In laser hardening of steel, the diode laser beam rapidly heats the surface layer to the austenitic phase , which is subsequently transformed into a hard martensitic structure utilizing the high cooling rates during self-quenching. Laser hardening permits selective hardening of locally well-defined areas on parts and tools made of a broad range of carbon steel alloys. Typical case depths reach from 0.3mm to 1.5mm depending on the material and pre-existing state of heat treatment. The precise energy input results in minimum distortion and often requires no finishing operation of the hardened surfaces.
While surface hardening takes places in the solid phase, laser surface remelting is a different form of heat treatment where a hard and wear resistant surface layer is formed via rapid melting and subsequent quenching of the material. The remelting leads to grain refinement and formation of fine dispersed hard phases that improve wear resistance of carbon and tool steels as well as cast iron.
Visotek high-power diode lasers conduct essential surface hardening and remelting processes of metals effectively and efficiently. Compared to other heat sources, the required energy can be locally applied. The width of the treated zone depends on the spot size of the laser beam and can be adjusted in a wide range via the focusing optic. Round, square, rectangular and line shaped spot sizes are available that can be tailored to the specific requirements of the application.
The Visotek high power direct diode laser is particularly well-suited for large-area applications in surface treatment due to its uniform “top-hat” intensity distribution. Compared to CO2 lasers, the diode laser benefits from its shorter wavelength (808 nm or/and 940 nm), which leads to increased absorption on metal surfaces and does not require the use of absorption enhancing coatings.