 2 or 3.
[0019]
5. In any one of the above 1-4,
Ti: Less than 0.7 mass%,
Nb: Less than 0.7 mass%,
Ta: Less than 0.7 mass% and
Zr: Stainless steel for civil engineering and building structures with excellent fatigue characteristics and coating film adhesion, characterized by containing one or more selected from less than 0.5 mass%.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
Next, in the present invention, the reason why the chemical composition of stainless steel is limited to the above-described gist configuration will be described.
[0021]
Cr: Over 8 mass%, less than 15 mass%
Cr is an element effective for improving corrosion resistance, but if its content is 8 mass% or less, it is difficult to ensure sufficient corrosion resistance. In addition, since Cr is a ferrite phase (α phase) stabilizing element, addition of 15 mass% or more not only causes a decrease in workability, but also reduces the stability of the austenite phase (γ phase) Since a predetermined amount of martensite phase cannot be secured during quenching, the weld strength is reduced.
Therefore, in this invention, the Cr content is set to exceed 8 mass% and less than 15 mass%. In addition, the range of especially preferable Cr content is 10.0-13.5 mass% in order to combine rust resistance, workability, and weldability.
[0022]
C and N: both exceeding 0.0025 mass% and less than 0.03 mass% As previously known, reduction of C and N is effective in improving the toughness and workability of the weld heat-affected zone and preventing weld cracking. C and N not only greatly affect the hardness of the martensite phase, but also (Fe, Cr) ₂₃ C ₆ , (Fe, Cr) ₇ C ₃ , (Fe, Cr) ₃ C, (Fe , Cr) ₂ N, Fe—Cr carbides and nitrides such as (Fe, Cr) are formed, which also causes corrosion resistance deterioration due to the Cr-deficient phase, and each of the contents of C and N Since the formation of carbides and the like becomes remarkable when the content is 0.03 mass% or more, the contents of C and N are both less than 0.03 mass%. However, in the steel composition range of the present invention, the reduction of the C and N contents is effective in improving the welded part properties, workability, corrosion resistance, etc., but the C and N contents are each 0.0025 mass% or less. Since this increases the refining load, the C and N contents are both more than 0.0025 mass% and less than 0.03 mass%. The C and N contents are more preferably 0.005 to 0.02 mass%.
[0023]
S: Less than 0.03 mass% S combines with Mn to form MnS, and becomes an initial rusting start point. S is also a harmful element that segregates at the grain boundaries and promotes embrittlement of the grain boundaries, so it is preferably reduced as much as possible. In particular, when the S content is 0.03 mass% or more, the adverse effect becomes remarkable. Therefore, the S content is suppressed to less than 0.03 mass%, more preferably 0.006 mass% or less.
[0024]
Mn: Over 0.5 mass%, 3.0 mass% or less
Mn is an austenite phase (γ phase) stabilizing element and effectively contributes to the improvement of weld toughness with the weld heat affected zone structure being a martensite structure. In addition, Mn is an element useful as a deoxidizer, as is Si, and if the Mn content is 0.5 mass% or less, an effect as a sufficient deoxidizer cannot be obtained, so the Mn content is 0.5 The mass was exceeded. On the other hand, excessive addition exceeding 3.0 mass% leads to deterioration of workability and corrosion resistance due to formation of MnS, so the Mn content is limited to 3.0 mass% or less. The Mn content is more preferably in the range of 0.7 to 1.5 mass%.
[0025]
Al: Less than 0.5 mass%
Al is not only an element useful as a deoxidizer, but also contributes to improving the toughness of welds. However, when its content exceeds 0.5 mass%, inclusions increase and mechanical properties deteriorate. Therefore, the Al content is limited to less than 0.5 mass%. Al may not be contained in the steel.
[0026]
P: Less than 0.04 mass% P is an element harmful not only to hot workability, formability and toughness, but also to corrosion resistance. Especially when the P content is 0.04 mass% or more, its effect Therefore, the P content is suppressed to less than 0.04 mass%. The P content is more preferably 0.025 mass% or less.
[0027]
Si: More than 0.1 mass%, less than 2.0 mass%
Si is a useful element as a deoxidizer, but if its content is less than 0.1 mass%, a sufficient deoxidation effect cannot be obtained. On the other hand, excessive addition of 2.0 mass% or more will reduce toughness and workability. Therefore, the Si content exceeds 0.1 mass% and is less than 2.0 mass%. The Si content is more preferably 0.3 to 0.5 mass%.
[0028]
As described above, the essential components contained in the stainless steel according to the present invention have been described. However, in the present invention, various elements described below can be appropriately contained.
[0029]
Cu: Less than 3.0 mass%
Cu is an austenite stabilizing element, and is an element effective in improving toughness by improving corrosion resistance, forming an austenite phase, suppressing grain growth in the weld heat affected zone. However, when the Cu content is 3.0 mass% or more, the embrittlement, particularly the sensitivity to hot cracking, tends to increase, so the Cu content is preferably in the range of less than 3.0 mass%. In addition, it is more preferable that the Cu content has a lower limit of 0.1 mass% at which the corrosion resistance improving effect is remarkably exhibited and an upper limit of 0.6 mass% at which hot cracking susceptibility tends to increase.
[0030]
Mo: less than 3.0 mass%
Mo, as well as Cu, is an element effective for improving corrosion resistance. However, if the Mo content is 3.0 mass% or more, the stability of the austenite phase tends to decrease, and the toughness and workability tend to decrease. Therefore, the Mo content is preferably in the range of less than 3.0 mass%. . From the viewpoint of balance between corrosion resistance and workability, the Mo content is more preferably in the range of 0.1 to 0.5 mass%.
[0031]
Ni: Less than 3.0 mass%
Ni is an element that improves ductility and toughness, and is preferably added particularly when it is necessary to improve the toughness of the weld heat affected zone. However, if the Ni content is 3.0 mass% or more, the material tends to harden and the effect tends to be reduced, so the Ni content is preferably in the range of less than 3.0 mass%. Moreover, when it is necessary to make the rust resistance improving effect remarkably exhibited, the Ni content is preferably set to 0.1 mass% or more.
[0032]
Co: 0.01 mass% or more, less than 0.5 mass%, V: 0.01 mass% or more, less than 0.5 mass%, W: 0.001 mass% or more, less than 0.05 mass%
Co, V and W are effective elements for improving the initial rust resistance of steel without adding a large amount of expensive Cr, Ni, Mo or the like or extremely reducing C and N. It can be added appropriately as necessary. The contents of Co, V, and W are preferably set to 0.01 mass%, 0.01 mass%, and 0.001 mass%, respectively, at which the above improvement effect becomes apparent. In addition, when the contents of V and W are 0.5 mass% or more and 0.05 mass% or more respectively, since the material tends to be hardened due to the precipitation of carbide, less than 0.5 mass% and 0.05 mass%, respectively. It is preferable to limit to less than 0.5 mass%, and if the Co content is 0.5 mass% or more, the steel may be hardened, so it is preferable to limit to less than 0.5 mass%. More preferably, the Co content is 0.03 to 0.2 mass%, the V content is 0.05 to 0.2 mass%, and the W content is 0.005 to 0.02 mass%.
[0033]
B: 0.0002 to 0.002 mass%
B is an element effective for improving the hardenability of steel. However, if the B content is less than 0.0002 mass%, the above-mentioned improvement effect cannot be obtained sufficiently, and if it exceeds 0.002 mass%, the material becomes harder and the toughness and workability tend to be impaired. The content is preferably 0.0002 to 0.002 mass%. The B content is more preferably 0.0005 to 0.001 mass%.
[0034]
Ti: Less than 0.7 mass%, Nb: Less than 0.7 mass%, Ta: Less than 0.7 mass%, Zr: Less than 0.5 mass%
Ti, Nb, Ta, and Zr are all carbonitride-forming elements, and effectively suppress the grain boundary precipitation of Cr carbonitride during welding or heat treatment, thereby effectively acting to improve corrosion resistance. Further, Ti is an element effective for improving hardenability. However, when the Ti, Nb, Ta content is 0.7 mass% or more and the Zr content is 0.5 mass% or more, the material tends to harden, so the contents of Ti, Nb and Ta are all 0.7 mass. % And the Zr content are preferably less than 0.5 mass%. In addition, the suitable range of content of Ti, Nb, Ta, and Zr is 0.01-0.3 mass% in all.
[0035]
Remaining Fe and Inevitable Impurities The remainder other than the steel composition components described above is Fe and inevitable impurities. As an inevitable impurity, for example, it is accepted that the O content is in the range of 0.010 mass% or less.
[0036]
The main structural features of the present invention are limited to the above steel composition, the arithmetic mean roughness Ra of the steel surface is set to 0.2 to 50 μm, and the steel surface layer corresponds to a residual compressive stress of 0.01 to 50 MPa. Is to introduce distortion.
[0037]
Arithmetic mean roughness Ra of steel surface: 0.2-50μm
The arithmetic average roughness Ra of the steel surface has a great influence on the adhesion of the coating film, so it is set to 0.2 to 50 μm. That is, if the arithmetic average roughness Ra of the steel surface is less than 0.2 μm, sufficient coating film adhesion cannot be obtained, and if it exceeds 50 μm, the unevenness of the surface becomes severe and the adhesion is rather poor. This is because the color tone and unevenness of the painted surface become conspicuous as it decreases.
Here, the arithmetic surface roughness Ra means the arithmetic average roughness Ra specified in JIS B0601.
[0038]
Introducing strain in which a residual compressive stress of 0.01 to 50 MPa is introduced into the steel surface layer Introducing strain in which a residual compressive stress of 0.01 to 50 MPa is introduced into the steel surface layer is the most important feature in the configuration of the present invention.
[0039]
The inventors have studied to improve fatigue characteristics, especially fatigue strength. Using a brush, shot blast, dull roll, etc., a strain corresponding to a residual compressive stress of 0.01 to 50 MPa is applied to the steel surface layer in the thickness direction. It has been found that the fatigue strength is remarkably improved by the introduction. That is, fatigue fracture occurs when tensile stress is applied, starting from the stress concentration part, but by introducing strain corresponding to residual compressive stress of 0.01 to 50 MPa into the steel surface layer, stress concentration is relaxed, They found that the fatigue strength increased and succeeded in completing the present invention. The reason why the residual compressive stress is limited to 0.01 to 50 MPa is that if the residual compressive stress is less than 0.01 MPa, the stress concentration cannot be sufficiently relaxed and the effect of increasing fatigue strength is not remarkable. In addition, if the residual compressive stress is larger than 50 MPa, the material is markedly cured. Further, the “steel surface layer” herein means a value when measured from the plate surface by the X-ray diffraction method, and is specifically considered to be a layer having a thickness of about 200 μm including from the steel surface. .
The X-ray diffraction method was performed using a RINT1500 X-ray diffractometer manufactured by Rigaku Denki Co., Ltd., using CoKα rays and a θ-2θ method under conditions of a voltage of 46 kV and a current of 150 mA.
[0040]
FIG. 1 shows a diagram in which a fatigue test is performed on a stainless steel plate having a steel composition according to the present invention, and the relationship between the cyclic stress (MPa) and the number of cycles until fatigue failure is plotted, that is, an SN diagram. In FIG. 1, “●” is data in the case of a stainless steel plate introduced with a strain corresponding to a residual compressive stress of 0.80 MPa by performing shot blasting, and “◯” is shot blasting. The data is for a stainless steel plate (residual compressive stress: 0.002 MPa) that is not treated.
[0041]
As is apparent from FIG. 1, it can be seen that the fatigue characteristics of the stainless steel plate into which the residual compressive stress is introduced are remarkably improved.
[0042]
Next, an example of a preferred method for producing the stainless steel of the present invention will be described.
First, the molten steel adjusted to the above steel component composition is melted in a generally known melting furnace such as a converter or an electric furnace, and then a known method such as a vacuum degassing method (RH method), VOD method, AOD method or the like. It is preferable that the steel material is refined by a refining method and then cast into a slab or the like by a continuous casting method or an ingot forming method.
[0043]
Next, the steel material is heated and made into a hot-rolled steel sheet by a hot rolling process. The heating temperature in the hot rolling process is not particularly limited, but if the heating temperature is too high, crystal grains become coarse and the toughness and workability deteriorate, so the heating temperature is preferably 1300 ° C. or lower.
[0044]
In addition, it is sufficient that the hot-rolled steel sheet has a desired thickness in the hot-rolling process, and the hot-rolling conditions are not particularly limited. However, the hot rolling finishing temperature should be 700 ° C or higher. It is preferable from the viewpoint of ensuring.
[0045]
However, when workability, ductility, and even good surface properties are required, the finishing temperature in hot rolling is preferably 820 ° C or higher and 1000 ° C or lower.
[0046]
The winding temperature is preferably in the range of 500 to 800 ° C.
[0047]
After the hot rolling is completed, it is preferable to perform hot-rolled sheet annealing for softening. In this hot-rolled sheet annealing, it is preferable to set the annealing temperature: 600 to 1100 ° C. and the holding time: 0.01 to 20 h from the viewpoint of improving workability and securing ductility as well as softening.
[0048]
When a martensitic structure is formed on a hot-rolled sheet, after annealing the hot-rolled sheet, the temperature range of 600 to 730 ° C is gradually cooled at a cooling rate of 50 ° C / h or less in terms of softening. More preferred.
[0049]
Thereafter, the scale is removed by pickling, etc., and further, if necessary, after alkaline degreasing, water washing and drying, the steel surface is reformed using a brush, shot blast or dull roll, etc. It is preferable to apply the coating after appropriately controlling the roughness and the strain introduced into the steel surface layer. The coating is, for example, a baking coating for 15 seconds to 3 minutes in a temperature range of 180 to 300 ° C. The baking coating is, for example, a paint containing a urethane-modified epoxy resin containing titanium oxide, an anticorrosive pigment, and the like. A representative example is a paint containing about 30% of a 3 μm iron phosphide powder in a nonvolatile content ratio.
[0050]
【Example】
Molten steel having the composition shown in Table 1 is melted in the converter-secondary refining process and made into a slab by the continuous casting method, and then reheated to 1150 to 1250 ° C., and the rolling reduction of the final rough rolling is 30 to 45%. After the 6-pass rough rolling, a final rolling temperature of 840 to 990 ° C is used for 7-pass finish rolling to obtain a 4.2 mm hot-rolled steel sheet, and then the normal process of hot-rolled sheet annealing-pickling treatment Then, the steel sheet surface was subjected to surface modification treatment with shot plast or dull roll to produce a stainless steel sheet with various changes in surface roughness and various changes in residual compressive stress in the thickness direction.
[0051]
[Table 1]

[0052]
The various stainless steel plates thus prepared were measured for residual compressive stress on the plate surface, then measured for surface roughness by the stylus method (JIS B 0601) and subjected to a fatigue test to measure fatigue strength.
[0053]
The measurement of the residual compressive stress is based on a general X-ray diffraction method (conditions) based on the X-ray diffraction theory (author BDCULLITY, translated by Gentaro Matsumura, Agne Co., Ltd., 1971, 9th edition, p435-458). : Θ-2θ method, using CoKα ray, voltage 46 kV, current 150 mA, using RINT 1500 X-ray diffractometer manufactured by Rigaku Corporation. In this case, however, it is necessary to be careful when adjusting the sample. That is, when the X-ray diffraction method is used, the surface unevenness has a great influence on the X-ray reflection, and thus the surface unevenness must be removed. Careful attention was paid here, and the surface layer of the steel sheet was first mechanically carefully scraped with fine emery paper (# 800-1200), then electropolished with 5% perchloric acid acetic acid (10 ° C). Then, the distortion caused by mechanical polishing was removed before use in the measurement.
[0054]
The surface roughness was measured by a touch method based on JIS B 0601.
[0055]
The fatigue strength was measured according to JIS Z 2273. The fatigue strength measured here means the fatigue strength for 10 ⁶ times.
[0056]
In addition, in order to evaluate the coating film adhesion of the above various stainless steel plates, after washing with alkali and degreasing, washing with water and drying, and further performing chromate treatment so that the Cr adhesion amount is 30 to 35 mg / m ² , urethane Using a paint containing titanium oxide, rust-preventive pigment, etc. in a modified epoxy resin and further containing about 30% of iron phosphide powder with an average particle size of 3 μm in a non-volatile content ratio (trade name: Well Color P) A coated steel sheet was manufactured by performing heat coating at 280 ° C. for 60 seconds so that the amount was 17.5 mg / m ² . Thereafter, each coated steel sheet was cross-cut on the surface, immersed in 5 mass% hydrochloric acid (28 ° C.) for 96 hours, washed with water and dried, and then subjected to a peeling test using a cello tape. The coating film adhesion was evaluated by measuring the maximum width (mm) of the coating peeled off at the cross-cut portion. In the present invention, the coating film adhesion was rejected when the coating film peeling width was 5 mm or more.
[0057]
Table 2 shows the results of the residual stress (MPa), the surface roughness (μm), the fatigue strength (MPa), and the coating film adhesion (peeling width: mm) of the steel sheet surface layer measured by the method described above. In Table 2, the values of residual stress mean that the positive value is the residual compressive stress and the negative value is the residual tensile stress.
[0058]
[Table 2]

[0059]
From the results shown in Table 2, it can be seen that all of the inventive examples have high fatigue strength and excellent coating film adhesion.
Moreover, when compared in the same steel No., it turns out that the fatigue strength of the steel plate with a large residual compressive stress is larger than the steel plate with a small residual compressive stress. In addition, about the thing with low fatigue strength within the same steel No., the underline was attached in Table 2 and it was set as the comparative example. Furthermore, it can be seen that a steel sheet having a surface roughness of less than 0.2 μm has a large peeling width of the coating film and is poor in coating film adhesion.
[0060]
【The invention's effect】
According to the present invention, after optimizing the steel composition, the arithmetic mean roughness Ra of the steel sheet surface and the residual compressive stress of the steel sheet surface layer are optimized to provide excellent fatigue characteristics and coating film adhesion. It is now possible to provide stainless steel for civil engineering and building structures.
[Brief description of the drawings]
FIG. 1 is an SN diagram when residual compressive stress is introduced into a steel sheet surface layer and when it is not introduced.

Claims (5)

Cr: Exceeding 8 mass%, less than 15 mass% C: Exceeding 0.0025 mass%, less than 0.03 mass% N: Exceeding 0.0025 mass%, less than 0.03 mass% S: Less than 0.03 mass%
Mn: More than 0.5 mass%, less than 3.0 mass%
Al: Less than 0.5 mass% P: Less than 0.04 mass%
Si: contains more than 0.1 mass% and less than 2.0 mass%, the balance is the composition of Fe and inevitable impurities, and the arithmetic average roughness (Ra) of the surface is 0.2 to 50 μm, and the surface layer is 0.01 Stainless steel for civil engineering and building structures with excellent fatigue characteristics and coating film adhesion, characterized by introducing strain that generates residual compressive stress of ~ 50MPa. In claim 1, further
Cu: less than 3.0 mass%,
Mo: less than 3.0 mass% and
Ni: Stainless steel for civil engineering and building structures with excellent fatigue properties and coating film adhesion characterized by a composition containing one or more selected from less than 3.0 mass%. In claim 1 or 2, further
Co: 0.01 mass% or more, less than 0.5 mass%,
V: 0.01 mass% or more, less than 0.5 mass%, and W: 0.001 mass% or more, less than 0.05 mass%, a fatigue property and a coating film characterized by containing one or more kinds selected from Stainless steel for civil engineering and building structures with excellent adhesion. 4. The stainless steel for civil engineering and building structure according to claim 1, wherein the composition further contains B: 0.0002 to 0.002 mass%, and is excellent in fatigue characteristics and coating film adhesion. In any one of Claims 1-4, Furthermore,
Ti: Less than 0.7 mass%,
Nb: Less than 0.7 mass%,
Ta: Less than 0.7 mass% and
Zr: Stainless steel for civil engineering and building structures with excellent fatigue characteristics and coating film adhesion, characterized by containing one or more selected from less than 0.5 mass%.

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