SUJ2 vs 100Cr6 – Composition, Heat Treatment, Properties, and Applications
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Table Of Content
Table Of Content
Introduction
SUJ2 and 100Cr6 are two industry-recognized designations for high‑carbon, high‑chromium bearing steels used worldwide for rolling elements, rings, and other wear‑resistant components. Engineers, procurement managers, and manufacturing planners commonly face the choice between these grades when specifying bearing components, shafts, or wear parts where hardenability, surface finish, and dimensional stability under rolling contact are critical.
The practical selection dilemma typically centers on regional standardization and supply chain (Japanese vs European design/spec practices), versus metallurgical equivalence—both grades are intended for the same application space but are governed by different standards and manufacturing tolerances. This article compares standards, chemistry, microstructure, heat treatment response, mechanical performance, fabrication issues, and application guidance so technical professionals can make an informed choice.
1. Standards and Designations
- SUJ2: Japanese Industrial Standard (JIS) designation commonly cited as JIS G4805 SUJ2. Equivalent to AISI 52100 in many respects.
- 100Cr6: European Standard EN designation (EN 100Cr6). Also referenced as 1.3505 in the EN numeric system.
- AISI/ASTM equivalents: AISI 52100 is commonly treated as equivalent to both SUJ2 and 100Cr6 for many bearing applications.
- GB (China): Typically supplied under Chinese GB equivalents for bearing steels, which align closely to these chemistries.
Classification: Both SUJ2 and 100Cr6 are high‑carbon, chromium alloyed bearing steels (non‑stainless, tool/rolling contact steels). They are not stainless steels nor HSLA grades.
2. Chemical Composition and Alloying Strategy
The following table summarizes typical composition ranges for SUJ2 and 100Cr6. Values are given as mass percent and represent common specification ranges; specific suppliers’ certificates should be consulted for exact limits.
| Element | SUJ2 (typical range, wt%) | 100Cr6 (typical range, wt%) |
|---|---|---|
| C | 0.95 – 1.10 | 0.95 – 1.05 |
| Mn | 0.25 – 0.45 | 0.25 – 0.45 |
| Si | 0.15 – 0.35 | 0.15 – 0.35 |
| P | ≤ 0.03 – 0.04 | ≤ 0.03 – 0.04 |
| S | ≤ 0.03 – 0.04 | ≤ 0.03 – 0.04 |
| Cr | 1.30 – 1.60 | 1.30 – 1.65 |
| Ni | ≤ 0.30 (trace) | ≤ 0.30 (trace) |
| Mo | ≤ 0.08 (generally none) | ≤ 0.08 (generally none) |
| V, Nb, Ti, B, N | typically not specified or present at trace levels | typically not specified or present at trace levels |
How alloying affects performance: - Carbon: Primary hardenability and martensite hardness contributor; ~1.0% C enables high hardness and high abrasive wear resistance after quench and temper. - Chromium (~1.3–1.6%): Increases hardenability and contributes to wear resistance and tempering stability; not high enough to confer stainless corrosion resistance. - Mn/Si: Deoxidation and strength contributors; Mn also aids hardenability. - Low levels of P/S are controlled for fatigue performance and inclusion control.
Overall alloy strategy: maximize achievable hardness and wear resistance via a high carbon plus modest chromium content while keeping chemistry simple to control inclusions and fatigue life.
3. Microstructure and Heat Treatment Response
Typical microstructures: - Annealed/soft‑annealed condition: predominantly spheroidized carbides in a ferritic matrix for good machinability. This is the preferred starting microstructure for forming and machining. - Quenched and tempered: martensitic matrix with fine, dispersed chromium carbides; provides high hardness and wear resistance. Through‑hardening is typical for bearing rings and balls up to certain section sizes. - Case hardened variants: less common for these grades; carburizing is generally not used since the steel already contains high carbon.
Effect of processes: - Normalizing (above A3 and air cooling) refines grain size and can produce more uniform hardenability prior to final hardening. - Quenching (oil or air, depending on section size and required hardness) transforms austenite to martensite. For thicker sections or when reduced distortion is required, interrupted quenching or austempering variants may be used. - Tempering reduces brittleness while retaining high hardness; tempering temperature controls the final HRC and toughness trade‑off. Lower tempering temperatures yield higher hardness and lower toughness; higher tempering increases toughness at the cost of hardness.
Differences between SUJ2 and 100Cr6 in microstructure tuning are mainly procedural (heat‑treatment cycles, quench media, and manufacturing tolerances) rather than chemistry‑driven.
4. Mechanical Properties
Mechanical properties depend strongly on heat treatment and section size. The table below provides indicative ranges for annealed and through‑hardened conditions; use as a reference and verify with supplier data sheets or tensile testing.
| Property | Annealed (typical) | Through‑hardened (quenched & tempered) typical |
|---|---|---|
| Tensile Strength (MPa) | ~600 – 900 (annealed) | often >1500 (hardened martensite; can exceed 2000 MPa depending on hardness) |
| Yield Strength (MPa) | ~300 – 600 (annealed) | >1200 (hardened) |
| Elongation (%) | ~10 – 20 (annealed) | ~1 – 6 (hardened) |
| Impact Toughness (Charpy, J) | moderate (annealed, application dependent) | low to moderate (high hardness reduces toughness) |
| Hardness | ~HB 180–260 (annealed) | ~58 – 66 HRC (typical for bearing applications) |
Which is stronger/tougher/more ductile: - Both SUJ2 and 100Cr6 exhibit very similar mechanical response because their chemistries are essentially equivalent. Through‑hardened martensite provides high strength and hardness but at the expense of ductility and impact toughness; annealing produces a softer, more ductile structure for machining and forming.
5. Weldability
High carbon (~1.0%) makes these grades poor candidates for conventional welding without pre‑ and post‑weld treatments. Key considerations: - High carbon content increases the risk of hard, brittle martensite formation in the heat‑affected zone (HAZ) and raises susceptibility to cold cracking. - Hardenability driven by Cr and Mn further increases HAZ hardness.
Useful weldability indices: - Carbon equivalent (IIW): $$ CE_{IIW} = C + \frac{Mn}{6} + \frac{Cr+Mo+V}{5} + \frac{Ni+Cu}{15} $$ - A more comprehensive Pcm: $$ P_{cm} = C + \frac{Si}{30} + \frac{Mn+Cu}{20} + \frac{Cr+Mo+V}{10} + \frac{Ni}{40} + \frac{Nb}{50} + \frac{Ti}{30} + \frac{B}{1000} $$
Interpretation: - Both formulas indicate that with C ≈ 1.0 and measurable Cr, $CE_{IIW}$ and $P_{cm}$ values will be elevated relative to low‑carbon steels, signaling a need for preheating, low hydrogen procedures, and post‑weld tempering. For critical components, welding is normally avoided; mechanical joining, machining, or designing for separable parts is preferred.
6. Corrosion and Surface Protection
- These grades are non‑stainless; chromium at ~1.3–1.6% improves corrosion resistance slightly versus plain carbon steels but is insufficient to call them corrosion resistant.
- Common protection measures: painting, oiling, phosphating, or electroplating; galvanizing is possible for some subcomponents but not common for precision rolling elements.
- PREN (pitting resistance equivalent number) is not applicable in a meaningful way because PREN is used for stainless grades with substantially higher Cr, Mo, and N: $$ \text{PREN} = \text{Cr} + 3.3 \times \text{Mo} + 16 \times \text{N} $$
- For bearing components exposed to corrosion, surface treatments such as hard chrome plating or DLC coatings are frequent, or a switch to stainless bearing steels (e.g., AISI 440C or martensitic stainless bearings) is specified.
7. Fabrication, Machinability, and Formability
- Machinability: Best in annealed (spheroidized) condition—high‑speed machining of quenched hard components requires carbide tooling and slow feeds. SUJ2/100Cr6 in annealed state machines comparably to AISI 52100.
- Grinding and finishing: Precision grinding is common for rolling elements and rings after heat treatment; good carbide or CBN tooling is used on hardened parts.
- Forming/bending: Limited in hardened condition; parts intended to be formed should be formed in annealed state and then finish‑machined and heat treated.
- Surface finishing: Achieving low surface roughness and high dimensional accuracy is critical for bearing life; fine grinding and superfinishing are standard.
8. Typical Applications
| SUJ2 (JIS) typical uses | 100Cr6 (EN) typical uses |
|---|---|
| Precision balls, rollers, small bearings, shafts and spindles for Japanese‑market machinery | Rolling element bearings (balls, rollers, rings), shafts, precision wear components in European market |
| Small to medium‑sized bearing components for automotive and industrial equipment | High‑precision bearings for machine tools, automotive transmissions, and heavy industry |
| Components where JIS standard documentation and supplier chain are required | Components requiring EN/European standard traceability and supply chain alignment |
Selection rationale: choose these grades for rolling contact parts where high hardness, good fatigue strength, and predictable wear behavior are required. Selection between SUJ2 and 100Cr6 is frequently driven by regional standards, supplier qualification, and traceability requirements rather than metallurgical performance.
9. Cost and Availability
- Both grades are commodity bearing steels with wide global availability in bars, rings, strip, and precision‑ball forms.
- Regional differences: SUJ2 is commonly stocked in Asia and by Asian suppliers; 100Cr6 is standard in Europe. In many markets, AISI 52100 is the common commercial name.
- Cost: Generally comparable; price differences are more likely due to form (bar, ring, ball), surface finish, and required heat treatment/processing rather than intrinsic chemical differences.
10. Summary and Recommendation
Summary table (qualitative):
| Attribute | SUJ2 | 100Cr6 |
|---|---|---|
| Weldability | Poor (high C, require preheat/post‑heat) | Poor (similar to SUJ2) |
| Strength–Toughness tradeoff | High hardness/strength achievable; moderate to low toughness when hardened | Equivalent behavior; depends on heat treatment |
| Cost & Availability | Widely available in Asia; competitive pricing | Widely available in Europe; competitive pricing |
Recommendations: - Choose SUJ2 if your supply chain, specifications, or component acceptance are JIS‑based, or if you source primarily from Japanese or Asian suppliers who stock SUJ2 product forms and certifications. - Choose 100Cr6 if you require EN/European standard documentation, traceability, or are operating within European procurement practices and supplier networks.
Practical guidance: - For critical bearing parts, specify the grade plus required heat treatment, hardness range, surface finish tolerance, and fatigue testing requirements—these processing details matter more to performance than the minor differences between SUJ2 and 100Cr6 chemistry. - Avoid welding on components made from these steels unless weld procedure qualification, appropriate preheat, low hydrogen consumables, and post‑weld tempering are part of the process specification.
In short: metallurgically SUJ2 and 100Cr6 are equivalent for most bearing and wear applications; choose based on standards, supplier availability, and processing specifications rather than expecting major intrinsic performance differences.