Investigation of the Microstructure, Micro-Texture and Mechanical Properties of a HSLA Steel, Hot-Rolled and Quenched at Different Cooling Rates

In this research, the role of cooling rate on the microstructure, micro-texture and mechanical properties of hot-rolled high-strength low-alloy steel were studied. A specific composition was casted, hot-rolled and quenched at different cooling rates. Tensile test, hardness test and scanning electron microscope equipped with EBSD detector were used to evaluate the different properties of the samples. The results showed that the increase in cooling rate led to the formation of nonequilibrium structures such as acicular ferrite (AF) and martensite (M) instead of polygonal ferrite. Micro-texture analysis revealed that Cube and Goss components formed in the ferrite–pearlite sample and Rotated Cube and shear components formed in the samples with AF and M phases. Tensile strength increased while elongation decreased due to microstructure variations. Moreover, it was seen that enhancement of cooling rate resulted in grain refinement and increased hardness. The relation between the maximum Schmid factor and the main micro-texture components seems to be another factor governing strength. Fractography also revealed that an increase in cooling rate led to a decrease in average dimple size and dimple surface ratio and, consequently, variation in fracture mechanism from ductile to shear ductile fracture.