Carbonitriding

1. A Presentation on : CARBONITRIDING Prepared by : Daksh Patel

2. Index Introduction Process Objectives Of Carbonitriding Advantages Disadvantages Application

3. CARBONITRING It is a modified form of gas carburizing. It is a case Hardening process which involves the diffusion of both carbon and nitrogen into the base metal in the temperature range700-900° C. Carbonitriding is carried out at a lower temperature and for a shorter time than is gas carburizing. It produces a shallower case (0.075 to 0.75mm) than carburizing . Used for Plain Carbon Steel or Low Alloy S teel.

4. Process 2 - 12 % Ammonia is added to the carburizing atmosphere, which provides a source of nitrogen. Process variables – Temperature - 700-900° C Gas Composition – Methane + Ammonia Duration Ammonia decomposes at the surface as : 2NH 3 ↔ N 2 + 3h 2 This molecular Nitrogen can not be Absorbed to the steel surface.

5. It is only the portion that does not decompose – called residual ammonia – that is the active component for nitriding expressed by the reaction. NH 3 (residual) → N + 3/2H 2  0.5 to 0.8% carbon and 0.2-0.4% Nitrogen is added to the Steel surface.  The carbon provides the base metal with a high carbon surface, and the nitrogen provides the case with an added boost of hardenability to insure full case hardness.

6. Carbonitriding is used primarily to impart a hard, wear-resistant case.  A carbonitrided case has better hardenability than a carburized case. Quenching is done after Heating to get hard martensitic structure. Sometimes Tempering is done to ensure ductility by eliminating internal micro stresses and by somewhat reducing the hardness. Carbonitriding cycle including cooling(quenching) and Tempering Step.

7. Objectives Of Carbonitriding To obtain higher surface hardness To increase wear resistance & Fatigue Strength To obtain higher corrosion resistance To have good high temperature properties

8. ADVANTAGES It has a greater resistance to softening during  Tempering.   Increased   Fatigue  and impact strength. Better case hardenability in lower alloy or plain  carbon steels. The carbonitrided case has better wear and temper resistance than a straight carburized case.  It is carried out at a lower temperature and for a shorter time than is gas carburizing. Reduced distortion due to lower temperature.

9. Disadvantages It produces shallower cases. It is not possible to obtain higher core hardness and deeper case depths. Only useful for Plain carbon steel or Low alloy Steel. Ammonia can produce harmful effects.

10. APPLICATIONS Carbonitriding is used to treat Plain Carbon Steel or Low Alloy Steel. It is successfully applied to generally mass produced components, and those of smaller dimensions, where great resistance to wear is required and where the case depth requirements ranges from 0.1 to max 0.75 mm. Typical applications include: G ears and Shafts P istons R ollers and Bearings levers in hydraulic, pneumatic and mechanical actuated systems . Tools and Dies

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