Physical simulation-based analysis of multipass welding in S500 shipbuilding steel

Novel generations of shipbuilding steels have outstanding toughness due to the improved steel producing processes. Their microstructure mainly consists of ferrite and bainite, while the presence of acicular ferrite has a role in high impact energy of the welded joint. This research aims to analyze the effect of multipass welding on weld characteristics of S500 shipbuilding steel. A Gleeble 3500 simulator machine is used to produce the welding thermal cycles by the Rykalin-3D model on 70 ×10 ×10 mm samples manufactured in transversal direction from a submerged arc welded joint of 16 mm plate. Temperatures for the simulations were set at 1350 °C for the coarse-grained zone forming in the weld metal (CGHAZ-W), 815 °C for the intercritical zone (ICHAZ-W), and a combination of these peak temperatures for the intercritically reheated coarse-grained zone (ICCGHAZ-W). The examined t8/5interval was 5–30 s. The weld properties were examined by microstructural examination, hardness test, and instrumented Charpy V-notch impact toughness test. The impact energy values of subzones were below the unaffected weld metal. Longer cooling time resulted in lower impact energy in ICHAZ-W. However, this tendency was not observed in CGHAZ-W. ICHAZ-W and ICCGHAZ-W resulted in the lowest impact toughness, which was indicated by the large unstable crack propagation.