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Stainless Bearing Steel
BRAND: PROMISTEEL
GRADES: 440C, 440B, 9Cr18, 9Cr18Mo, 1.4125, SUS440C
SHAPES: Round Bar, Wire Rod, Seamless Tube
DELIVERY CONDITION: EAF+LF+VD+(ESR), Annealed, Ground/Polished
SURFACE: Centerless Ground, Peeled, Pickled
HARDNESS: Annealed ≤269 HB; Quenched ≥58 HRC
FEATURE: High Hardness + Corrosion Resistance
APPLICATION: Food Machinery, Medical Bearings, Fishing Reels, Knives
MOQ: 25 Tons
Stainless Bearing Steel is a specialized high-carbon martensitic stainless steel designed for applications requiring both high hardness and corrosion resistance. Unlike standard chrome steel (52100), which rusts easily, Stainless Bearing Steel creates a protective passivation layer that resists water, steam, mild acids, and food products.
Our primary grade, AISI 440C (1.4125 / 9Cr18), contains high chromium (~17%) and carbon (~1.0%). This unique composition allows it to be heat-treated to a hardness of 58-60 HRC, matching the wear resistance of tool steels while providing the rust protection needed for food processing equipment, medical instruments, and marine applications.
Product Specifications & Grade Equivalents
We supply high-purity Stainless Bearing Steel suitable for manufacturing precision miniature bearings and corrosion-resistant components.
Table-1
Compare global standards for martensitic stainless bearing steel.
International Grade Comparison |
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| GB (China) | ASTM / AISI (USA) | DIN (Germany) | JIS (Japan) | Characteristics |
| 9Cr18 | 440C | 1.4125 (X105CrMo17) | SUS440C |
Highest Hardness & Wear Resistance |
| 9Cr18Mo | 440C (Mod) | 1.4112 (X90CrMoV18) | SUS440C |
Added Molybdenum for Pitting Resistance |
| 8Cr17 | 440B | 1.4109 (X65CrMo14) | SUS440B |
Improved Toughness, Lower Hardness |
| 11Cr17 | - | - | - |
High Carbon for Knives & Bearings |
Table-2
High chromium content ensures corrosion resistance.
Chemical Composition (Mass Fraction %) |
|||||||
| Grade | C | Cr | Mo | Mn | Si | P | S |
| 440C / 9Cr18 | 0.95~1.20 | 16.00~18.00 | 0.40~0.75 | ≤1.00 | ≤1.00 | ≤0.04 | ≤0.03 |
| 1.4125 | 0.95~1.20 | 16.00~18.00 | ≤0.80 | ≤1.00 | ≤1.00 | ≤0.04 | ≤0.03 |
| 9Cr18Mo | 0.95~1.05 | 17.00~19.00 | 0.40~0.70 | ≤0.80 | ≤0.80 | ≤0.035 | ≤0.03 |
Table-3
Precision ground bars for Swiss lathe machining.
Supply Range & Formats |
|||
| Product Form | Dimensions (mm) | Delivery Condition | Surface Quality |
| Round Bar | Dia: 2.0 - 150 | Annealed / Quenched |
Centerless Ground / Peeled |
| Wire Rod | Dia: 2.0 - 16 | Annealed / Cold Drawn |
Pickled / Polished |
| Seamless Tube | OD: 10 - 80 | Cold Rolled / Annealed |
Pickled / Polished |
Key Features and Advantages
- Dual Performance: It is one of the few steels that offers the wear resistance of bearing steel combined with the corrosion resistance of stainless steel.
- High Hardness: capable of achieving 58-60 HRC after heat treatment, making it suitable for high-load bearings (unlike 304 stainless which is too soft).
- Environment Suitability: Excellent resistance to fresh water, steam, crude oil, gasoline, and alcohol.
- Magnetic Property: Being a martensitic structure, 440C is ferromagnetic (magnetic), which allows it to be held by magnetic chucks during grinding operations.
- ESR Quality Available: For critical medical or high-speed applications, we offer Electro-Slag Remelted (ESR) steel for ultra-low inclusion levels and superior polishability.
Typical Applications
Stainless Bearing Steel is essential where standard lubrication is difficult or where hygiene is strict:
Food & Beverage Industry
Bearings in conveyor belts, mixers, and filling machines that undergo frequent washdowns.
Medical Devices
Surgical instruments (scalpels, clamps) and precision bearings in medical scanners (MRI/CT).
Marine & Fishing
Ball bearings in high-end fishing reels and marine hardware exposed to salt spray.
Chemical Processing
Valves, nozzles, and pump shafts handling mild chemicals.
High-End Cutlery
Because of its edge retention, 440C is also a classic steel for high-quality knives.
FAQ
Q1: Is 440C stainless steel magnetic?
A1: Yes. This is a common misunderstanding. Unlike 304 or 316 (Austenitic) stainless steel, which is non-magnetic, 440C is martensitic. It must be magnetic to be heat-treatable and achieve the high hardness required for bearings.
Q2: How does 440C compare to 52100 (GCr15)?
A2: 440C offers excellent rust resistance but has a slightly lower load-carrying capacity and fatigue life compared to the cleaner 52100. Use 440C only when corrosion is a concern. Use 52100 for general industrial load-bearing applications.
Q3: Can I weld 440C steel?
A3: No. 440C has a very high carbon content (~1%). It is considered "non-weldable" because it will almost certainly crack during air cooling after welding. It is designed for machined parts, not welded structures.
Q4: What is the difference between 440C and 9Cr18?
A4: They are technically equivalent. 440C is the ASTM (USA) standard, while 9Cr18 is the GB (China) standard. Their chemical composition overlaps, and they offer identical performance in hardness and corrosion resistance.
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