Modeling of temperature field and grain growth of a dual phase steel DP980 in direct diode laser heat treatment

The temperature field due to heating from a high-powered direct diode laser is calculated first by using an experiment-based finite element model. The Monte Carlo method is applied, which uses the calculated temperature history as thermal loading to obtain the grain growth in the heat-affected zone (HAZ) of dual phase steel DP980. The martensite decomposition in the heat treatment is considered to be a function of the scanning speed. Numerical results demonstrate that the increased scanning speed of the laser beam under laser power of 2 kW decreases the temperature gradient in the HAZ, resulting in finer martensite grains and a smaller percentage of martensite decomposition in the HAZ. This is in good agreement with the experimental data.