Effects of coiling temperature on microstructure and mechanical properties of high-strength hot-rolled steel plates containing Cu, Cr and Ni

Abstract

In this study, four kinds of high-strength hot-rolled steel plates were fabricated with additions of tramp elements of Cr and Ni to a basic C-Mn-Si-Cu steel, and their microstructures and mechanical properties were investigated to analyze the effects of coiling temperature and tramp elements. When the steels were coiled at 400 degrees C, their volume fraction of retained austenite was lower than the case of coiling at 450 degrees C. The steels containing Cr individually or together with Ni had the volume fraction of retained austenite above 10%, but showed the characteristics of dual phase steels having high tensile strength and low elongation as a large amount of austenite was transformed to martensite during cooling. In the case of coiling at 450 degrees C, both elongation and strength-elongation balance were increased owing to the increase in the fraction of retained austenite and the transformation induced plasticity (TRIP) effect. The addition of Ni resulted in a great increase in the fraction of retained austenite at the higher coiling temperature, thereby improving tensile strength and elongation.