Effect of Recrystallization Temperature on the Bake Hardening Properties in Ultra - Low Carbon Steels

In order to reduce weight and energy, an extensive amount of bake hardening steels are being used in automotive industry. These steels offer good formability during press stamping operations and also provide high final yield strength during paint baking treatments for good dent resistance. The baking operation is usually simulated by a heat treatment at 180˚C for 30 minutes. In this research work, the effect of increasing recrystallization annealing temperature on the bake hardening properties in ultra - low carbon steels, used in the automobile industry, has been investigated. The steel making process was done in an induction furnace. The cast- ingots were hot-forged, hot – rolled and then cold – rolled. Tensile specimens were prepared from the sheets. Box annealing was performed at 750 and 800˚C for 30 minutes. Tensile specimens were pre strained to 8 and 12% along rolling direction, aged at 180˚C for 30 minutes in a silicon oil bath. The results indicate that with increasing annealing temperature, despite the increase in grain size, the BH values increased.