Ans: (5M|Jun2014) 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

Applications

Flame hardening is a very common surface hardening technique, which is often used to provide a very wear-resistant surface. A common use is for hardening the surface of gears, making the teeth more resistant to erosion. The gear will usually be quenched and tempered to a specific hardness first; making a majority of the gear tough, and then the teeth are quickly heated and immediately quenched, hardening only the surface. Afterward, it may or may not be tempered again to achieve the final differential hardness.

Benefits

• Rapid annealing of desired material areas
• Minimal heating of surrounding material with acetylene as fuel gas
• Quench hardening upon effective cooling

• Burner selection adapted to customer demands
• Special burners with integrated water shower
• Customized gas supply solutions

Limitations

• 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