JIS SUJ2 Bearing Steel: Comprehensive Guide to Properties, Uses

If you’re involved in manufacturing, automotive, or precision engineering, you know how crucial high-quality bearing steel is. JIS SUJ2 bearing steel—a Japanese industrial standard alloy—stands out for its exceptional durability and performance in high-stress applications. This guide covers everything from its core properties to real-world uses, helping you decide if it’s the right choice for your project.

1. Material Properties of JIS SUJ2 Bearing Steel

JIS SUJ2’s unique properties make it a top pick for bearings and high-wear components. Let’s break down its key characteristics.

1.1 Chemical Composition

JIS SUJ2 follows strict Japanese Industrial Standards (JIS G4805), ensuring consistent performance. Below is its typical chemical makeup:

1.2 Physical Properties

These properties define how JIS SUJ2 behaves under physical conditions like temperature and magnetism:

• Density: 7.85 g/cm³ (consistent with most carbon-chromium steels)
• Melting Point: 1,420 – 1,460 °C (2,588 – 2,660 °F)
• Thermal Conductivity: 46.0 W/(m·K) at 20 °C (room temperature)
• Coefficient of Thermal Expansion: 11.6 × 10⁻⁶/°C (from 20 – 100 °C)
• Magnetic Properties: Ferromagnetic (attracts magnets), useful for sorting and non-destructive testing.

1.3 Mechanical Properties

Mechanical properties determine JIS SUJ2’s performance under force. All values below are measured after standard heat treatment (quenching and tempering):

1.4 Other Properties

Two key properties make JIS SUJ2 ideal for bearings:

• Wear Resistance: High carbon and chromium form hard carbides, reducing wear from rolling/sliding contact.
• Fatigue Resistance: Withstands millions of load cycles, critical for long-lasting bearings in motors or machinery.
• Corrosion Resistance: Moderate—needs coatings (e.g., zinc plating) for wet/harsh environments (inferior to stainless steel).
• Hardenability: Easy to heat treat to uniform hardness across thick sections, ensuring consistent performance in large parts.

2. Applications of JIS SUJ2 Bearing Steel

JIS SUJ2’s properties make it perfect for components facing repeated stress and wear. Here are its most common uses:

• Bearings: The primary application—including ball bearings, roller bearings, and needle bearings for cars, bikes, and industrial equipment.
• Rolling Elements: Balls, rollers, or needles inside bearings rely on JIS SUJ2’s wear resistance to stay functional.
• Races: Inner/outer rings of bearings (where rolling elements move) are often made from JIS SUJ2.
• Automotive Components: Camshafts, valve lifters, and gearbox parts—all requiring high durability under engine stress.
• Industrial Machinery: Gearboxes, conveyors, and pumps use JIS SUJ2 parts to handle heavy loads and long operating hours.
• Aerospace Components: Small bearings in aircraft landing gear or engine accessories (where reliability and weight matter).
• Medical Devices: Precision bearings in MRI machines or surgical tools (thanks to its magnetic properties and strength).
• Electrical Motors: Bearings in electric motors (e.g., for appliances or industrial motors) benefit from its fatigue resistance.

3. Manufacturing Techniques for JIS SUJ2

Producing JIS SUJ2 requires precise steps to meet JIS standards. Here’s the typical process:

1. Steelmaking:
   • Most JIS SUJ2 is made via Electric Arc Furnace (EAF) (for scrap steel recycling) or Basic Oxygen Furnace (BOF) (for iron ore-based production). The goal is to adjust chemical composition to match JIS G4805 requirements.
2. Rolling:
   • After steelmaking, the metal is Hot Rolled (1,100 – 1,200 °C) into billets or bars to shape it. For precision parts, it’s then Cold Rolled (room temperature) to improve surface finish and dimensional accuracy.
3. Heat Treatment:
   • Critical for JIS SUJ2’s performance:
     • Quenching: Heat to 820 – 860 °C, then rapid cooling in oil/water to harden the steel.
     • Tempering: Reheat to 150 – 200 °C to reduce brittleness while maintaining high hardness.
     • Carburizing: Sometimes used for parts needing a hard outer layer (e.g., gear teeth)—heat in a carbon-rich atmosphere to add surface carbon.
4. Machining:
   • Post-heat treatment, parts are machined to final shapes using Turning (for cylindrical parts like bearing races) or Grinding (for ultra-smooth surfaces, essential for bearing performance).
5. Surface Treatment:
   • Optional steps to enhance performance:
     • Nitriding: Adds a hard surface layer to boost wear resistance.
     • Blackening: Creates a protective oxide layer to prevent minor rust.
6. Quality Control:
   • Inspections include:
     • Chemical analysis (to verify element content).
     • Hardness testing (Rockwell/Vickers machines).
     • Non-destructive testing (ultrasonic testing for internal cracks).
     • Dimensional checks (calipers/CNC tools to ensure fit).

4. Case Studies: JIS SUJ2 in Action

Real-world examples show how JIS SUJ2 solves industry problems.

Case Study 1: Electric Motor Bearing Durability

A manufacturer of industrial electric motors faced frequent bearing failures (after 8,000 hours of use). They switched from a low-grade steel to JIS SUJ2 bearings. Post-switch, bearing life extended to 20,000 hours, reducing maintenance costs by 40%.

Case Study 2: Automotive Bearing Failure Analysis

A Japanese carmaker noticed bearing failures in their compact car engines (after 60,000 km). Testing revealed the original bearings used a non-standard steel. Switching to JIS SUJ2 bearings cut failure rates by 75%, with bearings lasting 150,000 km.

5. JIS SUJ2 vs. Other Bearing Materials

How does JIS SUJ2 compare to other common bearing materials? The table below breaks it down:

Yigu Technology’s Perspective on JIS SUJ2

At Yigu Technology, JIS SUJ2 is a go-to for clients in automotive and electrical motor industries. Its balance of wear resistance, fatigue strength, and cost-effectiveness is unmatched for most bearing needs. We pair JIS SUJ2 with precision machining to make parts that last 15-20% longer than standard steel options. For harsh environments, we offer custom nitriding or zinc plating to boost its corrosion resistance, meeting strict client requirements.

FAQ About JIS SUJ2 Bearing Steel

1. Can JIS SUJ2 be used in wet or corrosive environments?
   JIS SUJ2 has moderate corrosion resistance. For wet/harsh environments (e.g., marine or food processing), apply a protective coating like zinc plating or nitriding to prevent rust.
2. What surface treatments work best for JIS SUJ2?
   Nitriding enhances wear resistance, while zinc plating boosts corrosion resistance. Blackening is a low-cost option for minor rust protection in dry environments.
3. How does JIS SUJ2 compare to 100Cr6?
   They are nearly identical! JIS SUJ2 is the Japanese standard, and 100Cr6 is the European (EN) standard. Both have the same carbon (0.95–1.05%) and chromium (1.30–1.65%) content, so they’re interchangeable in most applications.