2. Tempering

2.1 Austenitization conditions

As the temperature rises, the – carbides ferrite structure of the tool steel transforms into austenite, with or without carbides depending on the chemical composition of the steel. Austenite formation begins at around 720°C in the case of unalloyed tool steel, with or without an intermediate Ac ₁ -Ac ₃ zone depending on the carbon content. This temperature is greatly increased by all alphagenic elements (chromium, molybdenum, tungsten, vanadium, silicon), which tend to reduce the austenitic domain of the iron-carbon diagram, and is lowered by gammagenic elements such as nickel and manganese, which have the opposite effect.

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