Stress relaxation during hot deformation of austenite.

概要

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In order to understand effects of straightening points of continuous caster on surface cracking susceptibility of slabs, stress relaxation during hot deformation of low alloy steels and austenitic steels has been studied by means of intermittent tensile testing at temperatures ranging from 700 to 1300°C, in which the processes of deformation to given strains at a slow strain rate of 4×10-4s-1 and the subsequent stress relaxation for 3 min are repeated. Stress relaxation is largely suppressed by lowering the deformation temperature especially in Nb bearing steels because of the dynamic precipitation of NbC. Although the dynamically nucleated carbonitride precipitates can grow into considerably coarse particles in the subsequent relaxation process, the dynamic precipitation introducing the ductility loss occurs successively in the following deformation processes. Thus the ductility in the intermittent deformation becomes almost the same as in the continuous deformation, indicating that increase of the straightening points will enhance the dynamic precipitation because of decrease in the average strain rate, resulting in significant enhancement of surface cracking frequency. While at higher temperatures, since stress relaxation can occur much easily, the straightening point increase could reduce inner cracking which is usually formed at temperatures close to the solidus points.
The Iron and Steel Institute of Japanの論文