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 170-180?C for 20-30 minutes. In this research work, the bake hardenability of a low carbon steel contains 0.12% carbon has been investigated. The steel making process was done in an induction furnace. The cast-ingots were hot-forged and hot-rolled in order to reduce thickness. The hot-rolled sheets were pickled and given 70-75% cold reduction. Tensile specimens were prepared from the sheets. Box annealing was performed at 650 and 700?C for 60 and 120 minutes. To examine the effect of cooling conditions, water-ice quenching and air cooling were applied. Tensile specimens were prestrained to 4-12% along rolling direction, aged at 175?C for 30 minutes in a silicon oil bath, then air cooled and tensile tested at room temperature. The effect of prestrain, grain size, annealing temperature and cooling rate on BH values were investigated. The results indicate that the BH values increased with the prestrain until it reaches a maximum at 10%. When the prestrain is further increased the bake hardening decreased. It was found that, increase in annealing temperature led to increase in grain size as in the amount of solute carbon content. The BH values decrease with increasing in grain size. The amount of annealing temperature effect on BH depends on its influence on solute carbon content. Results also indicate that, an increase of the cooling rate led to higher BH values for the specimens annealed at 700?C but had no significant effect for those annealed at 650?C.
