Abstract
The heat treatment conditions for the medium-carbon steel strengthened by plastic deformation-induced martensitic transformation of the retained austenite (Transformation Induced Plasticity or TRIP) were developed. After heat treatment according to an optimum variant, the structure of the investigated steel is ferritic bainite, with a 23% fraction of retained austenite showing thermal stability. It was found that the bainite contains a very small fraction of carbides. Their precipitation is hampered by a Si concentration of 1.35%. The retained austenite occurs as regular grains of 3 m in diameter or as films between bainite laths. On the basis of the tensile test, it was found that the steel is characterised by high strength properties (UTS = 1120 MPa, YS = 790MPa) and excellent ductile properties (TEL = UEL = 34%). The high strength and excellent ductile properties as well as the instantaneous work-hardening exponent n ~ 0.4 show that optimum utilisation of the TRIP effect improves the mechanical and technological properties of the steel.
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