Steel 35CD4 - 1.7220 - 34CrMo4 - 35CrMo4 - FE-PL1503

General Introduction to the 35CD4 Steel Alloy

35CD4 steel is a low-alloy construction steel containing chromium and molybdenum, belonging to the so-called “Chromnile” (Cr-Mo) family. It offers high strength, toughness, and excellent heat treatability, making it suitable for parts subjected to significant mechanical or thermal stress.

From a standards perspective, 35CD4 (AFNOR, with specification AIR 9160/C) is also referred to as 34CrMo4 (EN 10083-3) or 1.7220 (WNr) in Germany. In the United States, its equivalent is 4135 (AISI/SAE).

Mechanical Properties, Heat Treatment, and Weldability

Depending on the heat treatment applied, 35CD4 steel can achieve a tensile strength of up to 1320 MPa and a yield strength above 740 MPa. It is particularly valued for its resilience (> 500 kJ/m²) and its hardness (> 217HB). The significant variation in tensile strength largely depends on the various treatment methods used, whether for bars or tubes.

This grade is generally selected for its quenching and tempering capabilities. Oil quenching, performed at around 850  to  930 °C, is followed by controlled cooling and then tempering, which helps to fine-tune the final hardness and reduce internal stresses.

Initially, 35CD4 exhibits a fine, homogeneous ferrite-perlite structure; after quenching, it transforms into martensite, which tempering subsequently converts into sorbite or troostite depending on the temperature and duration of the process.

35CD4 demonstrates weldability that is considered rather… delicate. To minimize the risk of cracking, it is recommended to preheat the steel (between 200 and 300 °C) and then apply a stress relief or tempering treatment after welding to manage internal stresses.

Industrial Applications

Thanks to its excellent mechanical properties, 35CD4 is commonly used for parts:

• Subject to high mechanical loads: crankshafts, connecting rods, gears, transmission shafts, rotors, etc.
• Operating at moderate temperatures (up to around 500–525 °C): boilers, gas turbines, jet engines, bolting in refineries or power plants, etc.
• Exposed to high pressure: gas cylinders, pressure vessels, drilling pipes (down to about 2,000 m in some cases).
• Used in transmission components: gears for locomotives, turbine shafts, gear reducers, etc.

This alloy is therefore widely employed in various industries (mechanical, petrochemical, railway, aeronautical…) to produce critical parts. For use in corrosive environments or at very high temperatures, more specialized grades are required (e.g., stainless steels or superalloys).