# Advantages of Corrosion-Resistant Overlay Welding on Steel S355J2N
## 1 Introduction  
Many components are expected to have a tough internal microstructure, while their surfaces should be wear-resistant or corrosion-resistant. Failures, especially in pressure vessels and pipe fittings, occur along boundary conditions, leading to perforation [1, 2]. In such cases, stress corrosion or wall thinning caused by internal cavitation can lead to leakage [3]. A local repair of this failure, using overlay welding in the installed environment, can be an effective and environmentally friendly solution. Naturally, research is also underway to explore materials that attempt to eliminate the perforation conditions in tanks and other pipe fittings [4]. Other research directions focus on developing the technological databases of laser overlay welding [5]. This is a relatively new area of usage in industry. In addition, research is also underway to reduce the heat-induced deformations and deflections in the field of various overlay welding processes as well [6]. Given the ongoing energy management challenges of our time, overlay welding interventions are becoming increasingly significant [7, 8, 9, 10]. As the demand for corrosion-resistant materials grows across various applications, there is an ongoing need for innovative solutions that enhance material performance and cost-effectiveness. Thus, choosing appropriate materials and measurements is essential to guarantee safe and reliable operations. Overlay welding is a widely used technique for improving the surface properties of base materials by creating a layer that protects the base metal from corrosion. When overlay-welding different components, a key factor is cost-effectiveness, as the proper choice of welding material and technology can ensure a long service life for the product [11]. Considering that the composition of the deposited layer in the welding of heat-treated steels may differ significantly from that of the base material [12], it is important to select technological parameters that reduce the proportion of the base material in the weld. A well-adjusted mixing ratio in the buffer and cladding layers helps to create the right ratio of alloying elements to achieve the desired corrosion resistance and homogeneous material structure. This requires controlled heat input, adequate seam overlap, and well-designed welding technology and welding speed [13; 14]. In our research, we investigated the overlay welding of S355J2N structural steel with a multi-layer, highly alloyed, corrosion-resistant austenitic filler material. Unalloyed structural steels are widely used types of steel, primarily used in welded joints exposed to constant or time-varying mechanical stresses, depending on their application. Their popularity is due to their favourable mechanical properties, low cost, versatility in production, and high formability [15; 16]. In industry, it is common to replace more expensive steel types with this steel group when the requirements for mechanical stresses allow doing so, in order to minimize material costs [12]. Since we welded with a filler material of significantly different composition and properties, it was necessary to create an intermediate layer made of an austenitic filler material, which we refer to as the buffer layer [17]. An important objective of our work was to determine at what depth we can speak of the formation of a corrosion-resistant layer. The study employs various testing techniques, including visual testing, macroscopic and microscopic examination, Vickers hardness testing, salt spray testing and electron microscopic examination. The formation of a suitable corrosion-resistant layer depends significantly on the Cr content enriched in the \(\delta\)-ferrite of the mixing zone. Taking all this into account, we aimed for a \(\delta\)-ferrite-austenite-type solidified material structure, which is ensured by Cr/Ni equivalent ratios between 1.48-1.95 [18]. At the same time, we had to avoid the appearance of sigma phases as well.