Investigation on Laser Beam Weldability of AISI 304L Plates Based on Thermal Field Simulation by Experimentally-Fitted Analytical Modeling

The objective of the work is to present a new approach to the simulation of the thermal field in laser beam welding, based on an experimentally-fitted analytical model, applied to investigate the weldability of AISI 304L austenitic steel. Reference is made to the welding trial in a single pass of two 10 mm thick butt-positioned plates. Welding was performed under the keyhole full penetration mode, which is characteristic of high-power laser beam, and simulated by an analytical model based on a multipoint-line thermal source system and fitted on the experimental fusion zone profile. The model was applied to simulate the effects of welding speed changes on thermal fields and cooling rates, in order to determine how they can affect the weld composition, the solidification mode and the possible formation of a sensitized zone in the heat affected zone. A limit value of welding speed, which allows the weld formation without lack of fusion, was identified. For all the welding speeds considered, the formation of a sensitized zone can be excluded. The contribution of welding speed on cooling rate, not significant near the welding axis, results to be determinant at the boundary of the fused zone with base metal. The combined choice of the filler material and the welding speed, which in all cases gives rise to primary ferrite solidification modes, affects the content of residual ferrite, which must be balanced to enhance the resistance to solidification cracking, avoiding the adverse effects due to too high contents. As a conclusion, the model proves to be a valid support in investigating the thermal effects, which result from the setup of welding parameters, on the weldability of the base metal-filler system.