Effects of the amount of retained austenite on the microstructures and mechanical properties of a precipitation hardening martensitic stainless steel

Abstract

The influences of the amount of retained austenite on the microstructure and the mechanical properties were investigated for the martensitic stainless steel whose chemical composition was Fe-1.8Cu-15.9Cr-7.3Ni-1.2Mo-0.08Nb-low C, N (wt%). The main results obtained are as follows; (1) Microstructures of all specimens after aging (753K × 14.4ks) are lath martensitic with film like retained austenite dispersed among the lathes. The reverted austenite phase dose not appear. The ε-Cu phase which contributes to the precipitation hardening can not be observed clearly. (2) The mechanical properties are linearly approximated to the amount of retained austenite, so that the following equations are obtained. : 0.2%Y.S. (MPa) = 1192.3-13.6×γ%, T.S. (MPa) =1250.1-9.3× γ%, E.L.(%) =12.16+0.43× γ%, R.A.(%) =64.25+ 0.14× γ%, A.E. (J) =72.5+0.8× γ% (3) The balance between the tensile strength and ductility is improved with increment of the amount of austenite. It is in the same level as the microduplex stainless steel and the low carbon martensitic stainless steel with the excellent ductility and toughness, although inferior to the work hardening austenitic stainless steel.