# Advantages of Corrosion-Resistant Overlay Welding on Steel S355J2N
## 6 Conclusions  
In this study, the primary objective was to investigate the minimum welding seam requirement for a corrosion-resistant overlay in repairing various pressure vessels. Our tests were performed with a less commonly used wire electrode pairing, aiming to minimize welding time and maximize weld quality. During our tests, we concluded that the buffer layer provides a good microstructure transition between simple carbon steels and corrosion-resistant flux-cored wire types; therefore, a buffer layer is always necessary due to the uniform structure of the subsequent overlay layers. Based on our measurements, the thickness of the fusion zone formed between the base metal and the buffer layer did not exceed 10 microns, sharply separating the corroded and intact material structure. Consequently, we were able to determine that the applied layer structure and welding technology are suitable for the application of material-saving overlay welding. Accordingly, a suitable corrosion-resistant material structure can be created in the buffer layer (3.9-4.1 mm thickness); however, for durability, at least one cladding layer is needed. The minimum layer thickness, already in the first cladding layer, can be set depending on the thickness of the base metal. In the case of our test, the proper cladding layer thickness is at least 3 mm or more compared to the surface of the basic metal. This distance can be found above the buffer layer, in the first cladding layer, near point 11 given in Figure 11.  
We have summarized our main observations and the conclusions that can be drawn from them in the following three points:  
* In the case of a uniform-overlay welded material structure, a linear relationship can be determined between the Cr equivalents predicted in the mixture and the measured Cr values. All this is an important aspect due to the expected corrosion-resistance level. The novelty of the relationships is that in both the Schaeffler and WRC-92 methods, Equations (5) and (6) are relationships independent of the layer type; therefore, using these relationships, the expected Cr content can be estimated in the buffer and cladding layers very accurately. * A quadratic regression relationship can be established between the Cr or Ni content and the phase elements. On the basis of the relationship, the limit of phase element changes in a given system can be estimated (but not defined). The functional relationship allows identifying the phases present based on the measurement of the Cr  
Figure 18: Cr and Ni values of spot analyses performed in welds. or Ni content. The exact boundary transition so far is missing, but a transition zone can be determined based on our studies, which falls between 11.29-11.73% based on the Ni content. Below it, only the delta ferrite phase is present, and above it, only the austenite phase is present. * We observed that the Cr content in the delta ferrite shows stronger changes with the increase in the number of layers. We were able to demonstrate all this numerically based on the data in Table 3 and our measurement results. According to the technical certificate, the Cr content of the E316L filler material is 19%, while according to the measurements, the average Cr content of the cladding layer is 19.63%. At the same time, the filler material of the E309 LMo buffer weld had a Cr content of 22.9%, but our measurements indicated an average Cr content of only 18.67% in the buffer layer. Based on the above, we can identify that the Cr was enriched in the delta ferrite towards the surface. All in all, in terms of reducing the environmental load, we presented an effective overlay welding solution in our study, in which we managed to identify further research directions in the topic, which requires a wider expansion of the studies in the future. Conceptualization, F.T. and L.V. ; Methodology, F.T., N.L. and L.V. ; Validation, F.T. ; Formal analysis, H.H. ; Investigation, N.L. and L.V. ; Resources, N.L. ; Data curation, N.L. ; Writing--original draft, F.T. ; Writing--review & editing, H.H.