Neutron Diffraction Studies of Si–Mn Trip Steel In Situ upon Thermomechanical Processing

Abstract

An excellent combination of high strength and formability can be obtained in a Si–Mn TRIP steels when processed by thermomechanical treatment consisting of high temperature deformation followed by isothermal holding in the bainite region and cooling to room temperature. Microstructure of these steels consists of ferrite, bainite and retained austenite. The combination of high strength and ductility is attributed to the transformation-induced plasticity (TRIP) effect resulting from the strain induced transformation of the retained austenite to martensite. These steels exhibit tensile strengths ranging 800–1000 MPa and elongation up to 30%. In the present paper, the influence of transformation conditions on volume fraction of ferrite and retained austenite in selected 0.2C1.9Si1.45Mn TRIP steel was investigated. Based on results of in situ high-temperature neutron diffraction experiments, the set of specimens was prepared and their transformation characteristics at room temperature were studied again by neutron diffraction experiments realized in situ upon tensile tests. The reported neutron diffraction method has been found as an efficient tool for characterization of austenite transformation proceeding in TRIP steels during combined thermomechanical treatments.