Microstructural-constraint Induced Ferrite Refinement During Compressive Deformation of a Triplex Ferrite-Based Low Density Steel

The present work deals with proposing a new refinement mechanism in triplex microstructure of a ferrite-based low density steel in the course of thermomechanical processing. Toward this end, the material was deformed in compressive mode at 500 degrees C down to various strain levels and the microstructures was studied step by step with the aim of advanced characterization methods. Owing to the partially transformation of austenite to martensite, the softer lamella-type ferrites were encapsulated between austenite and/or martensite laths. It was found that the imposed strain was primarily accommodated in ferrite phase, due to the strain incompatibility between ferrite and martensite and the constraints coming from martensite, and the higher load-bearing capability of ferrite. This was led to substructure development within the ferrite, and groove formation through boundary splitting mechanism. Finally, the stepped ferrites were fragmented at higher imposed strain, and such constraint induced ferrite refinement was led to the formation of the grains down to the size of 0.5-2 mu m.