Abstract

Deformation-induced martensitic transformation (DIMT) under cyclic loading in metastable austenitic steel AISI 348 was in-situ monitored through the magnetic permeability method with a Feritscope. Stepwise cyclic loading tests under room temperature revealed nonlinear and non-monotonic variations of the magnetic permeability within single loading cycles. The magnetic response was confirmed to be influenced by internal stress and plastic deformation. Villari effect under cyclic loadings was systematically investigated in the metastable austenitic steel and a model was introduced to correlate the Feritscope output with effective stress. A phenomenological model was proposed to describe the variation of Feritscope output of martensitic phases under zero internal stress within single loading cycles. The band-like structure of α′-martensite was observed along the principal stress axis and forming a material with composite nature. A stress partitioning model based on the dual-phase concept was established and the macroscopic stress is distributed in constituent phases. Mechanical behaviors of both phases were modeled by the cyclic plasticity model and the obtained stress-strain curves match well with the experimental results. On knowing the evolutions of internal stresses in the martensitic phase, the variations of magnetic properties under both loaded and unloaded states were well modeled.

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