Application of a Soft Root Technique to the Welding of High Strength Steels (HSS)

• Ano de defesa: 2025
• Autor(a) principal: Souza, Gabriel Barbosa Coutinho Freire de
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: eng
• Instituição de defesa: Cranfield University
• Palavras-chave em Português: Undermatched welds; Soft root technique; HSS welding; Weld metal mismatch; Cold cracking mitigation; Fracture toughness; S690 steel; Engenharia nuclear; Diretoria-Geral do Desenvolvimento Nuclear e Tecnologia da Marinha (DGDNTM)
• Link de acesso: https://repositorio.marinha.mil.br/handle/ripcmb/848020

The increasing use of High-Strength Steels (HSS) in structural applications poses significant challenges to welding, particularly in selecting compatible filler metals with the same level of strength and in reducing the likelihood of cold cracking. Among the strategies proposed to address these issues, the use of a “soft root”, a root pass made with a lower-strength filler metal, has been studied. This research investigates the effects of applying a soft root configuration in the welding of a HSS (S690). The study explores the use of two different filler metals: a lower-strength wire applied to the root and a higher-strength wire used in the fill and cap passes. The experimental set included tensile tests, Charpy impact tests, hardness surveys, Scanning Electron Microscopy (SEM), and metallographic analysis to evaluate joint performance. The results indicate that the soft root configurations, even with mismatch ratios as low as 0.57, did not compromise mechanical integrity, reducing hardness and increasing ductility. Samples with a soft root did not behave as unmatched joints, outperforming the predictions of Eurocode 3 (EC3) curve. These findings support the strategy as a viable design alternative for welding HSS, especially in scenarios where matching or overmatching consumables and cold cracking are concerns. More research is recommended to unlock the full potential of this technique.