100Cr6 (1.3505) is the standard choice for bearing components with cross-sections below 30–40 mm and service temperatures under 120 °C. 100CrMo7-3 (1.3536) is required when cross-sections exceed 40–80 mm, service temperatures reach 150–200 °C, or for wind turbine bearings and large slewing rings — its molybdenum addition raises the ideal critical quench diameter from ~30 mm to ~80 mm, enabling uniform through-hardness that 100Cr6 cannot achieve at large sections. Both comply with ISO 683-17. Jiangsu Liangyi Co., Limited supplies EN 10204 type 3.1 mill test reports with every delivery.
Jiangsu Liangyi Co., Limited holds ISO 9001:2015 Quality Management System certification. EN 10204 type 3.1 mill test reports are supplied with every delivery; type 3.2 with third-party inspector co-signature is available on request. EN 10204 is an inspection document standard — not a company certification.
Engineering Decision Summary: Both 100Cr6 (1.3505) and 100CrMo7-3 (1.3536) are ISO 683-17 through-hardening bearing steels. 100CrMo7-3's molybdenum addition raises the ideal critical quench diameter from ~30 mm to ~80 mm — making it the correct specification for large bearing rings, wind turbine bearings, and elevated-temperature service up to 200 °C. 100Cr6 remains the proven default for sections below 30 mm.
Grade Overview Section 01
100Cr6 (EN material number 1.3505, also known as AISI 52100, GCr15, and SUJ2) is a high-carbon chromium through-hardening bearing steel containing approximately 1.0% carbon and 1.5% chromium, standardized under ISO 683-17. 100CrMo7-3 (1.3536) is the molybdenum-enhanced variant, with 0.20–0.35% Mo added to extend hardenability to large-section forgings beyond the capability of 100Cr6.
Engineers frequently treat 100Cr6 as the universal bearing steel — and for small-section, room-temperature bearing components, that instinct is correct. But when the part cross-section grows beyond 30 mm, when the service temperature climbs toward 200 °C, or when dimensional stability under cyclical load becomes non-negotiable, the single-alloying-element limitation of 100Cr6 becomes apparent. That is precisely where 100CrMo7-3 was engineered to step in.
The world's most widely produced bearing steel. High carbon (~1.0% C) and moderate chromium (~1.5% Cr) deliver exceptional surface hardness and rolling-contact fatigue resistance in sections up to 30 mm. Cost-effective and universally available on global markets.
The engineered upgrade for large sections. Molybdenum (0.20–0.35%) and elevated manganese raise the ideal critical quench diameter from ~30 mm to ~60–80 mm — the ISO 683-17 standard choice for large bearing rings, slewing rings, and wind turbine main shaft bearings.
Chemical Composition Section 02
The critical difference between 100Cr6 and 100CrMo7-3 is molybdenum (0.20–0.35%) in 100CrMo7-3. Molybdenum suppresses the bainite nose on the TTT diagram, slowing transformation speed during oil quenching and enabling the core of a large forged ring to reach full martensite hardness before the quench front passes.
| Element | 100Cr6 (1.3505) | 100CrMo7-3 (1.3536) | Metallurgical Role |
|---|---|---|---|
| Carbon (C) | 0.93–1.05 % | 0.93–1.05 % | Hardness; carbide formation |
| Silicon (Si) | 0.15–0.35 % | 0.40–0.65 % | Deoxidation; temper stability |
| Manganese (Mn) | 0.25–0.45 % | 0.50–0.80 % | Hardenability; Ms point shift |
| Chromium (Cr) | 1.35–1.65 % | 1.65–1.95 % | Carbide stability; mild corrosion resistance |
| Molybdenum (Mo) | — (absent) | 0.20–0.35 % | Deep hardenability; bainite nose suppression |
| Phosphorus (P) max | 0.025 % | 0.025 % | Impurity limit |
| Sulfur (S) max | 0.015 % | 0.015 % | Inclusion cleanliness limit |
Source: ISO 683-17:2014. Actual heat chemistry reported in EN 10204 type 3.1 mill test report with each delivery.
100CrMo7-3's higher silicon (0.40–0.65% vs 0.15–0.35%) shifts the lower bainite formation region, improving resistance to temper softening above 120 °C — a direct benefit in wind turbine pitch and yaw ring bearings where frictional heat generation is significant.
Mechanical Properties Section 03
After optimal heat treatment — hardening plus low-temperature tempering at 150–180 °C — both steels achieve similar surface hardness in small sections. The divergence is decisive at larger sections, where 100Cr6's hardenability is exhausted and core hardness drops below the minimum required for subsurface fatigue resistance.
Heat Treatment Parameters Section 04
Both steels follow similar hardening sequences, but the recommended temperature windows differ to account for 100CrMo7-3's higher alloy content. Precise control is especially critical for large-section forgings where thermal gradients affect microstructure uniformity.
| Process Step | 100Cr6 (1.3505) | 100CrMo7-3 (1.3536) |
|---|---|---|
| Soft Annealing | 750–800 °C, slow cool | 750–800 °C, slow cool |
| Spheroidizing Anneal (pre-machining) | 780–820 °C, cycle/isothermal | 790–830 °C, cycle/isothermal |
| Austenitizing (hardening) | 830–860 °C | 840–870 °C |
| Quench Media | Oil or polymer | Oil, polymer, or air (small sections) |
| Tempering Temperature | 150–180 °C | 150–200 °C |
| Target Hardness after Q+T | 60–64 HRC (≤30 mm) | 60–64 HRC (≤80 mm) |
| Stress Relief Anneal (forgings) | 650–680 °C, air cool | 650–680 °C, air cool |
Temperatures are furnace setpoints. All heat treatment records are documented and included in the delivery package.
Rolling Contact Fatigue Life Section 05
For bearing steels, material selection ultimately resolves to one question: how long will the part survive under cyclic Hertzian contact stress? The accepted metric is L10 life — the operating hours at which 10% of a bearing population will have failed by subsurface fatigue initiation. Three material factors directly control this:
- Carbide size and distribution — Coarse, banded carbides act as crack initiation sites. Forging with a minimum forge ratio of 4:1 mechanically breaks up this network.
- Steel cleanliness — Oxygen and sulfide inclusions nucleate subsurface fatigue cracks. Both grades are triple-refined via EAF + LF + VD melting to minimize inclusion content.
- Through-hardness uniformity — At sections above 30 mm, 100CrMo7-3's hardenability advantage produces 20–40% higher L10 fatigue life by ensuring uniformly hardened martensite across the entire cross-section.
For a wind turbine main bearing ring with 250 mm OD and 80 mm wall thickness, specifying 100Cr6 instead of 100CrMo7-3 can result in core hardness of only 35–42 HRC — far below the 58+ HRC required at the subsurface rolling zone. This is a documented failure mode in premature wind turbine bearing fatigue.
Temperature Limits & Temper Stability Section 06
Through-hardened bearing steels are metastable: held in their hardened state only because there is insufficient thermal energy for carbide coarsening and martensite decomposition. When operating temperatures exceed the original tempering temperature, the material begins to over-temper and hardness drops irreversibly.
| Condition | 100Cr6 (1.3505) | 100CrMo7-3 (1.3536) |
|---|---|---|
| Normal maximum service temperature | 150 °C | 200 °C |
| Hardness drop onset (prolonged exposure) | ~120 °C | ~160 °C |
| Suitable for sealed / lubricated bearings | Yes — to ~120 °C | Yes — to ~160 °C |
| Wind turbine main bearing (>80 mm section) | ❌ Not recommended | ✅ Standard specification |
| Automotive wheel bearing hub (≤40 mm) | ✅ Standard choice | ⚠️ Not typically required |
Machinability, Weldability & Cost Section 07
Machinability in the Annealed Condition
Both grades are supplied in spheroidized-annealed condition for rough machining before hardening. 100Cr6's lower silicon (0.15–0.35%) gives it a marginal machinability advantage — tooling wear rates are slightly lower and surface finish is more consistent in high-volume automated turning operations.
Weldability
Neither steel is intended for welding. Both have carbon equivalents well above 0.50, making them highly susceptible to hydrogen-induced cold cracking in the heat-affected zone. If welding is unavoidable in a repair context, controlled pre-heat (≥150 °C), low-hydrogen filler, and immediate post-weld stress relief are essential.
Relative Material and Forging Cost
100CrMo7-3 carries a price premium of approximately 8–18% over 100Cr6 bar stock, driven primarily by molybdenum raw material costs. However, for large bearing rings where 100Cr6 cannot achieve the required through-hardness, premature bearing failure and unplanned downtime costs dwarf material price differences by orders of magnitude.
Application Guide Section 08
100Cr6 — Best Applications
Ball and roller bearing rings up to ~80 mm OD. Automotive wheel bearing hubs, water pump bearings, spindle bearings. Machine tool spindles. Small-section precision shafts, pins, cam followers, tappets, punching dies, and gauging tools.
100CrMo7-3 — Best Applications
Large bearing rings above 80 mm OD — wind turbine pitch, yaw, and main shaft bearings. Slewing rings for cranes and excavators. Mill roll necks. Railway axle bearing journals. Large rolling mill work rolls. Gear unit bearings with elevated operating temperatures.
100Cr6 — Key Industries
Automotive drivetrain, suspension, and transmission. Machine tools and industrial equipment. Precision instruments. Agricultural machinery. Electric motors. Conveyor systems.
100CrMo7-3 — Key Industries
Wind energy — main bearings, pitch/yaw rings. Mining and heavy industry. Steel mill rolling equipment. Railway infrastructure. Marine propulsion. Large industrial gearboxes. Offshore oil & gas rotating equipment.
Selection Matrix Section 09
Use this matrix at specification stage. Any row showing ⚠️ or ❌ for 100Cr6 should prompt evaluation of 100CrMo7-3 before committing to a grade.
| Criterion | 100Cr6 (1.3505) | 100CrMo7-3 (1.3536) |
|---|---|---|
| Section size ≤ 30 mm | ✅ Preferred | ✅ Acceptable |
| Section size 30–80 mm | ⚠️ Verify core hardness | ✅ Preferred |
| Section size > 80 mm | ❌ Not recommended | ✅ Required |
| Operating temp. ≤ 120 °C | ✅ Suitable | ✅ Suitable |
| Operating temp. 120–200 °C | ❌ Over-tempering risk | ✅ Suitable |
| Wind turbine bearing | ❌ Not specified | ✅ Industry standard |
| Cost sensitivity (small parts) | ✅ 8–18% lower cost | ⚠️ Higher material cost |
| High-volume automotive | ✅ Standard choice | ⚠️ Overspecified |
| ISO 683-17 compliance | ✅ Yes | ✅ Yes |
| EN 10204 type 3.1 mill test report | ✅ Standard delivery | ✅ Standard delivery |
| EN 10204 type 3.2 (third-party) | ✅ On request | ✅ On request |
| UT per EN 10228-3 | ✅ Standard protocol | ✅ Standard protocol |
Forging Considerations Section 10
Both grades are forgeable, but their high carbon content demands careful process control. The most common defects are carbide network reformation due to slow post-forge cooling, and surface cracking from excessive temperature drop during working.
Forging Temperature Window
Recommended forging start temperature: 1,050–1,100 °C. Minimum finish temperature: 850 °C. Our 2,000T to 6,300T hydraulic presses maintain sufficient forging force to work both grades consistently above this threshold.
Post-Forge Cooling and Annealing
Controlled slow cooling after forging prevents reformation of a continuous Widmanstätten carbide network at prior austenite grain boundaries. Post-forge annealing at 780–820 °C produces the spheroidized carbide microstructure required for both machinability and optimal hardening response.
Non-Destructive Testing
All forged bearing steel components undergo ultrasonic testing (UT) per EN 10228-3 and magnetic particle inspection (MPI) per EN 10228-1. For bearing rings above 200 mm OD, 100% volumetric UT scanning is performed as standard.
If 100Cr6 is the correct specification for your application, you can view our full range of 100Cr6 forged rings, bars, discs and seamless rolled rings — including available dimensions, delivery forms, and how to request a quote.
Engineering Verdict Section 11
- Part cross-section is below 30–40 mm
- Operating temperature stays below 120 °C
- High-volume automotive or consumer application
- Material cost is a primary specification driver
- Application is a ball, small roller, or needle bearing
- Broad global stock availability required
- Section thickness exceeds 40–80 mm in any dimension
- Operating temperature reaches 150–200 °C
- Wind turbine, crane, or heavy-industry slewing ring
- Uniform through-hardness is a fatigue prerequisite
- Failure consequence cost far exceeds material price
- Guaranteed core hardness across variable wall thickness
The rule most bearing engineers apply: if the wall thickness exceeds 30 mm, start the specification with 100CrMo7-3 and work backward only if cost constraints genuinely preclude it — not the other way around. The fatigue life and failure consequence mathematics almost always favour the upgrade.
Frequently Asked Questions FAQ
- ISO 683-17:2014 — Heat-treated steels, alloy steels and free-cutting steels — Part 17: Ball and roller bearing steels (ISO)
- EN 10204:2004 — Metallic products — Types of inspection documents (CEN)
- EN 10228-3 — Non-destructive testing of steel forgings — Part 3: Ultrasonic testing of ferritic or martensitic steel forgings
- EN 10228-1 — Non-destructive testing of steel forgings — Part 1: Magnetic particle inspection
- ISO 9001:2015 — Quality management systems — Requirements (ISO)
- Aggarwal, N. et al. (2024). GEO: Generative Engine Optimization. Princeton University / arXiv:2311.09735
Published: · Jiangsu Liangyi Co., Limited · Jiangyin, Jiangsu, China✓ July 2026