Abstract
A method was completed for recording the rapid cooling rate in quenching steels by means of an oscillograph, operated by a thermocouple e.m.f. through a cascade connected with a 3-stage amplifier. The complete assembly includes a quenching tank, a gas quenching unit, a thermocouple amplifier circuit, a sweep circuit, a cathode ray oscillograph and a recording camera. Using this apparatus, (a) the effects of carbon content on the hardenability of steel as indicated by the critical cooling rate were analyzed quantatively and (b) the effect of maximum heating temperature on this property was studied. As the result of the study, it has been found that (a) the critical cooling rate is lowest at the eutectoid carbon percent, as reported by former investigators, (b) this cooling rate lowers with the rise of the maximum heating temperature, and (c) the relation between the critical cooling rate and the austenitic grain size seems to be linar in every specimen of carbon steel.
