Effect Of Pre-deformation On Temperature-induced Martensitic Transformation

In the paper.Based on the precise control of the thermal stability of the metastable austenite in the high strength and high plastic design process of advanced high strength steel,the influence law and action mechanism of the pre-deformation on the thermal stability of the austenite were explored.321 austenitic stainless steel is selected as the research object It is mainly analyzed that the influence of pre-deformation and pre-deformation temperature on temperature-induced martensitic transformation.The mechanism of temperature-induced martensitic transformation under pre-deformation is explored respectively from the perspective of nucleation,growth,variant selection and crystallography of martensitic site.They are analyzed that the effects of pre-deformation and pre-deformation temperature on the stability of austenite.First of all,with room temperature pre-deformation samples as the research object,through to the prestressing sample on low temperature environment,explore the deformation on the influence of the temperature induced martensite phase transformation,Temperatureinduced martensitic transformation is promoted under the condition of low strain predeformation,Temperature-induced martensitic transformation is inhibited under the condition of high strain pre-deformation.The slip bands introduced by low strain pre-deformation provide nucleation sites to promote the temperature-induced martensitic transformation.It is embodied in the increase of Ms point and the increase of temperature induced martensite phase variable.the slip band spacing decreases under the condition of high strain pre-deformation,which inhibits the temperature-induced martensite growth,which is manifested as the suppression of martensitic transformation which is reflected in the decrease of Ms point and the decrease of the final martensitic phase variable.At the same time,the crystallographic analysis of martensite in pre-deformed samples shows that the slip band introduced by predeformed samples can effectively change the variation selection behavior and pairing phenomenon of martensite.Secondly,the effect of pre-deformation temperature on temperature-induced martensitic transformation was investigated by applying low temperature to pre-deformation samples at 300℃.The mechanism that pre-deformation at 300℃ is more conducive to promoting temperature-induced martensitic transformation than that at room temperature was explained.The slip bands and dislocations introduced by the 300℃ pre-deformation provide nucleation sites for temperature-induced martensite and promote the temperature-induced martensite transformation.The maximum phase variable of the pre-deformation martensite at 300℃ is 15%,and the maximum phase variable of the room temperature pre-deformation martensite is only 11%.At the same time,the crystallographic analysis of martensite in the 300℃ predeformation specimen shows that the 300℃ pre-deformation enhances the variation selection and pairing phenomenon of temperature-induced martensite.Finally,the effect of pre-deformation temperature on temperature-induced martensitic transformation was investigated by applying low-temperature environment to pre-deformation samples at-30℃ as the research object.The mechanism of temperature induced martensitic transformation induced by lower strain pre-deformation at-30℃ was discussed from the perspective of nucleation and growth,while higher strain pre-deformation at-30℃ inhibited temperature induced martensitic transformation.The slip band introduced by the low strain pre-deformation at-30℃ and the deformation-induced ε-M provide nucleation sites for temperature-induced martensite and promote the temperature-induced martensitic transformation.A large number of deformation-induced martensite was introduced into the higher strain pre-deformation,and the nuclear sites of temperature induced martensite were reduced,and martensitic transformation was inhibited.At the same time,the crystallographic analysis of martensite in pre-deformed samples at-30℃ shows that the slip band introduced by pre-deformed samples at-30℃ and the deformation-induced martensite can effectively change the variation selection behavior and pairing phenomenon of martensite.