Heat Treating Steel

Heat treating transforms steel's mechanical properties through controlled heating and cooling cycles.

Core Processes

Hardening

1. Heat steel to critical temperature (color: bright cherry red, ~1500°F for medium carbon)
2. Quench rapidly in oil, water, or brine
3. Result: hard but brittle (martensite formation)

Tempering

1. After hardening, reheat to lower temperature (300-700°F)
2. Hold for 1-2 hours
3. Result: reduces brittleness while retaining hardness
4. Higher temp = softer but tougher

Annealing

1. Heat to critical temperature
2. Cool slowly (in furnace or vermiculite)
3. Result: soft, machinable, stress-free

Color Guide (Tempering)

• Straw (430°F) — springs, cutting tools
• Brown (490°F) — axes, wood chisels
• Purple (530°F) — cold chisels, punches
• Blue (590°F) — screwdrivers, springs

Tips

• Carbon content matters — below 0.3% carbon won't harden well
• Even heating prevents warping
• Quench medium affects cooling rate and final properties
• Test with a file — hardened steel resists filing