Research On The Heat Treatment Process And Dynamic Mechanical Properties Of 15Mn-3Al Steel With Low-carbon

With the increasing demand for lightweight and safety of automobile steel,the development of the new generation of automobile steel has become a hot research topic.High manganese TRIP/TWIP effect steels have both TRIP(Transformation Induced Plasticity)and TWIP(Twins Induced Plasticity)effects,which have excellent properties such as high strength,ductility,and work hardening rate.So it has a strong competitive advantage and broad prospects for development.Currently,the mechanical properties of impact exerted by annealing temperature,holding time and cooling mode in the heat treatment process of high manganese steel is not clear.And the study on the mechanical properties of the mechanical properties is mainly confined to quasi-static mechanical properties.In this paper,the high manganese steel(0.19C-15Mn-3Al-0.025Nb)with excellent comprehensive mechanical properties was selected as the research object and the effects exerted by different heat treatment processes and dynamic deformations of different strain rates on microstructural evolution and mechanical properties of experimental steels were researched.By using the hot rolling,cold rolling and different heat treatment processes,high manganese steel with excellent comprehensive performance was obtained.The research fills the gap of the lack research of dynamic deformation behavior of the medium manganese steel,decides the best heat treatment process and provides the experimental and theoretical basis for the development of stamping technology and the improvement of its collision resistance performance.The main contents and achievements of this paper are as follows:(1)Under consistent annealing time and cooling method,the grain size increases gradually with the rise of annealing temperature.Both the ultimate tensile strength and the total elongation increase first and then decrease,among which the heat treatment that 850?annealing temperature is kept for 2 minutes before water cooling achieves the best product of ultimate tensile strength and total elongation with 971 MPa the ultimate tensile strength,56%the total elongation,and the 54.4 GPa%plasticity.(2)Under consistent annealing time and cooling method,the grain size gradually increases with the lengthening of annealing time,but the ultimate tensile strength and yield strength decrease gradually.The total elongation increase first and then decrease.Among which,the product of ultimate tensile strength and total elongation of experimental steel that is kept at 800? for 2 min before air cooling and water quenching reached 48.71 GPa·%and 49.16 GPa·%respectively.(3)Under consistent annealing time and cooling method,the effects exerted by different cooling methods(air cooling and water quenching)on the microstructure and mechanical properties of the experimental steel were compared.The results show that the experimental steel obtained by the air cooling method has a higher total elongation and a relatively small grain size,while the experimental steel with a water-quenching has a higher strength.Among which the TRIP effect of experimental steel kept at 850? for 2 min before air cooling is more remarkable than that of the experimental steel under water-quenching,and the grain size is smaller and the strength is higher.(4)Through the analysis of the experimental steel structure and quasi-static mechanical properties,it can be seen that the best mechanical properties are obtained at 850? for 2 min.The cooling mode has little effect on the mechanical properties.After the dynamic mechanical test,there are big differences among the experimental steels obtained by different cooling methods.The mechanical properties of air-cooled experimental steel in the dynamic deformation has higher strength,and water-cooled experimental steel has a high ductility.(5)The tensile tests were carried out at different stretching rates(0.002 s-1,7 s-1,70 s-1,700 s-1)for the experimental steels that is kept at 850? for 2 min before air cooling or water quenching.The results show that the elongation increases first and then decreases with the raise of the tensile rate,and reaches the maximum at the increasing rate of 70 s-1,while its strength decreases first and then increases.At the tensile rate of 70 s-1 The total elongation of the experimental steels after air cooling and water quenching were respectively 64%and 67%,and their priduct of ultimate tensile strength and total elongation were respectively 62.9 GPa·%,and 59.8 GPa·%...