Precipitation behavior of primary precipitates in Ti-microalloyed H13 tool steel

Abstract

The characteristics and thermal stability of the primary precipitates in H13 ingot modified with 0.034 wt% Ti were studied. A large number of (Ti,V) carbonitrides were observed, including the homogeneous Ti-rich ones and the inhomogeneous Ti-V-rich ones. The atomic ratios of Ti/V in Ti-rich precipitates range from 3.36 to 9.53, while those in Ti-V-rich precipitates range from 0 to 7.60. A certain number of sulfide and Mo-Cr-rich carbides also exist in the ingot. Ti-rich carbonitride is stable at 1 150°C and 1 250°C. Ti-Vrich precipitates with low content of Ti are unstable and start to decompose after holding a short time at high temperature. No Mo-Cr-rich carbide is left after 3 h at 1 150°C or even 0.5 h at 1 250°C. These precipitates are generated during solidification and the generating process could be well speculated by Thermo-Calc. During solidification, Ti-N-rich carbonitride precipitates first and the composition changes little until the generation of Ti-V-rich precipitates. With the development of solidification, the contents of Ti and N in newly generated Ti-V-rich precipitates decrease, while that of V and C increase. Sulfide and Mo-Cr-rich carbides precipitate at the end of solidification.