Characterization of the welded joint on unalloyed titanium pipe

U ovom radu provedena je karakterizacija zavarenog spoja na cijevi od nelegiranog titanija oznake ASTM B265 GR2. U teorijskom dijelu rada opisan je titanij i njegove legure, a posebna pozornost posvećena je zavarivanju titanija te utjecaju zavarivanja na mikrostrukturu i mehanička svojstva. U eksperimentalnom dijelu rada provedeno je savojno ispitivanje, statičko vlačno ispitivanje te analiza makrostrukture i mikrostrukture u području zavarenog spoja izvedenog TIG postupkom. Pri savojnom ispitivanju pod kutom od 180° pojavile su se sitne pukotine u metalu zavara, ali nije došlo do loma ispitnih uzoraka. Pri statičkom vlačnom ispitivanju dobivene su znatno više vrijednosti vlačne čvrstoće od tražene vrijednosti koja iznosi 345 MPa. Zavar ima pravilnu geometriju, zona utjecaja topline je relativno široka, a linija staljivanja nije izražena kao ni granica između pojedinih prolaza. Mikrostruktura osnovnog materijala je relativno sitnozrnata, a sastoji se od α-kristala i vrlo male količine β-faze koja je prisutna i u zoni utjecaja topline te metalu zavara. U relativno širokoj zoni utjecaja topline kristalna zrna α-faze su puno krupnija, a njihova veličina raste prema liniji staljivanja. Metal zavara ima tipičnu ljevačku mikrostrukturu, podjednaku u tjemenu, sredini i korijenu zavara. Na temelju analize dobivenih rezultata utvrđena je zadovoljavajuća kvaliteta zavarenog spoja.In this thesis, the characterization of the welded joint on a pipe made of unalloyed titanium mark ASTM B265 GR2 was carried out. In the theoretical part of the work, titanium, and its alloys are described, and special attention is paid to the welding of titanium and the influence of welding on the microstructure and mechanical properties. In the experimental part of the work, flexural testing, tensile testing, and analysis of the macrostructure and microstructure of the TIG welded joint were performed. During the bending test at an angle of 180°, small cracks appeared in the weld metal, but the test specimens did not break. During the tensile test, significantly higher tensile strength values than the required value of 345 MPa were obtained. The weld has a regular geometry, the heat-affected zone is relatively wide, the melting line is not observed, nor is the boundary between individual passes. The microstructure of the base material is relatively fine-grained, consisting of α-crystals and a very small amount of β-phase, which is also present in the heat-affected zone and the weld metal. In the relatively wide heat-affected zone, the crystal grains of the α-phase are much larger, and their size increases towards the melting line. The weld metal has a typical foundry microstructure, equal in the face, middle, and root of the weld. Based on the analysis of the obtained results, the satisfactory quality of the welded joint was determined