Research On Deformation Induced Plastic Behavior Of The Lean Duplex Stainless Steel

Duplex stainless steel is a multiphase metal alloy material composed of a ferrite phase having a body-centered cubic(bcc)structure and an austenite phase having a face centered cubic(fcc)structure.In recent years,Mn-N-bearing duplex stainless steel has begun to appear in large quantities and has been rapidly applied,replacing Ni with Mn and N reduces the austenite stability in stainless steel while reducing the cost,so that it produces the TRIP effect during deformation,thereby improving plasticity.The TRIP effect is produced in the austenite matrix.Therefore,it is important to understand the influence of the austenite phase characteristics on the TRIP effect.This not only reveals the mechanism of TRIP effect,but also guides the processing technology better to rationally utilize the TRIP effect to achieve plasticizing effect,which plays an important role in promoting the application of such duplex stainless steel..In this study,a new type of Mn-N alloyed economical duplex stainless steel was studied.The influence of the metastable austenite matrix characteristics(mechanical stability,phase size and distribution characteristics)on the TRIP effect was studied through the mechanical property test and microstructure characterization.The related nature of the metastable austenite matrix phase and the TRIP effect is clarified,and the plastic deformation mechanism of the duplex stainless steel with TRIP effect is revealed.The main results are as follows:(1)The overall deformation of the test steel is mainly controlled by the deformation of the austenite phase,and the work hardening rate decreases first and then decreases with the increase of strain,showing a "three-stage" hardening characteristic.The test steel breaks rapidly after deformation and the fracture is characterized by quasi-cleavage fracture.The metastable austenite deforms and induces martensite during deformation,which induces the TRIP effect.The martensitic transformation mainly exhibits two mechanisms of ?????? and ????,and the deformation of ferrite Mainly due to dislocation slip.The uneven deformation between the components causes the "true" transformation of the martensite in the metastable austenite phase to be different from the overall "apparent" law of the material.Loading along the RD direction of the test steel strip is more favorable for promoting the TRIP effect than loading along the TD direction.(2)Austenite phase stability is sensitive to solution temperature.With the increase of solid solution temperature,the austenite phase austenite stability increases,the tensile strength of the test steel decreases gradually,the elongation increases first and then decreases,and the optimum plasticity is exhibited at 1100 °C.The overall work hardening law of the test steel depends on the deformation induced martensite transformation and the retained austenite hardening rate.Under the same deformation amount,the higher the solution temperature,the smaller the martensite transformation.(3)The austenite phase(thickness)size in the test steel is in the range of 10-50 ?m,the finer the austenite phase size,the smaller the martensite transformation saturation amount,but the early stage of deformation(true strain ? 0.25)due to the nucleation site The result is a higher martensite transformation.Test steel with a fine austenite phase(thickness)size has high tensile strength and yield strength,but the elongation is slightly decreased..