Hot ductility of high alloy Fe-Mn-C austenite TWIP steel

The high temperature tensile behavior of Fe-22Mn-0.7C Twinning induced plasticity (TWIP) steel has been experimentally investigated from 700 degrees C to 1250 degrees C. It is shown that TWIP steel presents higher tensile strengths and lower reduction area (RA) than low carbon (LC) steel under as cast condition. There is just one peak in each stress-strain curve of TWIP steel, while multi-peak has been observed in that of LC steel above 900 degrees C. The hot ductility of as cast Fe-22Mn-0.7C TWIP steel is not appreciable with most of RAs lower than 40% in the temperature range of 700-1250 degrees C. Interdendritic brittle cracks are observed in the fracture of as cast samples without any dimple. The hot ductility of Fe-22Mn-0.7C TWIP steel increases effectively with RAs higher than 60% in the range of 900-1200 degrees C when the Mn and C microsegregation ratio decrease to 0.9-1.1 and 0.75-1.3 respectively, together with the grain size reducing to 50 pm in diameter. Increasing the strain rate results in the increase of RAs of as cast TWIP steel, in which more uniform deformation and less microcrack in the matrix has been observed, along with deformation bands along the stretching direction. The inevitable solute microsegregation Mn and C, along with the microporosity in as cast structure result in the matrix homogeneity weakening of TWIP steel, leading to the deterioration of deformation continuity in the interdendritic zone. Dynamic re crystallization (DRX) retardation by high Mn alloying with extremely large grains is also a factor influencing the hot ductility of TWIP steel, although it improves the RA of as cast matrix in a very limited level. According to the stacking fault energy calculation, the low hot ductility of as cast TWIP steel with noteless necking behavior in the hot tensile test is not related to mechanical twining. (C) 2016 Elsevier B.V. All rights reserved.