Effect of C-Mn ratio on the maximum hardness and toughness in TMCP steels with an identical carbon equivalent

Abstract

In this study, the mechanical properties of two types of thermo-mechanically controlled processed (TMCP) steels with the same carbon equivalent but different alloying constituents of C and Mn were examined. Tensile, impact, hardness, and through-thickness tensile tests were employed for this examination. The taper hardness test was conducted in the weld heat-affected zones (HAZs) by using common onsite welding methods. The results revealed that the two distinct steel plates exhibited different microstructures in the base metal; however, their maximum hardness and microstructures in the HAZs were similar within the heat input range (10-30 kJ/cm) that is often used at manufacturing sites. Moreover, the continuous cooling transformation diagrams for the HAZs and the base metal used for welding the TMCP steels were simulated to validate the experimental results for the microstructure. The drop weight test and weld bead bend test were employed to compare the toughness related with the weldability of the two steel plates. The steel with composition of 0.08% C-1.5% Mn exhibited lower nil-ductility transition temperature and better crack arrestability than that with the composition of 0.15% C-1.1% Mn.