Tempering Steel
This chart shows the colors that are elicited by tempering a 0.95-percent carbon content steel at the temperatures shown.
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In steel, tempering is reheating hardened steel to a temperature below the lower critical temperature for the purpose of decreasing hardness and increasing toughness. (The lower critical temperature is the temperature of the austenite-to-pearlite eutectoid transformation. In steels below this temperature, austenite does not exist.)
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Tempering is sometimes applied to normalized steels for similar reasons: It decreases hardness and improves toughness.
The chart above shows the colors that are elicited by tempering a 0.95-percent carbon content steel at the temperatures shown. (For example, think about a drill rod.)
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