经淬火+回火或正火+回火两种不同热处理的2 1/4Cr-1Mo高压容器钢,在高温高压氢中抗氢腐蚀的能力显著不同。在550°～580℃的温度范围和13.5～31兆帕的高压氢作用下,正火+回火处理的2 1/4Cr-1Mo钢的膨胀速率比淬火+回火处理的大一个数量级以上。经金相、电镜、扫描电镜、透射扫描电镜和能量发射谱分析,发现正火+回火钢的组织发生了显著变化,而淬火+回火钢组织则比较稳定。其原因是正火+回火钢中M_3C碳化物的含铬量较淬火+回火钢中的低。正火+回火钢中的M_2C型碳化物也欠稳定,因而其抗氢腐蚀能力较差。
2 1/4-Cr-1Mo steel samples which had been tempered after quenching and normalizing were exposed to hydrogen at 13.5 to 31 MPa in the temperature range of 500° to 580℃. Previous work showed that the hydrogen attack(HA) resistance of normalized and tempered(N+T)steel was lower than that of quenched and tempered(Q+T)steel at temperatures above 500℃. The expansion rate of N+T sample was about one order of magnitude higher than that of Q+T Sample. This paper presents a systematic metallographic investigation in anattempt to correlate the difference of HA resistance with the difference in the microstructure. TEM, SEM, STEM EDAX and optical microscopical examination showed that the carbides in the N+T sample were less stable than those of the Q+T sample. As a consequence of heat treatment, the M_3C carbides in N+T sample contained less chromium than those in the Q+T sample. During exposure to high temperature and high pressure hydrogen, M_3C carbides in the N+T sample diminished with time much more quickly than those in the Q+T sample. Correspondingly M_2C carbides in the N+T sample were also less stable. This resulted in lower HA resistance of the N+T sample.
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