CHANGES IN TRANSFORMATION BEHAVIOR AND MICROSTRUCTURE OF A CRV-SPRINGSTEEL BY THERMOMECHANICAL TREATMENT

The effect of austenite deformation on the transformation behaviour wa s investigated on a CrV-spring steel with the major attention put on t he martensitic transformation. In the first part, a small review is gi ven on the relation between the stale of austenite after hot deformati on and its influence on the formation of martensite. In the laboratory tests, the second part of the paper, a conventional heat treatment (C HT) was compared with two types of austenite conditioning by thermomec hanical treatment (TMT): TMT(R) - with deformation above the recrystal lization temperature theta(R) leading to a fully recrystallized austen ite and TMT(N)- with deformation below theta(R) with a not recrystalli zed but possibly polygonized austenite. For the laboratory tests, the hot deformation simulator Wumsi was employed. After quenching in oil, the martensite after TMT consisted of associations of many fine fragme nts with a Smaller number of large acicular martensitic units than obs erved after CHT, in both TMT-variants small ferritic areas (< 1 mu m) could be revealed, Different behaviour of martensite during tempering at low temperatures was observed after CHT and TMT. it can be explaine d by reduced inherent stresses generated during martensitic transforma tion after TMT, presumably as a result of a better ability of deformed austenite to withstand the accommodation strain during martensitic tr ansformation. This may have considerable consequences for the toughnes s properties of tempered martensite.