Using a focused laser beam, the area to be hardened is very quickly heated to the critical temperature and subsequently quenched by the cold component volume. The material distortion is considerably reduced because of how quickly heat is applied with almost simultaneous self-quenching. This is thus considered a low-distortion or even distortion-free heat treatment. The carbon atoms change their position in the metal grid due to the high temperature. This behavior is desirable and called austenitization.

Quick cooling keeps the metal grid from returning to its original shape. The result is martensite (a very tough metal structure that looks very fine under the microscope), which increases the hardness of the material.

Even for large tools from forming technology, laser hardening is a very cost-efficient, extremely fast process for marginalized layer hardening, because it enables partial hardening of selected stressed functional areas on the workpiece surface.

This results in a zonally hard surface with a tough core, and the areas in the immediate vicinity are unaffected. The toughness of the basic material remains unchanged. Track widths from 1 to approx. 100 mm are possible depending on the laser power and system. The achievable hardness penetration depth is about 0.6 mm to 0.8 mm, and with many materials it can be up to 2 mm.