Creep Properties of Advanced Heat-Resistant Martensitic Steels Strengthened by L1_0, Type Ordered Intermetallic Phase

摘要

Creep properties of advanced heat-resistantmartensitic steels with the compositions of 0.08C-0.3Si-0.5Mn-9Cr-3.3W-(0/3)Pd-0.2V-0.05Nb-0.05N-Fe (in mass percent)have been studied to explore the fundamental guiding principlesfor the development of new steels with improved creep strengthat higher temperatures over 650 deg C. The steel with 3percent Pd exhibits higher creep strength than that of the basesteel, in particular, at higher temperatures. The microstructureof the steel with Pd is characterized by fine precipitation of aFePd based L1_0 type ordered phase, #alpha#" phase. The#alpha#" phase forms in the tempered martensitic matrix,#alpha#, along with the existing phases such as MX (M; V, Nb,X; C, N) carbonitride and M_(23)C_6 (M; Cr, Fe, W) carbideafter normalizing at 1100 deg C and tempering at 770 deg C.A detailed TEM observation has shown that the #alpha#" phaseprecipitates in a plate-shaped with the habit plane parallel to{00l}_#alpha# and with a crystallographic orientationrelationship with the matrix, {00l}_#alpha#//{00l}_#alpha#"and _#alpha#// <1l0>_#alpha#". The #alpha#" phase isfound to be a most effective precipitate to increase creepresistance of the steel in terms of the inter-particle spacingestimated. The #alpha#" phase is stable even after aging at 700deg C and hence is more useful at higher temperatures. It isthus concluded that the creep resistance of the ferritic steels canbe increased further by optimizing the, combination of fineprecipitation such as the #alpha#" phase and MX carbonitride.