Microstructural evolution and performance investigation of 316L stainless steel thin-walled structures fabricated by LWAM

Laser wire feeding additive manufacturing (LWAM) technology is increasingly being regarded in the field of additive manufacturing due to its high deposition efficiency, low cost, and flexible manufacturing capabilities. However, the impact of heat input on the microstructure and mechanical properties of deposited parts during the LWAM process has not been fully explored. This study investigated mechanical properties and structural evolution of 316L stainless steel thin-walled structures at different printing parameters. Results indicate that reducing energy input induces epitaxial grain growth. Increasing energy density input transforms columnar grains into equiaxed grains within the material while increasing linear and cellular dislocations. Lower energy density input results in coarse columnar grain growth along the <001> direction, whereas increased energy density disrupts columnar grain growth, achieving 44% grain refinement and promoting grain growth along the <101> and <111> directions. The tensile properties of the deposited samples were also affected, with the average ultimate tensile strength (UTS) increasing by 26% and the average yield strength (YS) increasing by 30%. Simultaneously, high-energy-density samples substantially reduce both porosity and the diameter of pinhole defects. The energy input corresponding to a wire feed rate of 14 mm/s and a deposition moving speed of 500 mm/min, finer grain refinement and lower porosity are achieved. The material exhibits increased ferrite δ distribution at grain boundaries within the austenite γ matrix, yielding optimal comprehensive properties. This study provides both theoretical insights and technical foundations for the LWAM of thin-walled parts.