Material Guide – 42CrMo4 Alloy Steels

The properties and delivery conditions of 42CrMo4 steel are regulated by several international standards, ensuring consistency and reliability of the material quality.

• EN 10083-3 (42CrMo4): This European standard specifies the technical delivery conditions for heat-treatable alloy steels. It details the chemical composition and mechanical properties of 42CrMo4 in various heat-treated states. In the designation, "42" refers to the approximate carbon content (0.42%), "CrMo" to the chromium and molybdenum alloying, and "4" to the chromium content (approx. 1%).

• EN 10277: This standard applies to the technical delivery conditions for bright steel products, which is relevant for precision bars (e.g., f7 tolerance).

• DIN EN 10204:2005-01 – 3.1 Inspection Certificate (Inspection Certificate 3.1): This standard specifies the types of inspection documents for metallic products. The 3.1 type certificate (manufacturer's inspection certificate) contains the results of the manufacturer's own tests and formally certifies the product's compliance with the order requirements. This certificate ensures the full traceability of the material.

• AISI / SAE 4140: This is the American identifier for the European equivalent 42CrMo4. Their chemical compositions and areas of application are very similar.

• ISO 9227 NSS (Neutral Salt Spray test): This international standard describes the neutral salt spray corrosion test, which aims to assess the corrosion resistance of materials.

The alloy of 42CrMo4 steel is carefully balanced to ensure optimal mechanical properties after heat treatment. The table below compares the typical limit values according to the EN 10083-3 standard and the characteristic values found in practice, indicating the role of the alloying elements.

Chemical Composition (typical values according to EN 10083-3 standard and values found in practice, %):

For hydraulic rods made of 42CrMo4 steel, surface treatment, specifically hard chrome plating, is crucial. This process not only provides excellent corrosion resistance but also further increases the surface hardness and wear resistance.

• Chromium layer thickness: A chromium layer thickness of 20-30 µm provides optimal protection against external environmental influences and mechanical stresses.

• Chromium hardness: The typical value of 900-1100 HV (Vickers hardness) is extremely high, significantly contributing to the rod's wear resistance and lifespan.

• Corrosion resistance: Chrome-plated surfaces show excellent resistance to salt spray tests (according to ISO 9227 NSS), often for a minimum of 200 hours, which indicates the high corrosion protection capability of the chrome coating. This is essential for the long-term operational safety of hydraulic systems in wet or corrosive environments.

42CrMo4 steel, and especially its quenched, tempered, induction-hardened, and chrome-plated versions, are widely used in hydraulics and pneumatics, as well as in other industries where outstanding mechanical properties are required:

• Piston rods for hydraulic cylinders: The most important application area, where high strength, surface hardness, wear resistance, and corrosion protection are essential.

• Linear motion systems: Guide rails, columns, shafts, where precise movement and wear resistance are critical.

• Agricultural and construction machinery: High-load components, hydraulic components.

• Mechanical engineering components: Shafts, gears, transmission parts, where fatigue strength and hardness are important.

• Pneumatic systems: Piston rods for larger, more robust pneumatic cylinders.

The machinability of 42CrMo4 steel depends on its heat treatment condition.

• In +QT (Quenched and Tempered) condition: The steel shows good machinability, although due to its higher hardness, carbide tools and appropriate machining parameters are necessary. Good chip removal and cooling are important.

• In +QT+IH (Induction Hardened) condition: The surface is extremely hard (HRC 50-60), so traditional machining is only possible after removing the induction-hardened layer. Machining the surface (e.g., grinding, honing) requires special procedures to achieve the desired surface roughness and dimensional accuracy, especially because of the chrome-plated layer.

42CrMo4 steel, like all steel products, is 100% recyclable. This contributes to the conservation of resources and the reduction of environmental impact. The chrome coating can be removed with appropriate recycling processes, ensuring the material's return to the circular economy. The long service life of the material in hydraulic systems also reduces the need for frequent replacements and thus the ecological footprint.