Hardening steels through heat treatment increases their strength and hardness, making them suitable for structural components under high stress and tools that require resistance to wear and deformation. However, quenching leaves steels very brittle, so a tempering process is required to reduce brittleness without significantly lowering hardness or strength. Common quenching mediums include brine for fastest cooling, water for moderate cooling, oil for slowest cooling, and gas in automatic furnaces, with liquid nitrogen providing very fast cooling but risking cracks in complex shapes.

1. Hardening

2. • Steels can be heat treated to high hardness and
strength levels. The reasons for doing this are
obvious. Structural components subjected to high
operating stress need the high strength of a hardened
structure. Similarly, tools such as dies, knives, cutting
devices, and forming devices need a hardened
structure to resist wear and deformation.
• As-quenched hardened steels are so brittle that even
slight impacts may cause fracture. Tempering is a heat
treatment that reduces the brittleness of a steel
without significantly lowering its hardness and
strength. All hardened steels must be tempered
before use.

3. Quenching Media
Four commonly used quenching media:
• Brine – the fastest cooling rate
• Water – moderate cooling rate
• Oil – slowest cooling rate
• Gas – used in automatic furnaces, usually
liquid nitrogen, can be very fast cooling.
Too rapid cooling can cause cracking in
complex and heavy sections.