Preparation Technology And Strengthening Mechanism Of Ultra-high Strength Martensitic-austenite Composite Steel

In the context of the current dual carbon goals,the development of higher-performance steel materials is an effective way to reduce carbon emissions.In this study,martensitic steel with high strength and austenitic steel with high plasticity were selected as matrix materials,and martensitic steel and austenitic steel were compounded by high-temperature vacuum rolling to prepare high-performance steel.Composite steel material.Various microstructures in the composite steel were characterized,and the corresponding strengthening and toughening mechanisms were analyzed.Under the condition of element diffusion,the influence of the thickness of the single layer on the microstructure and properties of the composite steel plate was studied with the same total thickness.It was found that the mechanical properties of the 9-layer composite steel plate were the best,with a tensile strength of 1733 MPa,an elongation of 23.6%,and a uniform elongation of 8.9%.The main reason for the high strength of the composite steel plate is that the C element in the austenite layer diffuses into the martensite layer,which strengthens the martensite matrix.The high plasticity benefits from the better synergistic deformation effect and interfacial bonding strength of the 9-layer clad steel plate.The tensile strength and elongation of the composite steel plate are the highest when treated with different holding times for 2 min,which are 1733 MPa and 23.7%.When holding for 30 min,the diffusion of C element did not change significantly,and the tensile strength and elongation of the composite steel plate decreased to 1542 MPa and 15.1%.This is due to the increase in the martensite lath and austenite grain size and the weakening of the coordinated deformation ability of the austenite layer due to the prolonged holding time.The clad steel plate was rolled at different temperatures,and it was found that the tensile strength of the clad steel plate after warm rolling at 450℃ was 1970 MPa,and the total elongation was 16.5%.Warm rolling introduces a large number of movable dislocations,increases the dislocation density of the austenite layer,and generates a large number of deformation twins in the austenite layer,which strengthens the austenite layer.After 10%cold rolling of the 5-layer clad steel plate,the tensile strength increased from 1666 MPa to1742 MPa,the elongation decreased from 21.9% to 4.1%,and the overall performance decreased.The effect of trace diffusion of N element on the mechanical properties of clad steel plate was studied.It is found that the N-clad steel sheet has high plasticity,which is benefited from the stronger work hardening ability of the austenite phase.The strength of the martensite layer in the clad steel sheet is not improved,and the diffusion of trace N elements cannot significantly improve the strength of the clad steel sheet.