Characterization of the Interfacial Zone Between a HIPed Fe-Based Alloy and a Stainless Steel Container

Abstract

Norem02, an Fe-based alloy with a high carbon and chromium content, is elaborated by hot isostatic pressing (HIP). HIP is an attractive pressure-assisted sintering technique allowing for the elaboration of dense fine-grained materials from metal powder placed in a container. AISI 316L and 304L stainless steels were chosen as container materials. Two kinds of Norem02 powders of different particle-size distributions yet rather similar chemical compositions were tested. Detailed investigations of the interfacial zone between the Norem02 and stainless steel container were performed. In both HIPed samples, a microstructural transition band of approximately 500-700 µm was found within the Norem02 near the austenitic container. The presence inside Norem02 of coarse M23C6-type carbides, as well as ferrite, was highlighted. Silicon and manganese enrichment and nickel depletion were revealed in the 316L and 304L steels. χ-phase formation was confirmed at the Norem02 grain boundaries, depending on sintering temperature and on the composition of the initial powder. σ-phase was not detected, suggesting incomplete transformation of χ-phase. Finally, carbon diffusion inside the austenitic steel was noted and quantified and a diffusion coefficient was calculated. Despite the formation of carbides inside the 304L, experimental results suggest that the carbon diffused mainly in solid solution.