An Investigation of the Formability, Mechanical Properties and Microstructure of Niobium and Niobium-Titanium Microalloyed Steels

Abstract

Microalloyed steels are widely used in the automotive sector due to their formability and strength. One example application is rim manufacturing where the cost of wheel is expected to be low. In this study, formability, microstructure and mechanical properties of low carbon steels containing Niobium and Niobium-Titanium as microalloying elements were investigated. The measurements showed that the tensile strength of non-alloyed steel was 433.5 MPa, the yield strength was 292.6 MPa, the tensile strength of Nb alloyed steel was 489 MPa and the yield strength was 385.4 MPa. These values indicate that the tensile strength increase of about 12 % and the yield strength increase of 24 % were obtained. Also for Nb-Ti added steel, the tensile strength was 591.3 MPa and the yield strength was 462.6 MPa. These correspond to 27 % increase in the tensile strength and 37 % increase in the yield strength. Furthermore, elongation values were measured as 27.6 % in non-alloyed steel, 32 % in Nb-added steel, and 28 % in Nb-Ti added steel. In the microstructure analysis, the grain size of Nb and Nb-Ti added alloys were found to be approximately 50 % smaller than the grain size of unalloyed steel. These results indicated that we achieved high elongation values and improved mechanical properties for Nb and Nb-Ti added steel. Furthermore, we managed to hold the elongation value at 27.7 % while achieving higher yield and tensile strengths and formability by adding a small amount of Nb-Ti to the steel.