Bearing Steel GCr15 vs SUJ2 vs 100Cr6: Material Comparison for Needle Roller Bearings

time 2026-05-18

Published: May 18, 2026 | Audience: Procurement engineers, bearing application engineers, materials specialists

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TL;DR: GCr15 (China), SUJ2 (Japan), 100Cr6 (Europe), and AISI 52100 (USA) are functionally equivalent high-carbon chromium bearing steels. Differences are in trace impurity limits, deoxidation method, and inclusion rating. For most needle roller bearing applications, all four are interchangeable at the material specification level — but the manufacturing process behind each can vary widely.

1. Chemical Composition Comparison

Element	GCr15 (GB/T 18254)	SUJ2 (JIS G 4805)	100Cr6 (DIN EN ISO 683-17)	AISI 52100 (ASTM A295)
C (Carbon)	0.95-1.05	0.95-1.10	0.93-1.05	0.98-1.10
Si	0.15-0.35	0.15-0.35	0.15-0.35	0.15-0.35
Mn	0.25-0.45	<0.50	0.25-0.45	0.25-0.45
Cr (Chromium)	1.40-1.65	1.30-1.60	1.35-1.60	1.30-1.60
P (max)	0.025	0.025	0.025	0.025
S (max)	0.025	0.025	0.015	0.025
O (Oxygen, ppm max)	15	10 (premium)	10-15	15

All four are 1% carbon, 1.5% chromium steels. The narrow chemistry windows produce comparable martensitic microstructures after hardening.

2. Mechanical Properties After Heat Treatment

Standard treatment: oil quench from 830-860°C + low-temperature temper 150-180°C.

Hardness: HRC 60-65 (all four standards)
Retained austenite: 6-10% target
Surface finish achievable: Ra 0.05-0.2 µm after lapping
Fatigue strength (L10 rolling contact): 4-6 GPa contact stress for 10⁶ cycles

3. Where the Real Differences Lie

While chemistry is nearly identical, the actual bearing fatigue life depends heavily on:

3.1 Steel cleanliness (oxide inclusion content)

Modern bearing steels use vacuum-degassing (VD) or vacuum arc remelting (VAR) to lower oxygen content. Premium SUJ2 from Japanese mills targets <7 ppm oxygen. Standard GCr15 from Chinese mills is typically 10-15 ppm. DW Bearing sources VD-treated GCr15 (<9 ppm) for all automotive-grade products.

3.2 Inclusion rating per ISO 4967 (Method A)

Each non-metallic inclusion is a stress concentrator and potential crack initiation site. Premium steel rating: D-fine <1.0, D-thick <0.5.

3.3 Macrostructure (carbide network, segregation)

Hot rolling + spheroidization controls carbide distribution. Poor spheroidization leaves coarse network carbides that cause premature spalling.

4. Selection Guide by Application

Application	Recommended Grade	Reason
Automotive transmission	GCr15 VD or SUJ2	L10 life requirement, fatigue cleanliness
Power tool gearbox	Standard GCr15	Cost-sensitive, moderate duty cycle
EV traction motor	GCr15 + insulated coating	EDM resistance more important than steel grade
Aerospace	M50 / 52100 VIM-VAR	Higher cleanliness, elevated temperature
Marine / corrosive	440C stainless	Corrosion resistance trumps fatigue rating

5. DW Bearing Steel Sourcing Practice

For ISO/TS 16949 automotive customers, DW exclusively uses GCr15 with: VD or VAR processing, oxygen <9 ppm verified by oxygen analyzer, macrostructure inspected per ISO 4967, mill cert traceability per part lot. For general industrial: standard GCr15 (oxygen 10-15 ppm). All steels purchased from mills with ISO 9001 certification.

6. FAQ

Q1: Can I substitute GCr15 for SUJ2 in a Japanese OEM spec?
Yes for most applications. Confirm steel cleanliness grade with your customer if the part is high-precision or safety-critical.

Q2: What is the equivalent of 100Cr6 in Chinese standard?
GCr15 per GB/T 18254. Chemistry windows overlap fully.

Q3: Why is bearing fatigue life so dependent on cleanliness?
Subsurface oxide inclusions create stress concentrations 2-3x base material. Cracks initiate at these inclusions during rolling contact.