Abstract: In the current work，the segregation of elements was studied on basis of segregation model and influence of cooling rate on precipitating and growing up of nitride inclusions was investigated during solidification. The calculating results showed that concentration of Ti，V，C and N elements were 4.68，2.34，4.55，and 3.3 times than initial concentration near the liquid-solid interfaces. It could postpone the precipitation of TiN inclusions and decrease the size of them by reducing the content of Ti and N in molten steel and increasing cooling rate from 0.27 K/s to 37.96 K/s. According to regular solution sublattice model，themodynamic calculation of carbonitrides inclusions formation mechanism was performed in heavy rail steel.

Key words: heavy rail steel, carbonitrides inclusions, precipitation, dynamics analysis