Local Laser Heat Treatment Of Dual-phase Auto Steel

Dual-phase steel is of enormous interest in the automotive industrydue to its potential in realizing light weight structures. However, itsrelatively poor formability limits the application to many parts in the carbody. Because during the process of stamping, the poor formability maylead to cracks. An effective solution to this limitation could be the locallaser heat treatment that uses the laser energy absorbed to soften the steelplate where a high formability is needed. Therefore, the measuring of thelaser absorption rate is of reference value for not only the calculation of thetemperature field in the steel plate, but also the optimization of processingparameters during the laser heat treatment of the dual-phase steel.In this paper, laser heat treatment is performed with Yd:YAG laser toprocess two different types of dual-phase steel samples, namely DP600and DP1180. By analyzing the microhardness, microstructure, tensile testresults and the coating properties, we can find that the softening occurredin the active area of the laser beam, and the molding performance of thedual-phase steelis improved.Measure the laser absorption rate of the dual-phase steel samples withboth the integrating sphere method and the lumped parameter method. Thetest results show that the laser absorption rate of dual-phase steel is atemperature-related variable. By comparing the variation curve of the laserabsorption rate measured by two methods, we can find that the two curvesare quite similar, sothat the feasibility ofthe test methods is verified.Based on the heat transfer theory, the physical and mathematicalmodelof three-dimensional and non-steady-state heat transfer process withthe stationary heat source is established. By substituting the laser absorption rate measured by experiment and the numericalsimulation withthe help of the finite element analysis software COMSOL, the temperaturefield in the steel plate could be obtained. Finally we compare thetemperature curve calculated by COMSOL and measured by thethermocouple so that the accuracy of the laser absorption rate measured byexperiments is verified.