用慢应变速率试验方法研究Cr18Mo2铁素体不锈钢的应力腐蚀开裂敏感性

用慢应变速率试验方法在143℃沸腾MgCl_2溶液中研究了不同碳含量、钛的加入量及热处理对Cr18Mo2铁素体不锈钢SCC敏感性的影响。随着碳含量的降低,钢的晶间腐蚀和点腐蚀程度减小,SCC敏感性相应减小。加入适量的钛可以明显减小其SCC敏感性,当Ti/(C+N)比在9.1～13.0时最显著。加入过量的钛引起σ相在晶界附近沉淀,致使SCC敏感性明显增大。 经1100℃处理的Cr18Mo2钢,晶间腐蚀程度显著增大,成为SCC敏感性的控制因素,断口呈沿晶开裂,SCC敏感性明显增大。经850℃处理后,晶间腐蚀明显减轻,点腐蚀成为SCC敏感性的主要的影响因素,断口呈穿晶开裂,SCC敏感性显著减小。 Cr18Mo2钢开裂敏感的应变速率为9×10~(*7)s~(-1)。断裂时间、断裂时延伸率ε_f和断面收缩车RA等参数可适用于评价铁素体不锈钢的SCC敏感性。

AN INVESTIGATION OF STRESS CORROSION CRACKING SUSCEPTIBILITY OF TYPE Crl8Mo2 FERRITIC STAINLESS STEEL USING SLOW STRAIN RATE TESTING

The effect of carbon content and various amount of titanium additions, as well as heat treatment conditions, on stress corrosion cracking(SCC) susceptibility of Cr18Mo2 ferritic stainless steel in 143℃ boiling MgCl_2 solution was investigated by slow strain-rate technique. Results indicate that with the lowering of carbon content, both intergranular and pitting corrosion rates are reduced and, correspondingly, the SCC susceptibility decreases. The amount of appropriate titanium additions that gives Ti/(C+N)ratios ranging from 9.1 to 13.0 has the most inhibitory effect on SCC,Excessive addition of titanium will cause precipitation of cr phase near the grain boundaries, resulting in higher susceptibility to SCC. The intergranular corrosion rate of Crl8Mo2 steel considerably increases if the steel is heat-treated at 1100℃. Under such a condition, SCC becomes very pronounced and the fracture is decidedly intergranular. In contrast, the intergranular corrosion remarkably decreases and the pitting corrosion becomes the predominant factor responsible for the susceptibility to SCC if the heat treatment of the steel is performed at 850℃. In the latter case, transgranular cracking is observed and SCC susceptibility of the steel greatly decreases. Experimental results obtained for the effect of strain rate show that the strain rate of 9×10~(-7s~(-1) gives rise to the most susceptible cracking. The parameters including fracture time t, elongation e; and reduction in area RA can be used to properly evaluate the SCC susceptibility of this ferritic stainless steel,