what is laser hardening process of laser hardening hardening of cast iron process variables differences with other conventional process advantages and disadvantages

1. Presentation on
Laser
Hardening
Prepared by,
Sohini Mondal (511119028)
2nd Year UG ,4th Semester

2. Contents:
• Introduction
• Laser Heat Treatment Process
• Relationship between depth of
hardening and power
• Laser heat treatment of Cast Iron
• Process variables connected with
laser heat treatment
• Coatings
• Differences with other heat
treatment process
• Advantages & Disadvantages

3. • Laser hardening, also referred to as laser case hardening—is a heat
treating process used to improve the strength, durability & wear
resistance of component surfaces.
• Laser beams are used for surface hardening treatment.
• In laser hardening process less time is required than in induction and
flame hardening process.
• There is no chemistry change produced by laser hardening.
• No separate quench media is required since the material self-quenches.
• In laser hardening thin surface zones that are heated and cooled very
rapidly results in very fine martensitic microstructure.
Laser Hardening:

4. Laser Hardening Process:
• As laser beams are of high intensity, a lens is used to reduce the
intensity by producing a defocused spot or scans from 1-25 mm
wide.
• A laser beam of 1kW produces a circular spot of diameter 0.50 to
0.25 mm.
• Industrial lasers up to 20kW are now available.
• Case depth of about 0.75mm is obtained by self quenching.
• The effect of heat on the surrounding surface is less, thus leads to
less distortion.

5. Laser heat treatment Process:
• Laser heat treatment process is best suited for steel and cast irons.
• During laser heating, heat transfer takes place by inverse
Bremsstrahlung effect i.e. by interaction of laser beam with the
free electrons of the substrate.
• For successful laser heat treatment it is necessary that the
temperature of the zone which is being hardened must reach closer
to the austenitizing range.

6. • Between the heating and
cooling cycles, the material
must be maintained at the
austenitizing temperature for
sufficiently long time to ensure
adequate diffusion of carbon.
• There should be enough mass
so that the cooling rate
achieved by self quenching is
greater than the critical cooling
rate required for martensite
transformation.
Laser heat treatment
Process (continued…):

7. Relationship between depth of hardening and power:
The depth of hardening is governed by both time and energy density.
Y= -0.11+[3.02P/{(DᵇV)˄½}]
Where,
Y= case depth (mm)
P= Laser Power (W)
Dᵇ= incident beam diameter (mm)
V= traverse speed (mm/s)

8. Different method of beam manipulation can be adopted to
obtain a broad beam with uniform intensity distribution:

9. Laser heat treatment of Cast Iron:
• Cast iron with a combination of pearlite and graphite can be heat
treated successfully with lasers.
• When the pearlite is being dissolved to be converted into austenite and
subsequently to martensite , some carbon diffusion takes place out of
graphite flakes which will produce martensite around the original
graphite flakes.
• The predominant hardening mechanism will be based on austenite
formed by dissolution of pearlite.

10. Process variables connected with laser hardening:
INDEPENDENT VARIABLES DEPENDENT VARIABLES
Incident laser beam power
Diameter of incident laser beam
Absorptivity of laser beam by the
coating
The substrate and traverse speed
across the surface
Depth of hardness
Geometry of heat treated zone
Microstructure and
metallurgical properties of
laser heat treated material

11. Coatings:
• For efficient laser heat treatment, proper absorption of light energy by work piece
is very necessary.
• Melting and key hole formation should be strictly avoided during laser heat
treatment. Hence some absorbent coatings are used during laser heat treatment.
• Colloidal graphite, manganese phosphate, zinc phosphate and black paint are some
commonly used coatings.
• High absorptivity can also be achieved with the help of a mixer of sodium and
potassium silicate.
• Absorptivity depends on coating thickness, coarseness and adherence to the
substrate.
• Heat transfer between the coating and the substrate also plays an important role.

12. Basic differences with other conventional process:
• It is possible to harden low carbon steel with relative ease due to extremely
rapid heating and cooling rates associated with laser heating. There is hardly
any effect due to differences in hardenability between plain carbon steel and
aloy steels since the cooling rates normally achieved during laser heat
treatment are much higher than the critical cooling rate required for
martensitic transformation.
• It has generally been observed that the level of hardness achieved by laser
hardening is higher than that obtained by conventional hardening.
• Laser heat treatment is not well suited for alloys requiring rather long
soaking time such as steel containing spherodial carbides or cast irons rich in
graphite instead of pearlite. The large soaking time is required for the
diffusion of carbon would restrict the operating parameter associated with
the laser. Consequently, the process would lose its inherent advantage of
rapid heating and cooling rate.

13. Advantages of laser hardening:
• High production rates since light has no inertia. Consequently, high
processing speed with rapid stopping and starting.
• Input distortion is low because specific energy is very low.
• It is possible to give localized treatment with this process.
• No external quenching is needed.
• There is hardly any contamination during surface hardening treatment.
• Possible to control the process with the help of a computer.
• Those areas which are difficult to be treated by conventional methods can be
easily treated with this technique.
• It is not necessary to carry out any final machining operation subsequent to
hardening.

14. Disadvantages of Laser Hardening:
• High initial cost particularly of large lasers.
• Lasers use 10% of the input energy, i.e., there is inefficiency.
• The depth of case is very limited.
• Working cost is high.
• Difficult to surface harden high alloy steels.
• Extra care is needed to avoid fusion.

15. Resources:
1. Heat Treatment by T.V.Ranjan, C.P.Sharma &
Ashok Sharma
2. https://www.titanovalaser.com /
Thank You