Investigation Of Bake Hardening Behaviors And Mechanism For A Cold-rolled Dual-phase Steel

A cold-rolled dual-phase steel was investigated. The heattreatment of the experimental steel was carried out in high temperaturebox-tybe electrical resistance furnace of lab；The samples were baked at170℃for20min in the oven， the pre-strained applied and bake-hardeningperformance measurement was carried out on the UTM5305universal testmachine，the microstructure with different process conditions was observedby Optical microscope, scanning electron microscopy and transmissionelectron microscopy， the internal friction of the samples under differentprocess conditions was determinated by wiggler internal friction instrument。The main findings are as follows:（1）The BH value of the DP steel is45MPa，when the prestrain is2%。When the baking process is same， the BH value of the steel increasescontinuously with an increase of prestrain in20%of the pre-deformationrange。（2）The experiment of natural aging at room temperature shows thatthe BH value is stable。（3）When the prestrain and baking temperature is same，the BH valueof the steel increases continuously with an increase of baking time。（4）When the heat preservation time is same,the BH value is increasingwith the quenching temperature increases in the range of750℃~850℃;When the quenching temperature is850℃, the BH value increases firstly andthen decreases with the increase of heat preservation in the range of1min to10min;When the quenching temperature is850℃and heat preservation is10min, the BH value of the sample increases firstly and then decreases aftertempering in the range of0℃to600℃.（5）The bake hardening behaviors of the dual-phase steel is mainlyaffected by：①the formation of the cottrell air mass;②martensite tempered;③the decomposition of the residual austenite;④the precipitation of carbide。...