# Advantages of Corrosion-Resistant Overlay Welding on Steel S355J2N
## 3 Experimental  
### Theoretical Background of the Weldability of Corrosion-Resistant Stets  
From the perspective of weldability, the carbon equivalent (CEV) is of crucial importance, as it helps determine the combined effect of carbon and other chemical elements on the steel's susceptibility to cold cracking. For good weldability, it is important that the steel grade has a low carbon equivalent, as the heat introduced during welding not only melts  
Figure 2: Welding procedure specification—key parameters for setting. The RUN column means: the number of layers/the number of seam rows in the layer. the base material and filler material but also significantly heats the surrounding area of the weld. The equation required to calculate the carbon equivalent, according to the EN 1011-2/A1 standard [24], is as follows:  
\[CEV=C+\frac{Mn+Si}{6}+\frac{Cr+Mo+V}{5}+\frac{Ni+Cu}{15} \tag{1}\]  
Using the Graville diagram, structural steels can be categorized into three groups based on their weldability. In zone I, there are easily weldable steels; in zone II, there are steels that should be welded carefully, and in zone III, structural steels that are difficult to weld due to their higher carbon content are found (Figure 3). Due to its low carbon content and the small proportion of alloying elements, the S355]2N belongs to the carefully weldable category, meaning that controlled heat input can prevent the structure from becoming prone to cracking. A wide range of corrosion-resistant steels are available in the industry, offering applications in various fields. If the steel contains at least 12% chromium (level I resistance limit) and the corrosion rate in a given medium does not exceed 0.1 mm/year, the steel is considered to be corrosion-resistant [26]. The corrosion resistance of these steel types is due to the thin, pore-free oxide layer that forms on their surface. They generally contain low amounts of carbon and more alloying elements. Minimizing the carbon content is particularly important for improving corrosion resistance. Austenitic corrosion-resistant steels are among the most well-known and commonly used steel types due to their excellent formability, heat resistance, and weldability. In their microstructure, the dominant phase is austenite, which provides good corrosion resistance against most media. Their strength is roughly comparable to unalloyed steels, with outstanding toughness, and their tear elongation is around 35-45% [26]. A common issue in overlay welds is that the first pass of the heavily alloyed weld, mixed with the base material, results in a brittle, martensitic microstructure. The bond between the two materials with significantly different compositions can only be achieved by creating a buffer layer. Based on the microstructure of the weld, the mechanical properties, welding characteristics, and resistance to corrosion can be well estimated. The most widely used method for determining (or estimating) the microstructure of the weld metal is the  
Figure 3: Graville diagram [25]. Schaeffler diagram, which has been in use since 1949 and shows the phase relationships of heavily alloyed steels [27; 28]. During the production of austenitic corrosion-resistant steels, the goal is to achieve a homogeneous austenitic microstructure in order to avoid precipitates, lattice defects running to the surface, irregularities, cracks, and corrosion damage. However, in many cases, other phase elements and precipitates make the microstructure somewhat heterogeneous. In practice, corrosion-resistant steels are not completely austenitic but contain small amounts of \(\delta\)-ferrite, which is specifically beneficial, as it reduces cracking sensitivity [28]. In addition to the above, it must also be noted that the presence of ferrite above 10% reduces corrosion resistance. Between 800-850 \({}^{\circ}\)C, ferrite transforms into the \(\sigma\)-phase, which is highly susceptible to corrosion. The ferrite content, or ferrite number (FN), can be determined from the chemical composition of the welding seam.