Temperature-induced Martensitic Transformation Behavior Under Magnetic Field

Martensitic transformation is one of the important research directions in the field of metal materials,especially in steel materials.The research on its phase transformation mechanism is a hot and difficult problem in the field.In order to understand the stability of austenite under the action of magnetic field,the temperature-induced martensitic transformation behavior and mechanism under magnetic field are studied.The morphology and crystallographic characteristics of martensite under magnetic field are revealed.The effect of lower grain size and stacking fault energy on austenite stability is evaluated.The main research work is as follows:(1)This paper taked SUS321-0.015%C as the research object.By applying magnetic field and low temperature environment treatment,the behavior of athermal martensite transformation under magnetic field was studied,and the mechanism of strong magnetic field accelerating martensite transformation process and increasing phase variable was explained.The strong magnetic field provided magnetization energy to increase Ms,promoted the ?????' phase transformation path,formed more intermediate ?-martensite which provided nucleation sites for ?'-martensitic transformation,and promoted the growth of ?-martensite which induced larger ?'-martensite.In addition,the morphology of ?-martensite and ?'-martensite,the crystallographic relationship between the new phase and the parent phase and the variant selection rule of ?-martensite and ?'-martensite were also revealed.Under the action of magnetic field,SUS321-0.015%C and SUS321-0.015%C introduced into the nucleation sites by pre-deformation did not undergo isothermal martensitic transformation.The reason for the analysis may be that the current applied magnetic field strength and holding time are insufficient.It was indicated that the magnetic field is sensitive to the athermal martensite transformation compared with the isothermal martensitic transformation.(2)This paper taked SUS321-0.015%C with grain size of 6.6 ?m,29.3 ?m and 203 ?m as the research objects.The behavior of athermal martensite transformation of austenites with different grain size under the action of magnetic field was studied by applying magnetic field and low temperature environment.Under the action of magnetic field,the increase of grain size was beneficial to the formation of ?-martensite during the athermal treatment process,thus providing more phase transformation nucleation sites.Therefore,increasing the grain size could increase the Ms and reduce the stability of the austenite.In addition,under the action of magnetic field,the morphology of ?-martensite and ?'-martensite of martensitic transformation of austenite with different grain size under magnetic field was basically same.However,the variation selection rule of ?-martensite and ?'-martensite was weakened with the increase of austenite grain size.(3)This paper taked austenitic stainless steels with a stacking fault energy(SFE)of 17.3 mJ·m-2,21.7 mJ·m-2,29.26 mJ·m-2 as the research objects,the behavior of athermal martensite transformation of austenites with different stacking fault energy under the action of magnetic field was studied by applying magnetic field and low temperature environment.Under the action of magnetic field,the reduction of stacking fault energy was beneficial to the formation of ?-martensite during the athermal treatment process,thus providing more phase transformation nucleation sites.Therefore,reducing the stacking fault energy could increase the Ms and reduce the stability of the austenite.In addition,under the action of magnetic field,the morphology of ?-martensite and ?'-martensite of martensitic transformation of austenite with different grain size under magnetic field was basically same,and the variant selection rule of ?-martensite and ?'-martensite under the action of a magnetic field was not affected by the austenite stacking fault energy.