Study on primary carbonitrides in H13 steel based on the two-sublattice model

Three kinds of primary carbonitrides were classified in H13 hot work die steel through experiment,including (V_x,Mo_1-x)(Cy,N_1-y) rich in V and C,(Ti_x,V_1-x)(C_y,N_1-y) rich in Ti and N,and (Ti_x,V_1-x)(C_y,N_1-y) rich in V and C,some having a core in the center.The element variation and Gibbs energy of the carbonitrides during H13 solidification were analyzed based on the solidification segregation model and the two-sublattice model,taking the interaction between components into account as well as the alloying element content and C/N ratio of the three types of primary carbonitrides.It is found that Tiand N-rich (Ti_x,V_1-x)(C_y,N_1-y) forms when the solid fraction reaches 0.9,while the other Vand C-rich (Ti_x,V_1-x)(C_y,N_1-y) generates when the solid fraction is greater than 0.96 during solidification.The critical solid fraction for the formation of these two (Ti_x,V_1-x)(C_y,N_1-y) decreases with increasing Ti and N contents soluted in the carbonitrides.The formation of (V_x,Mo_1-x)(C_y,N_1-y) during solidification can be affected by the x value.The critical solid fraction decreases as less vanadium is soluted in (V_x,Mo_1-x)(C_y,N_1-y),leading to larger size carbonitrides demonstrated by the models,which fit well with experimental data.The influence of oxides and carbonitrides on heterogeneous nucleation for the carbonitrides was also researched through lattice misfitting analysis.