The Simulation Of Laser Hardening For45Steel With Shaping Laser Beam And Research On Its Microstructure And Property

The laser has got wide attentions from every field due to its own great applied value since it appeared in1960s.In the last few decades, the laser surface processing technology has made speedy development. Laser hardening as a kind of laser surface treatment is feasible to apply in transport, textile machinery, mould manufacturing and precise instrument for its high heating speed, high quenching hardness, high productivity, small deformation, non-oxidation, non-pollution and other advantages of the process. Because Gaussian beam intensity profiles occur naturally as the operating mode for many lasers, which means the large disparity between the intensity at the centre of the Gaussian beam and that at its outside edge leads to significant overheat-ing at the centre of the processed area, it is extremely difficult for the conventional laser to make the integral working layer hardened by single scan.To solve the problem of overheating in the centre of the area under the path of the moving beam, people always use the method of overlapping adjacent passes of the beamto compensate the low temperature on the edge of the beam, however, Overlapping the beam can cause fluctuation in the surface properties due to tempering effect on the edge of beam. Therefore, designing a kind of laser beam with new energy distribution which is appropriate for laser hardening becomes the key point to the process applied in indus-trial production.In this paper, the three-dimensional dynamic simulation model is established by the fundamental theory of laser hardening making comprehensive consideration about the latent heat of phase change, the change of thermal coefficient and the deviation of Austenitic conversion during the continuous-heating process.Then the laser beam with different energy distribution along the front and the end, the centre and the edge of the beam is built by changing the parameter of the model, the process of laser hardening with new kinds of beams is simulated and studied by utilizing the software of COMSOL Multiphysics, including the distribution role of the temperature flied and the cross section of geometries of the hardening layers.Meanwhile, a new kind of laser beam shaped by top-hat beam has been created with the shaper designed by Dr. Danial Wellburn. And the laser hardening experiment with this new laser beam on45steel has been completed under different scan power and scan speed. The microstructure, geometries, depth and width of the hardening layer are detected and analysed by Scanning Electron Microscopy, Optical Micro-scopy, and Microhardness Tester respectively. The error rate of the max depth of hardening layer between analogue results and experimental results is lower than10%.