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Surface Hardening of Steel
The document discusses various surface hardening treatments for steel, including carburizing, induction hardening, and nitriding, emphasizing their importance for enhancing toughness and wear resistance in components like gears. Carburizing involves carbon diffusion at high temperatures, while induction hardening uses an electric field to induce hardness in medium carbon steel. Nitriding introduces nitrogen to form hard nitrides on the surface, improving the material's properties.
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Introduction to surface hardening, its necessity for toughness, and treatments like carburizing, induction hardening, and nitriding.
Details on carburizing, including methods of carbon infusion, diffusion depths, and hardening processes.
Description of induction hardening process, its applications, and the materials used for selective hardening.
Explanation of nitriding, the reaction with nitrogen, and resulting microstructures in nitrided steel.
List of references and sources for additional information on heat treatment of steels.
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Surface Hardening of Steel
- 1. CARBURIZING AND HARDENING INDUCTIONHARDENING N I T R I D I N G SURFACE HARDNING OF STEEL By VAIBHAV TAILOR
- 2. Why is SurfaceHardening Required? Some components require good toughness but very hard and wear Different treatments needed for surface than bulk of the component resistant surface especially parts rotating against each other e.g. gears engaged in each other and rotating at several thousand RPM Gear teeth rub against each other and also exert bending forces on each other
- 3. Various Surface HardeningTreatments Carburizing and Hardening Induction Hardening Nitriding
- 4. Carburizing At ahigh temperature, carbon is continuously added on the surface of the component from a solid, liquid or gas source
- 5. Carburizing With time,carbon diffuses into the steel. Depth up to which carbon diffuses into steel controlled by “time” and “temperature” At a given temperature, doubling diffusion depth requires four times longer carburizing time
- 6. Hardening after Carburizing It is necessary to carry out carburizing at a temperature above A3 temperature for the steel It is necessary to quench the component after carburizing to achieve the desired hardness Tempering is necessary after hardening for reducing brittleness
- 7. Induction Hardening Thedesired part of the component kept inside an induction coil A.C. current passed through the coil induces magnetic field around the component The magnetic field induces eddy currents in the component
- 8. Induction Hardening: Materialsand Use Induction hardening is used where selective parts of a heavy duty component has to be case hardened Since no carburizing is done, the induction hardenable part has to contain medium carbon, typically equivalent carbon content of 0.4-0.45 wt% Examples of application are crank shaft, cam shafts etc.
- 9. NITRIDING Steel isexposed to nitrogenous atmosphere NH3 = N + 3H (at 525-550°C) The nascent nitrogen reacts with various alloying elements in the steel (e.g. Al, Mo, Cr etc.) to form nitrides The nascent nitrogen reacts with various alloying elements in the steel (e.g. Al, Mo, Cr etc.) to form nitrides
- 10. Nitrided Steel Microstructure 3-4 microns of white layer has to be removed A nitride layer of a few tens of microns thick on the surface Tempered martensite in the subsurface and core
- 11. Helpful References R.C. Sharma; Principles of Heat Treatment of Steels’ New Age International Limited Publishers https://www.google.co.in https://www.asminternational.org