High speed steel specimens were worked by torsion at the temperature of 1000∼1200°, and austenite grain-growth was observed with microscope. Austenite grain-boundaries were revealed by keeping the specimens at 800° for 10 minutes, the temperature bringing the nose in S curve. The outlines of the experiments are as follows :\ oindent(1) The relation between the degree of deformation, grain size and the working temperature was measured.\ oindent(2) The progress of recrystallization or grain-growth with the lapse of time after hot working was observed.\ oindent(3) The relation between the degree of deformation and the lapse of time before recrystallizing was found out.\ oindent(4) It was observed that the successive alternating working diminished the capacity of recrystallization.\ oindent(5) Coarse austenite grains were incapable of being recovered by the heat treatment.
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