How to Flame Harden Small Steel Parts

Flame hardening involves using an oxy-fuel gas flame to heat steel above a certain "critical" temperature, then cooling the steel, thus allowing it to harden to some depth beneath its surface. Flame hardening differs from other heat treating processes because it treats only the surface of a steel part, and hardens only a thin layer of the work piece below the surface. Thus, while flame hardening hardens a part, it leaves the part sufficiently malleable that it can be worked.

Things You'll Need

• Blow torch
• Furnace
• Tongs
• Vat of room-temperature water

Instructions

1. Use either a blow torch or a furnace with bellows to heat your steel. Allow your steel to go through several color changes, until it becomes red-hot.

2. Pick up your steel with tongs, and dunk it into a vat of room-temperature water, quenching it. After cooling in the water, your steel will be harder, but extremely brittle.

3. Pick up the steel with tongs, and reheat it, either in your furnace or with your blow torch, until the steel glows blue.

4. Pick up the steel with tongs, and dump it into a vat of room-temperature water.

Tips & Warnings

• Take safety precautions to protect yourself from the heat. Wear adequate eye protection, heavy gloves, and heat-resistant clothing and shoes.

References

• FlameTech: Standard Flame Hardening Heads
• SweetHaven: Types of Heat Treatment