Different types of stainless steel balls, such as AISI 440C, AISI 430, AISI 420/420C, AISI 316L/316, AISI 304/302, have different characteristics, corrosion resistanc, hardness and so on. Let's take a look together at the differences among them.

Stainless Steel Balls: AISI 440C
Martensitic Steel

Profile
Stainless steel balls of this straight chromium steel provide maximum hardness, toughness and dimensional stability. They are highly resistant to rolling-contact fatigue. 440C stainless steel balls are always used in a hardened condition, perform similarly to tool steels, and are ideal for use in antifriction bearings (rolling bearings). After quenching, the balls are immediately subjected to ultra-low temperatures to stabilize their structure and further enhance hardness.
Characteristics
440C stainless steel balls achieve the highest hardness following heat treatment: ≥58 HRC. The material is ferro-magnetic and makes a good permanent magnet. H.R.T. 440C stainless steel balls are passivated to remove free iron contaminants and facilitate spontaneous formation of a protective passive film.
Characteristics
440C stainless steel balls have excellent resistance to steam, crude oil, gasoline, blood, perspiration, alcohol, sterilizing solutions, fresh water, and foodstuffs.
Hardness
HRC 58-65
Sizes
Available in sizes from .5mm to 50.8mm (2") in Grades 10 through 1000.

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Stainless Steel Balls: AISI 430
Ferritic Steel

Profile
Economical alternative to 302/304 for corrosive environments and conditions. Magnetic properties offer advantages in assembly of 430 products.
Characteristics
Offers good resistance to mild atmospheric conditions. Provides superior resistance to chloride stress corrosion at elevated temperatures compared to 302/304 or 316 materials. All balls of this alloy are passivated.
Corrosion Resistance
430 stainless steel balls are resistant to steam, dairy products, nitric acid and many petroleum products and organic materials. Superior material for use in cosmetic applications.
Hardness
Annealed – Rockwell B 75-95 measured on parallel flats.
Sizes
Available in sizes from .1mm to 25.4mm in Grades 100 through 1000.

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Stainless Steel Balls: AISI 420/420C
Martensitic Steel

Profile
420 stainless steel balls demonstrate good wear characteristics and hardness. Slightly less hardness, and greater corrosion resistance, compared to 440C.
Corrosion Resistance
Excellent resistance to corrosion from mild atmospheres, fresh water, steam,blood, ammonia, petroleum products, and mild acidic environments.
Hardness
≥HRC52
Sizes
Available in sizes from .5mm to 50.8mm (2") in Grades 10 through 1000.

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Stainless Steel Balls: AISI 316/316L
Austenitic Stainless Steels

Profile
316/316L stainless steel balls have exceptional corrosion resistance, thanks to their higher nickel and molybdenum content. Developed to resist attack by sulphuric, phosphoric and acetic acid compounds; used extensively in applications involving photographic chemicals, inks, rayon, rubber, textilebleaches, dye stuffs and high temperature equipment. FDA approved for medical grade material.
Characteristics　
These balls made from type 316 have higher tensile and creep strength atelevated temperatures than conventional 316 alloys. This material is passivated to reduce reactivity.
Physical Constants
Density – 0.29 lbs./cu. in.
Typical Hardness　
Annealed – Rockwell B 75-95.
≤HRC 28.
Sizes　
Available in sizes from .5mm to 50.8mm (2") in Grades 100 through 1000.

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Stainless Steel Balls - AISI 304/302 (18-8)
Austenitic Stainless Steels

Profile
Type 18-8 stainless steel balls are used when conditions require corrosion performance and toughness not available in hardenable stainless steels. Principal applications are in couplings, valves and pumps.
Characteristics
Low magnetic permeability: annealed, 1.003; cold worked, 1.10; severely cold worked, 10.0. High tensile strength at elevated temperatures. 18-8 stainless steel work-hardens rapidly. Stainless steel balls of this material are passivated.
Corrosion Resistance
Type 18-8 stainless steel balls resist attack by oxidizing solutions, foodstuffs, sterilizing solution and most organic chemicals. They are susceptible to attack by halogen acids and moderately resistant to the sulphur acids.
Typical Hardness
Annealed – Rockwell B 75-95.
≤HRC26.
Sizes
Available in sizes from .5mm to 25.4mm (1") in Grades 100 through 1000.