Effect of two-stage heat treatment on the microstructure and mechanical properties of high chrome austenitic manganese steel

In this research, heat-treatment was used to determine changes in the microstructure and mechanical characteristics of austenitic manganese steel equivalent to ASTM A128-C. Carbide formed in as-cast conditions is transformed into dispersed hardened austenite to increase the toughness of the material because it can inhibit dislocation movement. Heat treatment is carried out in two heating stages. The first stage of heating was carried out at a temperature of 625°C with a holding time varying by 2.5, 3.5, and 4.5 h, and the second stage was carried out at a temperature of 1000°C with a constant holding time of 1.5 h. Microstructure observations were carried out to observe the structural morphology and carbide transformation in both the first and second stages of heating. Tensile and hardness tests were also carried out to determine the mechanical properties and their effect on two-stage heating. The research results show that the pearlite structure is formed in the first stage of heating with different lamella thicknesses. With the help of ImageJ software, the measured pearlite fraction was higher as the holding time increased in the first stage of heating. This affects the morphology of the carbide colonies formed in the second stage of heating. The higher the pearlite fraction, the more uniform the morphology of the carbide formed with round shapes that are more evenly distributed. These dispersed carbide colonies can increase the toughness of the material up to 17 times higher than the as-cast condition obtained through mechanical testing.