Heat Treatment Process And Performance Analysis Of Martensite TRIP Steel

TRIP (Transformation Induced Plasticity) steel is a potential automobile steel at present. It has both the high strength and high ductility. The tensile strength and the total elongation can achieve 1200 MPa and 30% respectively. The adjustable range of properties for TRIP steel is very wide, and the TRIP steel with the different component can get the different combination of strength and ductility under different heat treatment process, which can meet the different demand of Suspension System, drive system and security structure. The TRIP steel which is studied in the paper is low carbon Si-Mn TRIP steel which contain alloy element C, Si, Mn and so on.The reserve of TRIP effect is through the transformation of retained austenite to martensite, then, the samples achieve the aim of strength and toughness. In the paper, different microstructure is obtained through the different heat treatment process, the microstructure at the different heat treatment process is analyzed through the optical microscope, scanning electron microscope and transmission electron microscope, the mechanical properties after heat treatment is tested through the tensile experiment, detecting the content of retained austenite by using the X-ray diffraction and understanding the relation between the microstructure and properties. at last, proceed baking hardening treatment to TRIP steel, the outcome is that TRIP steel has the better property of baking hardening. Mostly draw some conclusions at follows:(1) The test TRIP steel is mainly made up of ferrite, bainite and a small amount of retained austenite. The retained austenite present block or film form distributing at the boundary of ferrite grain.(2) The sample which its original structure is martensite has the best strength and ductility when it is heated at 760℃for 5 min then heated at 400℃for 5 min.(3)We compute the Ms temperature of test steel is 11.3℃by empirical formula. After static tension, the retained austenite transform to twin martensite.(4)TRIP steel can achieve the best strength effect on the condition of 170℃heat preservation and 2% predeformation.