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通过慢应变速率拉伸(SSRT)试验和高温电化学相结合的方法,研究外加电位对奥氏体不锈钢316NG焊接接头在含氯离子的高温高压水中应力腐蚀开裂(SCC)倾向的影响。试验结果表明:退火态316NG焊接接头SCC敏感性随外加电极电位升高而增大,且存在一个介于+50~+100 mV[相对标准氢电极(vs.SHE)]之间的SCC临界电位;低于该电位时,SCC敏感性较小,无明显沿晶开裂,仅断口边缘处存在少量穿晶开裂,随电极电位变化不明显;高于该临界电位时,SCC敏感性急剧增加,并出现明显的沿晶开裂。此外,高温Ar和腐蚀性低(电极电位≤50 mV)的环境中,焊接接头的断裂为力学主导的塑形开裂,其与焊接接头的硬度分布密切相关,硬度越低,越容易断裂;强腐蚀性(电极电位>50 mV)环境中,焊接接头的断裂为腐蚀主导的脆性开裂;显然,焊缝及热影响区的SCC敏感性高于母材。
The effects of applied potential on the stress corrosion cracking (SCC) tendency of austenitic stainless steel 316NG welded joints in high temperature and high pressure water containing chloride ions were studied by the combination of slow strain rate stretching (SSRT) and high temperature electrochemical. The experimental results show that the SCC sensitivity of annealed 316NG welded joints increases with the increase of the applied electrode potential, and there is a SCC threshold potential between +50 and +100 mV [vs. standard hydrogen electrode (vs.SHE)] Below this potential, SCC was less sensitive and no obvious intergranular cleavage. Only a small amount of transgranular cleavage existed at the edge of the fracture, with no obvious change with the electrode potential. Above this critical potential, SCC sensitivity increased sharply Significant intergranular cracking appears. In addition, high temperature Ar and corrosive low (electrode potential ≤ 50 mV) environment, the fracture of the welded joint is a mechanical dominated shape cracking, which is closely related to the hardness distribution of the welded joint, the lower the hardness, the more likely to fracture; In the corrosive (electrode potential> 50 mV) environment, the fracture of the welded joints is a corrosion-induced brittle fracture; it is clear that the SCC sensitivity of the weld and the HAZ is higher than that of the base metal.