Research on Durability Estimation for Steel Buildings

该研究揭示了腐蚀环境加载后的应力-腐蚀-开裂行为以及屈服和/或抗拉强度。采用SUS304奥氏体不锈钢，焊接结构用SMA490B耐候钢，建筑结构用SN490B轧钢。腐蚀条件为：含5%盐的酸雨喷淋2小时，温度60□、湿度20%、全湿度人工环境试验仪灌淋4小时。在这些条件下循环加载650次应力腐蚀试验和200次静拉试验。应力-腐蚀-裂纹试验结果表明：(1)SUS304在650个腐蚀循环后才出现应力-腐蚀-裂纹，但裂纹尖端前的Luders带逐渐增大，且随着腐蚀循环的增加，Luders带不断扩展。以Luders带为裂纹，SUS304的应力腐蚀开裂阈值母材为25.3 ~ 26.2 MN/m^<3/2>，热影响区为24.2 ~ 25.0 MN/m^<3/2>。(2) SMA490B钢也在85次腐蚀循环后才出现应力腐蚀裂纹，且该钢的锈蚀形成速度快于应力腐蚀裂纹扩展速度。认为钢表面的锈层阻止了应力腐蚀裂纹的扩展。因此，耐候钢几乎不发生应力腐蚀裂纹。(3)由于腐蚀作用，钢板表面出现凹凸不平的状况。SN490B的凹凸状况比SMA490B耐候钢更为显著。因此，由于凹凸不平条件下的应力集中，腐蚀后钢材的屈服强度和抗拉强度大大降低。

This study showed that stress-corrosion-cracking behaviors and yield and/or tension strength after corrosion environmental loading. Used steels were SUS304 austenitic stainless steel, SMA490B weather proof steel for welding structure and SN490B rolled steel for building structure. Corrosion conditions were 2 hours spray of acid-rain contain 5% salts, 4 hours dray with 60□ temperature, 20% humidity and 2 hours full-humidity using artificial environmental testing apparatus. Those conditions were loaded cyclically with 650 times for stress-corrosion-test and 200 times for statically tension test.The results of stress-corrosion-cracking-test were as follows,(1)For SUS304, stress-corrosion-crack did not occurred until 650 corrosion cycles, but Luders band grew in front of the crack tip and the Luders band propagated according to the corrosion cycles. Consider the Luders band to be the crack, stress-corrosion-cracking threshold for SUS304 was 25.3-26.2 MN/m^<3/2> for base metal, 24.2-25.0 MN/m^<3/2> for heat affected zone respectively.(2)For SMA490B, stress-corrosion-crack did not occurred until 85 corrosion cycles too, and for this steel, rust formative rate was faster than stress corrosion crack propagation rate. It was thought that the rust layer of steel surface prevented the stress corrosion crack propagation. So that, the stress corrosion cracks hardly occurred for weather proof steel.(3)The surface of steel plate had bumpy condition by the corrosion. The bumpy conditions of SN490B were more remarkably than that of SMA490B weather proof steel. So that yield and/or tension strength of steels after corrosion deteriorated very much on account of the stress concentration by bumpy conditions.