Grade Designations.
| BS EN 10085:2001 | 31CrMo12 / 1.8515 |
| BS 970:1991 (withdrawn) | 722M24 |
| DIN | 31CrMo12 / 1.8515 |
| ISO | 31CrMo12 |
| Alt. designation | 32CrMo12 / 1.7361 (some suppliers) |
| AISI/SAE | No direct equivalent — closest 4140 Mod. |
Availability & Supply Condition.
Bright Rounds (Q+T): 20–100mm | Black Rounds: 22–300mm
Supply condition: Bright Drawn or Hot Rolled Black in the Q+T (pre-treated) condition, ready for nitriding.
Cut to length from 1 piece — −0/+2mm standard tolerance — 2–3 day turnaround — Cutting service details ›
Chemical Analysis.
Values shown as percentages by weight (% wt). Values are ranges unless stated as maxima.
| Designation | C | Si | Mn | P max | S max | Cr | Mo |
|---|---|---|---|---|---|---|---|
| 722M24 | 0.20–0.28 | 0.10–0.40 | 0.40–0.70 | 0.04 | 0.04 | 2.80–3.30 | 0.45–0.65 |
| 31CrMo12 | 0.26–0.34 | 0.10–0.40 | 0.40–0.70 | 0.035 | 0.035 | 2.50–3.00 | 0.30–0.50 |
For full chemical analysis with heat number, request an EN 10204 3.1 material test certificate when ordering — available on all alloy grades. Certificate types explained ›
Mechanical Properties.
Values shown for standard supply condition. Properties vary by section size and heat treatment condition.
| Condition | Tensile Rm (N/mm²) | Yield Re (N/mm²) | A% min | Surface HV (after nitriding) |
|---|---|---|---|---|
| Q+T (pre-nitride) | ~850–1000 | ~650–800 | ~12 | — |
| After gas nitriding (5–8 hr) | — | — | — | ~700–850 HV |
Hardness values: see our hardness conversion table to convert between HRC, HB, HV and tensile strength.
Typical Applications.
- Nitrided shafts — gearboxes and machine tools
- Hydraulic cylinder rods (nitrided finish)
- Precision crankshafts
- Gear flanks subject to surface fatigue
- Cam followers and cams
- Precision spindles for machine tools
Key Benefits.
- Extremely hard case (65–70 HRC equiv.) achievable by nitriding
- Minimal dimensional change — no quenching required
- Excellent fatigue resistance due to compressive surface stresses
- High chromium provides good corrosion resistance after nitriding
- Pre-treated supply condition — no core treatment needed before nitriding
Remarks & Guidance.
Must be in Q+T condition before nitriding. Core properties established at this stage. Gas nitriding at 500–530°C for 20–80 hours produces case depth of 0.15–0.6mm. Ion (plasma) nitriding also suitable. Welding is difficult — preheat to 200–300°C and post-weld heat treat if essential.
Relevant Heat Treatment Processes.
This grade responds to the following heat treatment processes. Click any card for temperatures, cooling methods and expected hardness values.
