ISO 683-2
Heat-treatable steels, alloy steels and free-cutting steels — Part 2: Alloy steels for quenching and tempering
Technical delivery requirements for alloy steels for quenching and tempering (Cr, Cr-Mo, Cr-Ni-Mo, Cr-V, Mn-B and Ni-Cr-Mo grades such as 41Cr4, 25CrMo4, 42CrMo4, 34CrNiMo6, 30CrNiMo8, 51CrV4) as bar, rod, flat products and forgings.
What ISO 683-2 specifies
ISO 683-2 (aligned with EN 10083-3) covers the alloy steels used when a carbon steel cannot reach the strength or section size required: 34Cr4, 37Cr4, 41Cr4, 25CrMo4, 34CrMo4, 42CrMo4, 34CrNiMo6, 30CrNiMo8, 36NiCrMo16, 51CrV4, 20MnB5 and others, in the +U, +S, +A, +QT and +TH delivery conditions with optional hardenability bands (+H, +HH, +HL). Mechanical properties in +QT are tabulated by ruling section; for 42CrMo4 the minimum yield, tensile range and minimum elongation are 900 MPa, 1100–1300 MPa and 10 % up to 16 mm; 750 MPa, 1000–1200 MPa and 11 % for 16–40 mm; 650 MPa, 900–1100 MPa and 12 % for 40–100 mm; 550 MPa, 800–950 MPa and 13 % for 100–160 mm; and 500 MPa, 750–900 MPa and 14 % for 160–250 mm. Informative annexes give hardening (42CrMo4: 820–860 °C, oil or water) and tempering (540–680 °C) ranges. Testing uses ISO 6892-1, ISO 148-1, ISO 6506-1 and ISO 642.
ISO 683-2 types and classes
Every designation the document defines, with the thickness it requires and the tests it imposes.
| Designation | Meaning | Requirement / test |
|---|---|---|
+U | Untreated (as rolled or as forged). | — |
+A | Soft annealed to a hardness maximum for machining. | Brinell hardness per ISO 6506-1 |
+QT | Quenched and tempered by the supplier; e.g. 42CrMo4 up to 16 mm: yield 900 MPa min, tensile 1100–1300 MPa, elongation 10 % min; 40–100 mm: 650 MPa, 900–1100 MPa, 12 %. | Tension per ISO 6892-1; impact per ISO 148-1 |
+TH | Treated to a specified hardness range. | Brinell hardness per ISO 6506-1 |
+H / +HH / +HL | Normal, restricted-upper or restricted-lower Jominy scatter band supplied with the grade. | End-quench test per ISO 642 |
Tests and the drawing call-out
Tests the document imposes
- Tensile test per ISO 6892-1 by ruling section (+QT)
- Charpy V-notch impact per ISO 148-1 (room-temperature minimum for +QT when specified)
- Brinell hardness per ISO 6506-1 for the +A, +S and +TH conditions
- End-quench hardenability per ISO 642 for +H / +HH / +HL
- Grain size (ISO 643), decarburization (ISO 3887), inclusion rating (ISO 4967) when ordered
- Product analysis
How to cite it
Drawing call-out
MATERIAL: 42CrMo4 +QT PER ISO 683-2, RULING SECTION 100 MM MAX (RE 650 MPA MIN, RM 900–1100 MPA)Angle brackets mark the choices the drawing must make; every finish page shows a completed example.
Heat treatments specified to ISO 683-2
| Treatment | Role | Cost |
|---|---|---|
Austempering forms bainite by quenching austenitized steel or ductile iron into a hot bath and holding isothermally. | Related | $$$ |
Full annealing heats steel through its critical transformation range and then furnace-cools it slowly. | Related | $$ |
Normalizing heats steel above its critical range and cools it in air. | Related | $ |
Quench and temper transforms hardenable steel to martensite and then tempers it to the required balance of strength and toughness. | Related | $$ |
ISO 683-2 — frequently asked
Is 42CrMo4 the same as 4140?
A near equivalent (0.38–0.45 % C, 0.9–1.2 % Cr, 0.15–0.30 % Mo). 42CrMo4 +QT bought to ISO 683-2 arrives already quenched and tempered to a section-dependent property table, whereas 4140 is usually bought annealed or as-rolled and heat treated per a drawing note (for example AMS 2759/1) after machining. Substitution is common, but the properties must be checked against the ruling section.
Why does strength drop so much with section size?
Because even alloy steel hardens only as deep as the quench can extract heat: a 40 mm bar of 42CrMo4 quenches through, a 200 mm bar forms bainite and pearlite at the core. Hence 1100–1300 MPa up to 16 mm but 750–900 MPa at 160–250 mm; 34CrNiMo6 or 30CrNiMo8 (more nickel and molybdenum) push full hardening to larger sections.
What are +HH and +HL?
Restricted hardenability bands: +H is the normal Jominy scatter band for the grade, +HH the upper (harder) half and +HL the lower half. Specifying +HH gives a more uniform response for through-hardened parts; +HL is chosen where distortion or cracking is the concern.
Can I harden 42CrMo4 myself after buying +A?
Yes: austenitize at 820–860 °C, quench in oil (water for large simple shapes), and temper at 540–680 °C to the required strength — the higher the temper, the tougher and softer the part. Use a protective atmosphere or leave machining stock, and cite the heat-treatment specification and the ISO 15787 note on the drawing.
ISO 683-2 is copyrighted by International Organization for Standardization. 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 ↗