AFNOR 25CD4 Alloy Steel Chrome Moly Bars

Product Description

AFNOR 25CD4 (commonly referred to in modern standards as 25CrMo4 or material number 1.7218) is a premium, low-alloy structural chrome-moly steel under the French national standardization system.

Characterized by its lower carbon threshold (around 0.25%), 25CD4 is heavily favored in high-performance engineering fields like motorsport, aerospace, and light aircraft construction. It hits a sweet spot that higher-carbon alternatives like 4140 cannot touch: excellent structural weldability paired with massive dynamic fatigue resistance.

Global Equivalents

Because 25CD4 is an industry standard across European precision manufacturing, it aligns with these prominent designations:

• USA (AISI/SAE): AISI 4130 / UNS G41300

• Germany (DIN / WNr): 25CrMo4 / 1.7218

• UK (BS): 708A25

• Japan (JIS): SCM420 / SCM430 variants

• Euronorm: 25CrMo4

Chemical Composition (Typical %)

The modest carbon level makes the alloy considerably less prone to localized cracking during welding, while the chromium and molybdenum ensure deep, uniform heat-treatment properties.

| Carbon (C) | Chromium (Cr) | Molybdenum (Mo) | Manganese (Mn) | Silicon (Si) | Phosphorus (P) | Sulfur (S) |

|---|---|---|---|---|---|

| 0.22% – 0.29% | 0.90% – 1.20% | 0.15% – 0.30% | 0.60% – 0.90% | 0.10% – 0.40% | ≤ 0.025% | ≤ 0.035% |

Mechanical Properties (Quenched & Tempered, +QT)

25CD4 round bars are highly versatile and can be tailored via heat treatment. Below are typical minimum values when supplied or treated in the standard hardened and tempered condition (varying slightly by section diameter $d$):

• Tensile Strength ($R_m$): 700 – 1100 MPa (depending on thickness)

• Yield Strength ($R_{p0.2}$): ≥ 450 – 700 MPa

• Elongation ($A_5$): ≥ 12% – 15%

• Impact Toughness (ISO-V): ≥ 45 – 50 J

• Typical Hardness Range: 200 – 240 HBW (annealed) | up to 300+ HBW (hardened)

Key Technical Advantages

• Superior Weldability: Unlike 42CD4 (AISI 4140), 25CD4 does not necessarily require intensive pre-heating cycles for thinner sections, making it the premier material for complex, multi-joint tubular spaceframes and structures.

• Excellent Strength-to-Weight Ratio: Its high fatigue resistance allows engineers to design thin-walled tubular parts that handle high cyclic loads without adding unnecessary dead weight.

• Nitridation Ready: If localized wear resistance is needed on a component (like a steering knuckle or small shaft), 25CD4 can be nitrided to give it an intensely hard surface layer.

Typical Applications

Due to its outstanding mechanical reliability under vibration and dynamic impacts, 25CD4 alloy bars find a home in demanding structural contexts:

• Motorsport & Aerospace: Welded safety roll cages, spaceframe chassis, go-kart structures, and aircraft engine mounts.

• Automotive Control Parts: Steering knuckles, connection racks, stabilizer bars, and anti-roll assemblies.

• Energy & Mechanical Engineering: High-durability threaded fasteners, turbine rotor pins, and high-pressure structural bolts.