What is flame hardening?

Q.  In which of the following methods, surface of a steel component becomes hard due to phase transformation  austenite to martensite?
- Published on 11 Sep 15

a. Carbonitriding
b. Flame hardening
c. Both a. and b.
d. None of the above

ANSWER: Flame hardening


  • Sravanthi   -Posted on 12 Nov 15
    Surface hardening: This method is used to increase surface hardness by changing composition of surface layers with heat treatment.

    - The different methods used for this purpose are:

    1) Flame hardening: In this method, oxyacetylene flame is used to heat the surface to it's critical temperature. After heating, the surface is immediately quenched with water and cold base metal. It produces thin and hard surfaces due to the transformation of austenite to martensite. In this method, surface layer gets austenatized because the temperature of flame is about 3000°C.

    2) Induction hardening: In this method, instead of heating the surface it is hardened with the help of induction hardening. Here, increase in frequency of the current decreases depth of hardening.

    - Carbonitriding: This method is also used to increase surface hardness of metals. The surface of steel component becomes hard due to simultaneous diffusion of atomic carbon and nitrogen. Carbon and nitrogen are produced when carbonizing gas is added with ammonia and nitrogen in carburizing atmosphere.

Post your comment / Share knowledge

Enter the code shown above:
(Note: If you cannot read the numbers in the above image, reload the page to generate a new one.)