34CrNiMo6 Steel in the Wind Power Industry

34CrNiMo6 can be through-hardened in sections up to approximately 250 mm diameter when oil quenched. Beyond this size, the core cooling rate becomes insufficient for full martensitic transformation, and mechanical properties degrade toward the center.

For sections with a diameter greater than 250 mm, steel grades with higher hardenability should be considered, such as 30CrNiMo8 (1.6580).

These two grades serve different purposes. 34CrNiMo6 is a medium-carbon through-hardening steel used primarily for shafts and through-hardened gears, achieving 300–360 HB after QT. 18CrNiMo7-6 is a low-carbon carburizing grade designed for case-hardened gears — it produces a very hard wear-resistant case (58–62 HRC) with a tough, ductile core.

For wind turbine gearbox gears subject to high contact stresses and pitting risk, 18CrNiMo7-6 is generally preferred. For shafts, couplings, and gears where through-hardening is sufficient, 34CrNiMo6 is the more economical choice.

34CrNiMo6 is used in offshore wind turbine components, but it is not inherently corrosion-resistant. For offshore applications, components are protected by coatings (epoxy or polyurethane paint systems), grease, or sealed environments.

The grade’s primary advantage in offshore turbines is its mechanical performance,high fatigue strength and low-temperature toughness ,rather than corrosion resistance. Where components are directly exposed to salt spray, stainless steel or coated carbon steel is used for external surfaces, while 34CrNiMo6 remains the choice for internal load-bearing shafts.

Induction hardening of 34CrNiMo6 typically produces surface hardness of 50–55 HRC, with case depths ranging from 2 to 8 mm depending on the induction frequency and power settings.

This is commonly applied to bearing journals, seal surfaces, and gear teeth. After induction hardening, a low-temperature temper at 150–200 °C is applied to relieve residual stresses without significantly reducing surface hardness.

Yes, but welding requires careful preheat and post-weld heat treatment due to the grade’s high carbon and alloy content, which makes it susceptible to cold cracking. Preheat to 200–300 °C, use low-hydrogen electrodes, and perform post-weld stress relieving at 600–650 °C.

For wind turbine main shafts, welding on the primary load path is generally avoided — the shaft is forged as a single piece. Welding is limited to non-critical attachments such as brackets or lifting lugs.

34CrNiMo6 steel is suitable for induction hardening processes.

For 34CrNiMo6 steel, induction hardening is typically applied after an initial quenching and tempering treatment to establish a strong and tough core structure. The subsequent localized induction hardening, followed by low-temperature tempering, produces a deep hardened case with beneficial compressive residual stresses. This combination significantly enhances wear resistance and fatigue strength, making the process a preferred surface‑strengthening method for critical heavy‑duty components such as large gears and crankshafts.

34CrNiMo6 steel can be used to manufacture wind turbine main shafts.

34CrNiMo6, a high-hardenability alloy structural steel, delivers excellent strength-toughness balance and fatigue resistance after quenching and tempering. It is capable of withstanding the sustained alternating loads, torsional forces and impact loads acting on wind turbine main shafts during service, meeting the operational requirements of megawatt-class wind turbines and serving as a reliable material solution for wind turbine shaft manufacturing.Learn More

34CrNiMo6 steel is wear-resistant, but not the most wear-resistant.

As an alloy structural steel, the wear resistance of 34CrNiMo6 mainly comes from the high hardness/high strength after quenching and tempering heat treatment, which is sufficient to meet the conventional heavy-load, low-wear requirements of components such as gears and heavy-duty shafts.

The surface hardness of 34CrNiMo6 after quenching and tempering did not reach the high wear resistance level, which could not meet the stringent wear resistance requirements of high load and high friction. Therefore, it is necessary to add a surface strengthening process (surface quenching, nitriding) to further improve its surface hardness and wear resistance performance.

Both 34CrNiMo6 and 30CrNiMo8 are high-strength alloy structural steels under the European standard system. As an upgraded version of 34CrNiMo6, the increased proportion of alloying elements in 30CrNiMo8 leads to a targeted improvement in performance:

• Higher toughness: especially significantly improved low-temperature impact toughness and fracture toughness.
• Stronger impact and fatigue resistance: better able to withstand sudden loads and repeated alternating stresses.
• Better hardenability: enables the core of larger cross-section parts to achieve excellent mechanical properties after heat treatment.

Therefore, 34CrNiMo6, due to its excellent strength-toughness balance, is the most versatile high-strength alloy steel, fully meeting the needs of most conventional heavy-duty components. 30CrNiMo8, with its upgraded performance, is even more suitable for core components with larger cross-sections, higher loads, and extremely stringent safety and reliability requirements.Learn More