Influence of Some Processing Factors on Susceptibility to Caustic Stress Corrosion Cracking of Modified Alloy 800
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摘要: 通过显微组织检验、拉伸试验、应力分析、C形环应力腐蚀试验、俄歇电子能谱(AES)分析、腐蚀形貌观察,研究了某些加工因素(冷加工和热处理)对国产改性800合金(800M)在沸腾的50%NaOH+0.3%SiO2+0.3%Na2S2O3溶液中的应力腐蚀破裂(SCC)敏感性的影响。冷加工拉伸25%的800M合金管的晶粒变形拉长,屈服强度和抗拉强度增大而延伸率降低,管的残余应力增加,SCC敏感性增加。对冷变形800M合金管热处理,随温度的升高,晶粒逐渐等轴化并变大,延伸率增大,屈服强度、抗拉强度和残余拉应力和SCC敏感性降低。AES分析表明,800M合金在沸腾碱液中恒电位极化后的表面膜是富Ni而贫Fe、Cr的。C形环试样碱性SCC裂纹在点蚀坑起源萌生,裂纹沿晶界扩展。Abstract: The influence of some processing factors such as cold work and heat treatment on the susceptibility to caustic stress corrosion cracking (SCC) of modified alloy 800, referred to alloy 800M, in a boiling solution of 50%NaOH+0.3%SiO_2+0.3%Na_2S_2O_3 was investigated by means of microstructure examination, tensile test, stress analysis, SCC test of C-rings, Auger electron spectroscopy(AES) and corrosion mode. Cold work led to lengthening of grains, decrease in ductility, increase in strength, residential stress and susceptibility to SCC. With increasing temperature of heat treatment on alloy 800M after cold work, grains became bigger, ductility increased but strength, residential stress and susceptibility to SCC decreased. SCC cracks on C-ring specimens initiated from pitting and propagated along grain boundaries. AES analysis indicates that the surface films on alloy 800M are enriched in nickel and depleted in iron and chromium.
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Keywords:
- cold work ,
- heat treatment ,
- caustic stress corrosion cracking ,
- modified alloy 800
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