In this paper, the effects of the deposition speed and thermal cycles in gas-metal arc-welding (GMAW) additive manufacturing on the quality of as-built 308L stainless steel thin walls were investigated. The results exhibit that the deposition speed and thermal cycles play a crucial role in the quality of produced parts. An increase in deposition speed results in an improvement in the surface waviness. The surface waviness (Sa) decreases from 286 to 138 µm as the deposition speed increases from 0.2 to 0.4 m/min. On the other hand, the growth of microstructures in the walls fabricated with different deposition speeds shows a similar trend. The microstructure of as-built 308L-stainless-steel walls consists of dominant columnar/equiaxed dendrites of austenite and small amount of ferrite remaining in grain boundaries. The deposition speed mainly influences the grain size in microstructures. In the middle part of the walls, an augmentation in the deposition speed leads to a decrease of the secondary dendrite arm spacing, which results in an enhancement in mechanical properties of the walls. The microhardness and ultimate tensile strength increase from 153 ± 7.16 to 164 ± 8.96 HV0.1 and from 483 ± 4.24 to 518 ± 2.83 MPa, respectively, when the deposition speed increases from 0.2 to 0.4 m/min.

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