Stainless Steel Bearings Complete Handbook: Material Comparison, Accuracy Grades, and Key Technologies

What are stainless steel bearings?

Generally, stainless steel bearings are made from iron-based alloys containing at least 10.5% chromium (Cr) by mass. Their primary function is to resist rust and corrosion.

The key to their corrosion resistance lies in the chromium-rich oxide film (Cr₂O₃) that forms on the surface. This film uniformly covers the metal at a nanoscale thickness, creating a dense and chemically inert protective barrier. It remains stable in oxygen-containing environments and effectively blocks corrosive media, such as water and chloride ions.

More importantly, this protective film has a self-repairing ability. If the surface is scratched, the exposed chromium quickly reacts with oxygen to regenerate the oxide layer, providing a “self-healing” effect that maintains the bearing’s corrosion resistance over time.

What materials are used for stainless steel bearings?

According to their microstructure after heat treatment, stainless steels are mainly classified into martensitic stainless steel (AISI 440C, AISI 420), austenitic stainless steel (AISI 316, AISI 304), and precipitation-hardening stainless steel (AISI 630)

AISI 440C stainless steel bearings 

Supplier Inspection Report — Cixi Baoci Bearing Co., Ltd.

AISI 440C Stainless Steel Raw Material

AISI 440C offers excellent corrosion resistance. After quenching and tempering, it achieves extremely high strength, hardness, and wear resistance.

The Rockwell hardness (HRC) of AISI 440C stainless steel bearings is approximately 58, making it an ideal choice for applications requiring high durability and long service life.

Standard of 440C Stainless Steel and Equivalent Steel Grades

Country	USA	BS & DIN	Japan
Standard	ASTM A276	EN 10088	JIS G4303
Grades	S44004/440C	X105CrMo17/1.4125	SUS440C

Bearing processing procedure: Heat treatment + Grinding + Lapping/Finishing

Bearing accuracy: Approximately 1 micrometer

AISI 420 stainless steel bearings

 

Supplier Inspection Report — Cixi Baoci Bearing Co., Ltd.

AISI 420 Stainless Steel Raw Material

AISI 420 is the most commonly used material for manufacturing stainless steel bearings. It offers mechanical properties and corrosion resistance comparable to those of AISI 440, though its chromium content is slightly lower. After heat treatment, AISI 420 can achieve a hardness of approximately HRC 55, while maintaining a lower material cost compared to AISI 440.

Without surface treatment, the corrosion resistance of AISI 420 is somewhat lower than that of AISI 440. However, with proper surface treatment, AISI 420 bearings can pass a 96-hour neutral salt spray test, providing corrosion resistance that can even exceed that of AISI 440.

Bearing processing procedure: Heat treatment + Grinding + Lapping/Finishing

Bearing accuracy: Approximately 1 micrometer

AISI 316 stainless steel bearings

AISI 316 is a molybdenum-containing austenitic stainless steel. In its annealed condition, it has a Rockwell hardness (HRC) of 25–30. The addition of molybdenum makes AISI 316 especially suitable for high-chloride environments, such as chemical processing and marine engineering applications.

Compared to AISI 304, AISI 316 offers better overall performance, particularly in corrosion resistance, but comes at a higher cost.

Bearing processing procedure: Turning only, no grinding

Bearing accuracy: Approximately 20 micrometers

AISI 304 stainless steel bearings

AISI 304 is the most commonly used austenitic stainless steel, containing 8%–11% nickel and 18%–20% chromium. Its corrosion resistance is lower than that of AISI 316, but higher than that of AISI 440 and AISI 420.

For bearings made from AISI 304, the outer diameter is ground, while the raceways and bore are directly turned without grinding. As a result, the radial clearance of bearings made from 304 or 316 materials cannot be controlled to the micrometer level.

Bearing processing procedure: Turning only, no grinding

Bearing accuracy: Approximately 20 micrometers

AISI 630 stainless steel bearings

AISI 630 is a stainless steel alloy containing chromium, niobium, copper, and nickel. Its common designations include 17-4 PH, PH17-4, and 17Cr-4Ni.

Through solution and aging treatments, AISI 630 achieves high strength and corrosion resistance, with corrosion resistance comparable to that of AISI 304. After heat treatment, its Rockwell hardness (HRC) reaches approximately 40. When both high strength and corrosion resistance are required, AISI 630 is the ideal choice.

The AISI 630 bearings developed by BaoCi Bearing undergo solution treatment at 1050°C, followed by aging treatment at 480°C, resulting in excellent mechanical properties and reliable performance for demanding applications.

Bearing processing procedure: Heat treatment + Grinding + Lapping/Finishing

Bearing accuracy: Approximately 1 micrometer

Advantages of Stainless Steel Bearings

Compared to plastic bearings and ceramic bearings, stainless steel bearings offer the same coefficient of thermal expansion and accuracy as bearing steel, making them an ideal substitute for most applications.

Plastic bearings are limited by their low load capacity, while ceramic bearings are generally unsuitable for applications involving impact loads.

Therefore, for operating temperatures up to 250–300°C, when high rigidity, high load capacity, impact resistance, and corrosion resistance are required, stainless steel bearings are the preferred choice.

Lubrication grease, sealing, tolerance, clearance, and vibration of stainless steel bearings

Grease

Any grease that can be used for bearing steel can also be used for stainless steel bearings. We can also make recommendations based on the customer's operating conditions.

Sealed Bearings

Bearings are generally sealed with metal shields (ZZ) or rubber seals (2RS, 2RZ).

Bearing Tolerance

Bearing tolerance includes both dimensional tolerance and revolving tolerance.

Dimensional tolerance refers to the required deviations when bearings are mounted on shafts or in housings. It covers bore and outer diameter deviations from the basic dimensions, inner ring and outer ring width deviations, and radius allowances. Geometric tolerances also fall under this category, including bore and outer diameter deviations in a single plane, as well as inner ring and outer ring width deviations in a single radial plane.

Revolving tolerance refers to the allowable radial and axial runout of an assembled bearing. This includes the runout of the inner and outer rings, the reference face runout of the inner ring relative to the bore, and the cylindrical surface runout of the outer ring relative to its reference face.

The accuracy of stainless steel bearings is classified into grades P2, P4, P5, P6, and P0, with P2 representing the highest precision and P0 the lowest, suitable for general working conditions.

Bearing clearance

Bearing clearance refers to the amount of displacement of the free (unfixed) ring when it moves relative to the fixed ring, either in the radial or axial direction, before the bearing is mounted on a shaft or in a housing.

Based on the direction of movement, bearing clearance is classified into two types: radial clearance and axial clearance.

Bearing vibration

Bearing vibration refers to the elastic deformation of bearing components that varies over time, as well as any movement that deviates from the theoretical position, except for the motion necessary for the bearing’s function.

Bearing vibration can be measured in two ways: acceleration (dB) and velocity (μm/s).

• Vibration acceleration is assessed using the grades Z, Z1, Z2, and Z3. Grade Z represents the fundamental level, while Z1, Z2, and Z3 indicate progressively higher vibration levels.

• Vibration velocity is measured using the grades V, V1, V2, and V3. Similarly, grade V is the fundamental level, and V1, V2, and V3 indicate successively higher vibration ranges.

In general, velocity measurement is preferred over acceleration measurement because it provides a better indication of the bearing’s manufacturing quality and inherent performance characteristics.

What types of stainless steel bearings are there?

Stainless Steel Deep Groove Ball Bearing

Stainless Steel Angular Contact Bearing

Stainless Steel Double-Row Ball Bearing

Stainless Steel Double-Row Angular Contact Bearing

Stainless Steel Thrust Ball Bearing

Stainless Steel LR Series Bearing

Stainless Steel Self-aligning Ball Bearing

Stainless Steel Inch Size Bearing

Stainless Steel Spherical Ball Bearing

Stainless Steel Tapered Roller Bearing

Stainless Steel Rod End Bearing

Stainless Steel Needle Bearing

Stainless Steel Track Roller

Stainless Steel Flange Bearing

Stainless Steel Linear Bearing

Stainless Steel Pillow Block Bearing

Stainless Steel Coated Bearing

How are the stainless steel bearings of Cixi BaoCi Bearing processed?？

 

Our company is equipped with advanced inspection equipment and the necessary measuring instruments for every stage of production.

Starting with raw materials, we use a spectrometer for material verification.

In the machining workshop, we utilize a roundness tester, roughness tester, contour measuring instrument, 2D measuring instrument, and clearance tester to ensure that all bearing dimensions and accuracy meet customer requirements.

In addition, the noise and rotational accuracy of finished bearings are tested using S910 and BVT instruments.

Please see the flow chart for the detailed process.

How does BaoCi Bearing strictly control the quality of stainless steel bearings?

Our company is equipped with advanced inspection equipment and the necessary measuring instruments for every stage of production. Starting with raw materials, we use a spectrometer for material verification.

In the machining workshop, we utilize a roundness tester, roughness tester, contour measuring instrument, 2D measuring instrument, and clearance tester to ensure that all bearing dimensions and accuracy meet customer requirements.

In addition, the noise and rotational accuracy of finished bearings are tested using S910 and BVT instruments.

Inspection Equipment List

Why Choose BaoCi Bearing? Our Team Introduction

Our core team consists of experienced professionals with many years in the bearing industry. Each member brings expertise in their respective field and works closely together to ensure smooth collaboration.

With a strong focus on teamwork, we are dedicated to the research and development, production, and quality control of high-quality stainless steel bearings. Our combined experience allows us to maintain consistent quality and meet the diverse needs of our customers.