Abstract
The new welding method called as F-MAG, which has been developed based on CO2 gas-shielded arc welding method (MAG) increase deposition rate of weld metal. F-MAG welding method is combined with hot-wire, as having been used in TIG arc- and laser-welding methods. F-MAG is performed using hot-wire which is inserted into the rear part of weld pool made with leading electrode. Hot-wire melts by both electrical heating of itself and heat of weld pool.
Multi-layered weld metals were prepared using F-MAG and MAG. Microstructures and mechanical properties of both as-weld and reheated zones in uppermost layer of the multi-layered weld metals formed with F-MAG and MAG were examined and the effects of hot-wire on microstructures and mechanical properties were analyzed.
Both the as-weld and reheated zones of weld metal formed with F-MAG consisted of acicular ferrite (AF), equiaxed ferrite and so on. Both strength and elongation in as-weld and reheated zones formed with F-MAG were superior compared with those formed with MAG. It could be suggested that strength increased by refinement of AF due to increase in the concentration of alloying elements being contained in hot-wire. Larger elongation of weld metal in F-MAG compared with that in MAG could be analyzed in terms of the Aggregate of acicular ferrite Laths with nearly Parallel Slip systems between neighboring acicular ferrite laths (ALPS). The number of AFs contained in an ALPS formed with F-MAG is larger than that with MAG, in spite of the sizes of ALPSs formed with MAG and F-MAG being almost same. Deformation occurs over a lot of AFs in the case of finer AF formed with F-MAG through the rotation of tensile test piece during deformation, resulting in the larger elongation.
