Ultra-high-power laser welding of thick-section steel: Current research progress and future perspectives

•An introduction to two ultra-high-power laser welding techniques and their respective advantages and disadvantages are presented.•Formation of macroscopic weld defects in ultra-high-power laser welding process of thick-section steel and their current prevention methods are sorted and elaborated.•Insufficient filler wire distribution, inhomogeneous microstructural characteristics, and poor mechanical properties of ultra-high-power laser welded thick-section steel joints are discussed.•The future research perspectives of ultra-high-power laser welding process of thick-section steel are prospected. Thick-section steel is widely used in large structural applications, taking advantage of its characteristics, including high strength, good toughness, and low cost. Ultra-high-power laser welding (UHPLW), with laser power of 10 kW or higher, offers a new approach for manufacturing large thick-section steel structures due to its core ability to provide deep penetration. However, UHPLW of thick-section steel faces several welding defects problems such as spatter, root hump, porosity, and solidification cracks. Additionally, inhomogeneous microstructure and poor mechanical properties remain challenging issues. These problems impede the widespread use of UHPLW technology in thick-section steel applications and require continuous efforts to address. This review aims to provide an introduction to UHPLW technology, describe the macroscopic defects problems and research progress in prevention methods, and highlight the microstructure inhomogeneity along with the detrimental effects on mechanical properties. Finally, four future research perspectives and a conclusion are presented to provide new ideas for the current dilemma and guide future development towards achieving high-quality welded joints of thick-section steel.