Optimizing the toughness of high strength steel weld metal

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For many steel constructions, high toughness of welds is a critical parameter to meet with current safety standards. For some high strength steel (HSS) grades, the required weld metal toughness can be hard to reach due to non-uniform metallurgy achieved by means of standard welding techniques. In OptoSteel, a novel experimental and simulation-based approach, combined with an extensive toughness testing and a detailed metallurgical characterization of welds, will allow defining the new welding strategies and procedures, including filler metal development. This will lead to optimized weld metal toughness, enabled by using advanced laser welding techniques and methods which are non-conventional LAHW and narrow gap multi-layer laser welding with wire addition, NGMLW. OptoSteel is to develop a new methodology for optimized welding of two high strength steel types (pipeline steels and Q+T steels) leading to homogeneous and predictable toughness values along the weld metal thickness. This includes improved understanding of the link between the weld metallurgy and microstructure with toughness and the way these are affected by the welding process and consumable used. Aimen will apply conventional/non-conventional LAHW and will carry out metallurgical and mechanical characterization of welds, including CVN, CTOD and modified toughness testing. For non-conventional LAHW, Aimen will study torch positioning, laser-arc pulse harmonization, twin spot laser beams and different arc modes (normal, pulse and modified spray arc) for optimum mixing of the filler metal wire into the melt pool and the homogenous distribution of alloying elements. AIMEN will perform remelting of welds experiments and develop CFD models for simulation of LAHW process.

**This project has received funding from the Research Fund for Coal and Steel under grant agreement No 709936. The dissemination of results herein reflects only the author's view and the European Commission is not responsible for any use that may be made of the information it contains.

• Sectors: Automotive, Nuclear, Oil
• Financing programme: THE RESEARCH PROGRAMME OF THE RESEARCH FUND FOR COAL AND STEEL (RFCS)
• R&D&i: Laser assisted processing, Materials under extreme conditions
• Leader: LULEA UNIVERSITY OF TECHNOLOGY
• Partners: AIMEN Centro Tecnológico, THYSSENKRUPP FORGING GROUP, Salzgitter Mannesmann Forschung GmbH, ENSA, Lincoln Electric Europe BV
• Acronym: OPTOSTEEL
• Ambit: International