High strength C-Mn steels for automotive applications

Many automotive structural components are formed from hot rolled sheet steels produced on continuous hot strip mills. Higher strength steels can be used either to improve component strength or to compensate for a decrease in ga uge to achieve weight reduction. The loss in formability which occurs with increasing strength presents problems with the use of higher strength steels for a number of automotive applications. To allow wider usage, British Steel is developing a range of C-Mn steels combining tensile strengths of between 500 and 800 MPa with good cold formability. Strengthening is obtained by generating ferrite-bainite or ferrite-bainite-retained austenite microstructures in conjunction with microstructural refinement and solid solution strengthening. The desired microstructure is developed by precise control of thermomechanical and runout cooling conditions during hot strip mill processing. The presence of retained austenite and its transformation to martensite during cold deformation increases the workhardening rate by the transformation induced plasticity (TRIP) mechanism. (C) 1997 The Institute of Materials.