Investigation on the microstructure and mechanical properties of large-tube forging manufactured by additive forging

Abstract Large-tube forgings were formed using nine layers of continuous-casting billet made from 15CrNi3MoV alloy steel via additive forging. The interfacial microstructural evolution under different hot-compression bonding temperatures and strains was investigated using optical microscopy, scanning electron microscopy, and electron backscatter diffraction. The tensile properties of the hot-compression-bonded and tube-forged samples were also evaluated. The results showed that as the hot-compression bonding temperature and strain increased, the bonding interface gradually disappeared and the voids at the bonding interface closed. Finally, the interface was replaced with recrystallised grains. The tensile properties of the hot-compression-bonded samples at different temperatures and strains were identical. The tensile properties of the interface and base samples of the tube forging were comparable, and the fracture morphologies were consistent. The fracture position of the large tensile sample with a length of 1000 mm containing three original interfaces is the base, indicating the complete metallurgical bonding of the forging.