Effect Of Two-stage Austenitizing Treatment On Microstructure And Mechanical Properties Of TRIP590 Steel

Automobile industry has been developing rapidly in recent years,along with the environmental problems and energy crisis which have become increasingly worse.Automotive lightweighting production and safety production have become the main goals of the automobile industry development.Transformation induced plasticity(TRIP)steel has the characteristics of the combination of high strength and high plasticity,and TRIP steel is widely used in automobile industry.The experiment is carried out on the TRIP590 steel by two-stage austenitizing treatment,in order to obtain more excellent mechanical properties.The experiment is conducted mainly from the following contents.The TRIP590 steel has been treated by austenitizing heat treatment process.And then the steel has been treated in the two-phase region and the bainite transformation zone under different temperature and time.The microstructure of the experimental steel and the content of retained austenite have been observed by the optical micrograph,SEM,XRD and TEM.The mechanical properties have been tested at room temperature.The obtained results are as follows:The grain size of the steel refined after austenitizing quenching treatment.Apart from that,the yield strength,tensile strength and elongation of the steelhave been improved.After rapid cooling to room temperature,the retained austenite content and its carbon content in the experimental steel are higher than those without austenitizing treatment.The yield strength,tensile strength and elongation of the steel increase with the rise of temperature at a certain temperature range in the two-phase region.The content of ferrite decreases with the rise of temperature while the content of austenite increases.The experimental steel-s yield strength,tensile strength and elongation increase with the rise of temperature and holding time at a certain range in the bainite transformation zone.However,too high heating emperature and too long holding time will make degradation to its mechanical performance.In the 920 ?× 40 s +800 ?× 100 s+420 ?× 300 s process,the elongation of the experimental steel reached a maximum of 40%,its product of strength and elongation is 25880 MPa%.Both ferrite and retained austenite contribute to excellent elongation of the experimental steel.In the 920 ?× 40 s +820 ?× 100 s+400 ?× 200 s process,the experimental steel shows excellent mechanical properties with yield strength of 556 MPa,tensile strength of 691 MPa,and its product of strength and elongation reachs 26258 MPa%.