Microstructure evolution and mechanical properties in the depth direction of ultra-high power laser-arc hybrid weld joint of 316L stainless steel

•Ultra-high power laser-arc hybrid welding as a novel technology is adopted to join thick 316L stainless steel.•The evolution of microstructure and properties in the depth direction of 316L stainless steel are explored.•The growth direction of δ dendrites changes from “Ʌ” to “→←” and ‘’fx1’’ along the penetration direction.•A “teardrop-like” morphology appears in the lower layer with shrinkage cavities.•Shrinkage cavities are the key factor leading to weak mechanical properties of lower layer.