Technological ductility of high-speed steels

Abstract

1. We observed distinct maxima and minima on the curves of ductility and resistance to deformation of high-speed steels R18, R12, R9, and R6M3. Up to 600°C the ductility does not change, while the strength decreases monotonically; above 600°C the ductility increases sharply, reaching a peak near Ac1. The ductility decreases sharply in the phase transformation range. 2. The sharp increase of ductility at temperatures somewhat below Ac1 is one of the phenomena of superplasticity first observed by Academician A. A. Bochvar. 3. Decarburization of steel R18 to ferrite leads to a change in ductility, which increases continuously with the temperature and has no extreme values in the phase transformation range. 4. The direction of the grain and grain size affect the ductility of high-speed steel. In samples with a transverse grain the ductility is approximately half that of samples with a longitudinal grain, while the strength decreases slightly. Coarse grains, characteristic of so-called “crystalline” fracture, also reduce the ductility, the strength increasing somewhat. 5. The effect of carbide heterogeneity on the ductility is negligible. In samples with a carbide heterogeneity of grade 4 the ductility is somewhat higher than in samples with a carbide heterogeneity of grade 6. An increase of carbide heterogeneity from grade 6 to grade 8 does not lead to any further reduction of the ductility.