Effect of Carbon Content on Microstructure and Mechanical Properties of Cold-rolled Medium Manganese Steel

The effects of carbon content of 0.1%～0.4% on the microstructure and mechanical properties of cold-rolled medium manganese steel after annealing at 650 ℃ were investigated.The microstructure evolution during annealing process was characterized by scanning electron microscopy,the residual austenite content in the steel was determined by X-ray diffraction analysis,the mechanical properties of the annealed steel were measured by tensile tests.The results show that the austenite reverted transformation takes place,which results in a certain amount of austenite phase in the ultrafine grained annealed matrix.When carbon content increases from 0.1% to 0.2%,the tensile strength(Rm) changes little(about 1000 MPa),the failure elongation(A) and the product of tensile strength and failure elongation(Rm × A) increases from 27% to 43% and from 28 GPa% to 45 GPa%,respectively.The carbon content of 0.4% significantly improves the strength of the steel(about 1200 MPa),but the plasticity decreases.Analysis thinks that the carbon of cold-rolled medium manganese steel is conducive to the formation of reverted austenite and its stability.However,high carbon content can help form a large number of carbides,which is not conducive to the formation of austenite,reducing the plasticity.The Rm,A and Rm × A are attributed to the enhanced TRIP effects of the large fractioned metastable austenite and the superfine grain size.