The Effect Of Rolling And Heat Treatment Process On Microstructure And Properties Of Q?P Steels

With the increasingly prominent contradiction between social and economic development and energy and environmental issues,energy-saving and weight-loss have become the main development trend of modern automobile manufacturing industry.And at the same time,they have brought higher requirements for the process and performance of new generation automobile steel.Quenching and Partitioning(Q&P)steel is superior to the first generation of Advanced High Strength Steel(AHSS)steel in strength and plasticity,and its alloy content is lower than the second generation of AHSS steel.In addition,it has the advantage of low cost,and has gradually become one of the research hotspots in the field of automotive advanced steel material development.Asynchronous rolling can significantly reduce rolling force and increase rolling reduction due to its asymmetrical deformation.It can effectively refine grain size,improve the uneven distribution of structure and improve the comprehensive mechanical properties of steel.And it has good production effect and wide application prospects.At present,there are few studies on the effect of asynchronous rolling on the structure and properties of Q&P steel,which need to be further studied.In this paper,three kinds of low carbon microalloyed steels with different alloy compositions were designed.The effects of alloying elements(Si,Al and Nb),heat treatment and rolling on the structure and properties of Q&P steel were systematically studied.The processing process of high strength and plasticity Q&P steel was obtained,and its strengthening and toughening mechanism and plastic deformation mechanism were revealed.The main research contents and results are as follows:(1)The effects of Al,Si and Nb on the structure and properties of experimental Q&P steel were studied.The results show that with the decrease of Si content,the strength of the steel decreases and the plasticity increases.The addition of Al and Nb increased the content of retained austenite and the comprehensive mechanical properties of the experimental steel.(2)The effects of cooling methods(water cooling and air cooling)after rolling on the structure and properties of experimental Q&P steel were studied.The results show that the structure of water-cooled Q&P steel is more uniform,its grain size is smaller,and its tensile strength and elongation are higher.The retained austenite content in air cooling Q&P steel is high,but its stability is poor,and its comprehensive mechanical properties are poor.(3)The effect of heat treatment process on the structure and properties of sample Q&P steel was studied.The results show that with the increase of annealing temperature,the tensile strength increases gradually,the elongation increases slightly at first and then decreases gradually,and the content of retained austenite increases first and then decreases.With the increase of carbon partition temperature,the tensile strength decreases first,then increases and then decreases,the elongation decreases first and then increases,and the content of retained austenite increases first and then decreases.With the increase of carbon partition time,the tensile strength decreases first,then increases slowly and then decreases,the elongation increases slowly and then decreases slightly,and the retained austenite increases first and then decreases.When the asynchronous ratio is 17/16,the product of strength and elongation reaches 25.7GPa·%.The ultimate tensile strength and elongation are 984MPa and 26%respectively.The mechanical properties are better than those of synchronous rolling.(4)The effect of asynchronous rolling process on the structure and properties of experimental Q&P steel was studied.The results show that with the increase of asynchronous ratio,the grain size of the experimental steel decreases gradually.After heat treatment,the content of retained austenite in experimental steel increases first and then decreases,and the maximum value is 17.19%when the asynchronous ratio is 17/16.With the increase of asynchronous ratio,the tensile strength and elongation of the experimental steel increase first and then decrease.When the asynchronous ratio is 17/16,the experimental steel has good comprehensive mechanical properties,its tensile strength reaches 984 MPa,its elongation is 26%,and its product of strength elongation reaches 25.6 GPa·%.