(57) A method of heat treating a component formed of a high-chromium cast ferrous-based
alloy consisting of 11-28 wt% chromium, 1 - 3.6 wt% carbon and at least 0.2 wt% molybden
um and/or at least 0.6 wt% tungsten, the remainder (apart from any incidental ingredients
and impurities) being iron, said method comprising the steps of:-
a) holding said component at a temperature between the solidus temperature of the
alloy and 1050°C for a period of time not exceeding 3 days in a non-oxidising atmosphere
or vacuum so as to produce a partially spheroidised hard carbide phase in an austenitic
matrix throughout the component, and
b) quenching the component at a mean rate of from 40'C/min to 3'C/min in the critical
temperature range in order to retain the austenitic matrix.
Before heat treatment, carbon and chromium form a hard sharp, angular carbide phase
and the molybdenum and/or tungsten serves to increase the rate of change in the morphology
of the carbide phase during heat treatment from sharp angularity to a partly spheroidised
morphology.
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