The Influence of Welding Mode on the Structural-Phase State of Steel 0.12С-18Cr-10Ni-1Ti-Fe at Welding by Modulated Current

Abstract

Investigations conducted by transmission electron microscopy on thin foils were aimed at studying the structural-phase state of heat-affected zone of the welding joint performed by modulated current at two welding modes: coarse-droplet and fine-droplet transfer. Welding was conducted on the austenitic steel 0.12С-18Cr-10Ni-1Ti-Fe using the facility UDI-203. Welding modes were: Ii = 175 А (coarse-droplet transfer) and 140 А (fine-droplet transfer). Welding was performed on thin foils sized 200 × 15 × 4 mm3. Investigations were focused on heat-affected zone at the distance of 1 mm from the weld line towards the base metal – the base metal zone and at the distance of 0.5 mm towards the welded metal – the welded metal zone. The studies showed that in the state before welding the steel matrix presents γ-phase (austenite), which has face-centered cubic (fcc) crystal lattice. Morphologically the steel structure is given as grains where defect structure is presented by only network dislocation substructure, and grains where along with the dislocation substructure there are mechanical (or deformation) microtwins in the form of packages of one, two and three systems. It was established that welding of steel 0.12С-18Cr-10Ni-1Ti-Fe by modulated current with coarse-droplet transfer leads to martensitic transformation γ → ε only in the welded metal zone. At fine-droplet transfer welding leads to martensitic transformation γ → ε both in the base metal zone and in the welded metal zone. In the welded metal zone phase transformation γ → ε occurs more intensively. It was revealed that crystal lattice distortion in the whole heat-affected zone at welding by modulated current has only plastic nature, irrespective of the welding mode. Welding by modulated current with fine-droplet transfer leads to lower internal stresses in the whole heat-affected zone.