高Nb含量316LN不锈钢的时效析出行为

Precipitation behavior of 316LN stainless steel with high Nb content during aging treatment

对高Nb含量的316LN奥氏体不锈钢,在650、750和800℃时效处理不同时间。通过定量金相,SEM、XRD及TEM等分析技术,分析了析出相随时效时间和温度的变化关系。结果表明:时效初期,析出相沿晶界呈颗粒状、短棒状析出,随时效时间延长析出相沿晶界呈链状析出,析出量不断增多,并逐渐向晶内生长,最终以不连续的片状布满整个晶面。750℃为时效敏感温度,该时效温度下,析出相的量最多,孕育时间最短。整个时效阶段,时效优先析出相为Z-Cr Nb N相,且作为氮化物的主要存在形式,而不是常见的ε-Cr2N相。316LN不锈钢中,Nb元素的添加,一定程度上抑制了ε-Cr2N相和Z-Cr23C6相的析出,加速了σ-FeCrMo相的析出。

316LN austenitic stainless steel with high Nb content was aged at 650,750 and 850 ℃ for different time.Effect of aging temperature and time on precipitated phase of the 316 LN steel was analyzed by means of quantitative metallography,scanning electron microscopy（SEM）,X-ray diffraction（XRD） and transmission electron microscopy（TEM）.The results show that at the early stage of aging,the precipitation phase along the grain boundary is granular and short rod-shape,with the increasing of aging time,precipitation phase along the grain boundary is chain-like and the volume fraction increases,gradually growing from grain boundaries into grains,and finally the block precipitates are dispersively distributed in the steel.When the aging temperature is 750 ℃,the maximum volume fraction of the precipitation phase and the shortest incubation time is observed compared with that at the aging temperatures of 650 ℃ and 850 ℃.In the process of aging,the precipitation of Z-Cr Nb N phase prevails in the 316 LN stainless steel with high content of N instead of ε-Cr2 N in the commercial 316 LN stainless steel.The addition of Nb inhibis the precipitation of ε-Cr2 N and Z-Cr23C6 phases,accelerates the precipitation of σ-Fe Cr Mo phase.