Alloy Steel 40NiMoCr10-5 Round Bar 40NiMoCr10-5 Bars & Rods

Product Description

Since 40NiMoCr10-5 is the exact alphanumeric EN/DIN designation for the material number 1.6745 we just looked at, you are dealing with the exact same ultra-high-strength, deep-hardening aerospace and heavy-engineering alloy steel.

Because it is widely traded under both the name 40NiMoCr10-5 and the British Standards BS S99 / 826M40 (EN26), here is a practical guide on procurement specifications, sizing tolerances, and machining advice for these bars and rods.

📐 Standard Sizing & Supply Conditions

When sourcing 40NiMoCr10-5 round bars and rods, they are typically processed to specific surface finishes and structural conditions depending on how you plan to machine them:

Common Surface Finishes

• Black Hot-Rolled / Forged: Features a dark oxide scale from the mill. Best if you plan to do heavy rough-machining or further forging.

• Peeled / Bright Turned: The outer scale is mechanically removed, offering tighter dimensional tolerances and making it ready for automated CNC lathe work.

• Cold Drawn / Ground: Provided with smooth, highly precise outer diameter tolerances, ideal for high-precision machining or direct use as shafts.

Delivery States

• Soft Annealed (+A): Supplied at a lower hardness (typically under 250 HB). This is the best state to buy if your parts require intricate, heavy milling or deep drilling before you perform your own final quenching and tempering.

• Quenched and Tempered (+QT): Pre-hardened at the mill to its signature 1000–1200 MPa tensile strength range. Buying it "+QT" eliminates the risk of part distortion or cracking during your own heat treatment, though it is tougher on your cutting tools.

⚙️ Quick Technical Snapshot (40NiMoCr10-5)

💡 Practical Machining & Fabrication Tips

• Tooling for Pre-Hardened (+QT) Bars: If you are turning 40NiMoCr10-5 in its pre-hardened state, utilize rigid machine setups, heavy-duty carbide tooling, and constant, sulfurized cutting oils or high-pressure coolants to manage heat build-up and prevent work-hardening.

• Managing Hydrogen Embrittlement: If your finished 40NiMoCr10-5 components are destined for acid-pickling, heavy electroplating, or phosphating, they must be baked immediately afterward (typically around $190^\circ\text{C}$ to $210^\circ\text{C}$) to drive out trapped hydrogen and prevent catastrophic brittle fracturing under load.

• Avoid Conventional Welding: Due to the high alloy content, welding creates an incredibly brittle martensitic zone next to the weld. If a component must be repaired or joined, strict preheating to around $300^\circ\text{C}$ is necessary, followed immediately by a controlled post-weld stress relief or full re-tempering cycle.