Case hardening is a surface hardening technique used to harden the outer surface of low-carbon steels. It involves adding carbon to the surface through carburizing or nitriding processes, then hardening the case. This produces a hard outer layer while leaving the soft inner core intact. Benefits include wear resistance on rotating parts like gears while maintaining the core's flexibility. Common methods are pack carburizing, gas carburizing, cyaniding, and nitriding.

2. WHAT WHY HOW

3.  Case hardening is a simple method of hardening
steel. It is less complex than hardening and
tempering. This techniques is used for steels
with a low carbon content. Carbon is added to
the outer surface of the steel, to a depth of
approximately 0.03mm. One advantage of this
method of hardening steel is that the inner core
is left untouched and so still processes
properties such as flexibility and is still relatively
soft.

4. • Some components require good
toughness but very hard and wear
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

5. Carburizing and Hardening
---Carbon is added to certain
depth on the surface of a low
carbon steel
--The component is hardened
aTer carburizing

6. Carburizing—method of introducing
carbon into solid iron base alloys such
as low carbon steels in order to
produce a hard case………..
Also called cementation……..
Increase carbon content of steel
surface by a absorption and diffusion

7.  At a high temperature(T = 860-900°C),
carbon is continuously added on the surface
of the component from a solid, liquid or gas
source
 With time, carbon diffuses into the steel
 Depth up to which carbon diffuses into steel
controlled by time and temperature
 Time required to achieve desired case depth
decreases with increasing temperature

9. 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

10.  case depth is about 0.05 inch
Hardeness after heat
treatment
Negligible change in
dimensions
Hardness decreases from
surface to core

11.  PACK CARBURIZING

IT INVOLVES PACKING THE
COMPONENTS INTO CAST IRON OR
STEEL BOXES ALONG WITH THE
CARBURIZING MATERIAL SO THAT A
SPACE OF APPOX. 50MM EXISTS

12. Most often Methane (CH4) is used as
carburizing gas
• Methane is mixed with a carrier gas to
avoid soot formation on components
Desired carbon potential is maintained by
adjusting the reaction equilibrium in
furnace atmosphere
For mass production

13. It is employed for hallow cases
Done in baths containing 20-50%
Nacn,40%NA2CO3 and varying amount of
NACL
This cyanide rich is heated to a temp. of
870-950 c
Equation
2NACN+2CO2---NA2CO3+2N +CO

14. The characteristics of case which are
desired
Equipment available
The quantity of parts which is to be
handled

15. Principle
 Steel is exposed 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 nitride layer formed on the surface is very
hard
 No quenching is done

16. Case depth is about 0.381mm
Extreme hardness
Case has improved corrosion resistance
Since nitrided parts are not quenched so
less cracks
Good fatigue resistance

17. IN cyaniding carbon and nitrogen are
introduced into the surface of steel by
heating it to a suitable temp. and holding it
in contact with molten cyanide to form a
thin skin which is subsequently quenched
Bath consists of
30% NACN,40%NA2CO3,30%NACL

18. CASE DEPTH IS ABOUT 0.25MM
NEGLIGIBLE CHANGE IN DIMENSION
DISTORITION MAY OCCUR
 TYPICAL USES
SCREWS
NUTS AMD BOLTS
SMALL GEARS

20.  • The desired 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
 • The eddy currents are predominantly generated
at or near the surface
 • By adjusting the frequency of the A.C. current,
depth of heating can be adjusted
 • Heated part is then quenched in water or oil

21. • Induction hardening is used where
selective parts of a heavy duty component
has to be case hardened
Since no carburizing is done, the induction
hard enable 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.

22. Time required for hardening a component
is sharply reduced
It can be applied to both external and
internal surfaces
Components may be heated with pratically
no scaling and distortion
Hard case an tough core is obtained

23. Cost of equipment is high
Steels having less than 0.40% carbon
cannot be processed
Only for mass production
High maintaince cost
Before induction hardness the components
needs some treatment e.g normalising

24. 
Definition - What does Flame
Hardening mean?
Flame hardening is a surface-hardening
method that involves heating a metal with
a high-temperature flame, followed by
quenching. It is used on medium carbon,
mild or alloy steels or cast iron to produce
a hard, wear-resistant surface.

25. Flame hardening uses direct impingement
of an oxy-gas flame onto a defined surface
area. The result of the hardening process
is controlled by four factors:
Design of the flame head
Duration of heating
Target temperature to be reached
Composition of the metal being treated

26.  There are four types of flame hardening:
 Stationary flame hardening - requires that the
specified area be heated
 Progressive flame hardening - involves the
use of a flame head with integrated quench
capability
 Spin flame hardening - requires the specified
area being treated to be spun in front of the
flame head(s)
 Combination flame hardening - couples the
progressive and spinning methods

27. Increased wear resistance
Less distortion
Reduced processing time
Ability to use low to medium carbon steels
Reduces cost by hardening only selective
areas
Achieves high hardness for increased life
Less machining and grinding than other
methods