First step of any hardening cycle: bringing steel to a temperature where it transforms to austenite and dissolves enough carbon and alloy for full hardness. Typical setpoints are about 815 to 870 °C for medium-carbon alloy steels, 925 to 1,025 °C for air-hardening tool steels like A2 and D2, and above 1,175 °C for high-speed steels. Too low leaves free ferrite or undissolved carbide; too high coarsens grain and raises retained austenite.
Austenitizing at 1,550 for an hour at heat, then straight into the oil, no parking it on the cart.
A classic austenitizing mistake is reusing one grade's setpoint for another: the 4140 number underheats D2 and overheats 1095.
Also heard as
- austenitize
- hardening temperature
- hardening heat
Related terms
Austenite
The face-centered cubic form of iron that dissolves carbon and must form before steel can be hardened.
Critical temperature
A temperature at which steel's structure changes phase on heating or cooling, such as Ac1 or Ac3.
Soak
To hold parts at a set temperature until they are evenly heated and the intended change is complete.
Quench
To cool hot metal rapidly in a liquid or gas so that it hardens, or the act of doing so.
Grain size
The average size of the crystals in a metal, usually reported as an ASTM number where higher means finer.