This document discusses various surface treatment methods for metals including case hardening, selective hardening, and layer additions. It provides details on specific processes like carburizing, cyaniding, nitriding, and carbonitriding for case hardening as well as flame hardening, induction hardening, and laser/electron beam hardening. Layer addition methods like physical vapor deposition, chemical vapor deposition, and thermal spraying are also outlined.

1. Metallurgy &Metallurgy &
Material ScienceMaterial Science
Dr.S.Jose
Dept of Mechanical Engg.,
TKM College of Engineering, Kollam

2. 2
 Diffusion methods (case hardening)
 Selective hardening methods
 Layer additions
 Metal Coating
Surface Treatments

3. 3
 Diffusion methods (case hardening)
 Carburising
 Cyaniding
 Nitriding
 Carbonitriding
 Selective hardening methods
 Flame hardening
 Induction hardening
 Laser hardening
 Electron Beam Hardening
Surface Treatments

4. 4
 Layer additions
 Physical vapour deposition
 Chemical vapour deposition
 Thermal spraying
 Metal Coating
 Galvanising
 Electroplating
 Metal cladding
Surface Treatments

5. Case Hardening
 The primary purpose of case hardening is to
produce a surface which is resistant to wear
while maintaining the overall toughness and
strength of the steel core.
 Normally used on steel with a low carbon
content and introduces carbon by diffusion
(carburising) into the local surfaces
requiring treatment.
 Heating steel in the presence of a solid,
liquid or gas rich in carbon.

6. Case Hardening

7. Cyaniding
 Hardening the surface of steel with
carbon and nitrogen obtained from
a bath of liquid cyanide solution.
 Steel is heated in molten cyanide
at about 850 °C followed by
quenching.
 Carbon and nitrogen are absorbed
by steel.

8. Carbonitriding
 Hardening the surface of steel with
carbon and nitrogen
 Steel is heated in a gaseous
mixture of ammonia and
hydrocarons

9. Nitriding
 Another process called Nitriding consists
of the diffusion of nitrogen.
 Nitrogen is introduced into steel by
passing ammonia gas through a muffle
furnace containing the steel to be
nitrided.
 Temperature used is below the lower
critical temperature
 Greater resistance to wear and
corrosion, greater surface hardness.

10. Flame Hardening
 Heating the surface being hardened above the
upper critical temperature with an oxy
acetylene flame before quenching it in a spray
of water.
 This is a surface hardening process resulting in
a hard surface layer of about 2mm to 6mm
deep.
 The main difference between this process and
other surface hardening processes is that the
composition of the steel being hardened is not
changed.

11. Flame Hardening

12. Flame Hardening
 The steel must itself have sufficient
hardenability .
 Limits this process to steels having carbon
contents of above 0.35%.
 Steels with carbon contents of 0.4%-0.7% are
most suitable for this process.
 Steels with higher C content and high alloy
steels may not be suitable as they a liable to
cracking.
 Result similar to the conventional hardening
process but with less hardness penetration.

13. Induction Hardening
 Surface to be hardened is heated
using inductive heating.
 Depth of hardness can be closely
monitored by controlling current.
 Time required for the process is less.
 Used for producing hard surfaces on
crankshafts, axles, gears etc.

14. Layer Additions
 Physical vapour deposition
 Chemical vapour deposition

15. Physical vapour deposition

16. Chemical Vapour deposition

17. Thermal spraying
 Use of heat source
 Combustion flame
 Electric arc
 Plasma arc
 Detonation gun
 Form of coating material
 Wire

18. Arc Spraying

19. Flame Spraying

20. Plasma spraying

21. Detonation gun spraying