Study of precipitation and growth processes of Ti-bearing inclusions in tire cord steel

Precipitation behavior and growth kinetics of Ti-bearing inclusions in SWRH 92A tire cord steel were analyzed in the present work. The calculated results showed that higher cooling rate would lead to a higher precipitation ratio of solution elements and make the precipitation time of inclusions earlier. However, both TiC_yN_{1− y} (a continuous solid solution between TiC and TiN, y denotes the molar ratio of TiC in TiC_yN_{1− y}) and TiN could only precipitate in the two-phase region at the very late stage during the solidification processes, with the solid fraction exceeds 0.99. The precipitation time of TiC_yN_{1− y} was a little earlier than that of TiN as well as the value of y in the range of 0.1577–0.1617 (cooling rate: 0.5–2 K/s) was also obtained. Particle size of Ti-bearing inclusions decreased with the increasing cooling rate and were within the range of 1.5–6.5 μm under the calculated conditions, which accorded well with the size observed by the FE-SEM (field emission scanning electronic microscope). Increasing the contents of both N and Ti could lead to an earlier precipitation time of Ti-bearing inclusions and make the particle size bigger, while the effect of N is much larger than that of Ti. The results obtained by the adopted model were in well consistent with those of the statistical analysis. This work may give an important guidance on the understanding of the precipitation and growth processes of Ti-bearing inclusions in tire cord steel.