Precipitation behavior of TiN in solidification of 20CrMnTi under continuous casting conditions

Abstract

This paper focused on the relationship between the precipitation of TiN and the continuous casting process of 20CrMnTi billet. A reliable cross scale simulation combining the heat transfer, solute micro-segregation, and TiN precipitation was carried out. Results show that for a specific site, the cooling rate in the mushy state increases with the solidification proceeding, especially in the later stage of solidification. The closer to the center of billet, the lower the initial cooling rate is. However, the cooling rate in the later stage of solidification near the center of billet is higher than that of the intermediate site. The solidification path of 20CrMnTi at 20, 40, and 60 mm below the inner arc surface is L → L + δ → L + δ + γ → L + γ → γ, and the peritectic reaction occurs at the solid fraction of 0.81. The solute segregates more severe as the site moves to the inner billet, especially among the coarse equiaxed dendrites at 60 mm. The precipitation of TiN just slows down the enriching rate of Ti in the liquid phase, but causes the concentration of N declining. The predicted maximum sizes of TiN are 6.128, 7.836, and 7.593 μm at 20, 40, and 60 mm, and its tendency is consistent with the measurements in the billet. With the decrease of N's initial content, the formation of TiN is postponed to higher solid fraction, and TiN becomes smaller. Moreover, the decisive factor for TiN's size at 40 and 60 mm changes from the concentration difference to the growth time. In addition, increasing the secondary cooling intensity can also refine TiN.

Keywords

• 20CrMnTi
• Continuous casting
• Solidification
• Solute micro-segregation
• TiN precipitation