Hydro Turbine Shaft Forgings

1. Specifications & Capability

FUSHUN METAL open-die forges hydro turbine main shafts in 42CrMo4 (1.7225) and 34CrNiMo6 (1.6582) as one-piece bodies, 500-1500 mm in diameter, up to 12 m long and up to 100 t single weight. Ingot capacity spans 4.5-80 t bottom-poured and 36-114 t vacuum-cast, backed by 550 t single-heat refining, giving full coverage for the largest hydro shaft forgings.

The forging ratio is at least 4:1, and the shaft flange is forged integrally with the body to remove weld seams. Properties are verified on body samples or separately forged prolonged test pieces for the largest sections.

Values follow EN 10250-3; for sections above 500 mm and ASTM A668 classes, properties are verified on separately forged prolonged test pieces, with body sampling on request.

2. Components & Service Conditions

These forgings serve as main shafts for Francis (mixed-flow) and Kaplan (axial-flow) turbines, together with their integrally forged main shaft flanges and couplings. The shaft transmits the full hydraulic thrust and torque from the runner to the generator, so it must sustain high bending and torsional loads for decades under continuous operation.

Pumped-storage units impose an additional demand, reversing rotation daily and cycling the shaft through repeated start-stop transients. Forging the flange as part of the body removes weld seams and improves fatigue strength, while the QT treatment with controlled cooling gives uniform through-section toughness and low residual stress. 34CrNiMo6 is preferred where low-temperature toughness at the core of very large sections is specified.

3. Grade Equivalents – 42CrMo4 / 34CrNiMo6

Designation	Standard	Notes
42CrMo4 / 1.7225	EN 10250-3	Primary QT steel
34CrNiMo6 / 1.6582	EN 10250-3	Higher toughness option
ASTM A668 Cl.F	ASTM A668	US carbon/alloy forging
AISI 4340	SAE J404	US equivalent of 34CrNiMo6
SNCM439	JIS G4053	Japanese equivalent
40CrNiMoA / 20SiMn	GB/T 3077	Reference only, not used in certification

The 1.3-1.7% nickel content of 34CrNiMo6 raises hardenability and low-temperature toughness, making it the preferred choice for the largest, most heavily loaded hydro shafts.

4. Manufacturing Process

Steelmaking. FUSHUN METAL melts in an electric arc furnace with ladle refining and vacuum degassing to lower hydrogen, oxygen and sulfur, then casts large ingots up to 114 t. Residual elements are controlled for low-temperature toughness.

Forging. The shaft is forged as a single piece on a 20/80 MN fast forging press with a reduction ratio of at least 4:1, closing central porosity and refining the grain along the shaft axis.

Heat treatment. Quenching and tempering are carried out with controlled heating and cooling to give uniform strength and low residual stress through the 1500 mm section.

Testing. Full-section UT to EN 10228-3, MT on machined surfaces, and mechanical tests with body sampling where specified. FUSHUN METAL documents every heat and every forging step for full traceability from ingot to final machining.

5. Standards & Certification

Hydro turbine shafts are supplied to EN 10250-3 (QT steel forging delivery conditions) and ASTM A668 (carbon and alloy steel forgings), with inspection certificates under EN 10204 3.1 and optional 3.2 third-party inspection.

FUSHUN METAL holds ISO 9001 and AS9120B quality system certification. Related shaft forgings: steam turbine main shafts and wind turbine main shafts.

6. Typical Applications

7. Inquiry Essentials

To quote your hydro turbine main shaft, please provide the shaft diameter and length, the flange requirements, the required grade or strength level, the ultrasonic testing acceptance level, and any body sampling or witness requirements.