Compared to conventional heat treatment of rim zones, the laser beam hardening has some specific advantages as the low distortion because of the local heat input by the laser beam, the possible abandonment of an external cooling medium and the easy integration in the automatical production. Hardening with a continuous or pulsed wave laser power produces temperature fluctuations caused by variations of output power and absorption of the surface. Further, the peak temperatures of the pulse can cause initial surface melting with cooperated decreasing of hardness, tensile residual stresses and crack initiation. Because of the development of a real time control system, the highest occurring temperature during the pulse can be quickly detected and a new control point is transferred to the laser before the next pulse in order to keep the peak temperature constant. With this system the pulse peak temperature can be kept constant in the range of ± 10 K and melting even at pulse frequencies of only 25 Hz can be avoided surely. The equipment for temperature controlled hardening was used for the pulsed laser as well as the continuous laser beam. For instance, a revolving hardening of a bore by rotation of the sample was achieved as a continuous laser beam with the described temperature control. The temperature measurement is coaxial to the laser beam and so the system works independently from the direction. It can also be used for complex component geometries, e.g. edges, or materials whose austenite- and melting temperature is relatively close to each other, as in the case of high-carbide steel or cast iron.

Figure 1: Control mode of pulsed laser beam hardening.	Figure 2: Laser beam hardening of a rotating sample, circumferential to a bore.