Retaining Ring Forgings

1. Specifications & Capability

FUSHUN METAL forges non-magnetic generator retaining rings to ASTM A289, 800-1600 mm in diameter, in the austenitic 18Mn-18Cr-N steel family – X8CrMnN18-18 (1.3816), P900 and XM-19 (S20910). These rings retain the end windings of a generator rotor against centrifugal force, so they combine a fully non-magnetic austenitic structure with a tensile strength of at least 895 MPa.

Strength is developed by cold working after solution treatment, since the austenitic structure cannot be hardened by quenching. Rings are supplied as forgings or cold-expanded to the final strength level, with magnetic permeability verified as essentially unity.

2. Components & Service Conditions

Retaining rings are shrink-fitted over each end of a generator rotor to hold the field winding end-turns against centrifugal force, with the ring itself rotating at 3000-3600 rpm. The ring must be non-magnetic so it does not disturb the magnetic circuit of the machine.

Because conventional hardenable steels are ferromagnetic, retaining rings use a metastable austenitic steel that is strengthened by cold working rather than heat treatment. The 18Mn-18Cr-N composition is fully austenitic at service temperature and retains its non-magnetic character, while the cold work raises the tensile strength above 895 MPa without impairing toughness. Rings are stress-relieved after cold expansion to minimise residual stress.

3. Grade Equivalents – ASTM A289 / X8CrMnN18-18

Designation	Standard	Notes
ASTM A289	ASTM A289	Non-magnetic retaining ring forgings
X8CrMnN18-18 / 1.3816	EN / DIN	European 18Mn-18Cr-N steel
P900	Proprietary	High-nitrogen retaining ring grade
XM-19 / S20910	ASTM A276	Nitronic 50 non-magnetic stainless
50Mn18Cr4	GB/T 1220	Reference only, not used in certification

The high manganese and nitrogen contents stabilise the austenite so the steel remains non-magnetic while cold working develops the required strength.

4. Manufacturing Process

Steelmaking. FUSHUN METAL melts the austenitic steel in an electric arc furnace with refining to keep carbon low and control nitrogen, then casts ingots for ring forging.

Forging. The ingot is upset, pierced and ring-rolled to the required diameter, orienting grain flow circumferentially around the ring.

Hardening. The ring is solution annealed, then cold-expanded to develop the tensile strength above 895 MPa, followed by stress relief.

Testing. UT, tensile tests, and magnetic permeability verification (relative permeability near unity), with full traceability.

5. Standards & Certification

Retaining rings are supplied to ASTM A289 (non-magnetic retaining rings for generators), with inspection certificates under EN 10204 3.1 and optional 3.2 third-party inspection. FUSHUN METAL holds ISO 9001 and AS9120B certification.

Related forging: generator rotors.

6. Typical Applications

7. Inquiry Essentials

To quote your retaining ring, please provide the ring dimensions, the required strength level (Class I or II), the magnetic permeability limit, and any witness or third-party inspection requirements.