ISO 683-3
Heat-treatable steels, alloy steels and free-cutting steels — Part 3: Case-hardening steels
Technical delivery requirements for case-hardening steels (C10E–C16E, 17Cr3, 16MnCr5, 20MnCr5, 18CrMo4, 20MoCr4, 16NiCr4, 18CrNiMo7-6, 17NiCrMo6-4, 20NiCrMo2-2 and others) as bar, rod, wire rod, flat products and forgings.
What ISO 683-3 specifies
ISO 683-3 (aligned with EN 10084) covers the low-carbon steels that are carburized or carbonitrided and then hardened so that a hard case sits on a tough core: plain carbon C10E–C16E, the Cr and Mn-Cr grades 17Cr3, 16MnCr5 and 20MnCr5, the Cr-Mo grades 18CrMo4 and 20MoCr4, and the nickel-bearing grades 16NiCr4, 20NiCrMo2-2 (close to AISI 8620), 17NiCrMo6-4 and 18CrNiMo7-6 for heavy gears. It specifies composition, delivery conditions (+U, +S, +A, +TH and +FP, a ferrite–pearlite structure within a hardness range) and, as the central property, hardenability as Jominy end-quench bands in the normal (+H), restricted-upper (+HH) or restricted-lower (+HL) scatter. Informative annexes give recommended carburizing temperatures (about 880–980 °C), core and case hardening temperatures (16MnCr5: core hardening 860–900 °C, case hardening 780–820 °C) and tempering at 150–200 °C, plus reference core strengths. Case depth is specified on the part drawing and measured per ISO 2639 / ISO 18203.
ISO 683-3 types and classes
Every designation the document defines, with the thickness it requires and the tests it imposes.
| Designation | Meaning | Requirement / test |
|---|---|---|
+H | Normal Jominy end-quench scatter band for the grade; the default when no band is ordered. | End-quench test per ISO 642 |
+HH | Restricted band covering the upper (harder) half of +H; more uniform, stronger core for highly loaded gears. | End-quench test per ISO 642 |
+HL | Restricted band covering the lower (softer) half of +H; less distortion and cracking risk on thin parts. | End-quench test per ISO 642 |
+FP | Treated to a ferrite–pearlite structure within a stated hardness range; the preferred condition for machining before carburizing. | Brinell hardness per ISO 6506-1; microstructure check |
Tests and the drawing call-out
Tests the document imposes
- End-quench hardenability (Jominy) per ISO 642 against the +H / +HH / +HL band
- Brinell hardness per ISO 6506-1 in the +A, +TH or +FP delivery condition
- Grain size per ISO 643 (fine-grain requirement for case-hardening steels)
- Decarburization per ISO 3887 and inclusion rating per ISO 4967 when ordered
- Product analysis; blank-hardened reference tensile test when agreed
How to cite it
Drawing call-out
MATERIAL: 16MnCr5 +HH PER ISO 683-3; CASE HARDEN, CHD 0.8 +0.4 MM (550 HV 1 PER ISO 2639), SURFACE 58 +4 HRC, CORE 30–40 HRCAngle brackets mark the choices the drawing must make; every finish page shows a completed example.
Heat treatments specified to ISO 683-3
| Treatment | Role | Cost |
|---|---|---|
Carburizing diffuses carbon into low-carbon steel at austenitizing temperature, then quenches and tempers the enriched surface into a hard martensitic case. | 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 | $$$ |
Spheroidize annealing converts lamellar cementite into rounded carbide particles in a ferrite matrix. | Related | $$ |
ISO 683-3 — frequently asked
Why is hardenability the key property?
The core of a carburized gear is hardened in the same quench as the case; its strength depends on how deep the base steel hardens, which the Jominy band predicts. +HH gives a consistently stronger core for heavy-duty gears, +HL less distortion for thin parts; state the band on the order, not just the grade.
Which grade for what?
16MnCr5 and 20MnCr5 for automotive gears and shafts of moderate section; 18CrNiMo7-6 for large, highly loaded gears (deep-hardening core, good toughness); 20NiCrMo2-2 as the 8620 equivalent; C15E for inexpensive small case-hardened pins. Nickel grades cost more but tolerate direct quenching from the carburizing temperature better.
What does +FP mean?
Delivered with a ferrite–pearlite structure within a stated hardness range — the condition preferred for machining before carburizing because it gives predictable tool life and uniform response in the furnace. +A (annealed) is softer but can machine gummily; +TH is treated to a hardness range by any route.
How is case depth called out with these steels?
By CHD (case hardening depth) per ISO 2639 / ISO 18203 — the depth to 550 HV 1 on a hardness traverse, written for example "CHD 0.8 +0.4" — with surface hardness in HRC or HV and core hardness where it matters, using the drawing conventions of ISO 15787. Carburizing temperature and quench are the heat treater's choice within the informative annex.
ISO 683-3 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 ↗