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Home ... Engineering Information... Miniature & Small ball bearings... Selecting a Bearing... 3. Material

Miniature & Small ball bearings -3. Material

Selecting proper material of inner and outer rings, and balls is critical for ball bearings because they have a significant influence on the bearing performance.


Severe stresses of higher than 1000MPa are applied repeatedly on the contact areas of outer and inner rings, and balls. Material types, purity, and hardness are very important factors because long life is required even when high stresses are applied repeatedly.
High carbon chromium bearing steels and high corrosion-resistant martensitic stainless steels are used for raceway rings and balls in our products.
High carbon chromium bearing steel raceway rings and balls are made from high quality vacuum outgassed high carbon chromium steel or equivalent material. With proper heat treatment, they have strong load resistance, longer life, and low noise level performance.
Minebea developed stainless steel "DD400". The hardness of DD400 after heat treatment is higher than that of SUS440C. The DD400 material also shows longer life, and strong load resistance performance.
The noise level of DD400 material gets close to that of chromium steel because carbon disperses spherically. From results of the test based on ASTM-A380, the corrosion resistance of DD400 material is equal to SUS440C.

We also provide ceramic ball bearings to meet longer life, and low noise level requests. Compared to the conventional chromium bearing steel balls, both better noise level and longer life can be achieved by using ceramic balls (Silicon Nitride) even if the material of raceway rings is still conventional chromium bearing steel. The extremely low conductive characteristics (insulation properties) of silicon nitride protect bearings from electric corrosion, which is generated under a conductive environment. Torque will be reduced because the ceramic material is lighter than bearing steel.


Chemical components of materials

Chromium bearing steel

Spec Symbol Chemical Component (wt%)
C Si Mn P S Cr Mo
JIS G 4805 SUJ 2 0.95~1.10 0.15~0.35 0.50MAX 0.025MAX 0.025MAX 1.30~1.60 -
AISI/SAE E52100 0.98~1.10 0.15~0.35 0.25~0.45 0.025MAX 0.025MAX 1.30~1.60 -

Stainless steel

Spec Symbol Chemical Component (wt%)
C Si Mn P S Cr Mo
- DD400 0.60~0.75 1.00MAX 1.00MAX 0.03MAX 0.02MAX 11.50~13.50 0.30MAX

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Home ... Engineering Information... Miniature & Small ball bearings... Selecting a Bearing... 3. Material