Microstructural and hardness analyses of welded joined by mig procedure

U ovom završnom radu napravljen je teorijski pregled i to elektrolučnog postupka zavarivanja s detaljnim opisom postupaka zavarivanja MIG metodom te pregled metoda mjerenja tvrdoće s detaljnim opisom Vickersove metode mjerenja. Ploče debljine 15 mm od konstrukcijskog čelika S235JR zavarene su sučeono K zavarom primjenom MIG metode. Zavareni spojevi hlađeni su nakon zavarivanja na različite načine, jedan je hlađen na zraku, a drugi u vodi. U eksperimentalnom dijelu završnog rada na sučeono zavarenim pločama nakon pripreme najprije je napravljena metalografska analiza mikrostrukture zavarenih spojeva, a zatim je izmjerena njihova tvrdoća Vickersovom metodom. Provedenim metalografskim ispitivanjima zaključilo se da zona utjecaja topline ima sitnozrnatu strukturu, a zona taljenja lijevanu strukturu. Nakon mjerenja tvrdoće vidljivo je da vrijednosti tvrdoća rastu od korijena prema licu zavara kako u zoni taljenja tako i u zoni utjecaja topline.In this final paper, a theoretical overview of the electric arc welding process with a detailed description of the MIG welding process and an overview of hardness measurement methods with a detailed description of the Vickers measurement method was made. The 15 mm thick plates made of structural steel S235JR are butt-welded with K welding using the MIG method. Welded joints were cooled after welding in different ways, one was cooled in air and the other in water. In the experimental part of the final work on the butt-welded plates after preparation, a metallographic analysis of the microstructure of the welded joints was first made, and then their hardness was measured using the Vickers method. The conducted metallographic tests concluded that the heat-affected zone has a fine-grained structure, and the melting zone has a cast structure. After measuring the hardness, it is evident that the hardness values increase from the root to the face of the weld, both in the melting zone and in the heat-affected zone