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Experiment 5: Heat Treatment - Quenching & Tempering

Henry Tan's picture

Conventional heat treatment procedures for producing martensitic steels generally involve continuous and rapid cooling of an austenitized specimen in some type of quenching medium, such as water, oil, or air. The properties of a steel that has been quenched and then tempered depends largely on the rate of cooling and tempering times and temperatures. During the quenching heat treatment, the specimen can be converted to a variety of microstructures including soft and ductile spheroidite to hard and brittle martensite. The production of pearlitic and bainitic steels is lower in cost and suffices for most applications. Martensitic steels must be tempered prior to use due to their extreme brittleness. A range of heat treatments producing a variety of microstructures and mechanical properties will be investigated in this experiment beginning with a set of initially equivalent samples of SAE 1040 steel. Pearlite, Bainite and Martensite will all be produced through variations in the cooling rates of initially austenized samples.

The second experiment involved in the study of the heat treatment examines "Hardenability". The Jominy End-Quench Test is a widely utilized standard test procedure for determining the hardenability of ferrous alloys. The term "Hardenability" is not the same as hardness, "Hardenability" refers to an alloy's ability to be hardened by the formation of Martensite as a result of a given heat treatment. High "Hardenability" alloys are those that not only harden on the surface, but to a great extent harden throughout the part's interior. Hardenability may also be thought of as a measure of the depth to which a specific alloy may be hardened.

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