High hardness and retained austenite stability in Si-bearing hypereutectoid steel through new heat treatment design principles

Publication date: 15 March 2018
Source:Materials & Design, Volume 142
Author(s): T. Sourmail, F.G. Caballero, F. Moudian, D. De Castro, M. Benito
Austempering, and quenching and tempering heat treatments of high Si hyper-eutectoid steels are investigated using both dilatometry and salt-bath heat treatments. Changes in retained austenite content are measured using X-ray diffraction. Results are compared to the prevailing theory for bainite formation and published data. From the understanding of retained austenite evolution during tempering, a novel heat treatment is designed which is technologically identical to quenching and tempering with the exception that the principles guiding the selection of tempering temperature and duration are different. This heat treatment is shown to lead to a combination of hardness, retained austenite content and thermal stability entirely unprecedented for this category of alloys. In addition, this result is achieved for heat treatment durations that can be considered standard. In comparison, low temperature austempering is shown to require considerably longer holding durations to achieve somewhat lower combinations of hardness and retained austenite content.

Graphical abstract

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