Effects Of TMCP Processes On Microstructure And Mechanical Properties Of 600MPa Grade Hot Rolled Dual Phase Steel

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,and is a another new stamping steel.Automobiles can decrease the weight about 20% by using hot-rolled dual phase steel as steel structure parts,and it is especially widely used in the automotive applications panel.So,the study and exploitation of low cost hot-rolled dual phase steel have significant practical meaning to energy saving,environmental protection and vehicle safety improvement.The Si-Cr-Mn as basic chemical composition is designed,the phase transition point and transformation time of three experimental steels by adding Mo,V alloy elements was tested,the effects of tree different chemical composition to static CCT curve were comparatively analyzed,and the effects of cooling rate on microstructure and micohardness were studied.The thermal simulation experiments were carried out on the Gleeble-1500 test machine,the effects of cooling rate,deformation temperature and the ending temperature on the microstructure of Si-Cr-Mn-Mo-V steel were analyzed.The results showed that,the ferrite + martensite was unable to get by undercooled austenite continuous cooling in undeformed,as 1#steel of Mo,V elements composite adding,the ferrite was unable to get when the cooling rate was over than 5.55℃/s;as 2#steel of Mo elements adding merely,the ferrite was unable to get when the cooling rate was over than 13.89℃/s,as 1#steel of Mo,V elements composite adding in once deformation,a sufficient ferrite + trace martensite was got when the cooling rate was controlled in 10℃/s,at the same time,the content of ferrite and martensite came to a peak:85% and 15%.In order to simulate the process of TMCP more accurately,under the laboratory conditions,tree passes finishing rolling of each 40 percent deformation were added,the effects of TMCP on the microstructure and mechanical properties were studied,and the effects of cooling rates and the way of cooling after rolling to getting ferrite and martensite dual phase steel was discussed,the process parameter model of 600 MPa hot-rolled dual phase steel was initially established.The experimental results of rolling controlled and cooling controlled showed that,under the laboratory conditions,a high strength hot rolled dual-phase steel of the dispersed martensitic+ ferrite microstructure was got.The industrial trial of DP600 hot-rolled dual steel was finished in Pan Gang Steel XiChang Vanadium hot-rolled production line,the influence of air cooling time on proportions of ferrite and martensite and mechanical properties were analyzed.The suitable industrial production line for Pan Gang industrial production was ultimately determined.The heating temperature is 1200±15℃.Rolling passes in rough rolling mill is 5 to ensure the thickness of intermediate slab to be≥35mm.Final rolling temperature is 850±15℃;Taking two-stage cooling;the intermediate temperature is 740±15℃;the air cooling is 9~10s,and the coiling temperature is 530±20℃.a 81% ferrite + 18% martensite of hot rolled dual phase steel was got,Its yield strength is 370 MPa,tensile strength is 700MPa;the elongation is 24.5%~26%,the yield ratio is about 0.51,the comprehensive properties is excellent,meeting the DP600 requirements.