The Observation of the Structure of M₂₃C₆/γ Coherent Interface in the 100Mn13 High Carbon High Manganese Steel

The M₂₃C₆ carbides precipitate along the austenite grain boundary in the 100Mn13 high carbon high manganese steel after 1323 K (1050 °C) solution treatment and subsequent 748 K (475 °C) aging treatment. The grain boundary M₂₃C₆ carbides not only spread along the grain boundary and into the incoherent austenite grain, but also grow slowly into the coherent austenite grain. On the basis of the research with optical microscope, a further investigation for the M₂₃C₆/γ coherent interface was carried out by transmission electron microscope (TEM). The results show that the grain boundary M₂₃C₆ carbides have orientation relationships with only one of the adjacent austenite grains in the same planes: \( (\bar{1}1\bar{1})_{{{\text{M}}_{ 2 3} {\text{C}}_{ 6} }} //(\bar{1}1\bar{1})_{\gamma } , \) \( (\bar{1}11)_{{{\text{M}}_{ 2 3} {\text{C}}_{ 6} }} //(\bar{1}11)_{\gamma } ,[ 1 10]_{{{\text{M}}_{ 2 3} {\text{C}}_{ 6} }} //[ 1 10]_{\gamma } \). The flat M₂₃C₆/γ coherent interface lies on the low indexed crystal planes {111}. Moreover, in M₂₃C₆/γ coherent interface, there are embossments which stretch into the coherent austenite grain γ. Dislocations distribute in the embossments and coherent interface frontier. According to the experimental observation, the paper suggests that the embossments can promote the M₂₃C₆/γ coherent interface move. Besides, the present work has analyzed chemical composition of experimental material and the crystal structures of austenite and M₂₃C₆, which indicates that the transformation can be completed through a little diffusion for C atoms and a simple variant for austenite unit cell.