The Characteristics and Generating Mechanism of Large Precipitates in Ti-Containing H13 Tool Steel

摘要

The characteristics of large precipitates in H13 tool steel with 0.015wt Ti were studied. The result shows that three types of phases larger than 1 mu m exist in the as-cast ingot, that is, (Ti, V) (C, N) type phase, (V, Mo, Cr) C type phase and sulfide. (Ti, V) (C, N) type phase could be further classified as the homogeneous Ti-rich one and the Ti-V-rich one in which Ti/V ratio gradually changes. (V, Mo, Cr) C type phase contains the V-rich one and the Mo-Cr-rich one. The compositional characteristics in all of them have little relation with the cutting position or cooling rate. The precipitating process could be well described through calculation by Thermo-alc software. During solidification, the primary phase (Ti, V)(C, N) first starts to precipitate in the form of Ti-rich carbonitride. With the development of solidification, the ratio of Ti decreases and that of V increases. Then the primary phase Ti-V-rich (Ti, V)(C, N) and V-rich (V, Mo, Cr) C appears successively. Mo-Cr-rich (V, Mo, Cr) C phase does not precipitate until the solidification process reaches to the end. Sulfide precipitates before (V, Mo, Cr) C type phase and it could act as the nucleus of (V, Mo, Cr) C.