Title

THE EFFECT OF PRIOR TEMPERING ON CRYOGENIC TREATMENT TO REDUCE RETAINED AUSTENITE

THE EFFECT OF PRIOR TEMPERING ON CRYOGENIC TREATMENT TO REDUCE RETAINED AUSTENITE

Authorship

Stratton, Paul

Stratton, Paul

I am this author

DOI

10.5151/2594-5327-16866

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Abstract

The consensus view is that a high carbon case gives gears the best overall properties provided that there is no carbide network and that the retained austenite has been reduced below 20% by cryogenic treatment. This view is effectively enshrined in the SAE AMS 2759/7 standard. The cryogenic treatment usually takes place immediately after the quench to avoid austenite stabilisation. However, for some parts with complex geometries that might crack during the treatment, a short low temperature temper is carried out first. Little is known on how this temper affects the subsequent cryogenic treatment. Three carburising steels used extensively in the aerospace industry were carburised to produce high retained austenite levels in the case using two different, but typical carburising cycles. The retained austenite was determined by XRD before and after cryogenic treatment carried out in accordance with the standard and compared with that obtained when an intermediate temper was used. This study shows that for three typical carburising steels, carburised using typical cycles, the efficacy of the cryogenic treatment is reduced only slightly after the temper, and not enough to be industrially significant.

The consensus view is that a high carbon case gives gears the best overall properties provided that there is no carbide network and that the retained austenite has been reduced below 20% by cryogenic treatment. This view is effectively enshrined in the SAE AMS 2759/7 standard. The cryogenic treatment usually takes place immediately after the quench to avoid austenite stabilisation. However, for some parts with complex geometries that might crack during the treatment, a short low temperature temper is carried out first. Little is known on how this temper affects the subsequent cryogenic treatment. Three carburising steels used extensively in the aerospace industry were carburised to produce high retained austenite levels in the case using two different, but typical carburising cycles. The retained austenite was determined by XRD before and after cryogenic treatment carried out in accordance with the standard and compared with that obtained when an intermediate temper was used. This study shows that for three typical carburising steels, carburised using typical cycles, the efficacy of the cryogenic treatment is reduced only slightly after the temper, and not enough to be industrially significant.

Keywords

Cryogenic treatment; Tempering; Retained austenite.

Cryogenic treatment; Tempering; Retained austenite.