Microstructure of P92 Steel for Main Steam Pipeline of Ultra Supercritical Units after 50,000 h Service

Abstract

The microstructure of P92 steel used in the main steam pipeline of ultra-supercritical unit after 50,000 h service was studied by means of metallographic microscope, scanning electron microscope, energy dispersive spectroscopy and X-ray diffraction. The results show that the microstructure of P92 steel is still lath martensite after 50,000 hours of service at high temperature, but the martensite recovers. There are many large-sized M₂₃C₆ and Laves phases in the structure, and the aging phenomenon is obvious. The compound of bismuth is small in size and difficult to grow during service, which is beneficial to the improvement of creep rupture strength of P92 steel. The initial particle size of M₂₃C₆ and Laves phase is small, which is beneficial to improve the high temperature strength of the material. With the extension of service time, the size of M₂₃C₆ and Laves phase increases, which promotes the creep cavity and reduces the creep rupture strength of the material.