Microstructural changes due to secondary precipitation hardening of martensitic creep resistant steel X20CrMoWV 12 1 (AISI 422)

After development of the well-known T/P91 steel grade in the early 80’s and its long industrial experience since early 90’s, it has been necessary to develop new martensitic creep resistant steels to answer the demand of the power generation industry. New USC (ultra-super critical) boilers require materials with advanced creep properties to reach severe steam parameters. Addition of W to the steel has been found by many researches to be effective to increase creep rupture strength at high temperatures and already used in some developed steel grades such as T/P92, T/P122 and AISI 422 for the USC boilers. Recently, long-term creep strength of the advanced high Cr ferritic steels has been argued regarding the instability of their microstructures at high temperatures over 600 °C. This microstructural instability seems to be enhanced with increasing Cr content or with substitution of Mo by W in the steels. The aim of this paper is concentrated on the investigation of the microstructural development of the studied steel using the Jominy end-face quench test. Different hardness profiles from this test were introduced.