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Abstract
The production of low nickel austenitic stainless steel has increased considerably mainly due to nickel price evolution in the last years. Manganese steels exhibit the best combination of strength and ductility over the whole range of ductile steel grades for car manufacturing. But austenitic stainless steel containing manganese suffers from sigma phase and the material would be subjected to brittle fracture. Carbon decreases the sigma phase formation. However, carbon deteriorates the ductility of austenitic stainless steel. Therefore it was important to study the high temperature deformation of austenitic stainless steel containing manganese with low nickel. This thesis is a trial to process austenitic stainless steel with manganese content ranging from 4.35 to 9.27 wt.% and carbon content up to 1.3 wt.%. The high temperature deformation was in the range from 950°C to 1200°C to prevent the hot formability with severe cracks. The results of this investigation show that the tensile strength and hardness increase as the Mn content increases after thermomechanical treatment. The high deformation temperature accelerates the dynamic recrystallization of Fe-Mn steels leading to fine grains. The ferrite phase increases as the Mn contents are increased after thermomechanical treatment. Sigma phase after thermomechanical deformation disappears and the final microstructure is fully austenitic with thin carbides on the grain boundaries. At 9 wt.% Mn content, chromium carbide can not be controlled and deteriorates the strength and ductility.