18Cr10NiNb耐热钢析出相的热力学计算和平衡相分析

Thermodynamic Calculation and Analysis on Precipitated Phases in 18Cr10NiNb Heat-resistant Steel

将18Cr10NiNb耐热钢在650℃进行10,000h的时效试验,用扫描电镜和透射电镜分析了18Cr10NiNb奥氏体耐热钢的组织,通过热力学计算研究了500-1400℃碳、铌和氮含量的变化对平衡析出相的影响。结果表明:在18Cr10NiNb钢的时效过程中在晶内析出了富Nb的MX相,在晶界析出了富Cr的M_(23)C_6相。根据热力学计算,其平衡析出相为MX,M_(23)C_6和σ相。MX相和M_(23)C_6型碳化物的最高溶解温度分别约为1340℃和840℃。MX相的数量随C和Nb含量的提高而增加。σ相的数量随着C含量的提高而减少。添加0.2%的N元素后,MX相为含有N、Nb、Cr和少量C的复杂碳氮化物,且在其平衡组织中出现了Cr_2N相。

Long-term aging at 650℃for the austenitic heat-resistant steel 18Cr10NiNb was conducted till 10,000 h.Effect of aging time on microstructure was investigated by SEM and TEM,and the effects of Nb,C,and N content on equilibrium phases from 500℃to 1400℃in 18Cr10NiNb steel have been calculated by using Thermo-Calc software.The results show that Nb-rich MX phase particles precipitate in the grains and Cr-rich M_（23）C_6 carbide mainly precipitates at the grain boundaries.The main equilibrium phases in18Cr10NiNb steel at 500-1400℃are MX,M_（23）C_6 andσ.The solution temperatures of MX and M_（23）C_6 are about 1340℃and 840℃,respectively.The amount of MX phase increases with increasing of C and Nb contents.The amount ofσphase decreases with increasing of C content.Adding 0.2%N in this the steel,MX phase contains N,Nb,Cr with a small amount of C,which is a complex carbon nitride and makes excellent strengthen effect.Cr_2N phase appears as one of the equilibrium phases in the steel at the same time.