A. Peters et al., CHANGES IN TRANSFORMATION BEHAVIOR AND MICROSTRUCTURE OF A CRV-SPRINGSTEEL BY THERMOMECHANICAL TREATMENT, Steel research, 67(10), 1996, pp. 412-418
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.