PHASE-STABILITY AND FCC HCP MARTENSITIC-TRANSFORMATION IN FE-MN-SI ALLOYS - PART I - EXPERIMENTAL-STUDY AND SYSTEMATICS OF THE M-S AND A(S)TEMPERATURES/

This paper presents the first part of an experimental and thermodynami c study of the fcc/hcp relative phase stability and the fcc<->hcp Mart ensitic Transformation (MT) in the Fe-Mn-Si system. In the present wor k, the building up of an extensive experimental database is described in detail. Fe-Mn-Si alloys with 15 to 35 wt. % Mn and up to 6.5 wt.% S i are investigated. The fcc-->hcp (M-s) and the hcp-->fcc (A(s)) MT te mperatures are determined using a dilatometric technique. With this ne w information, the composition dependence of the M-s and A(s) temperat ures is established. A well defined picture of the systematics of the MT temperatures emerges from our measurements, which is critically com pared with the recent calculations due to Forsberg and Agren. The need for a new assessment of the fcc/hcp relative phase stability in Fe-Mn -Si alloys is emphasized. (C) 1998 Elsevier Science S.A. All rights re served.