Influence of the WAAM process and design aspects on residual stresses in high-strength structural steels

Abstract

Wire arc additive manufacturing (WAAM) enables the efficient production of weight-optimized modern engineering structures. Further increases in efficiency can be achieved by using high-strength structural steels. Commercial welding consumables for WAAM are already available on the market. Lack of knowledge and guidelines regarding welding residual stress and component safety during production and operation leads to severely limited use for industry applications. The sensitive microstructure of high-strength steels carries a high risk of cold cracking; therefore, residual stresses play a crucial role. For this reason, the influences of the material, the WAAM process, and the design on the formation of residual stresses and the risk of cold cracking are being investigated. The material used has a yield strength of over 800 MPa. This strength is adjusted via solid solution strengthening and a martensitic phase transformation. The volume expansion associated with martensite formation has a significant influence on the residual stresses. The focus of the present investigation is on the additive welding parameters and component design on their influence on hardness and residual stresses, which are analyzed by means of X-ray diffraction (XRD). Reference specimens (hollow cuboids) are welded fully automated with a systematic variation of heat control and design. Welding parameters and AM geometry are correlated with the resulting microstructure, hardness, and residual stress state. Increased heat input leads to lower tensile residual stresses which causes unfavorable microstructure and mechanical properties. The component design affects heat dissipation conditions and the intensity of restraint during welding and has a significant influence on the residual stress.

Residual Stress Evolution during Slot Milling for Repair Welding and Wire Arc Additive Manufacturing of High-Strength Steel Components

“…Moreover, microstructure investigations showed higher hardness and divergent microstructure for the last three weld layers of this filler material. The significantly higher hardness resulted from the lack of repeated annealing of the layers by subsequent weld beads [31]. Thus, it is assumed that the divergent microstructure of the top layers affects the residual stress distribution due to the predominant effects of a solid phase transformation in connection with a restrained volume expansion [30,32,33], primarily in longitudinal direction at the top 9 mm of the wall, causing a lower displacement due to slotting.…”

Multi-response optimisation of wire-arc additive manufacturing process parameters for AISI 4130 steel during remanufacturing process

“…WAAMed parts have limited application due to distortion and residual stress faults generated by the thermal effect during production [17]. These flaws occur during manufacturing due to process characteristics such as energy input, high deposition rate, and wide temperature gradient [30][31][32]. Recent research has focused on understanding and mitigating these flaws [33].…”