Product Code: ICAL05_905

Productivity Issues in Diode Laser Transformation Hardening
Authors:
Henrikki Pantsar, VTT Industrial Systems; Lappeenranta Finland
Presented at ICALEO 2005

The productivity in laser transformation hardening is a complex combination of physics and metallurgy. In many laser processes higher productivity is achieved by increasing the laser power together with the process velocity. In laser transformation hardening the material should remain in the solid state and the use of laser power is limited. Metallurgical transformations are based on kinetics and in order to achieve a given hardness the processing speed can be increased only within certain limits. Many parameter combinations can lead to the required hardened depth, but the consumption of electrical power may be increased drastically due to incorrect parameter selection.

Three types of steels were hardened with various parameter combinations using a high power diode laser. The hardened depth was measured from each sample to establish the dependence between the laser energy and the depth. The absorptivity of steel surfaces was measured by calorimetry. Surface hardness was measured from each sample and a microstructural analysis was made to study the metallurgical factors affecting productivity.

Although higher values for absorptivity were obtained using relatively low laser powers and slow traverse rates, productivity and electrical efficiency of the process were maximized by increasing the laser power and the traverse rate. Metallurgical phase transformations during hardening were limited by transformation kinetics and the process optimization was found to be highly dependant on the microstructure and alloy concentration of the steel.