Abstract
Following the 19th report (Tetsu-to-Hagané, Vol.40, 1959, No.11, p.44), the rapid softening of hardened high speed steels (SKH2, SKH9) by water-or air-annealing, isothermal transformation- annealing and stepped annealing were studied by means of hardness test and micrography as compared with the full annealing.
The results oftained were summariged as follows:
(1) With both quench-hardened SKTI2 and SKH9, the minimum hardness was obtained by full annealing in a furnace at 880-90O°C, when the steel was softened fully, but it took long hours in furnace-cooling after annealing.
(2) When the quench-hardened steel was annealed in air and water from 800°C, the degree of softening was fairly less than that in the case of full annealing, but the steel developed a machinable hardness such as nearly meeting the purpose of a simple and rapid softening.
(3) The method of isothermal transformation annealing showed somewhat less degree of softening as compared with the full annealing method, but softened the steel in such short time that the practical purpose of rapid softening could be attained.
(4) When the full annealing in a furnace was suspended and air-or oil-cooling was performed from 600°C (the so-called stepped annealing), the softening equivalent to the full annealing was attained.By the stepped annealing, the slow cooling period at below 600°C was shortened as compared with the method of full annealing and the purpose of rapid annealing was fully attained.It was useful moreover for saving of fuel because the annealing furnace at 600° with residual heat could be utilized for other annealing processes.
