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Temperature is often gauged by watching the color temperature of the work, with the transition from a deep cherry-red to orange-red (815 °C (1,499 °F) to 871 °C (1,600 °F)) corresponding to the formation of austenite in medium and high-carbon steel. In the visible spectrum, this glow increases in brightness as temperature increases.
The exact boundaries of the austenite phase region depend on the chemistry of the alloy being heat treated. However, austenitizing temperatures are typically between 790 and 915 °C (1,454 and 1,679 °F). [5] The amount of time spent at this temperature will vary with the alloy and process specifics for a through-hardened part.
Wide ranges in strength and ductility are possible. High temperature heat treatment (>400C) results in high ductility, good impact toughness, with a yield strength around 500 MPa. Lower temperatures (~260C) results in a higher yield strength of 1400 MPa and high hardness but much lower ductility. [1]
Heat treating furnace at 1,800 °F (980 °C) Heat treating (or heat treatment) is a group of industrial, thermal and metalworking processes used to alter the physical, and sometimes chemical, properties of a material.
The martensitic reaction begins during cooling when the austenite reaches the martensite start temperature (M s), and the parent austenite becomes mechanically unstable. As the sample is quenched, an increasingly large percentage of the austenite transforms to martensite until the lower transformation temperature M f is reached, at which time ...
Heat resisting grades can be used at elevated temperatures, usually above 600 °C (1,100 °F). [10] [11] They must resist corrosion (usually oxidation) and retain mechanical properties, mostly strength (yield stress) and creep resistance. Corrosion resistance is mostly provided by chromium, with additions of silicon and aluminium.
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.
Austenitizing, in which the steel is heated to a temperature in the range 980–1,050 °C (1,800–1,920 °F), depending on grade. The resulting austenite has a face-centered cubic crystal structure. Quenching. The austenite is transformed into martensite, a hard body-centered tetragonal crystal structure. The quenched martensite is very hard ...