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Steel with a high carbon content will reach a much harder state than steel with a low carbon content. Likewise, tempering high-carbon steel to a certain temperature will produce steel that is considerably harder than low-carbon steel that is tempered at the same temperature. The amount of time held at the tempering temperature also has an effect.
A hypoeutectoid carbon steel (carbon composition smaller than the eutectoid one) is heated to approximately 30 to 50 °C (54 to 90 °F) above the austenictic temperature (A 3), whereas a hypereutectoid steel is heated to a temperature above the eutectoid one (A 1) for a certain number of hours; this ensures all the ferrite transforms into ...
Depending on the temperature and composition of the steel, it can be hardened or softened. To make steel harder, it must be heated to very high temperatures. The final result of exactly how hard the steel becomes depends on the amount of carbon present in the metal. Only steel that is high in carbon can be hardened and tempered.
However, the final hardness of the tempered steel will vary, depending on the composition of the steel. Higher-carbon tool steel will remain much harder after tempering than spring steel (of slightly less carbon) when tempered at the same temperature. The oxide film will also increase in thickness over time.
The temperature range for process annealing ranges from 260 °C (500 °F) to 760 °C (1400 °F), depending on the alloy in question. This process is mainly suited for low-carbon steel. The material is heated up to a temperature just below the lower critical temperature of steel.
The blue appearance of the oxide film is also used as an indication of temperature when tempering carbon steel after hardening, indicating a state of temper suitable for springs. Bluing is also used in seasoning carbon steel cookware, to render it relatively rust-proof and non-stick.
Holloman and Jaffe determined the value of C experimentally by plotting hardness versus tempering time for a series of tempering temperatures of interest and interpolating the data to obtain the time necessary to yield a number of different hardness values. This work was based on six different heats of plain carbon steels with carbon contents ...
In metallurgy, quenching is most commonly used to harden steel by inducing a martensite transformation, where the steel must be rapidly cooled through its eutectoid point, the temperature at which austenite becomes unstable. Rapid cooling prevents the formation of cementite structure, instead forcibly dissolving carbon atoms in the ferrite ...