Equilibrium chart plotting temperature against carbon content for iron-carbon alloys, showing the austenite, ferrite, pearlite and cementite fields and the A1, A3 and Acm lines. The eutectoid point at about 0.77 percent carbon and 727 °C splits hypoeutectoid from hypereutectoid steels. It describes slow, near-equilibrium heating and cooling only, so it predicts annealing well but says nothing about quench products like martensite.
Look at the iron-carbon diagram, 1095 is hypereutectoid, so you harden it from above A1, not above Acm.
Also heard as
- iron-carbon phase diagram
- Fe-C diagram
- iron-cementite diagram
Do not mix it up with
- TTT diagram: The iron-carbon diagram shows equilibrium phases, while a TTT diagram shows how fast austenite transforms at a given temperature, including to bainite and martensite.
Related terms
Critical temperature
A temperature at which steel's structure changes phase on heating or cooling, such as Ac1 or Ac3.
Austenite
The face-centered cubic form of iron that dissolves carbon and must form before steel can be hardened.
Pearlite
A layered mix of ferrite and cementite that forms when austenite cools slowly through the eutectoid range.
TTT diagram
Time-temperature-transformation chart showing how long austenite takes to transform when held at a fixed temperature.