Influence of heat treatments on microstructural parameters and mechanical properties of P92 steel

The microstructural parameters (dislocation density, martensite lath width, precipitate diameters, and volume fractions) have been measured for the 9% Cr steel P92 (NF616) after different heat treatments. The austenitising tem peratures were 970, 1070, and 1145 degreesC and the tempering temperatures 715, 775, and 835 degreesC, Increasing the austenitising temperature led to an increase in the austenite grain size and in the martensite lath width, but no significant effect on the tensile properties at 20, 600, and 650 deg reesC was observed. The creep strength was, however, reduced by tempering a t 835 degreesC due to rapid recovery of the martensitic structure with a sh arp decrease in dislocation density, The lowest creep strength was found fo r the P92 steel subjected to a heat treatment that produced a fully ferriti c microstructure; the secondary creep rate was four orders of magnitude hig her than that of the steel in the usual martensitic condition.