High strength non-magnetic forgings. Resistant to stress corrosion cracking.
Introduction
Our company has been developing and manufacturing retaining rings since the 1970s. In the early stages, we produced retaining rings using 50Mn18Cr5 and 50Mn18Cr4WN materials, with specifications for units below 200MW and an annual production of approximately 300 pieces. After 2000, we began developing retaining rings using 1Mn18Cr18N material.
To date, we have produced over 6,000 retaining rings of various specifications using 50Mn18Cr5, 50Mn18Cr4WN, and 1Mn18Cr18N (commonly known as “18-18”) materials. Among these, more than 800 pieces are “18-18” retaining rings. Our product range covers more than twenty specifications from 3MW to 1000MW series. The strength has achieved Grade 8, the highest requirement in ASTM A289, with yield strength reaching 1430MPa.
Our products are widely used by domestic generator equipment manufacturers and exported to world.
Material Characteristics
It is Chromium, Manganese steel; a high strength steel that is non-magnetic and resistant to stress corrosion cracking. This material is commonly referred to as 18-18 steel forging due to the steel type being an example of X8CrMnN18-18 (18 percent being the nominal percentage of Chromium and Manganese).
We manufacture the following dimensions:
- Weight: 40 – 4300 kg
- Diameter: 100 – 2200 mm
Applications
Nonmagnetic retaining rings are specialized metal rings made from stainless steel or high-strength steel, designed to protect internal weak magnetic metal materials from external magnetic field interference. They are crucial components in turbine generators, serving as high-strength, non-magnetic, metallic ring structures that secure and hold the rotor winding ends against centrifugal forces. To prevent alternating magnetic field losses, these retaining rings must be manufactured using non-magnetic materials.
Main applications include:
- Turbine generators
- High-speed locomotive motors
- Battery backplates
- Aerospace
- Electronics
- Medical equipment
Standards
- ASTM A289: Alloy Steel Forgings for Nonmagnetic Retaining Rings
- JB/T 1268: Mn18Cr5 Series Nonmagnetic Retaining Ring Forgings for Turbine Generators
- JB/T 7030: Mn18Cr18N Nonmagnetic Retaining Ring Forgings for Turbine Generators
- JB/T 50196: 3MW~600MW Generator Nonmagnetic Retaining Ring Alloy Steel Forgings
- SEW 390: Non-magnetizable Steels; Technical Delivery Conditions
Chemical Component
| Grade | C | Mn | Si | P | S | Cr | N | Ni | W |
|---|---|---|---|---|---|---|---|---|---|
| ASTM A289 | 0.10 max | 17.50～20.00 | 0.80 max | ≤0.060 | ≤0.015 | 17.50～20.00 | 0.45～0.80 | 2.00 max | — |
| 1.3816
X8CrMnN18-18 |
0.12 max | 17.50～20.00 | 1.00 max | ≤0.060 | ≤0.030 | 17.50～20.00 | 0.45～0.70 | 1.00 max | — |
| Alloy P900 | 0.12 max | 17.50～20.00 | 0.80 max | ≤0.050 | ≤0.015 | 17.50～20.00 | ≥0.50 | — | — |
| 1Mn18Cr18N | 0.12 max | 17.50～20.00 | 0.80 max | ≤0.050 | ≤0.015 | 17.50～20.00 | ≥0.47 | — | — |
| 50Mn18Cr5 | 0.40～0.60 | 17.00～19.00 | 0.30～0.80 | ≤0.060 | ≤0.025 | 3.50～6.00 | — | — | — |
| 50Mn18Cr5N | 0.40～0.60 | 17.00～19.00 | 0.30～0.80 | ≤0.060 | ≤0.025 | 3.50～6.00 | ≥0.08 | — | — |
| 50Mn18Cr4WN | 0.40～0.60 | 17.00～19.00 | 0.30～0.80 | ≤0.060 | ≤0.025 | 3.00～5.00 | ≥0.08 | — | 0.70～1.20 |
Manufacturing Process
Electric furnace melting, vacuum degassing, ESR electroslag remelting, solution treatment at 1050°C, low-temperature forging, rough forging, rough machining, cold expansion, precision machining, finally obtaining the nonmagnetic retaining ring.
The steel is produced in an electric furnace and undergoes a refining process before being cast into an ingot. The chemical composition of the steel is checked during the molten stage, to ensure the quality prior to the ingot being formed. The ingot is then hot-forged into the approximate required shape prior to an initial machining operation to produce a uniform forging. Heat treatment then gives the material its strength characteristics, which are further increased by a highly specialised cold expanding technique. The stresses that have developed in the forging by the preceding processes are then removed by further heat treatment.
At this point a sample of the forging, normally a 25mm square section ring, is machined from one end of the ring for the necessary mechanical and quality checks to be carried out. Final machining to the customer’s requirements finishes the forging. The sample ring is cut up into small segments and further machined to produce test pieces for Tensile Tests, Impact Tests, Hardness Tests, Chemical Analysis, Grain Structure and Magnetic Permeability tests. The final machined forging also undergoes Dye Penetrant Testing to detect any surface defects on all surfaces, as well as 100% Ultra Sonic Testing to detect any material defects with in the forging.
Inspection & quality control
Every forging manufactured by FUSHUN METAL is fully inspected by our inspectors and when accepted given a coat of anti-rust protection and packed for transport. Every forging is supplied with a certificate of conformity and dimensional report. The certificate of conformity contains the results of all the mechanical tests, chemical analysis and heat treatment cycles. NTD and test reports will be also provided.
Non-destructive testing (NDT)
- Surface Defects: 100% Surface Area by Dye Penetrant Method
- Internal Defects: 100% of the forging by Ultra Sonic Testing.
