Flame Hardening
Flame Hardening
- The process consists of heating the surface of medium carbon steel by high temperature gas flame at 2400°C – 3300°C and immediately cooling in air or water. Heat may be supplied by oxyacetylene torch. The fuel caused by the flame may be oxyacetylene, natural gas or kerosene. The flame rapidly imparts large amounts of heat to the surface. The heat supply so quickly to the surface and for a short time, the core remains unaffected.
- As soon as the desire temperature is achieved water immediately sprayed which cools the surface.
- By proper control and cooling temperature. The core is not affected by treatment.
- The thickness of hardened layer is 2 – 4 mm and its surface structure is martensite.
Advantages :
- There is practically no distortion of the work piece because only small sections of the work piece are heated.
- As heating rate is high the work surface remains clean.
- The process rate can be automated
- The process is more efficient for large work as compared to induction heating . It is very economical for large work.
Disadvantages :
- Very thin section may get distorted extensively.
- Over heating may cause crack.
Uses
- It is used to increase wear resistance and surface hardness Eg: piston pins, large gears, hand tools, shaft, mill rolls etc.
- As it can be seen from the TTT diagram of high carbon steel that martensite finish line appears approximately at 25°C. Hardenability of hypo and hyper enteroid steel is lower than eutectoid steel. So upon quenching the material into bath maintained at room temperature, martensite, pro-eutectic, cementite and retained eutectic will be present in the sample.
- To convert the sample into 100% martensite, steel sample is quenched into a bath of liquid nitrogen. The process is called cryogenic treatment of material.
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