Carbon content and hardness of steel balls

How Carbon Content Affects Steel Ball Hardness
The secret to steel ball hardness lies in the dance of carbon and iron atoms: As the carbon content increases from 0.2% to 0.8%, the hardness increases in a stepwise manner. This is because carbon atoms embed in the iron lattice to form a solid solution, like adding a reinforcing scaffold to a metal skeleton. However, beyond 0.8%, the excess carbon forms brittle carbides, which actually reduces overall toughness.

Choice of Carbon Content for Different Applications

Wear Resistance Requirements: Bearing steel balls typically contain 0.95%-1.1% carbon, sacrificing some toughness for higher hardness.

Impact Resistance Applications: Crusher steel balls are controlled at 0.6%-0.8% carbon to maintain a balance between hardness and toughness.

Precision Instruments: 0.3%-0.5% low-carbon steel balls are more suitable for applications requiring dimensional stability.

Key Combinations of Heat Treatment
The same carbon content will exhibit drastically different properties after different heat treatments. Quenching can increase the hardness of high-carbon steel balls by 3 times, but it needs to be combined with tempering to eliminate internal stress. Medium carbon steel balls undergo quenching and tempering treatment, which enables them to maintain good hardness while achieving excellent fatigue resistance.