Choosing the right material can increase bearing life by 3–10 times. This article clearly explains the differences and selection logic of 304, 316, and 440C in the most straightforward way.

304 Stainless Steel Bearings (18/8 Steel)

• Composition: Cr≈18%, Ni≈8%, austenitic.
• Advantages: Good rust resistance, easy cleaning, affordable price, non-magnetic/weakly magnetic, food-grade safe.
• Limitations: Moderate hardness (HRC≈20), not resistant to heavy loads, prone to pitting corrosion in strong acid/concentrated salt spray.

• Best Scenarios: Food machinery, packaging equipment, clean rooms, ordinary humid environments, light-load medium-low speed.

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316 Stainless Steel Bearings (Molybdenum-Containing)

• Composition: Cr≈17%, Ni≈12%, Mo≈2%.
• Advantages: Stronger resistance to acid, alkali, seawater, and chemicals, pitting resistance far exceeds 304.
• Limitations: 20%–40% more expensive than 304, also low hardness.

• Best Scenarios: Chemical pumps and valves, marine ships, sewage treatment, pharmaceutical equipment, high salt spray/strong acid and alkali environments.

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440C Stainless Steel Bearings (High-Carbon Martensitic)

• Composition: C≈1.0%, Cr≈17%, vacuum heat treatment.
• Advantages: Extremely high hardness (HRC58–62), strong wear resistance, large load capacity, high temperature stability (-30℃～350℃).
• Limitations: Slightly weaker corrosion resistance than 304/316, surface strengthening required in strong acid and alkali environments.

• Best Scenarios: Precision instruments, medical devices, high-speed spindles, heavy-duty automation, high-temperature equipment, wear-resistant and durable transmission points.

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Quick Selection Formula

Choose 304 for food cleanliness, 316 for chemical and marine use; for heavy load, high temperature and wear resistance, directly use 440C.

Common Misconceptions

• ❌ Stainless steel never rusts: Pitting corrosion may still occur in long-term concentrated acid/concentrated salt spray, matching sealing and lubrication is required.
• ❌ The more expensive the better: Using 316 in scenarios where 304 is sufficient only increases costs.

• ❌ 440C is completely non-rust: It works well in daily humidity, but protection is needed in strong acid and alkali.

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