| Lightweighting is the development direction of the automobile industry.Thinning the thickness of the steel plate can effectively reduce the weight.Therefore,a new type of steel with higher strength and plasticity matching is a goal pursued by people.Duplex stainless steel is widely used in the automotive industry and other fields due to its good performance.In recent years,by rationally controlling the alloy composition in steel,the austenite in duplex stainless steel has a TRIP effect during deformation to enhance plasticization.Thus showing a broad application prospect.However,the deformation behavior of TRIP steel is very dependent on the martensitic transformation process,which is sensitive to a variety of deformation conditions.Changes in deformation conditions can cause dramatic changes in deformation behavior and cause uncontrollable deformation.Therefore,it is necessary to deeply study the principle of the influence of various deformation conditions on the martensite transformation behavior,in order to optimize the properties of the material by rationally using the TRIP effect,and provide a theoretical basis for the formulation of the forming process.In this paper,a new type of lean duplex stainless steel with TRIP effect is taken as the research object.The effects of three deformation conditions,namely strain rate,deformation temperature and pre-strain,on the mechanical properties of the test steel are obtained through a unidirectional tensile test.The results show that increasing the strain rate is detrimental to the TRIP effect and causes a decline in mechanical properties;As the temperature increases from-120°C to 70°C,the elongation first increases and then decreases,and the tensile strength decreases monotonously;The pre-strain has a great influence on the mechanical properties when the strain at the start point of the martensite transformation,and the mechanical properties are not sensitive to other pre-strains.With the help of EBSD and TEM,the evolution of martensite and the transformation of deformation mechanism under different deformation conditions were characterized.The influence of strain rate and temperature on the fracture behavior was analyzed by SEM.Aiming at the transformation behavior of martensite in the test steel,the martensite content under different deformation amounts was obtained by stepwise stretching method,and the martensite transformation kinetics under various deformation conditions was obtained by quantifying the martensite transformation process.Based on the martensite transformation kinetics data at different strain rates and temperature,the effect of strain rate is transformed into the influence of temperature factors,and a model that couples the strain rate and temperature is proposed.The prediction model at different rates and the measured curve have a good correspondence,indicating that increasing the temperature caused by increasing the strain rate is the main reason for the weakening of the TRIP effect.This paper presents a processing diagram of deformation conditions for evaluating and predicting mechanical properties under the influence of various deformation conditions. |
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