Process Parameters And Microstructure And Properties Of Dual Phase Steels

Dual phase steel is widely used in automobile manufacturing as a new type of punching steel, with the following properties such as low yield point, high initial work hardening rate, high strength and good ductility. Automobiles (especially cars) can decrease the weight of steel structure parts by about 20%, using dual phase steel. Therefore, study and exploitation of low-cost hot-rolled dual phase steel have significant practical meaning to resources saving, reducing energy consumption, and sustainable development. In this paper, steel with five components was designed. The process parameters, micro structure and mechanical properties of cold-rolled dual phase steel were investigated by thermal simulating and dual phase heat treatment experiment. The main work in the paper is as following:(1)Single pass compressing test was carried out on the Gleeble3500 thermal simulator. According to the experiment, the stress-strain curve of the specimens was measured, influence of deformation temperature and strain rate on austenite deformation behavior was investigated, effect of microalloy element on dynamic recrystallization was studied and the critical strain model of the steel was established.(2)Three processes of four passes compressing test on experiment steel was conducted. By controlling the distribution of deformation temperature and strain rate, dual phase structure (F+M) was obtained. According to the analysis of stress-strain curve, the change law of deformation resistance was determined, the soften fraction was calculated and the thermal deformation softening behavior of experiment steel was investigated.(3) Four types of dual phase heat treatment on experiment steel were designed. Dual phase structure (F+M) was obtained by means of the above-mentioned treatment. The micro-hardness of ferrite substrate and change law of microstructure and properties corresponding to different dual phase heat treatment processes were investigated by comparing the microstructure and morphology of dual phase steel, martensite volume fraction and the grain size of ferrite.