Abstract: Influence of the main process parameters (laser power, scanning speed, powder feeding rate) on the molten pool temperature and the geometry of single track clad layer during laser cladding on 420 stainless steel, as well as the variation of temperature, temperature gradient and flow rate at different positions of the clad layer were studied. A heat-flow coupled 3D transient numerical model for laser cladding of 420 stainless steel powder on Q235 carbon steel substrate was established to simulate the forming process of laser cladding. The buoyancy force, Darcy resistance and Marangoni effect driven by surface tension in the molten pool were considered. The apparent heat capacity method was used to consider the latent heat of the material phase transition. The arbitrary Lagrangian-Eulerian (ALE) method was used to trace the free surface of the molten pool and simulate the growth of the molten pool. The results show that the molten pool temperature increases with the increase of laser power and powder feeding rate, but decreases with the increase of scanning speed. The process parameter that has the greatest influence on the clad layer width is the laser power and when it increases from 800 W to 1000 W, the cladding width increases by 175.4051 μm. The powder feeding rate has the greatest influence on the height and depth of clad layer. The powder feeding rate increases from 1.49 g/min to 3.17 g/min, the clad layer height increases by 309.8188 μm, while the clad layer depth decreases by 152.0495 μm. Under different laser cladding process parameters, the hardness from the top to the bottom of the clad layer decreases continuously. The experimental results show that the model can accurately predict the laser cladding process with different process parameters.

Key words: laser cladding, 420 stainless steel powder, heat-flow coupling, Marangoni effect, hardness