# Advantages of Corrosion-Resistant Overlay Welding on Steel S355J2N
## 3 Experimental
### Mixing Between the Base Material and the First Layer  
In the case studied, the mixing with the S355]2N structural steel material must be kept below 35% during the welding of the first layer. If the mixing exceeds this value as a result of the welding process, the ferrite content of the weld must be determined with a calibrated ferrite content meter, or an estimate should be made based on the chemical composition, e.g., using the WRC-92 diagram. Among the listed issues, grain boundary corrosion is the potential source of failure that required special consideration during the experiments. When selecting the filler material for the first welding seam, we aimed to create a microstructure which, while allowing for the desired mixing, would not produce carbide precipitates, or would do so only in small amounts. The condition for this is that carbon must not be able to withdraw chromium in carbide form at the grain boundaries, thus reducing the corrosion resistance of the base metal below level I (12%, intergranular corrosion) [26]. One way to achieve this is by binding carbon through the previously mentioned titanium and niobium alloying or by increasing the ferrite number, which leads to the formation of carbon-enriched \(\delta\)- ferrite in the base material. This ferrite cannot harden because there is no austenitic phase during cooling. Therefore, with the proper technology (controlled cooling process and limited heat input energy), grain boundary corrosion can be excluded. The first layer is essentially the filler material of the buffer layer. During the process, care had to be taken to ensure that the joint did not heat to temperatures higher than the permissible limit; otherwise, the weld would become inhomogeneous, and cold cracking would occur. Achieving a homogeneous microstructure is a fundamental goal in corrosion-resistant steels, as any inhomogeneity can become a starting point for corrosion attack. In our experiment, the first weld pass served as an intermediate layer, since the composition of the second and third layers significantly differed from that of the low-alloy structural steel, and our goal was to achieve a purely austenitic structure. The appropriate mixing ratio of the buffer layer was determined based on the chromium and nickel equivalencies of the base metal and the E309 LMo filler wire, using the Schaeffler diagram as a reference. Here, we took into account that, in the classic case, the bonding surfaces of the filler material and the base metal generally melt at approximately the same rate, and the filler material typically \"dilutes\" about 20-40% of the molten base metal. Since, in the formation of the buffer layer, in addition to the composition differences, the heat input energy had to be controlled as well, we used the setup data from Figure 3 to consider 70% of the 30% average mixing, taking the technological settings into account. For the deposition of the second and third layers, the 30% mixing ratio was found to be appropriate. Since we used the Schaeffler diagram to determine the mixing points, we first clarified the methods for calculating Cr(E) and Ni(E) according to Schaeffler (2) and WRC-92 (3). The WRC-92 diagram was used to verify the obtained values. Schaeffler:  
\[Cr_{(ES)}=Cr\%+Mo\%+1.55i\%+0.5 Nb\%+2 Ti\%Ni_{(ES)}=Ni\%+30C\%+0.5 Mn\% \tag{2}\]  
WRC-92:  
\[Cr_{(EW)}=Cr\%+Mo\%+0.7 Nb\%Ni_{(EW)}=Ni\%+35C\%+20N\%+0.25 Cu\% \tag{3}\]  
During the experiments, the electrode used for welding the first layer, mixed with the base material (S355]2N) at approximately 21%, resulted in the weld microstructure shown in Figure 4.  
In Figure 4, the horizontal axis of the diagram shows the chromium equivalent containing ferrite-forming alloying elements, while the vertical axis represents the nickel equivalent derived from austenite-forming alloying elements. The multiplication factors of the individual alloying elements (2) indicate their strength of influence on the microstructure.