Precipitation Behavior of TiN During the Solidification of High-Titanium Steel

Abstract

TiN is an inevitable inclusion in high-titanium steel, and controlling its size and distribution is the key to balancing the wear resistance and service life of high-titanium steel. In this paper, the precipitation and distribution behavior of TiN in high-titanium steel ([Ti] > 0.4 wt pct) during near-continuous casting solidification were investigated using a self-developed dendritic horizontal growth thermal simulation device. The precipitation density of TiN was greater in the chill zone than in the stable growth zone (columnar zone), and TiN was mainly distributed in the secondary dendritic arms in the chill zone and mushy zone, while in the columnar zone, the quantity proportion of TiN distributed in the dendritic gaps increased. Moreover, the size distribution of TiN changes from unimodal to bimodal as solidification progresses. The equivalent diameter of TiN tends to increase with solidification time and then stabilizes at approximately 5 μm. The effects of the cooling rate on the growth rate and size of TiN are also revealed by using a modified model, which indicates that as the cooling rate increases from 0.5 °C/s to 100 °C/s, the final size of TiN decreases from 10.93 μm to approximately 0.77 μm. Moreover, thermodynamic calculations also indicated a significant impact of TiN precipitation on the localized N content during the solidification process. All the results indicate that reducing the N content and increasing the cooling rate are effective ways to reduce the TiN size.