Analysis of strength, microstructure and hardness of the butt-welded K-joint

  • 1 University of Zagreb, Faculty of Metallurgy, Croatia
  • 2 University of Zagreb, Faculty of Mechanical Engineering and Naval Architecture, Croatia


It is well known that there are several ways to make a butt weld depending on the thickness of the plates to be welded. This paper shows how important it is to prepare the surfaces to be joined by welding. In this paper, the 15 mm thick plates, made of mild steel S235JR, were welded face-to-face with a K-weld using the MIG welding method. The preparation of the plates before welding was not satisfactory, according to empirical instructions, and the resulting weld has defects. Four plates were welded face to face, resulting in two welds. The welds cooled in different ways after welding, one was cooled more slowly in air, and the other was cooled more quickly in water. After welding and cooling the welds, a metallographic analysis of the microstructures of the welds was carried out, 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 the hardness measurement, it can be seen that the hardness values in both the melting zone and the heat-affected zone increase from the root to the surface of the weld. Finally, a strength calculation was performed to determine how much static and dynamic alternating force the realized welded K-joint can withstand compared to the ideal value with good surface preparation



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