High Strength Hot Rolled Steel Sheet for Automobile - A Review

Large weight reduction by application of high strength steels to underbody parts can be expected since relatively thick sheets are now adopted. In several different approaches to improve press formability of high strength hot rolled steels are explained. The basic concept of mechanical property control and the performances of a couple of high strength hot rolled steels. The fatigue strength of the steel sheet with scale increases with the decrease in the roughness of the steel sheet surface. The fatigue strength of the sheared edge deteriorates with the increase in the fractured plane roughness of the sheared edge. In case of the microstructure consisting of pearlite and coarse carbides, these phases increase the fractured plane roughness through the connection of the micro-voids arising around them. Accordingly, the reduction of these phases is significant for improving the fatigue strength. Based on these findings, three types of the 780MPa grade high strength hot rolled steel sheet for truck frame use have been developed. Keywords - Hot rolled steel sheet, microstructures, and mechanical tests. The thickness of hot rolled steel usually greater than 1.83 mm for unexposed surface. Hot rolled steel are used in making chassis and underbody component that are about 25% of the total weight of the car. For some component, crashworthiness is required. Since relatively thick sheets are used for these components, considerable weight reductions are expected. Safety is a major concern for the chassis. High durability and reliability are required as well as good press formability to their complicated shapes. The application of hot rolled high-strength steel sheets to the chassis components, which leads to considerable weight reduction, is expected to expand rapidly in the coming years. It is, therefore, demanded to be developed as hot rolled high-