This ppt was made by Subha Das from MSRIT.For SI project of my college.

1. Laser Heat Treatment

2. INTRODUCTION
 In laser heat treating, energy is transmitted to the material*s surface in
order to create a hardened layer by metallurgical transformation. The
laser is used as a heat source, and rapidly raises the surface temperature
of the material. Heat sinking of the surrounding area provides rapid
self-quenching, thus producing a hardened transformation layer.
 The enhanced mechanical properties resulting from laser heat treating
depend upon the specific composition of the metal or alloy. For
example, laser casehardening of transformation hardening metals
provides high wear and abrasion resistance with minimum distortion.
In addition, laser spot annealing of precipitation and work hardened
metals (i.e., 300 series stainless steel and copper alloys) restores
ductility and improves formability and fatigue resistance in critical
areas.
 CO2 lasers, Diode lasers, Fiber lasers and Nd:YAG lasers are commonly
used for laser heat treating. If Nd:YAG lasers are used for heat treating,
the inherently high absorption properties translate to eliminating pre-
processing painting and increasing throughput.

3. The Process
 During heat treatment with laser radiation, the
material is heated locally to a temperature below the
melt temperature. The wall thickness determines
whether just the surface layer or, in the case of sheet
metal, the entire cross-section is heated. Unlike
furnace treatment, this technique invariably involves a
short-time heat treatment with cycle times in the
region of a few seconds. The heating rate, the
maximum temperature and the cooling rate can be set
specifically via temperature control.

4. Unique Characteristics of Laser
Heat Treating…
 Because a source of light can be concentrated to produce a small
spot of intense heat energy, there are numerous advantages
when considering the use of a laser.
 Minimal Heat Input - Since the source temperature is so high,
transformation occurs quickly and heat input to the part is low.
This reduces distortion in the heat affected zones.
 Precise Control - Since the light energy is concentrated, the area
of heat treating can be located with great precision. As for its
flexibility, the heat treat area can be projected within a small
diameter bore through the use of directing mirrors.
 Non-Contact, Open Air Processing - Since the energy comes
from light, nothing physically touches the workpiece. There is no
force exerted on the part. In addition, magnetism and air do not
affect the laser*s beam.

5. Suitable Lasers
 Both CO2 and Nd:YAG continuous wave lasers
currently have the power capabilities to heat treat
metals at reasonable rates. The CO2 laser, however, has
poorer surface absorption in most metals, and thus
requires the surface to be coated to improve its
absorption characteristics. Since the surface
absorption of the Nd:YAG laser wavelength is
significantly higher, generally less power is required.

6. Suitable Materials for Laser Heat
Treating…
 Low Carbon Steel (0.08% to 0.30% carbon) - Very rapid quenching is required to form martensite in
low carbon steel. A shallow case depth of up to 0.5 mm can be achieved. That maximum hardness
which can be reached is dependent upon the percent carbon content in the steel.
 Medium and High Carbon Steel (0.35% to 0.80% carbon) - These material are better choices than low
carbon steel because the higher carbon content allows a longer period for quenching in order to reach
high hardness. The maximum case depth without use of a water quench is around 1.0 mm.
 Alloy Steel - This is the most desirable type of steel to use with the laser process. The alloy elements,
specifically manganese, molybdenum, boron and chrome, aid in hardenability. These steels can be
heat treated up to a 3 mm case depth without concern for back tempering. The maximum hardness
which can be achieved is dependent upon the carbon content.
 Tool Steels - These also can be treated easily by the laser process. Results are similar to those achieved
with alloy steels.
 Martensitic Stainless Steel - Martensitic stainless steel can also be treated by the laser process.
Though its microstructure does not readily display the hardened region, microhardness
measurements clearly indicate high hardness.
 Pearlitic Cast Iron - All cast irons with pearlitic structures can be hardened by the laser. Because of
the uneven distribution of carbon along the graphite flakes, some finger melting can be occasionally
found close to the hardened surface.

7. Special Considerations for Laser
Surface Heat Treating…
 Microstructure of Parts - The most desirable types of microstructures for the laser process are
quenched and tempered or austenitized and tempered conditions. Fully annealed and
spherodized structures are not recommended for this process.
 Microstructural Homogeneity of the Parts - Laser surface heat treating requires a
homogeneous structure because there is little time in which to diffuse and redistribute the
alloy elements throughout the material. Parts with heavy segregation will not respond
uniformly to the laser process.
 Hardness of Core - Core hardness is important if the part will see service at high pressure
conditions after heat treating. If the background material is dead soft, the hardened layer will
peel off very quickly in service.
 Parts Cleaning - The surface of the parts which will be laser heat treated should be thoroughly
cleaned. Heavy dirt, rust, and grease on the surface will cause uneven case depth.
 Surface Coating - When using CO2 lasers, a thin layer of coating is commonly applied to the
metal surface to enhance the absorptivity of the metal by the laser beam. Phosphate and black
paint are the most common coatings due to their low susceptibility to moisture, but oxide and
graphite can also be used. The ideal thickness for the coating is around 0.02 mm to 0.05 mm.
This coating is generally not required when Nd: YAG lasers are used.

8. Major Laser Heat Treating
Parameters…
 Power Density - Generally speaking, the higher power density, the deeper the case
depth. However, if all other variables are fixed, there is a maximum depth that can
be achieved. When that limit is exceeded, surface melting will occur. If some
finish machining is a requirement as a final step after hardening, then some
surface melt (i.e. several thousandths) can be tolerated.
 Travel Speed - If, after maximizing all variables, travel speed is increased, case
depth will be decreased until there is no reaction with the material. Decreased
travel speed will cause significant surface melting and/or a lower hardness.
 Hardness Requirement - The maximum hardness that can be achieved on a given
material is governed by the carbon content in the material. When a maximum
hardness is required for a certain carbon content, then the case depth is controlled
by the cooling condition of the part. If the hardness requirement is lower, then we
can lower the power density and slow the travel speed to allow more time to drive
the heat down deeper and create a deeper case depth.
 Cooling Condition - As a general rule of thumb, at least six or seven times the case
depth thickness of material is needed beneath the surface to insure self-
quenching and to insure reaching the required case depth and hardness. This
requirement can sometimes be circumvented by using various methods to assist in
quenching. Air jets, water mist, or, if the part geometry allows, water or oil can be
utilized. These processes can aid in obtaining maximum surface hardness.

9. ADVANTAGE
 Precision control of heat input to localized areas
 Repeatability with increased processing speeds
 Minimal distortion
 Minimal residual stress input
 Self-quenching process; requires no quenching medium
 Time efficient process
 Line-of-sight access for hard to reach areas
 Able to process 0.050" to 2.0" (1.27mm to 50.8mm) wide
passes
 Increase local hardness over 60 Rc (material dependent)
without cracking

10. DISADVANTAGE
 The initial investment is very high.
 Maintenance cost is very high.
 Skilled worker is required.

11. Uses…
 Laser Hardening
 ID Laser Hardening
 Laser Softening / Laser Assisted Forming
 Laser Color Marking
 Process Control System

12. THANK YOU!
