Flame Hardening:

1. Flame hardening is often used to harden only a portion of an object, by quickly heating it with a very hot flame in a localized area, and then quenching the steel. This turns the heated portion into very hard martensite, but leaves the rest unchanged. Usually, an oxy-gas torch is used to provide such high temperatures.

2. Flame hardening is a very common surface hardening technique, which is often used to provide a very wear-resistant surface.

3. Here the application is heated by flame and quickly quenched in a bath which imparts only hardness to surface, common example is gear tooth which are flame burned and hardened for resistance to wear and tear.

4. Benefits are:

• Rapid annealing of desired material areas

• Minimal heating of surrounding material with acetylene as fuel gas

• Quench hardening upon effective cooling

5. Limitations are

• There is a possibility of overheating and thus damaging the part

• It is difficult to produced hardened zone less than 1.5mm in depth.

• Success of process depends on skill of operator

• Not so economical, hardly used for mass production hardening