Quenching is the rapid cooling of steel by immersion in water or brine. What is the typical consequence if quenching is used without tempering?

• A. The steel becomes more ductile
• B. The steel's color changes
• C. The steel becomes too hard and too brittle to use
• D. The steel's density changes

Answer: (C)

Quenching rapidly cools steel to form martensite, a very hard yet extremely brittle phase. The quick transformation traps carbon and introduces internal stresses, so the steel becomes hard but loses the toughness needed for most applications. Without tempering, this brittle condition makes the material prone to cracking under impact, fatigue, or ordinary service loads. Tempering heats the steel to a lower, controlled temperature and allows some diffusion and stress relief, reducing hardness enough to regain ductility and toughness while preserving much of the improved hardness. The idea here is that quenching alone pushes hardness up at the expense of toughness, and tempering balances those properties to produce usable steel.