The surface hardening with high power diode laser (short laser hardening and laser-beam hardening) is increasingly used in industrial manufacturing and toolmaking.
The laser hardening is a process in which the energy input takes place by means of radiation directly to the component surface. The laser beam heats short term and localized the top portion of the workpiece up to the austenitizing temperature of the material used. This leads to a homogenization of the carbon distribution and thus to a spread of a front of austenitization in the material.
Depending on the material used, the austenitizing temperature is about 900 ° C to 1400 ° C and time to temperature at about 3 s to 10 s.
Due to the small amount of heat input and rapid heat dissipation over the component a self-quenching is achieved, which causes a “freezing” of the hardness structure. The use of additional media for quenching, such as water, oil or compressed air is not required.
The laser hardening is suitable for all hardenable materials, which can be harded by flame hardening and induction hardening.
To harden the workpiece, the laser beam typically warms the outer layer to just under the melting temperature (about 900 to 1400 degrees Celsius). Once the desired temperature is reached, the laser beam starts moving. As the laser beam moves, it continuously warms the surface in the processing direction. The high temperature causes the iron atoms to change their position within the metal lattice (austenization). As soon as the laser beam moves away, the hot layer is cooled very rapidly by the surrounding material in a process known as self-quenching. Rapid cooling prevents the metal lattice from returning to its original structure, producing martensite. Martensite is a very hard metal structure. The transformation into martensite yields greater hardness.
The laser beam hardens the outer layer, or case, of the workpiece. The hardening depth of the outer layer is typically from 0.1 to 1.5 millimeters. On some materials, it may be 2.5 millimeters or more.
