Impact of modulated current welding on structural-phase state of 0.12 C-18Cr-10Ni-1 Ti-Fe austenitic steel

The structural-phase state of the heat-affected zone of a weld produced by modulated current (fine-droplet transfer) on 0.12 C-18Cr-10Ni-1Ti-Fe austenitic steel was studied by transmission diffraction electron microscopy method on thin foils. Welding modes: amperage and pulse time – 75 А, 0.15 sec., amperage and pause time – 15 A, 0.45 sec, average while-welding amperage – 42 A. The studies were carried out in a heat-affected zone at a 1 mm distance from the fusion line in the base metal’s direction – base metal’s zone; and the one at a distance of 0.5 mm in the deposited metal’s direction – the deposited metal’s zone. It was discovered that before welding the steel matrix is a γ-phase (austenite) having a face-centered cubic crystal lattice. Morphologically the steel structure is represented by the grains, a defective structure of which is only formed by a grid dislocation substructure, and the grains which host mechanical (or deformation) micro-twins in the form of packages of one, two or three systems along with the dislocation substructure. Micro-twins possess a crystal lattice and such parameter as γ-phase. The micro-twins’ allocation occurs along the {111} γ-phase planes. It was found out that welding in the base metal’s zone leads to ε-martensite formation both in the base (welded) and in the deposited (weld) metals. Moreover, γ → ε phase transformation in the weld metal’s zone is more intense and takes place in all γ-phase grains.