JIS SUS440C Stainless Bearing Steel: Properties, Uses & Comparison

If you’re dealing with wet, corrosive, or sanitary environments—like food processing or marine applications—standard bearing steel just won’t cut it. JIS SUS440C stainless bearing steel solves this problem: it’s a martensitic stainless steel that combines exceptional corrosion resistance with the wear resistance needed for bearings. This guide breaks down its key properties, real-world uses, manufacturing process, and how it stacks up against other materials, helping you pick the right steel for tough, wet conditions.

1. Material Properties of JIS SUS440C Stainless Bearing Steel

JIS SUS440C’s unique mix of high carbon and chromium makes it stand out: it resists rust and handles wear. Let’s dive into its properties.

1.1 Chemical Composition

JIS SUS440C follows strict Japanese Industrial Standards (JIS G4303), ensuring consistent performance. Below is its typical chemical makeup:

1.2 Physical Properties

These properties describe how JIS SUS440C behaves under physical conditions like heat and magnetism:

• Density: 7.75 g/cm³ (slightly less than standard carbon bearing steels)
• Melting Point: 1,450 – 1,480 °C (2,642 – 2,696 °F)
• Thermal Conductivity: 25.0 W/(m·K) at 20 °C (lower than carbon steels—common for stainless grades)
• Coefficient of Thermal Expansion: 10.5 × 10⁻⁶/°C (from 20 – 100 °C)
• Magnetic Properties: Ferromagnetic (attracts magnets)—unlike non-magnetic austenitic stainless steels (e.g., AISI 304).

1.3 Mechanical Properties

JIS SUS440C’s mechanical strength comes from heat treatment (quenching + tempering). Below are typical values:

1.4 Other Properties

JIS SUS440C’s key traits solve real-world problems:

• Corrosion Resistance: Excellent—resists water, salt spray, and mild chemicals. Perfect for marine or food processing (outperforms standard steels like JIS SUJ2).
• Wear Resistance: On par with carbon bearing steels (e.g., GCr15) thanks to high carbon content.
• Hardenability: Good—achieves uniform hardness across thick parts, so large bearings perform consistently.
• Dimensional Stability: Minimizes distortion during heat treatment, critical for precision parts like bearing races.
• Martensitic Structure: Yes—this structure (formed during quenching) gives it both hardness and magnetism, unlike austenitic stainless steels.

2. Applications of JIS SUS440C Stainless Bearing Steel

JIS SUS440C shines in environments where rust and wear are both concerns. Here are its top uses:

• Bearings: Corrosion-resistant bearings in food mixers, marine pumps, and chemical agitators—where water or chemicals would ruin standard steel.
• Rolling Elements: Balls/rollers in wet bearings (e.g., washing machine bearings or boat engine bearings).
• Races: Inner/outer rings of bearings in sanitary equipment (e.g., pharmaceutical mixers) that need frequent cleaning.
• Automotive Components: Bearings in car washes or undercarriages (exposed to salt, water, and dirt).
• Industrial Machinery: Bearings in wastewater treatment pumps, humid factory equipment, and chemical processing gear.
• Aerospace Components: Small bearings in aircraft fuel systems (resisting fuel and moisture).
• Medical Devices: Bearings in surgical tools and sterilizable equipment (can handle autoclaving).
• Food Processing Equipment: Bearings in conveyors, dough mixers, and filling machines—meets food safety standards (e.g., FDA).
• Marine Applications: Bearings in boat engines, propeller shafts, and deck gear (fights saltwater corrosion).
• Chemical Processing Equipment: Bearings in acid tanks, solvent pumps, and chemical mixers.

3. Manufacturing Techniques for JIS SUS440C

Making JIS SUS440C requires care to keep both corrosion and wear resistance intact. Here’s the process:

1. Steelmaking:
   • JIS SUS440C is made using an Electric Arc Furnace (EAF) with argon oxygen decarburization (AOD). This controls carbon (for hardness) and ensures enough chromium (for corrosion resistance).
2. Rolling:
   • After steelmaking, the metal is Hot Rolled (1,100 – 1,200 °C) into billets or bars. For precision parts, it’s Cold Rolled (room temperature) to improve surface finish—important for sanitary uses.
3. Precision Forging:
   • Complex parts (like custom bearing rings) are forged into near-final shapes. Forging refines the grain structure, boosting strength and corrosion resistance.
4. Heat Treatment:
   • Critical for balancing hardness and corrosion resistance:
     • Quenching: Heat to 950 – 1,000 °C, then cool quickly in oil to harden (forms a martensitic structure).
     • Tempering: Reheat to 150 – 200 °C to reduce brittleness while keeping hardness and corrosion resistance.
5. Machining:
   • Post-heat treatment, parts are Ground (for ultra-smooth surfaces—reduces friction and bacterial buildup) and Turned (for cylindrical shapes like bearing races).
6. Surface Treatment:
   • Optional steps to boost performance:
     • Passivation: Treat with nitric acid to strengthen the chromium oxide layer (better corrosion resistance).
     • Polishing: Creates a mirror finish for sanitary apps (easier to clean, no hidden spots for bacteria).
     • Coating: Thin PTFE coatings for extra chemical resistance (e.g., strong solvents).
7. Quality Control:
   • Rigorous testing ensures compliance:
     • Chemical analysis: Check chromium and carbon levels (via spectrometry) to confirm performance.
     • Corrosion testing: Salt spray tests (ASTM B117) to verify saltwater resistance.
     • Hardness testing: Ensure HRC 58–62 for wear resistance.
     • Dimensional inspection: Use CMMs (Coordinate Measuring Machines) to check bearing tolerances.

4. Case Studies: JIS SUS440C in Action

Real examples show how JIS SUS440C solves tough problems.

Case Study 1: Food Processing Bearing Durability

A bakery had monthly bearing failures in their dough mixers. The original bearings used JIS SUJ2, which rusted after daily water cleaning. Switching to JIS SUS440C bearings (with passivation) made them last 12 months. This cut maintenance costs by 80% and stopped production downtime.

Case Study 2: Marine Bearing Corrosion Resistance

A boat builder struggled with propeller shaft bearing failures every 6 months (saltwater rust). They switched to JIS SUS440C bearings. Now the bearings last 3 years, saving $20,000 per boat in replacements.

5. JIS SUS440C vs. Other Materials

How does JIS SUS440C compare to other bearing materials? The table below shows key differences:

Yigu Technology’s Perspective on JIS SUS440C

At Yigu Technology, JIS SUS440C is our go-to for clients in food, marine, and chemical industries. Its mix of corrosion and wear resistance fixes the biggest issue we see: rusted bearings in wet environments. We pair it with passivation and precision grinding to meet sanitary standards and tight tolerances. For extra protection, we add PTFE coatings—making JIS SUS440C parts last 5–10x longer than standard steel in wet conditions. It’s a cost-effective choice for long-term reliability.

FAQ About JIS SUS440C Stainless Bearing Steel

1. Is JIS SUS440C magnetic?
   Yes—it’s martensitic stainless steel, so it’s ferromagnetic (attracts magnets). This is different from non-magnetic austenitic stainless steels like AISI 304.
2. Can JIS SUS440C handle saltwater?
   Yes—its high chromium content (16–18%) resists saltwater corrosion, making it perfect for marine parts like boat engine bearings. Passivation can boost this resistance even more.
3. How does JIS SUS440C compare to EN 1.4125?
   They’re almost identical! Both are martensitic stainless bearing steels with similar corrosion and wear resistance. JIS SUS440C follows Japanese standards, while EN 1.4125 follows European standards—they’re usually interchangeable.