Comparative study on microstructure and hardness of P92 steel before and after long service

Abstract

Due to its exceptional mechanical properties, the P92 steel is extensively utilized in power plants for high-temperature and high-pressure components, such as main steam and reheated steam pipes. This study aims to characterize the microstructure and Brinell hardness of domestic and imported P92 steel before and after 50 kh of service under identical conditions using SEM (scanning electron microscope), EBSD (electron back scattering diffraction), TEM (transmission electron microscope), and a Brinell hardness tester. The findings reveal that the hardness of domestic P92 steel decreases from 222 HB to 200 HB after 50,000 hours (50 kh) of service, while the imported P92 steel experiences a slight decrease from 205 HB to 203 HB. During prolonged service, the martensitic lath broadening rate in domestic P92 steel surpasses that in imported P92 steel, which primarily accounts for the significant decline in hardness. Additionally, the presence of large-sized Laves phases at matrix lath boundaries, lath bundle boundaries, and grain boundaries in both domestic and imported P92 steels also contributes to the reduction in hardness.