Identification of Carbides and Phase Transformations in Sintered Fe–Mo–Mn–C Alloys Produced under a Slow Continuous Cooling

Abstract

Different sintered alloys were produced by sintering and slow cooling of powder compacts made from pre-alloyed Fe-0.50Mo-0.15Mn powder mixed with varied graphite powder contents (0.30–1.20 wt.% with 0.15% increment). According to microstructures, sintered alloys were divided into sintered hypo-eutectoid, near eutectoid, and hyper-eutectoid alloys. By using Groesbeck color tinting and X-ray diffraction technique, the common phase transformation products of these sintered alloys were found to include ferrite and carbides. The sintered hypo-eutectoid alloys had microstructures consisting of polygonal ferrite grains and two forms of ferrite + carbide mixtures, such as ferrite + M₂₃C₆ carbide and ferrite + M₃C carbide. In sintered near-eutectoid alloys, only ferrite + M₃C carbide mixtures occupied microstructures. In sintered hyper-eutectoid alloys, large proeutectoid M₂₃C₆ carbide formed first and followed by abnormal ferrite, degenerate ferrite + M₂₃C₆ pearlite, lamellar ferrite + M₂₃C₆ pearlite, Widmanstätten M₃C carbide, inverse bainite (ferrite + M₃C) and upper bainite (ferrite + M₃C).