Mechanical Alloying of Premixed δ and γ Stainless Steel Powders with a Tie Lined Chemical Compositions

Abstract

Mechanical alloying process of the mixture of ferritic(δ) and austenitic(γ) stainless steel powders has been investigated by means of X-ray diffraction and EPMA line analysis. The chemical compositions of δ and γ powders used is Fe-27mass%Cr-7mass%Ni and Fe-20mass%Cr-12mass%Ni, respectively, which are equilibrium compositions of δ and γ phase at 1473K.
The γ phase in the premixed (δ+γ) powders changes to bcc phase with ballmilling treatment and this phase change is promoted by increasing the volume fraction of δ powder. The structure of γ -70vol%δ premixed powder is of full bcc single phase after 360ks ball-milling treatment.
However, EPMA line analysis in premixed (δ+γ) powders with 360ks ball-milling treatment shows the inhomogeneity of the chemical composition of Cr and Ni, while the structure is of bcc single phase. The inhomogeneity of chemical composition is deeply related to the phase transformation of γ. The structural change to bcc phase is mainly due to the deformation induced transformation of γ to bcc martensite and partially due to the mechanical alloying at the interface between δ and γ phase.