Study On Relationship Between Processing Technology And Microstructure Properties Of Phosphorus-containing High-strength IF Steel

As the rapid development of worldwide economy,the car industry has gotten a rapid development,which makes energyconservationandemissionreduction necessary.To make the car body safe and economical,the weight of the car body has been the mainstream direction of the development of the car industry.High strength IF steel for car has gotten more and more scientific research personnel and automotive industry's attention.P-added high strength IF steel has became an important member in car-used high strength IF steel family for it contains the element P,which is thought to be harm to the steel in traditional contain design thought.To restrain the bad effect of the addition of P,according to the basic theory,it is necessary to regulate and control microstructure properties of the P-added high strength IF steel in the part of processing technology.In order to optimize production process and rich basic theory,the P added high strength interstitial free steel B250P and B210P were used to study the essential relationship between process,microstructure and properties.The main research contents and conclusions are as follows:(1)The cold rolling deformation resistance model was established.The influence of cold rolling reduction rate on microstructure and hardness were researched.The recrystallization law of cold deformation steel was revealed.Hot deformation constitutive model of the ferrite region of the P added high strength interstitial free steel was established.The influences of hot deformation parameters on microstructure and grain orientation of phosphorus steel were studied,(2)Using technology such as hot rolling,cold rolling,annealing in austenite zone,the influence of process parameters of continuous annealing(heating rate,soaking temperature,holding time,cooling rate)and batch annealing(holding temperature,holding time)on microstructure and mechanical properties were researched.There is no difference between mechanical properties of the best continuous annealing experimentsteel and batch annealing experiment steel.The yield strength and tensile strength is 440 MPa and 290 MPa respectively.The extension rate is about 36%.The n value and r value is 0.26 and 2.00,respectively.(3)Using technology such as hot rolling,cold rolling,annealing in austenite zone,the influence of process parameters of continuous annealing(heating rate,soaking temperature,holding time,cooling rate)and batch annealing(holding temperature,holding time)on microstructure evolution and formability of experiment steel were revealed.For continuous annealing,with the increase of heating rate and extending of holding time,the cupping formability of experiment steel varies insignificantly.As the increase of soaking temperature,the formability of experiment steel increases firstly and then gradually reached a plateau.With the increase of cooling rate,the formability of experiment steel increases firstly and then gradually reached a plateau.With the increase of heating rate and cooling rate,the hole expanding capability of experiment steel increases firstly and then decreases.The cavity expansion ratio peaks when holding time is 150s.For batch annealing,the best cupping value,earing ratio,cavity expansion ratio are obtained when the annealing temperature reaches 730?.(4)Using technology such as hot rolling-annealing in ferrite zone,the influence of ferrite region hot rolling and annealing on microstructrue evolution and mechanical properties were researched.The best y fiber texture of annealed experiment steel were obtained when the start-rolling temperature was 750°C.The excellent comprehensive mechanical properties of P added high strength interstitial free steel hot rolled in ferrite zone could obtain after recrystallization annealing.The start-rolling temperature of ferrite region hot rolling should be 750 'C.(5)Compared with P added high strength interstitial free steel hot rolling,cold rolling,annealing in austenite zone,the strength,extensibility and r value of P added high strength interstitial free steel hot rolled in ferrite zone slightly less.Some methods are proposed in this paper.And it is feasible to produce the P added high strength interstitial free steel through hot rolling-annealing in ferrite zone.