Phase parameter changes of specific positions of P92 steel specimens during creep rupture test at 625℃

Abstract

The variation in phase parameter and mechanical properties of specific positions (gauge and grip) of the P92 steel specimens tested at 625℃ and 110-180 MPa was studied by SEM-BSE, EDS, EBSD, TEM and multiphase separation technology (MPST). The results show that highly stressed regions near fracture surface in the gauge portion are of higher volume fractions of M23C6 carbide and Laves phase, higher coarsening/widening trend of M23C6 carbides/martensite laths, and lower concen-tration of Cr and W elements and smaller percentage of low angle grain boundaries in the matrix as compared to a stress-free condition at the gripped end. It is evident that all these changes lead to the transformation of martensite into ferrite and hardness decreasing. It is indicated through this study that the changes in microstructure and mechanical properties of the stress-free sample cannot actually reflect the real changes of the samples stressed at the same aging temperature and time.

Keywords

• p92 steel
• precipitated phase
• martensite lath
• low angle grain boundary
• microhardness