Influencing mechanism of the active elements on the surface tension of the laser cladding molten pool and the determination of the critical concentration

The addition of active elements during cladding will affect the molten pool flow, and different concentrations have different flow states. In this paper, a numerical model of heat-flow coupling in the ASTM 1045 laser cladding Fe60 process was established and the effects of different concentrations of S, O, and Se elements on the molten pool flow state were calculated and revealed. The results show that there is a critical concentration (CC) when the active element affects the molten pool flow. When the concentration is lower than CC, the flow direction of the melt in the molten pool is from the center to the edge. With the increase in concentration, the flow velocity of the molten pool gradually decreases. When the concentration of active elements reaches CC, the flow direction of the melt changes, but the concentration will make the molten pool flow disorderly appear. The concentration at which the melt flow direction begins to change is called the initial critical concentration (ICC), and the concentration at the end of the change in the melt flow direction (completely reversed) is called the perfect critical concentration (PCC). In the experiment, ICC and PCC intervals are not suitable for concentration selection. When the concentration of active elements exceeds PCC, the flow direction of molten pool does not change. The flow velocity of the molten pool gradually increases with the increase in the active element concentration. The morphology and microstructure of the cladding layer were analyzed with the same technological parameters. The effectiveness of numerical simulation is verified.