Effects of copper addition on mechanical properties of 0.15C-1.5Mn-1.5Si TRIP-aided multiphase cold-rolled steel sheets

Abstract

The main emphasis of the present study was placed on understanding the effects of copper addition on the mechanical properties and microstructures of low-carbon TRIP-aided multiphase cold-rolled steel sheets. These steel sheets were intercritically annealed at 790-800°C, and isothermally treated at 430°C for various times. Tensile tests were conducted, and the changes of retained austenite volume fractions as a function of tensile strain were measured using X-ray diffraction. The copper addition increased the volume fraction of retained austenite, although it did not affect the stability. However, the hardness of ferrite in Cu containing steel was higher than that of Cu free steel. As a result, the strain-induced transformation of retained austenite was sustained up to the high strain region, thereby leading to the simultaneous enhancement of strength and ductility. These findings indicated that when copper, a representative tramp element, was positively utilized in cold-rolled steel sheets, excellent mechanical properties could be achieved.