18CrNiMo7-6 Steel
Cr-Ni-Mo case-hardening steel for heavy gears
Typical values for the temper in the title
18CrNiMo7-6 (old name 17CrNiMo6) is the case-hardening steel for the heaviest loads. Nickel and molybdenum give a very strong and tough core even in large sections, and good shock resistance.
It is used for heavy gears in industrial gearboxes, wind turbines, mining equipment and heavy vehicles. It costs more than Mn-Cr steels, so it is chosen when they are not enough.
Mechanical and physical properties
| Property | Value | Note |
|---|---|---|
| Tensile strength Rm | 1080–1320 MPa (core, typical) | |
| Yield strength Rp0.2 | ≥785 MPa (core, typical) | |
| Elongation A | ≥8% | |
| Hardness | ≤229 (annealed) | |
| Modulus of elasticity E | 210 GPa | |
| Density ρ | 7.85 g/cm³ | |
| Machinability | 58% | relative rating in the site database |
Chemical composition (wt %)
| Element | Range | Role |
|---|---|---|
| C carbon | 0.15–0.21 | tough core |
| Cr chromium | 1.50–1.80 | hardenability |
| Ni nickel | 1.40–1.70 | core toughness |
| Mo molybdenum | 0.25–0.35 | hardenability in large sections |
| Mn manganese | 0.50–0.90 | |
| Fe iron | balance |
Ranges per EN 10084.
Conditions and heat treatment
Case-hardening steels are supplied annealed or normalized for machining, and get their final properties only after carburizing and hardening. Table values are for the core, and depend strongly on section size.
| Condition | Properties | When to choose it |
|---|---|---|
| Annealed (+A) / treated for machinability (+FP) | soft, easy to machine | machining before case hardening |
| Carburized, hardened and tempered | case HRC 58–62, tough core | the finished part |
Applications
- Gears in industrial gearboxes
- Wind turbine gears
- Mining equipment
- Heavy vehicles
- Heavily loaded shafts
Fabrication
Case hardening (carburizing)
Carburize at about 880–950 °C to the required case depth, quench and temper at about 150–200 °C. Case depth is set by the tooth load.
Machining
Most machining is done before case hardening. After it, precision surfaces are ground.
Distortion
Case hardening causes small distortion and dimensional change. Leave grinding allowance.
Compared with similar materials
| Material | Rm / Rp0.2 | Welding | When it is the better choice |
|---|---|---|---|
| 9310 | 1035–1380 / 795–1100 MPa | Good | American 9310: Ni-Cr-Mo for aerospace · material page |
| 20MnCr5 | ≥960 MPa (core, typical) / ≥645 MPa (core, typical) | Good — before case hardening | 20MnCr5: cheaper, for medium sections · material page |
| 4340 | 1080–1470 / 970–1380 MPa | Difficult — Preheat 200C | 4340: a QT steel, not for case hardening · material page |
Common mistakes
Choosing it where a Mn-Cr steel is enough
It is more expensive because of the nickel.
Welding without preheat
The high hardenability increases cracking risk.
Using it without case hardening
It is meant to be case hardened.
Equivalents, standards and supply
| DIN | 1.6587 |
|---|---|
| BS | 820A16 |
| Standards | EN 10084 / ISO 683-3 |
| Forms | bar · forging |
| Producers | Ovako · Saarstahl |
Learn more
Values are typical and for comparison only, and depend strongly on condition and diameter. For design, rely on the standard and on the mill certificate. Sources: SAE J403 and J404, ASTM A29, A322 and A519 (composition), producer data sheets, and the METAL HUB materials database.
Updated: October 31, 2026