γ-Loops in Fe-Mn-V, Fe-Mn-Mo and Fe-Mn-Si Systems

Abstract

Ferrite/austenite equilibrium in multi-component iron alloys has been studied on the bases of thermodynamic analysis of Fe-X binary systems. In addition, the α⁄γ equilibrium in Fe-Mn-V, Fe-Mn-Mo and Fe-Mn-Si systems has been experimentally determined to compare with the calculated ones.The results obtained were as follows:(1) The α⁄γ equilibrium in multi-component iron alloys with a lower alloy content level can be estimated by the ferrite/austenite stabilizing parameter of each alloying element. For higher alloy contents, however, the parameters concerning mutual interactions between iron and the alloying elements have a considerable effect on the phase relationship.(2) The α⁄γ equilibrium in Fe-Mn-X ternary systems shows various types of γ-loop depending on the value of the ferrite/austenite stabilizing parameter of X. In the case of Fe-Mn-V, Fe-Mn-Mo and Fe-Mn-Si systems, the α⁄γ phase boundary at the section of xMn⁄xX=1 is similar to the γ-loop of the Fe-Cr system; i.e. both of the A3 and A4 points are lowered by additions of the alloying elements. This is mainly due to a large temperature dependence of the ferrite/austenite stabilizing parameter of manganese.