The Effect of Simulated Repair Heat Treatments on the Physical Properties of High Strength Steels

High strength sheet steels continue to be used in automobile structural components for mass reduction. Depending on the metallurgical strengthening mechanism used in these steels, short term, high-temperature excursions such as those which might be encountered in welding or heating for flame straightening during body repair could reduce their strength. To study this effect, time-temperature cycles were obtained on instrumented automobile rail sections during typical repair procedures using flame heating and welding. These data were then used to generate a program for heat treating tensile specimens of selected steels intended to cover a range of steels used which could be applied to automobile structural components. Crush tests were also performed on simulated rail sections of these steels after undergoing flame heating and welding. Tensile tests showed some degradation of strength for a lean-chemistry dual phase steel and of ductility for galvanized steels. However, the crush tests on these steels did not show a significant loss in energy absorption.