Effect of cold radial forging on structure, texture and mechanical properties of lightweight austenitic steel

Introduction. Lightweight austenitic steels, exhibiting high mechanical properties combined with cost-effective alloying and low density, are promising materials for automotive and airspace industries. The purpose of this work is to study the evolution of the structure and properties of Fe-21Mn-6Al-1C lightweight austenitic steel after cold radial forging (CRF) under various modes. Methods. Microstructural studies were performed using transmission and scanning electron microscopy (TEM) on JEOL JEM-2100 and FEI Nova NanoSEM 450 microscopes, respectively. Microhardness was determined in the cross-section using a Wolpert 402MVD microhardness tester with a load of 200 g and a dwell time of 15 s. Uniaxial tension testing of samples cut from the edge and center was performed on an Instron 5882 machine at room temperature and a strain rate of 1×10-3 s−1. Results and discussion. The stages of structure formation were determined: after deformation (ε) of up to 20%, the formation of deformation microbands in the center and parallel deformation microbands at the rod edge takes place; after ε = 40–60%, the formation of single mechanical twins in the center and packets of twins/lamellas at the edge occurs; after ε = 80%, the intensive twinning in the center and formation of a fragmented structure at the edge takes place. Increasing the degree of CRF leads to the development of a sharp two-component axial texture <111>// rod axis (RA) and <100>//RA in the center, which is blurred towards the edge. At the edge of the rod, a shear texture B/B̅ is observed after CRF with ε = 40% and higher. After CRF with ε = 20%, the material in the center of the rod exhibits higher strength and hardness and lower ductility compared to the edge. Further CRF is accompanied by a change in this strength/hardness and ductility ratio between the center and the edge of the rod to the opposite. Thus, CRF is a promising method for producing industrial blanks from lightweight austenitic steels.