Lazer Hardening

LAZER HARDENING

Laser hardening is a heat treatment process that can be applied to all steels which have carbon content more than %0,2 and cast irons. Substance’s surface temperature is heated until it reachs a temperature which nearly below it’s melting point (900-1400 ○ C) with 1000K/s. When targeted temperature is reached, laser head starts moving with constant speed by looking to surface’s normal. During the heat treatment process, a pyrometer that attached to laser head, checks the surface temperature and with small changings at the laser power, surface temperature stays stable. That means, as long as the laser beam moves on the surface with constant speed, a homogeneous temperature pattern appears on the surface. High temperature changes material’s microstructure from body centered cubic (bcc) to face centered cubic (fcc) and we get austenite on the surface. When the laser beam leaves the heated area, surface temperature quickly decreases with self-quenching. There is no need to any coolant, becaue of the quick heat increase material’s inner side is still cold. Due to self-quenching and insant cooling, microstructure can’t transform back to body centered cubic and martensitic microstructure takes shape on the surface which is a very hard form of the material. Final hardness value of the material after process is directly connected with material’s carbon conten

Homogeneous heat distribution also leads to homogeneous microstructure and the brittleness problem of the hard materials’ dissapears due to this ordered, homogeneous microstructure.

With laser hardening, on the material’s surface, heat increase per second value is too high in the fact that thermal load to the material’s whole body is low . That means shape twisting after process is minimum. Local heat treatment prevents unnecessary thermal load to other parts of the body which are not needed to get harden. This also means cost of the process will be economic with local heat treatment. Unless the material has very small volume and very small amount of mass, final form of the material can be used without any extra process after laser hardening. That provides gain from both time and labor .