**6. Conclusions**

In this study, the influences of preheat temperature and interpass time on the longitudinal residual stress and vertical deflection of a T-joint fillet model were investigated. The local preheating technique, where the preheat temperature was kept constant only at the beginning of the welding process was simulated in the numerical calculations. The conclusions are as follows:


Generally speaking, the application of a local preheating procedure is very useful when the reduction of plate deflections is of primary concern. In this case, a preheat temperature should be imposed as high as practically possible, without interpass time, as was demonstrated with model M3. When the compressive longitudinal residual stress at the ends of the plates is minimized, the optimal solution is model M1 without any localized preheating and with no time gap between the two weld passes. In order to reduce the energy consumption that is needed for the preheat procedure, in the next phase of the investigations, the emphasis will be on optimization of the preheat zone size and temperature level in the high-productive buried arc welding of thick steel plates, when the heat inputs are very high.

**Author Contributions:** Conceptualization, methodology, data curation, investigation, writing—original draft preparation, formal analysis, funding acquisition, supervision and project administration, M.P.; data curation and supervision, I.G. and S.N.; data curation, H.D-J.

**Funding:** This research received no external funding.

**Acknowledgments:** The authors wish to express their deep gratitude to ISO Plus Croatia for financial support and to its engineers Ivica Cvrlje and Bruno Repar for their valuable comments.

**Conflicts of Interest:** The authors declare no conflicts of interest.
