Four Nb-Ti microalloyed steels were refined and rolled to study the composition optimization of Nb-Ti microalloyed steels.The effects of Nb and Ti on the microstructures,precipitates and properties of Nb-Ti microalloyed steel were investigated.The results showed that an increase in Ti content resulted in the appearance of many fine precipitates leading to a strong precipitation strengthening effect.Hence,the yield strength increased.Besides,the increased strength by the combined increase of Nb and Ti was similar to that observed for the increase in Ti content alone.This increase in strength was attributed widely to the increase in the Ti content alone rather than Nb.Moreover,the increase in Nb content beyond 0.036 wt% exerted no significant effect on the strength of Ti-Nb microalloyed steels,in which more Ti could be added to further improve the strength of steels.