Characterization of the austenitic stainless steel welded joint

Osnovni cilj ovog rada bila je karakterizacija zavarenog spoja između cijevi i ploče austenitnog nehrđajućeg čelika oznake X1CrNiMoCuN20-18-7. U teorijskom dijelu rada navedene su vrste nehrđajućih čelika, njihova svojstva i karakteristike. Detaljnije je opisana zavarljivost austenitnih nehrđajućih čelika. U eksperimentalnom dijelu rada provedena je metalografska priprema uzorka kako bi se analizirala makrostruktura i mikrostruktura te provelo ispitivanje mikrotvrdoće HV0,2 u osnovnom materijalu, zoni utjecaja topline i metalu zavara. Analizom makrostrukture utvrđen je nepotpuni provar i zavar nesimetričnog oblika, ali u dopuštenim granicama. Analizom mikrostrukture utvrđeno je da osnovni materijal ploče i cijevi imaju tipičnu austenitnu mikrostrukturu s udjelom delta-ferita manjim od 6 %. Linija staljivanja sa strane ploče jasno je izražena, zona utjecaja topline je uska, a mikrostruktura je austenitna s nešto krupnijim zrnima. Linija staljivanja sa strane cijevi je isto izražena, ali mikrostruktura zone utjecaja topline nije jasno vidljiva. Mikrostruktura metala zavara je tipična ljevačka dendritna s jasno izraženim prolazima. Najviše vrijednosti mikrotvrdoće HV0,2 izmjerene su u metalu zavara, nešto niže u zoni utjecaja topline, a najniže u osnovnom materijalu ploče. Izmjerena mikrotvrdoća u korijenu zavara viša je nego u sredini i tjemenu zavara.The main goal of this bachelor thesis was to characterize the welded joint between the pipe and the plate of austenitic stainless steel graded X1CrNiMoCuN20-18-7. Classification of stainless steels as their properties and characteristics were described in the theoretical part of the thesis. The weldeability of austenitic stainless steels was described in more detail. In the experimental part of the paper, metallographic sample preparation was carried out in order to analyse the macrostructure and microstructure along with microhardness HV0.2 test in the base material, heat-affected zone, and weld metal. The analysis of the macrostructure showed incomplete weld root and asymmetrical shape of weld within the allowed limits. The microstructure analysis showed that the base materials of the plate and pipe have a typical austenitic microstructure with a delta-ferrite content of less than 6%. The fusion line on the side of the plate is clearly expressed, the heat-affected zone is narrow, and the microstructure is austenitic with slightly larger grains. The fusion line on the pipe side is also noticeable, but the microstructure of the heat-affected zone is not visible. The weld metal microstructure is a typical as-cast dendritic structure with clearly defined passages. The highest values of microhardness HV0.2 were measured in the weld metal, slightly lower in the heat-affected zone and the lowest in the base material of the plate. The measured microhardness at the root of the weld is higher than in the middle and weld face