Microstructure and mechanical properties of low-carbon steel produced by WAAM with high deposition rate

Abstract

Wire arc additive manufacturing (WAAM) has the capacity to create large-scale metallic components for various applications with high deposition rate and energy efficiency. However, high deposition rates with the large energy input are inevitably associated with deterioration of surface quality, formation of defects and coarsening of the microstructure, which negatively affects mechanical properties. In this study, the possibility of large-sized parts producing by WAAM technique with high performance using the proposed deposition strategy was demonstrated. To determine the effect of high deposition rate on the microstructure and mechanical behavior, bulk low-carbon steel samples with dimensions of 90 х 90 х 90 mm³ was produced at high (10.3 kW) and low (2 kW) powers. The microstructure, consisting of (i) mixture of bainite/acicular ferrite (at 2 kW) or predominantly acicular ferrite (at 10.3 kW), (ii) allotriomorphic ferrite with (iii) carbides precipitation was observed. The size and volume fraction of phases, depending on process parameters and the thermal history during WAAM, defined the difference of the mechanical behavior. Although the high process power has resulted in some reduction in strength, namely the yield strength and ultimate tensile strength were 335 MPa and 560 MPa, respectively; the mechanical properties were comparable to those of mild steels, but produced by WAAM at significantly lower deposition rates. The microstructure formation mechanisms and relationships between microstructure and mechanical properties (e.g. strengthening mechanisms) were discussed.