High-Strength Steel Sheets for Automobile Body Panels

The overall suitability of various steels (strain-aging steels such as capped nitrogenized and rephosphorized steels, killed rephosphorized and microalloyed steels) for automobile body-panel applications is assessed by comparing their characteristics with the performance requirements (formability, weldability, paintability, etc.). The formability of the steel sheets is perhaps the most important requirement for body-panel applications. To minimize the loss of formability that occurs as strength is increased, steels having yield strengths of 40 to 50 ksi are considered the primary candidates for use in body panels. Of the different types of 40- to 50-ksi steels reviewed, the killed rephosphorized steels (especially a silicon-containing version) show the best combination of formability and weldability. Although some difficulty in meeting paint-performance requirements has been recently reported with these steels, additional studies are needed to identify those factors that determine paintability in the killed rephosphorized steels.

The future application of cold-rolled dual-phase steel sheets for body panels is discussed; the high strengths obtained after forming these steels offer greater weight savings potential provided adequate stiffness can be designed into the parts and provided the higher cost of the steels can be justified.