SITE MAP

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Chemical and microstructural analyses were performed on Ni depletion zones in 304 austenitic stainless steel

sheets after annealing and cooling with three different rates (0.2, 18.6, 160.0 ◦C/s). The analysis was focused on

the characteristics and the origin of the retained δ-ferrite and α’-martensite phases in the austenite matrix.

Simultaneous Ni depletion and Cr enrichment belong to the retained δ-ferrite due to incomplete decomposition

after the solidification process. Athermal α’-martensite was observed to grow within Ni-depleted zones with no

Cr enrichment. The fraction of α’-martensite increases as the cooling rate increases. EPMA analysis reveals that

the 1 wt% reduction of Ni contents to the bulk chemical composition promotes the thermally-activated

martensitic transformation. Such athermal martensite tended to grow within twinning boundaries holding the

Nishiyama-Wassermann orientation relationship with the austenite matrix confirmed with the electron diffraction

patterns in TEM and the misorientation analysis in EBSD.​