Product Code: ICAL05_1303

Mathematical Model Based on Kinetics and Thermodynamics for Estimating the Properties of Laser Hardened Steel Surfaces
Authors:
Henrikki Pantsar, VTT Industrial Systems; Lappeenranta FI Finland
Presented at ICALEO 2005

High power laser beam is scanned over a surface of a component in laser transformation hardening. The absorbed energy of the laser beam heats the surface rapidly to temperatures near the melting point. A high cooling rate is achieved by self-quenching and a hard martensitic surface is formed. Due to the rapid thermal cycle, the phase transformations occur far from equilibrium and the estimation of the resulting hardness is problematic.

In the present study a mathematical model for calculating the surface hardness is developed. The model takes data from equilibrium diagrams composed by thermodynamics and phase-equilibria software. A kinetic term to express the rate of change during hardening is introduced to relate equilibrium data to the non-equilibrium process. Hardening experiments were performed to 34 commercial steel grades with a carbon content varying from 0.03 to 3.06 wt-% and metallic alloy element content varying from 1 to 25 wt-%. 7 steels were studied in detail to establish the phase transformations occurring during the hardening process. A good correlation between the model and experimental results was achieved with all materials, excluding martensitic stainless steels.