Strength and toughness mechanism of single Ti microalloyed steels

The mechanism of strength and toughness variation in Ti microalloyed steel within the range of 0.04–0.157 wt.% was investigated. By adding 0.13 wt.% Ti, the steel achieves higher strength while maintaining a certain level of elongation and low-temperature impact toughness. With increasing Ti content, the grain size in the steel decreased from 17.7 to 8.9 μm. This decrease in grain size is accompanied by an increase in the percentage of low-angle grain boundaries and dislocations, which act as barriers to hinder crack propagation. The Ti microalloyed steel exhibits a 20% increase in yield strength and a 14% increase in tensile strength. The transformation of steel plasticity occurs when the Ti content exceeds 0.102 wt.%. The low-temperature impact toughness of the steel gradually decreases with increasing Ti content. At low Ti content, the low-temperature impact toughness is reduced due to crack initiation by large-size inclusions. At high Ti content, the low-temperature impact toughness of the steel deteriorates due to several factors. These include the narrower tough–brittle transition zone, grain boundary embrittlement caused by small-sized grains, and the decrease in the solid solution strengthening effect.