Turbine Main Shaft Forgings

1. Specifications & Capability

42CrMo4 (1.7225) and AISI 4140 are the workhorse quenched and tempered (QT) alloy steels for industrial steam turbine main shafts. FUSHUN METAL open-die forges these shafts as single-piece bodies from vacuum-degassed ingots of 4.5-80 t bottom-poured or 36-114 t vacuum-cast weight on a 20/80 MN fast forging press, delivering 500-1000 mm diameter sections up to 12 m long and 100 t single weight.

The forging ratio is at least 4:1, which closes the cast structure, refines the grain and orients the metal flow along the shaft axis. Mechanical properties are verified on body samples or separately forged prolonged test pieces, so results represent the actual delivered section rather than a coupon.

Values follow EN 10250-3 for the 42CrMo4 QT condition; for sections above 500 mm and for ASTM A668 classes, properties are agreed and verified on separately forged prolonged test pieces. Body sampling is available on request.

2. Components & Service Conditions

These forgings serve as integral main shafts for industrial steam turbines and small turbine units, where the shaft transmits the full steam torque from the blading to the driven machine. FUSHUN METAL forges the coupling and thrust flanges as part of the shaft body, eliminating weld seams and preserving a continuous grain flow along the load path.

Service conditions combine sustained temperatures up to roughly 500 C, steady bending stress and torsional vibration. Under these loads the dominant failure mechanisms are high-cycle fatigue and long-term creep, both of which are governed by internal soundness and grain size. A forged shaft therefore offers three to five times the fatigue life of an equivalent casting, since forging closes porosity, refines the as-cast structure and eliminates shrinkage and gas defects that initiate cracks. The QT treatment provides the uniform through-section strength and low residual stress the turbine requires.

3. Grade Equivalents – 42CrMo4 / AISI 4140

Designation	Standard	Notes
42CrMo4 / 1.7225	EN 10250-3	European QT steel, preferred
AISI 4140	SAE J404	US equivalent
C45E / 1.1191	EN 10083-2	Plain carbon option
SCM440	JIS G4105	Japanese equivalent
42ChMA	GOST 4543	Russian equivalent
40Cr	GB/T 3077	Reference only, not used in certification

The chromium and molybdenum additions give 42CrMo4 its deep hardenability and temper resistance; C45E is offered where lower strength and simpler heat treatment are acceptable. FUSHUN METAL helps you select the grade against the shaft’s strength class and section size.

4. Manufacturing Process

Steelmaking. FUSHUN METAL melts in an electric arc furnace followed by ladle refining and vacuum degassing, which lowers hydrogen, oxygen and sulfur and removes non-metallic inclusions that would otherwise shorten fatigue life. Residual elements are controlled to reduce temper embrittlement in large sections.

Forging. The ingot is upset and drawn on a 20/80 MN fast forging press with a reduction ratio of at least 4:1. This closes the central porosity, breaks up the coarse cast structure and orients the grain flow along the shaft axis for maximum bending and torsional fatigue resistance.

Heat treatment. The shaft is quenched and tempered to the ordered strength and toughness, with careful control of the heating and cooling rates to achieve uniform hardness and low residual stress through the section.

Testing. Every shaft is subjected to full-section UT to EN 10228-3 and MT on machined surfaces, plus hardness and metallographic checks, with body sampling where specified. Each heat is fully traceable from ingot to final machining.

5. Standards & Certification

Turbine main shafts are supplied to EN 10250-3 (technical delivery conditions for quenched and tempered steel forgings) and ASTM A668 (general requirements for carbon and alloy steel forgings), with inspection certificates under EN 10204 3.1. A 3.2 certificate with third-party inspection is available on request.

FUSHUN METAL holds ISO 9001 and AS9120B quality system certification and can provide body sampling, additional non-destructive testing and witness points to the turbine maker’s specification. Related shaft forgings: wind turbine main shafts, hydro turbine shafts and gearbox shafts.

6. Typical Applications

7. Inquiry Essentials

To quote your turbine main shaft, please provide the shaft drawing with diameter and length, the required strength class or hardness range, the ultrasonic testing acceptance level, the applicable standard or ASTM A668 class, and any body sampling or third-party inspection requirements.