Abstract
A washer-like specimen has been developed to study the dimensional movements that occur in the heat treatment ofcarburized components. In keeping with the effects noted in commercial practice, it has been shown that the rate of cooling from carburizing is a very important factor,. very fast cooling rates such as by water quenching completely outweigh the effects of major changes in composition. The carburizing treatment reduces dimensional movement in low-alloy steels but has a lesser effect in steels of high hardenability. Steel composition has a complex effect on distortion, and distinctions are therefore made between the effect of composition on increasing hardenability and that associated with the depression of the Ms temperature infully hardenable compositions. Both aspects have been considered in order to correlate dimensional movement over a wide range of compositions. The distortional behaviour in boron-treated steels is entirely different from that in boronfree steels of comparable hardenability. Although the former undergo significantly greater dimensional movement, their variability in distortion is no greater than that occurring in the more conventional boron-free grades. The specification of steels to restricted hardenability will reduce the variability of distortion very significantly. Even greater control would be obtained with the use of steels in which the hardenability is greater than that required for through-hardening in the section size involved.
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