Abstract
Following the 16th report (Tetsu to Hagane Vol. 39 (1953), p. 1177), the influence of austenitizing temperatures varying from 1260° to 1350°C on the behaviour in austempering at the intermediate region (200°-400°C) and subsequent tempering was studied by micrography and hardness test with a high speed steel containing 0.65% C, 15.92% W, 4.30% Cr, 0.76% V and 2.64% Co.
The results obtained were summarized as follows:
In any case, at the intermediate range the isothermal transformation of austenite, such as γ→lower-bainite+γ'(austenite of higher concentration), occurred. In responset to its progress the quantity and stability of retained austenite γ' increased. Hence the more the formation of lower-bainite in austempering proceeded, the secondary hardening in subsequent tempering occurred in the larger amount and at the higher temperature. As the austenitizing temperature rose, the transformation at the intermediate range was delayed, and consequently the above-mentioned effects of austempering on the secondary hardening also became less.
