Grade Designations.
| BS EN 10083-3:2006 | 34CrNiMo6 / 1.6582 |
| BS 970:1991 (withdrawn) | 817M40 / 817M40T |
| AISI/SAE | 4340 |
| DIN | 34CrNiMo6 / 1.6582 |
| JIS | SNCM439 |
Availability & Supply Condition.
T-condition bright rounds: 8–100mm | Normalised bright rounds: 16–100mm | Black rounds: 25–500mm
Supply condition: Bright Drawn in T (Quenched & Tempered) or Normalised condition. Hot Rolled Black available.
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 | Ni | Mo |
|---|---|---|---|---|---|---|---|---|
| 817M40 | 0.36–0.44 | 0.10–0.35 | 0.45–0.70 | 0.04 | 0.04 | 1.00–1.40 | 1.30–1.70 | 0.20–0.35 |
| 34CrNiMo6 | 0.30–0.38 | 0.17–0.37 | 0.50–0.80 | 0.035 | 0.035 | 1.30–1.70 | 1.30–1.70 | 0.20–0.30 |
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 | Size (mm) | Tensile Rm (N/mm²) | Yield Re (N/mm²) | A% min | HB approx |
|---|---|---|---|---|---|
| H&T (T) | ≤16 / >16–40 / >40–63 / >63–100 | 1150 / 1000 / 900 / 800 | ≥900 / ≥800 / ≥700 / ≥600 | 10 / 10 / 11 / 11 | 300–341 |
| Normalised | All | ~860 | ~600 | ~14 | ~248 |
Hardness values: see our hardness conversion table to convert between HRC, HB, HV and tensile strength.
Typical Applications.
- Heavy-duty shafts, axles and spindles
- High-performance gears and pinions
- Aerospace and defence structural components
- Oil and gas downhole and pressure components
- Large forgings and ring-rolled sections
- High-tensile bolting — aerospace grade
- Hydraulic cylinder rods and pistons
Key Benefits.
- Higher strength and toughness than EN19 in large sections
- Good deep hardenability due to nickel content
- 817M40T supplied pre-treated — no further heat treatment required
- Excellent fatigue strength for dynamic loading
- Recognised globally as AISI 4340 / 34CrNiMo6
- Comprehensive size range from stock
Remarks & Guidance.
Welding requires carefully controlled procedures. Preheat to 250–350°C and carry out post-weld heat treatment. For 817M40T (pre-treated bar), the heat treatment has already been applied — bar should not be re-hardened in service. For less demanding applications where cost is important, consider EN19 (708M40).
Relevant Heat Treatment Processes.
This grade responds to the following heat treatment processes. Click any card for temperatures, cooling methods and expected hardness values.
