Alloy Steel 1.6745 Round Bar 1.6745 Bars 1.6745 Rods

Product Description

1.6745 (European designation: 40NiMoCr10-5) is a premium, high-strength, ultra-high-hardenability nickel-chromium-molybdenum alloy steel. In engineering and commercial trade, it is most widely recognized under the British aerospace standards BS S99 (and its high-tensile sibling BS S98) as well as BS 970 826M40 (formerly EN26).

Because of its high nickel and molybdenum content, 1.6745 possesses outstanding through-hardening capabilities, ensuring uniform mechanical properties even in heavy, large-diameter cross-sections.

Here is the technical profile for 1.6745 alloy bars, round bars, and rods:

⚙️ Chemical Composition (%)

The high concentration of alloying elements—specifically Nickel, Chromium, and Molybdenum—combats temper brittleness while maximizing toughness and fatigue resistance under cyclic loads.

🌍 International Equivalents & Cross-References

• Werkstoff Number: 1.6745

• EN / DIN Standard: 40NiMoCr10-5

• British Standards (UK): BS S99, BS S98, 826M40, EN26

• USA / AISI Equivalent: Closely relates to AISI 4340 / 4330V variants, but 1.6745 features a distinctly higher molybdenum content for superior deep-hardening resistance.

💪 Mechanical Properties (Typical in Quenched & Tempered Condition)

When supplied in the fully hardened and tempered (+QT) state—the typical delivery condition for high-integrity components—1.6745 achieves formidable mechanical strength:

• Tensile Strength ($R_m$): $1000 - 1200 \text{ MPa}$ (Up to $1230 \text{ MPa}$ under strict aerospace compliance)

• Yield Strength ($R_e$): $\ge 850 \text{ MPa}$

• Elongation ($A_5$): $\ge 12\%$

• Hardness: Typically 293 – 352 HB (Brinell)

• Property Retention: Features high structural integrity and excellent creep resistance at elevated operating temperatures, alongside reliable notch toughness at low temperatures.

🛠️ Typical Applications

Given its premium, "aircraft-quality" pedigree, 1.6745 round bars and rods are chosen for high-stress structural components where failure is not an option:

• Aerospace & Defense: Landing gear assemblies, critical structural airframe parts, high-stress brackets, struts, and engine mounts.

• Heavy Power Transmission: High-torque shafts, heavy-duty gears, drive pinions, and high-load transmission axles.

• Industrial Fasteners: High-tensile, safety-critical structural bolts and specialized clamping hardware exposed to extreme fatigue conditions.

📐 Processing & Supply Characteristics

• Through-Hardening Capability: Can cleanly through-harden in nominal thicknesses up to 6 inches ($152.4\text{ mm}$), ensuring the center core matches the outer surface's strength.

• Machinability: Best machined in the annealed condition. When supplied in the pre-hardened and tempered (+QT) condition, carbide or high-performance tooling is required due to its high hardness.

• Welding: Welding is generally not recommended due to the high carbon and alloy content, which risks cold cracking. If unavoidable, specialized preheating, post-weld heat treatment (PWHT), and stress-relieving are mandatory.