Effect of microalloying and isothermal transformation on the microstructure and mechanical properties of SWRH82B steel

This study investigates the effects of microalloying elements vanadium (V) and niobium (Nb), along with varying isothermal transformation temperatures, on the microstructural evolution and mechanical properties of SWRH82B high-carbon pearlitic steel. Comprehensive microstructural characterization was conducted using optical microscopy, scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and transmission electron microscopy (TEM). The results show that the addition of V alone or in combination with V and Nb refines the lamellar spacing, pearlite clusters and pearlite ball clusters. Compared with the matrix steel, the lamellar spacing was refined by 46% at lower isothermal transitions; the dimensions of pearlite clusters and pearlite globule clusters were reduced by up to 43% and 31%.The additions of V and Nb significantly increased the microhardness, tensile strength, and yield strength of the steels. The tensile and yield strengths increased by 272 MPa and 178 MPa to 1172 MPa and 657 MPa, respectively. This increase in strength was dominated by the precipitation strengthening of VC and NbC particles and the fine grain strengthening effect. The impact toughness of pearlite steels increases with the refinement of the microstructure, which is attributed to the increase in fracture initiation energy and fracture extension energy. The increase in fracture initiation energy is greater than the extension energy under the same isothermal conditions. The fracture mode is a mixture of deconvoluted and ductile fracture. This research provides a scientific foundation for optimizing the manufacturing process of SWRH82B steel and offers significant insights into the study and application of other microalloyed high-strength steels.