抄録
In the earlier report the authors obtained the C.C.T. curve for 18-4-1 high speed steel (JES 2). In the present report the authors give the C.C.T. curve for 18-4-1+10 high speed steel (JIS4) containing Co (11%). Specimens are cooled under the method “end-cooling”, and rapidly cooled in water after the lapse of varying time, their structures being fixed at various phases thereby. Then, their microstructures and hardnesses are examined for determination of the C.C.T. curve. The results show that the temperature at which super-cooled austenite is most unstable is about 780° and the critical cooling velocity about 26°/min, which is slower than in still-air cooling. Compared with C.C.T. curve for 18-4-1, that of 18-4-1+10 is on a higher level and leans more to the left side. Presumably that is due to Co (11%), for this element tends as generally accepted to raise critical cooling velocity.
