Microstructure Investigation of Thermally Induced Phase Transformation in Fe–Mn– Mo–Si Alloys

Abstract

In this study, structural and crystallographic properties of phase transformations in Fe-Mn-Mo-Si (Mn = 15.14 wt.% and 18.45 wt.%) alloys were investigated. The effects of heat treatment temperature on microstructure were investigated by Scanning Electron Microscopy (SEM) and Metallurgical Microscopy (MM). In addition to this, crystallographic properties of phase transformations were revealed by using Transmission Electron Microscopy (TEM) and X-Ray Diffraction (XRD) methods. In the samples subjected to heat treatment at 750 C, it was observed that bainite structure was formed in the alloy where Mn amount was low and ferrite structure in the alloy where Mn amount was higher. In addition, it was found that both alloys heat-treated at 900 C had the same microstructure (pearlite structure) in SEM and MM microscopy. At the same time, microstructure observations revealed that bainite and pearlite structures contain a mixture of ferrite and cementite. In the TEM studies it was revealed by electron diffraction pattern analyses that bainite and ferrite phase crystallized in b.c.c. structure and cementite phase in orthorhombic structure. → type transformation was observed for -bainite formation, and orientation relationship was found as (1 ̅ 11)  //(011)  , [101]  //[1 ̅ 11 ̅ ]  .