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Among metal-based additive manufacturing, wire and arc additive manufacturing is receiving increasing attention for the production of components with medium to large dimensions. In the current research, the production of low-carbon steel thin-walled components by wire and arc additive manufacturing was addressed. Firstly, the influence of two depositing direction strategies on the wall shape was investigated. Subsequently, the effect of heat input on the shape stability and the microstructure evolution of the walls was studied. The results indicated that the alternating depositing direction strategy was more suited to build thin walls with relatively regular height. The heat input significantly influenced the shape stability, but had slight effects on the microstructure evolution. The microstructure of the walls varied from the top to the bottom regions, leading to a variation in hardness from 157 ± 3.11 to 192 ± 4.30 (HV5). The microstructure of the built thin walls can be distinguished in three regions: The upper region exhibited lamellar structures; the middle region dominantly featured granular structures of ferrites with a small proportion of pearlites, which appear in the boundaries of grains; and the lower region showed a mix of lamellar and equiaxed structures of ferrites. The tensile properties of the built material also exhibited anisotropic characteristics: The yield strength and ultimate tensile strength vary from 320 ± 6 to 362 ± 8 MPa and from 429 ± 8 to 479 ± 7 MPa, respectively.

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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.