Mechanism study on the microstructure and low-temperature toughness of Q355E welded joints with different wire compositions

• The influence of different elements on the microstructure of materials. • Simulation of phase transition process using different welding wires. • The influence of microstructure on low-temperature toughness. • The difference in low-temperature impact fracture caused by the second phase particles. The widespread application of construction machinery and equipment in the extremely cold mining market has led to an increasing demand for material impact resistance. This article investigates the effects of different welding wires on the microstructure and low-temperature impact performance of welded joints. These welded parts are widely used in the production of component materials for engineering machinery equipment operating in extremely cold markets, with the aim of obtaining materials with higher low-temperature impact toughness and mechanical properties. Microstructure analysis is conducted through electron backscatter diffraction experiments. The findings demonstrate that variations exist in the mechanical properties of distinct welded joints, arising from the combined effects of fine grain strengthening and dislocation strengthening mechanisms. Through the simulation of molten pool solidification, it was observed that different alloying elements exert a notable influence on the crystalline phase transformation during the solidification process. This gives rise to substantial discrepancies in grain size, high-angle grain boundaries, and dislocation density. These results suggest that titanium contributes to facilitating the nucleation of acicular ferrite, which leads to fracture that an energy-intensive form as the primary mode of impact fracture. This effect effectively suppresses crack propagation and enhances the low-temperature impact toughness of the welded joints.