Heat Treatment FAQ

Frequently asked questions

How should I heat treat the ASP® grades?
The recommended heat treating procedure for each grade is indicated in our data sheets. In most cases, a range of hardening temperatures is permissible, depending on the desired final hardness. Because of the high alloy content and high hardening temperatures for these grades, there is generally a high retained austenite content in the as-quenched condition. Multiple tempers are required to transform the retained austenite to tempered martensite. It is important to ensure that parts are thoroughly heated to the tempering temperature, and subsequently cooled completely to room temperature in between tempers, in order to ensure full conversion. More details can be found in our brochure Heat Treatment available on our web site to registered customers. For ASP® we always recommend tempering three times at 560°C (1040ºF).


Why does Erasteel recommend tempering at 560°C?
Tempering at 560°C (1040ºF) ensures thorough tempering, adequate diffusion to encourage conversion of retained austenite, and good stress relieving of the as-quenched structure. In most cases, the use of an adjusted hardening temperature is preferred for achieving a higher or lower final hardness, rather than adjusting the tempering temperature. Improved toughness is achieved more consistently with a lower hardening temperature than with a higher tempering temperature, while the risks of inadequate conversion of retained austenite become greater with low tempering temperatures. Our experience suggests that 560°C (1040°F) is generally a good compromise to reach an acceptable hardness, while ensuring reliable tempering. More details can be found in our brochure Heat Treatment available on our web site to registered customers


What happens with toughness if I temper down the hardness?
The toughness is not significantly affected by changes in the tempering temperature. The toughness is best improved by using a lower hardening temperature, as discussed in the question above.


Why is it so important to include a dummy when doing vacuum heat treatment?
A dummy, or an instrumented part of a comparable size to the parts being heat treated, will allow the heat treat operators to ensure that parts have fully reached the desired temperature during each process step in the heat treatment operations. In this way, the history of heating and cooling can be better tracked for each furnace load. A dummy is the only way to follow, and register, the temperature in the center part of material. In vacuum it is important to have a good control over the cooling process, especially in the temperature range of 1000ºC - 800ºC (1830ºF - 1470ºF) as too low cooling speed has a negative influence on the tool- hardness and toughness.


Is subzero treatment needed for Erasteel steels?
Subzero treatments (or cryogenic treatments) are primarily intended to convert retained austenite to martensite, especially when the temperature range for martensite transformation extends to below room temperature. For most ASP® grades, the recommended heat treating procedures, especially careful tempering including complete cooling between tempers, should ensure complete transformation. If subzero treatments are used, they should always be followed by tempering to ensure that any martensite formed is tempered.For most applications Erasteel´s recommendation to temper 3 x 560ºC (1040ºF) is enough. For applications where aging stability is important subzero treatment is a helpful complement.

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