The austenitising window and the martensite-start temperature for a steel, from its composition, using the Andrews (1965) equations. It also tells you when your steel sits outside the range those equations were fitted to — which is the part most calculators leave out.
Weight percent. Leave an element blank if it is not present or not reported.
Andrews (1965), composition in wt %
These are the expressions METALLAI uses internally, written out so you can check them. Two of the three are routinely mis-transcribed, so they are worth reading carefully.
Source: K. W. Andrews, “Empirical formulae for the calculation of some transformation temperatures”, Journal of the Iron and Steel Institute 203 (1965) 721–727.
Andrews fitted these to low-alloy steels. The commonly quoted envelope is:
| Element | Fitted up to (wt %) |
|---|---|
| Carbon | 0.6 |
| Chromium | 2.5 |
| Nickel | 5 |
| Molybdenum | 1 |
| Manganese | 2 |
Above Ac1 the steel re-austenitises, and on cooling that fresh austenite becomes untempered martensite — so instead of tempering the part you have re-hardened part of it. A margin of about 30 °C is normal, because the calculated Ac1 is itself an estimate.
Heating into the Ac1–Ac3 range gives a partly-ferritic structure and, after quenching, mixed hardness. Normal practice is Ac3 + 30 to +70 °C: high enough to be fully austenitic with a margin, low enough to avoid grain growth.
Carbon dominates Ms. A low Ms means the transformation may not complete before room temperature, leaving retained austenite — which is why high-carbon and high-alloy steels are sometimes given a sub-zero treatment. Martensite finish is roughly Ms − 215 °C.
METALLAI takes the same composition plus your actual route and schedule and predicts yield, tensile, hardness, elongation and fatigue life — and refuses the combinations that cannot work, like a temper above Ac1.
Run the full prediction — free Carbon equivalent calculator