核级316NG奥氏体不锈钢在热老化条件下的析出相

Precipitates of nuclear grade 316NG austenitic stainless steel under thermal aging

通过热老化模拟试验、电解萃取试验和热力学计算方法(CALPHAD)研究了核级316NG奥氏体不锈钢在核环境下的析出相情况。结果表明,316NG奥氏体不锈钢在450℃老化100 h无析出相;老化500 h的主要析出相为Cr_(23)C_(6);老化1000 h的主要析出相为Z-CrNbN、Cr_(23)C_(6)和Laves_C14。然后,采用CALPHAD方法建立了316NG奥氏体不锈钢的热力学数据库,并以此数据库为基础,利用Thermo-Calc软件计算了316NG奥氏体不锈钢在450℃平衡状态下的析出相组成为Cr_(23)C_(6)、Z-CrNbN、Laves_C14、Ni_(3)Si和MX,析出相总原子分数为3.5%,其中Ni_(3)Si和MX的含量很低(0.46%)。通过CALPHAD方法计算得到的析出相组成与450℃等温退火1000 h后的热老化试验结果符合得较好,从而获得关于316NG奥氏体不锈钢在长时间热老化条件下的析出相规律及组织成分的较为完善的信息。

Precipitation conditions of the 316NG austenitic stainless steel in the nuclear environment were studied by means of thermal aging simulation experiment,electrolytic extraction experiment and the CALPHAD method.Then,the thermodynamic database of the 316NG austenitic stainless steel was established by the CALPHAD method.The results show that the 316NG austenitic stainless steel has no precipitated phase during annealing at 450℃for 100 h,the Cr_(23)C_(6)is the main precipitated phase when annealed at 450℃for 500 h,and the main precipitated phases are Z-CrNbN,Cr_(23)C_(6)and Laves_C14 when annealed at 450℃for 1000 h.Based on the thermodynamic database,at 450℃,the equilibrium precipitated phases calculated by the Thermo-Calc software are Cr_(23)C_(6),Z-CrNbN,Laves_C14,Ni_(3)Si and MX,and the total atom fraction is 3.5%,among which the content of Ni3 Si and MX is only 0.46%.The calculated precipitated phases by CALPHAD are good agreement with the results by thermal aging experiment of annealing at 450℃for 1000 h,showing that the more complete information is obtained on the precipitated phases and their compositions of the 316NG austenitic stainless steel under long-term thermal aging.