Ferromagnetic properties of deformation-induced martensite transformation in AISI 304 stainless steel

Ferromagnetic properties of plastically deformed AISI 304ss have been studied using magnetic hysteresis and Barkhausen emissions methods. The present study has been concentrated on low volume fraction of martensite, i.e., below 58 pct, as compared to the available literature for a higher percentage of martensite. In measured materials, the coercivity increased with deformation and had a tendency to go toward saturation value. A linear increase in remanence with the deformation was observed. A large number of small amplitude of Barkhausen emissions were found at low percentage of martensite, indicating that magnetization rotation took place within a small region. However, large amplitude Barkhausen emissions were observed with the increase of deformations. Angular variation of Barkhausen emissions indicated the formation of rolling texture within the materials. A model has been proposed to explain the results. At the initial stage, small martensite clusters are formed, which grow with the deformation, and the intracluster exchange interaction becomes predominant. With the increase of deformation, martensite volume fraction increases. In this process, existing clusters grow and new clusters are formed. As a result, martensite clusters come closer and intercluster exchange interaction becomes important.