Abstract
With a view to establishing the quenching process for high speed steel, the authors have obtained the C.C.T. curve for 18-4-1 high speed steel (JES SKH 2). The experimental procedure follows: The surface except the end faces of a specimen is completely coated with thermal insulator. The whole piece is heated to 1300°, then put into the electric furnace with a predetermined temperature except the open end 10 mm long which is kept out of the furnace. In this state the exposed part is allowed to cool in still air while the inserted part is also cooled in the furnace at a slow rate. Thus the cooling curve of end quench is obtained. Similar specimens are cooled under the same conditions, their structures at various phases fixed, and their microstructures and hardnesses 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 720° and critical cooling velocity, about 17°/min.
