Effect of different grain sizes on the static strain aging behavior of bake hardening steel

Abstract

AbstractIn this study, the static strain aging behavior of a bake hardening steel (BH 220), suitable for cold forming and widely used in the automotive sector was investigated. Tensile specimens prepared from BH 220 steel were first subjected to a 40 minute solution treatment at 920 °C and 970 °C and then cooled in water to generate various grain sizes. Both as-received and heat-treated samples were pre-strained for 3 % tension and then aged at 180 °C for 10, 20, 30, 60, 180 and 300 min. Tensile tests were carried out to obtain the yield strength (YS), ultimate tensile strength (UTS), elongation (%) and bake hardening value (δY) of aged as-received and heat treated samples. Results indicated that BH 220 steel exhibited static strain aging behavior under as-received and heat-treated conditions. Heat treated samples showed higher susceptibility to static strain aging as compared to the as-received samples. Increased grain size in all the as-received and heat-treated samples decreased the YS and UTS but increased the bake hardening value δY.