改进型9Cr耐热钢高温长时时效组织演变研究

Investigation on the Microstructure Evolution of Modified 9Cr Heat-resistant Steel after Long-time Aging at High Temperature

汽轮机转子工作环境苛刻,其需要的耐热钢材料的组织稳定性对其安全运行具有至关重要的影响。对原始态和经过538℃时效8 000 h的改进型9Cr耐热钢进行对比研究。结果表明,经过高温长时时效后,改进型9Cr耐热钢的基体组织仍为马氏体,组织较稳定。利用扫描电子显微镜(SEM)对碳化物进行观察并统计,发现经高温时效后,碳化物的体积分数由原始态的0. 6%上升到约1. 5%,平均尺寸由146 nm增加至约186 nm,碳化物长宽比仍约为1. 5。碳化物尺寸虽略有增加,但未发生明显的粗化和聚集现象。在透射电子显微镜(TEM)下观察,发现时效后有Mn_(15)C_4和V_8C_7亚稳碳化物析出。研究表明,改进型9Cr耐热钢具有较好的高温组织稳定性,可以满足高温长时间工作的需要。

Turbine rotor works under extremely harsh conditions.The microstructure stability of heat-resistant steel has a great effect on the safe operation of turbine rotor.The microstructures of the modified 9Cr heat-resistant steel before and after being aged at 538℃for 8 000 h were comparatively studied.The results showed that the matrix of the modified 9Cr heat-resistant steel was still martensite,having no obvious change compared with the original microstructure.In terms of the carbides observed using scanning electron microscope(SEM),the volume fraction of carbides increased from 0.6%to 1.5%,the size of carbides increased from 146 nm to about 186 nm,length to width ratio of carbide was about 1.5,implying that no obvious coarsening and segregation occurred even after aging 8 000 h.In addition,the metastable Mn 15 C 4 and V 8C 7 carbides in the aged sample were detected using transmission electron microscope(TEM).This study indicated that the modified 9Cr heat-resistant steel was stable at high temperature,being capable of long-period working at high temperature.