Mechanical properties of wire and arc additively manufactured high-strength steel structures

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.

Influence of Heat Control on Properties and Residual Stresses of Additive-Welded High-Strength Steel Components

“…From a cooling time of approx. 25 s, the ultimate tensile strength of the WAAM wire remained more or less constant up to 45 s. This was in accordance with studies of other authors, who focused on testing of mechanical properties in tensile specimens of an actual WAAM component/wall [14], in which, however, a relatively high effect of the cooling conditions on the yield strength was found. In future investigations, testing of the yield strength should therefore be mandatory.…”

“…In addition, studies demonstrated the suitability and efficiency of the controlled MSG short arc (e.g., cold metal transfer (CMT) or ColdArc) for large components [11]. Different studies dealt with the strong dependence of the temperature distribution and the resulting component geometry on the welding parameters [12][13][14]. These investigations showed the great importance of heat control in setting the desired microstructural properties of high-strength steels using WAAM.…”

“…This can be achieved by adjusting the heat input: preheating and interlayer temperature in such a way that as little heat as possible is introduced in the component during production [13]. In addition, Mueller et al showed the influence of welding parameters on the mechanical-technological properties of WAAM-manufactured components [14]. The results indicated a lower yield strength and an increased tensile strength when welding with a higher heat input.…”

The effects of building position on surface and fatigue of DED-arc steel components

“…In comparison to the nominal values provided by the manufactures, the applied building parmeters caused lower values resulting from the interpass temperature applied. A full overview on tensile properties was published earlier [35].…”

“…The weld metal microstructure of all four specimens was comparable and mainly composed of upper and lower bainite. A detailed analysis of this feed material and its mechanical parameters can be found elsewhere [35].…”