Cyclic plastic deformation-induced martensitic transformation in austenitic steels

The paper is part of a broader research project aimed at studying changes in cyclic properties, energy cumulation and fatigue lift: of metastable austenitic steels undergoing the martensitic transformation at room temperature induced by externally applied cyclic stress. The study was aimed at evaluating the limit value of cyclic plastic strain on reaching which the martensitic transformation in high-nickel AISI 304L steel begins. Additionally, the crossed magnetomechanical effect (tile Villari effect) was shown to be fully applicable in evaluating the amount of the a'-martensite. Another problem consisted in working out an adequate analytical representation of the cyclic deformation curve (CSSc) covering a wide range of strain. A new four-parameter power model of an elastic-plastic material was used. The model is capable of allowing for the experimentally observed point of inflection on the CSSc. This point separates the single-phase martensite region from tile two-phase (austenite + martensite) one. The model incorporates a new material constant termed the martensitic transformation cyclic limit. The analysis was verified with results obtained from 304L steel. The tests were carried out at an increasing load level anti tile control signal was sinusoidal. The measured quantities were: total, elastic and plastic strains, stress and hysteresis loop area. The experimental results fully confirmed the validity of the model.