The high temperature transformation of high speed steel |
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Authors: | P Leckie-Ewing W A Jacobsen |
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Affiliation: | 1. A Division of Litton Industries, UTD Corporation, Athol, Mass 2. Latrobe Steel Company, Latrobe, Pa
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Abstract: | Low tempered hardnesses on high speed steels which had been hardened in vacuum or atmosphere furnaces and gas quenched led to a search for a reaction occurring above 1400°F and probably initiated as a result of the slower cooling rate of the gas quench. A standard TTT evaluation was carried out on Ml, M2 high carbon, M3, and M7 high speed steels, quenching from conventional hardening temperatures, into salt baths maintained at 2000° to 1500°F. Examination of these specimens indicated the presence of a reaction occurring at all temperatures investigated but having its maximum rate at 1700° to 1800°F. The reaction involved precipitation of an MoC/Mo2C carbide at grain boundaries and within the grains, with the amount of precipitate increasing with time. The precipitation of MoC/Mo2C is directly related to the loss in tempered hardness and apparently causes this effect by 1) reducing precipitation hardening on tempering, 2) drastically lowering retained austenite contents, and 3) reducing as-quenched hardnesses. |
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