Evolution Behaviors of Primary Carbides and Austenite Grains during Isothermal Austenitizing Process of H13 Steel

The evolution behaviors of primary carbides and austenite grains are of great significance to investigate the control mechanisms during isothermal austenitizing of H13 steel. Therefore, this study focuses on the thermal stability and transformation behaviors of V‐rich MC and Mo‐rich M 2 C carbides in H13 steel. They are characterized using scanning electron microscopy, energy dispersive spectroscopy, and high temperature confocal scanning laser microscopy. Meanwhile, the growth behavior of austenite grains is analyzed. The results show that the V‐rich MC carbides dissolve gradually during the isothermal austenitizing process of H13 steel, exhibiting good thermal stability. However, the Mo‐rich M 2 C carbides exhibit thermal instability. In addition, the melting phenomenon of M 2 C carbides is more significant than that of MC carbides. Fine‐dispersed secondary carbides form around the primary carbides and the grain boundaries. The dissolution rates V 1050 , V 1100 , and V 1150 of primary carbides are −1.05 ×10 −4 , −1.98 × 10 −4 , and −9.57 × 10 −5 μm s −1 , respectively. With the increase of soaking temperature and time, the austenite grain size increases significantly. Irregular austenite grain boundaries transitioned into a more regular morphology. After soaking at 1050, 1100, and 1150 °C for 720 min, the average equivalent circle diameters of austenite grains are 113.83 ± 51.31, 138.58 ± 54.02, and 181.14 ± 65.55 μm, respectively.