Abstract
Additive manufacturing with steel opens up new possibilities for the construction sector. Especially direct energy deposition processes like DED-arc, also known as wire arc additive manufacturing (WAAM), is capable of manufacturing large structures with a high degree of geometric freedom, which makes the process suitable for the manufacturing of force flow-optimized steel nodes and spaceframes. By the use of high strength steel, the manufacturing times can be reduced since less material needs to be deposited. To keep the advantages of the high strength steel, the effect of thermal cycling during WAAM needs to be understood, since it influences the phase transformation, the resulting microstructure, and hence the mechanical properties of the material. In this study, the influences of energy input, interpass temperature, and cooling rate were investigated by welding thin walled samples. From each sample, microsections were analyzed, and tensile test and Charpy-V specimens were extracted and tested. The specimens with an interpass temperature of 200 °C, low energy input and applied active cooling showed a tensile strength of ~ 860–900 MPa, a yield strength of 700–780 MPa, and an elongation at fracture between 17 and 22%. The results showed the formation of martensite for specimens with high interpass temperatures which led to low yield and high tensile strengths (Rp0.2 = 520–590 MPa, Rm = 780–940 MPa) for the specimens without active cooling. At low interpass temperatures, the increase of the energy input led to a decrease of the tensile and the yield strength while the elongation at fracture as well as the Charpy impact energy increased. The formation of upper bainite due to the higher energy input can be avoided by accelerated cooling while martensite caused by high interpass temperatures need to be counteracted by heat treatment.
Highlights
Conventional manufacturing methods and the use of semifinished products are currently state-of-the-art in the construction industry
As the aim of this study is to investigate the influence of thermal cycles on the mechanical properties of high strength steel, wall structures were manufactured under variation of energy input, interpass temperature, and cooling
For the specimen with high energy input and low interpass temperature, the t8/5-time decreased from ≈ 25 to ≈ 20 s, whereas the cooling times for specimens with low energy input were reduced less (29 s to 25 for 400 °C interpass temperature or 18 to 17 s for 200 °C interpass temperature)
Summary
Conventional manufacturing methods and the use of semifinished products are currently state-of-the-art in the construction industry. The new approaches of additive manufacturing in construction enable the free. Welding in the World heating of already deposited layers, which affects the mechanical properties of the parts to be manufactured [5,6,7]. With regard to the construction industry, where the parts to be manufactured have huge dimensions, the manufacturing time is long the material is frequently exposed to higher temperatures for a long time. One possibility to shorten the manufacturing time is the use of high strength steel. Combined with an active cooling technology, the cooling rate from convection is increased, the heat does not stay in the structure for such a long time, which saves manufacturing time and may have a positive effect on the mechanical properties of the high strength steel
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