利用以前报道过的恆电位量电法以及化学分析法,进一步研究了18鉻-8镍型不锈钢中的贫鉻区随着敏化处理时间的发展情况.得到了敏化时间不同时鉻在贫鉻区中的分布曲线,估计出鉻在650℃的溫度下在贫鉻区中离碳化物层100埃处的扩散系数为5×10~(-16)厘米~2/秒.结果表明,析出在晶界的碳化物的量大体上按对数规律随敏化时间增长.此外,18鉻-8镍型不锈钢中所含碳的总量中只要有1—2％析出在晶界,就足以引起严重的晶间腐蚀.
The development of the chromium-depleted zone with time of sensitization has been studied by the potentiostatic-coulometric method reported previously. The distribution curves of chromium in the depleted zone at different time of sensitization have been obtained. From these curves, the diffusion coefficient of Cr in the depleted zone at 650℃ is estimated to be 5×10~(-16)cm~2/sec. It is shown that the amount of chromium carbide precipitated at the grain boundaries increases nearly logarithmically with time of sensitization, and the precipitation of 1—2% of carbon contained in the steel at the grain boundaries is sufficient to cause severe intergranular corrosion.
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