Effect of austenitizing condition on mechanical properties, microstructure and precipitation behavior of AISI H13 steel

The effects of austenitizing temperature (1223, 1303, and 1373 K) and holding time (1-1500 s) on the microstructure, mechanical properties, and precipitation behavior of the H13 hot work die steel were investigated. The results indicate a softening phenomenon when H13 steel is austenitized at 1303 K beyond 900 s and 1373 K beyond 600 s, respectively. For the sample held for 1200 s, the tensile strength is found capable of reaching up to 2.2 GPa when quenched from a temperature above 1303 K. Meanwhile, prior-austenite grain size increases with the increase in austenitizing temperature. The kinetic behavior of the precipitates (mainly MC-type carbides) in H13 steel could be elaborated through the principles set forth by the Arrhenius and Avrami equations. Finally, the comprehensive strengthening of the H13 steel was discussed in detail. The results show that the activation energy of the transformed fraction of carbides is higher than that of the diffusion process for common alloying elements (Cr, V, Mo, and Ni) found in the austenite. This suggests that it would be difficult for precipitates to dissolve into the matrix when H13 steel is austenitized at high temperatures. With the increasing austenitizing temperature, the precipitation fraction decreases, and the dislocation density increases. The dislocation strengthening is regarded as the dominant strengthening contributed to yield strength in as-quenched H13 steel.