Control of the precipitation of TiN inclusions in gear steels

In the 20CrMnTi steel production process, the nitrogen content increased by 19 × 10⁻⁶ and 29 × 10⁻⁶, respectively, during ladle furnace (LF) refining and during the casting process from ladle to tundish. The protective casting is the key to decrease the N content. The results of thermodynamic calculations and a growth kinetics investigation show that TiN formation occurs only when the solidification fraction is greater than 0.533 under the controlled conditions used in this study for the manufacture of 20CrMnTi steel; the radius of TiN particles decreases as the Ti and N contents decrease and as the cooling rate increases. Furthermore, the theory of austenite grains controlled by second-phase particles was analyzed. The elemental analysis results showed that the Ti content was controlled at 0.04wt%–0.06wt% and the N content decreased to 0.005wt%, which satisfy the requirements for grain refinement but can also effectively prevent the precipitation of TiN inclusions in 20CrMnTi steel.