Laser hardening of materials by laser is a specialized and fast-growing field,
as it offers improved wear resistance, expansion of component life, and
increased strength and fatigue limits of the material.
Laser hardening is the perfect solution for processing highly stressed, complex
components. This is because
there is practically no warping of the component during processing due to targeted heat
input that is
confined to local areas. You can even open up applications that would not be possible
with conventional
hardening methods such as induction or flame hardening using the non-contact laser
process. Since the
machining process can be controlled precisely, even geometrically complex and delicate
components can be
hardened. The result is surfaces that can be strongly stressed mechanically and
chemically; they produce
significant benefits in tool making, the automotive industry, and in agricultural
technology.
While distortion is created during conventional hardening processes due to higher energy input and the subsequent quenching, the component remains in virtually its original state during laser hardening
In laser hardening, the skin of a carbon-containing work piece made from steel or cast
iron is heated up
to just below the melting temperature – this is generally around 900 to 1400°C. Around
40% of the
irradiated power is absorbed. The high temperature causes the carbon atoms in the metal
lattice to
rearrange (austenitization)
When the nominal temperature has been reached, the laser beam starts to move, thereby
steadily
heating the surface in the direction of feed.
As the laser beam moves on, the surrounding material cools down the hot surface very
quickly in a
process known as self-quenching. As a result of the rapid cooling, the metal lattice is
unable to return to
its original form, producing martensite. This results in a significant increase in
hardness.
The hardening depth of the outer layer is normally 0.1 to 1.5 millimeters, although on
some materials, it
may be 2.5 millimeters or more.
