**1. Introduction**

Micro-alloyed steel is a type of steel containing a minute amount of alloying elements (0.05–0.15%) including niobium, vanadium, titanium, molybdenum, zirconium, boron, and rare-earth metals [1]. They are mainly used to refine the grain microstructure or facilitate precipitation hardening. Micro-alloyed steel developed in the second half of twentieth century. A lot of advancements have taken place due to the development of micro-alloyed steels. Certainly, it improves the hardening, tensile strength, and other mechanical properties of steels. Micro-alloyed substituents like niobium, vanadium, titanium, etc. cause significant grain refinement by retarding recrystallization and forms precipitation of carbon-nitride by these micronutrients. Precipitation of Nb(C,N) that forms improve the microstructure and overall properties of final product. This precipitation further inhibits the recrystallization of austenite, as a result of which reduction of ferritic grains takes place after transformation of noncrystalline austenite. On the basis of this principle later, high-strength low-alloy (HSLA) was developed.
