Study On Microstructure And Properties Of Al-containing Medium Manganese TRIP Steel Under Intercritical Annealing

With the development of the automotive industry,energy saving and emission reduction have become an important factor restricting the development of the automotive industry,and lightweight vehicle is one of the effective methods to solve the energy and environmental problems facing the current Advanced automotive steel has become the mainstream of the world's automotive steel development.The comprehensive strength of Mn-Al medium manganese steel with high strength and high plasticity can meet the needs of contemporary automotive steel,and has become the research goal of the majority of automotive steel researchers.In this paper,Al-containing medium manganese TRIP steels were simulated by continuous annealing.Three kinds of medium manganese TRIP steels with different Al contents?1.0%,1.5%,2.5%?were annealed in short time.The phase transformation law,microstructure and mechanical properties of the annealed samples were studied by using Factsage 7.3 fsteel software,X-ray diffraction?XRD?,scanning electron microscopy?SEM?,transmission electron microscopy?TEM?and tensile testing machine:?1?Al changes the intercritical annealing temperature of medium manganese steel,especially the A₃ temperature,which makes the intercritical annealing zone of TRIP steel with Al shift to a larger range and higher temperature.When Al content reaches 2.5%,with the increase of temperature,there is no complete austenite zone in medium manganese steel,and?-ferrite appears in microstructure.?2?With the addition of Al,the medium manganese steel containing Al obtained good comprehensive mechanical properties in a short time.The tensile strength of 0.2C-5Mn-1.0Al steel sample was 1068 MPa and the elongation was 36.36%after intercritical annealing at 700?for 3 min,the tensile strength and elongation of 0.2C-5Mn-2.5 Al steel were927.7 MPa and 50.12%respectively at 760?when the Al content was increased to2.5%,mechanical Properties of 46.5 GPa·%of the strong plastic product.?3?There are two kinds of??-martensite in the fracture structure of medium manganese steel.The polygonal or quasi polygonal??-martensite in the early transformed retained austenite has little effect on plasticity.Another kind of??-martensite has large deformation,which is formed by some austenite transformed in the middle and later stage of tensile deformation,thus improving the mechanical properties.?4?With the increase of tensile strength,the microstructure of 0.2C-5Mn-2.5Al medium manganese TRIP steel hardly changes in the elastic deformation stage.With the increase of tensile strength,the retained austenite gradually changes and deforms along the tensile direction.?5?With the increase of the tensile rate,the residual austenite content of the manganese steel in 0.2C-5Mn-2.5Al has increased,and the martensite transformation has decreased,so the tensile strength and elongation of the sample have decreased.However,as the tensile speed increases,dislocation motion becomes difficult,resulting in a significant increase in the yield strength of the specimen.