The Study On Fatigue Performance And Welded-fatigue Performance Of TRIP Steel

TRIP steel is a kind of new high strength automotive steel, has good tensile strength and elongation. Because of its excellent mechanical properties, Such as,low yielding-to-tensile ratio,high initial strain hardening rate,good strength and plastic matching.which make it conform to the auto development theme of materials lightweight,high performance, security, pro-environment, energy conservation.Now,about TRIP steel,domestic and foreign research mainly focus on the microstructure, heat treatment, etc, but the study about the stamping formability, the fatigue characteristics, plating, welding less to carry out.which is not conducive to the downstream products to expand applications.Due to the auto lightweight is a long-term goal for the auto industry,And good fatigue performance is a prerequisite for many car bearing structure.As the car lightweight alternative material, TRIP steel must have a good fatigue performance,which male it have wider application prospect.Therefore, in this paper, fatigue performance and welded-fatigue performance of the strength of600MPa and800MPa TRIP steel is studied.It will provide reliable theoretical and experimental data for the application in the car of the steel.The main research content is as follows:1).Thoroughly analysis and learn about polyphase structure of base organization of the TRIP steel,reveals the principle of TRIP effect;2).A series of high cycle fatigue experiments were conducted, and the fatigue test data were fitted by the software of the Orange. Finally, we mapped S-N curves of the two levels of TRIP steel, and obtained their the fatigue limits;3). After determining the best welding process of steel plate, A series of high cycle fatigue experiments were conducted to the welded steels, and the fatigue test datas were fitted by the software of the Orange. Finally, we mapped S-N curves of and obtained their the fatigue limits;4).The experience formulas the strength of600MPa and800MPa TRIP steel and the two levels of welded steel is fitted;5).Through the fatigue fracture scanning and XRD experiment, the main methods and process of TRIP steel fatigue fracture were analyzed.and get the fracture mechanism;6).Observing of TRIP steel spot welding fatigue fracture, analysis and research the fatigue fracture mechanism of TRIP steel plates after welding.