What is Flame hardening? Flame hardening is a common surface hardening method. Metal surfaces, such as steel, by heating with an oxyacetylene or oxyhydrogen torch and immediately quenching with water. After quenching, the microstructure of the surface layer consists of hard martensite over a lower-strength interior core of other steel morphologies such as ferrite and pearlite. The main aim of flame-hardening is to obtain a high hardness and wear resistance of the surface, without effecting the reasonable toughness of unhardened core. It also improves fatigue, bending and torsion strength.

Process of Flame Hardening The flame-hardening process is used for a wide variety of applications. These include (1) parts that are so large that conventional furnace treatments are impractical or uneconomical, (2) prevention of detrimental treatment of the entire component when only small segments of the part require heat treatment, and (3) use of less costly material to obtain the desired surface properties where alloyed steels would be normally applied. The final results of flame hardening are determined by the heat of the flame, the duration of the heating, and the speed, temperature of the quenching process, as well as the elemental composition of the target material. The flame is based on gases that enable it to reach high and stable temperatures. In most common cases, it involves oxygen and acetylene, as well as propane in some cases

Material suitable for flame hardening Low/medium carbon steel (depending upon required surface hardness and core properties) . High carbon steel (use increases the risk of cracking, and careful control is required)

Advantage and disadvantage of flame hardening Advantages of Flame-Hardening: 1-The process is simple. 2. A large number of steels could be flame-hardened. 3. Flame hardening can be done of any shape, like flat, circular, irregular shapes, etc. 4. Mass distortion is absent. 5. The equipment cost is much less than for induction hardening. 6. It is faster than carburising or nitriding etc. 7. The flame could be directed to harden sections deep inside components. 9. Wider depth of hardening can be obtained. 10. Selective hardening is easily obtained. 11. Cheaper steels could be used.. 12.Less distortion. 13.Higher hardness

Disadvantage of flame hardening 1-It is difficult to control exactly the temperature of heating of the component. 2-Overheating of surface layers may take place. 3. As coarse martensite (due to overheating) may be present, the quality of case is relatively poor. 4. Explosive fuel gases have to be used cautiously. 5. Some oxidation or decarburisation may occur as compared to induction hardening. 6.Increased fire hazard: since flame hardening requries working with an open gas_fueled flame ;caution is advised. 7-hardness ,it might also become more susceptible to cracking and flaking.

Induction Hardening hardening a process used for the surface hardening of steel and other alloy components. The parts to be heat treated are placed inside a water cooled copper coil and then heated above their transformation temperature by applying an alternating current to the coil This operation is most commonly used in steel alloys. Many mechanical parts, such as shafts, gears, and springs, are subjected to surface treatments, before the delivering, in order to improve wear behavior. The effectiveness of these treatments depends both on surface materials properties modification and on the introduction ofresidual stress.

Induction Hardening After quenching, the steel undergoes tempering, a low-temperature heat treatment process, to reach the desired hardness / toughness ratio. The maximum hardness of a steel grade obtained through the hardening process gives the material a low toughness. Treating the steel through tempering reduces the hardness in the material and increases its toughness. In induction hardening, the electrical resistivity and magnetic properties of the alloy can produce significant differences in heating characteristics. Thus, different steels require differing induction-heating parameters.

Induction Hardening Induction hardening offers significant advantages over traditional methods for heat-treating steel, alloy, and other metal parts. This process is perfect for metal with a carbon content of more than 0.3%, particularly hardened steel with a low alloy content (C34, C35, C60, etc.),. Shafts, gears, armatures, sprockets and other components can all be hardened using this induction process.