ASTM A1033
Standard Practice for Quantitative Measurement and Reporting of Hypoeutectoid Carbon and Low-Alloy Steel Phase Transformations
Standard practice for measuring, by dilatometry, the transformation temperatures and phase-transformation kinetics of hypoeutectoid carbon and low-alloy steels, and for reporting the results (Ac1, Ac3, Ar3, Ar1, Bs, Ms, transformation start and finish).
What ASTM A1033 specifies
ASTM A1033 is not a heat-treatment requirement but the measurement practice behind the numbers heat treaters rely on. It describes how to determine, by dilatometry on small machined specimens heated and cooled at controlled rates with a thermocouple attached to the specimen, the critical temperatures of a hypoeutectoid carbon or low-alloy steel — Ac1 and Ac3 on heating, Ar3 and Ar1 on cooling, the bainite-start (Bs) and martensite-start (Ms) temperatures — and the fraction transformed as a function of time and temperature. The practice fixes specimen geometry, heating- and cooling-rate control, how the length–temperature curve is analysed (tangent / offset method) and how metallography and hardness confirm which phases formed, so that continuous-cooling (CCT) and isothermal (TTT) diagrams from different laboratories are comparable. Heat treaters use the output to set austenitizing temperatures above Ac3, to choose quenchants that clear the bainite nose, and to predict Ms for martempering and austempering.
Tests and the drawing call-out
Tests the document imposes
- Dilatometric length-change measurement on heating and cooling at controlled rates
- Temperature measurement with a thermocouple attached to the specimen
- Metallographic confirmation of phases (ASTM E3 / E407) after each thermal path
- Hardness after transformation (ASTM E18 / E384) to support phase identification
- Chemical analysis of the test steel (ASTM A751) for the report
How to cite it
Drawing call-out
REPORT TRANSFORMATION TEMPERATURES (Ac1, Ac3, Ms) AND CCT DATA PER ASTM A1033 (material data request, not a drawing note)Angle brackets mark the choices the drawing must make; every finish page shows a completed example.
Heat treatments specified to ASTM A1033
| Treatment | Role | Cost |
|---|---|---|
Austempering forms bainite by quenching austenitized steel or ductile iron into a hot bath and holding isothermally. | Related | $$$ |
Full annealing heats steel through its critical transformation range and then furnace-cools it slowly. | Related | $$ |
Martempering is an interrupted quench that equalizes austenitized steel just above its martensite-start temperature before cooling through martensite formation. | Related | $$$ |
Normalizing heats steel above its critical range and cools it in air. | Related | $ |
Process annealing is a subcritical softening cycle inserted between cold-working operations. | Related | $ |
Quench and temper transforms hardenable steel to martensite and then tempers it to the required balance of strength and toughness. | Related | $$ |
ASTM A1033 — frequently asked
Why would a machined-parts buyer care about A1033?
Because the Ac3 and Ms of the actual heat decide whether the heat treater's austenitizing temperature is adequate and whether a martemper or austemper can work; when a steel is new to a shop, A1033-derived data replaces handbook averages (for 4140, Ac3 near 800 °C and Ms near 340 °C). It is the reference to cite when asking a supplier for transformation data.
How is Ms measured?
On the cooling curve the specimen contracts linearly until martensite forms, when the volume expansion of the new phase bends the curve; the practice defines that deviation point as Ms and the point where linearity resumes as the transformation finish. Cooling fast enough to avoid bainite is required and is checked by metallography.
What is the difference between CCT and TTT diagrams?
TTT (isothermal) diagrams come from quenching to a hold temperature and timing the transformation there; CCT diagrams come from continuous cooling at different rates, which is what a real quench does. A1033 covers the dilatometric measurement for both; CCT curves sit later and lower than TTT curves for the same steel.
Does A1033 give heat-treatment acceptance criteria?
No. It standardises how transformation data are measured and reported; the acceptance criteria for a part come from the heat-treatment specification (AMS 2759/1, ISO 683) and the drawing.
ASTM A1033 is copyrighted by ASTM International. This page explains the document so a drawing can be read; it does not reproduce the standard. Purchase the current edition from the publisher. Official source ↗