抄録
Morphologies and internal defects of martensites in Fe–Mn–C alloys with 12.0∼4.1% Mn and 0.48∼1.25% C have been examined as a function of manganese and carbon compositions by means of optical and electron microscopy and two surface trace analyses. With decreasing manganese and increasing carbon, α′ martensites directly form in the γ matrix as well as in ε′ martensites. With further decreasing manganese and increasing carbon, ε′ martensites never form and so α′ martensites form only in the γ matrix. The α′ martensites formed in the γ matrix of alloys with higher manganese and lower carbon are characterized by smooth boundaries on both sides, while those of alloys with lower manganese and higher carbon are by smooth boundary on one side (nucleation side) and by irregular one on the other side (growing side). However, all very small α′ martensites have smooth boundaries on both sides irrespective of the morphlogies of grown ones. α′ martensites in the γ matrix are internally twinned on the (112) planes only near the nucleation side, while those in ε′ martensites are faulted on the (110) planes all over them. Two surface trace analyses show that habit plane normals of α′ martensites in the γ matrix lie near the {112} or {225}γ pole, which make an angle of 25° from the specific (111) plane associated with the α′ martensites, while those in ε′ martensites are far away (85°) from the (111) plane.
