Question: Explain Flame hardening & Induction hardening.
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Subject Material Technology

Topic Heat Treatment Processes

Difficulty Level Medium

mt(63) • 492 views
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modified 12 months ago  • written 12 months ago by gravatar for Atharv Inamdar Atharv Inamdar650
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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

Induction Hardening

  1. Induction hardening is a type of heat treatment in which metal parts are heated by electromagnetic induction and then quenched.

  2. It is also a type of case hardening and can be used for many steel and steel alloys to improve surface layer properties such as fatigue resistance and hardness.

  3. Materials such as steel are typically placed inside a water cooled copper coil where they are subject to an alternating magnetic field.

  4. They undergo electromagnetic induction by means of an electromagnet and an electronic oscillator.

  5. This oscillator sends alternating currents through the electromagnet, causing alternating magnetic fields that penetrate the material.

  6. The results are eddy currents which heat the object within the coil. Induction hardening is a form of surface hardening in which the depth can be up to 8mm.

  7. The deeper the currents penetrate, the higher the frequency of the alternating magnetic fields have to be.

  8. Directly after the induction heating process, the object has to be quenched; it has to be cooled down extremely quickly.

  9. Quenching ensures that only the surface is hardened and that heat doesn’t spread into the core of the material, avoiding phase transformations from arising.

  10. Furthermore, the rapid cooling down creates a martensitic or ferritic-martensitic structure on the surface layer.

  11. These structure display higher tensile strength and low initial yielding stress than a purely ferritic structure.

  12. Quenching also reduced grain size which is a key factor to increasing hardness of materials.

  13. A benefit of induction hardening is that if the depth of surface is more; the grain size can be considerably decreases and object gets resistance to wear and tear.

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modified 11 months ago by gravatar for Sanket Shingote Sanket Shingote270 written 12 months ago by gravatar for Atharv Inamdar Atharv Inamdar650
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