高温回火P91钢显微组织演变及再结晶机理

Effect of high-temperature tempering on microstructure evolution and recrystallization mechanism of P91 steel

通过热膨胀法测定试验所用P91钢的相变点,采用OM、TEM及EBSD等,研究P91钢在710、730、760、770、790、810、830、840℃回火过程中显微组织及特殊晶界的演变过程。发现随着回火温度的升高,P91钢中的板条马氏体形貌特征逐渐模糊,位错密度逐渐降低,并且出现等轴状的铁素体组织。经EBSD分析,高角度晶界的含量同样随回火温度的升高而逐渐升高并趋于稳定,而小角度晶界的含量显著减少。分析表明,P91钢在高温回火过程中发生了再结晶,形成了等轴晶铁素体,通过亚晶聚合及晶界迁移机制来形核,从而实现再结晶。

Phase transformation point of P91 steel was determined by thermal expansion method.The microstructure and the evolution of special grain boundaries of the P91 steel during tempering at 710,730,760,770,790,810,830 and 840℃were studied by means of OM,TEM and EBSD.It is found that with the increase of tempering temperature,the lath martensite morphology in the P91 steel is weakened,the dislocation density is gradually reduced,and the equiaxed ferrite structure appears.By EBSD analysis,the content of high angle grain boundaries increases gradually with the increase of tempering temperature and tends to be stable,while the content of low angle grain boundaries is significantly reduced.The analysis shows that during the tempering process,recrystallization occurs and a certain amount of equiaxed ferrite is formed,which nucleates through the mechanism of subgrain polymerization migration and grain boundary expansion,so as to realize recrystallization.