This paper investigates the changed in the microstructure in HAZ of the dissimilar weld between carbon steel and 304 austenitic stainless steel. Continuous cooling transformation diagrams (CCT), peak temperature profiles and cooling rates can be used to predict the change in the microstructure of the HAZ during the welding process. Optical microscopy, X -ray, SEM and TEM were used to determine the phases which formed in HAZ of carbon steel and austenitic stainless steel. The results of this study indicate that grain size in HAZ depended on the temperature at that point could be reached during the welding. Fully Martensitic layer observed at the interface in carbon side due to the combination of the rapid cooling subsequent to weld and local chemical composition. Cooling rate played the rule on forming Widmanstatten ferrite, Bainite and Pearlite. On the other hand, microstructures and grain size in HAZ of austenitic stainless steel were not affected by temperature and cooling rate. Carbides precipitation (M23C6, M7C3), however, were found in the boundary of grains.

The changing of properties of HMnS by alloy elements addition and heat treatment was presented. Studying about the hardness of HMnS were increased when the Mn contents increased. On the other hand, the Cr content has effective on the hardness and microstructure of this steel also, but with the Cr content was increased from 2% to 2,5%, the hardness of high Manganese steel was not much changed. With the research about HMnS, it was added the Cr and applied the advanced heat treatment process, the microstructure of this steel was formed the chrome carbide particles with grain fine which dispersed in the matrix with the formation of these dispersed carbide particles will contribute to increasing the alloy's abrasion resistance. With the difference in heat treatment processes, the microstructure and hardness were also changed. When the sample was heat-treated according to the model heat treating; the particle size of the sample is also significantly reduced. This explains why the hardness value of the sample increases significantly. Also, under the impact load, on the surface layer of this steel, the microstructure does not appear the martensite structure form but only see the twinning on the surface. These are new findings on the mechanism transformation of high manganese austenite steel when working under the impact of the impact force. The mechanism of transformation is quite different from the previous view of phase transformation under the impact force of high manganese austenitic steel.