316L和308L不锈钢应力腐蚀裂纹萌生行为研究

Research on Stress Corrosion Cracking Initiation Behavior of Cold Worked 316L and 308L Stainless Steel

目的研究载荷大小、加载方式和冷变形对材料裂纹萌生行为的影响规律。方法采用多轴多试样加载装置,在线测量冷变形316L和308L不锈钢在模拟反应堆高温高压水环境中恒载荷和慢应变速率拉伸状态下的应力腐蚀裂纹萌生行为。结果加载载荷低于屈服强度时,两种不锈钢均因具有较强的抗点蚀和晶界氧化性能而不易萌生裂纹。高于屈服强度后,伴随着载荷的增加,材料裂纹萌生时间显著缩短,断口包含沿晶和穿晶开裂两种典型的应力腐蚀开裂形貌。结论相较于同等程度冷变形的316L奥氏体不锈钢,308L不锈钢焊材在高应变速率下沿晶断裂或脆性断裂的敏感性更低,但降低应变速率将显著提高其沿晶开裂敏感性。冷变形因在不锈钢晶界和相界处引入了更高的残余应变,导致其裂纹沿晶界和相界萌生的倾向增大。

This paper aims to study the effects of load,loading mode and cold deformation on crack initiation behavior.Stress corrosion cracking initiation behavior of cold worked 316 L and 308 L stainless steel under constant load and slow strain rate test in simulated reactor high temperature and high pressure water environment was measured on-line by using a multi axial and multi sample loading device.When the loading load is lower than the yield strength,the two kinds of stainless steels are not easy to crack because of their strong resistance to pitting corrosion and grain boundary oxidation.When the loading load is above the yield stress,the crack initiation and fracture time decrease dramatically with the increment of applied load and the fracture includes two typical stress corrosion cracking morphologies:intergranular cracking and transgranular cracking.The susceptibility of 308 L stainless steel to intergranular or brittle fracture at high strain rate is lower compared with the same level cold worked 316L.The susceptibility to intergranular cracking significantly increased by decreasing the strain rate.Cold work increased the residual strain at both grain and phase boundaries,and thus increased the tendency of crack initiation along those boundaries.