In this paper, the effects of overlay welding of S355J2N steel were studied. We examined how the technological advantages of overlay welding can be taken into account to improve the service lifetime and applicability of components made from traditional S355J2N structural steel during the planning step. Increasing the service life of structures exposed to environmental influences is essential, especially on surfaces exposed to abrasive and chemical corrosion. The direct aim of the investigation was to present a comprehensive picture of technological advantages of the corrosion-resistant overlay welding on steel S355J2N. We mainly analysed experiments with powder-coated wire electrodes which are based on protective gas and robot technology usage. With various mechanical tests, we searched for the minimum number of layers that provides sufficient protection against corrosion. The aim of this paper is to present achieved results during development of a welding technology of a reliably functioning product with increased corrosion resistance.

With regard to the heating technology of small test specimens (D < 1 inch, i.e., 25.4 mm), only a limited amount of data and literature are available for making adequate technological decisions. Heating time of small geometric shapes is influenced by the technological parameters of the furnace, the temperature, the disposition technique in the furnace and the geometric characteristics of the workpiece. How to shorten heating time to achieve a suitable material structure is a vital question, while considerable energy is saved at the same time. Among the geometric characteristics, shape dependence is one of the important aspects that must be taken into account in terms of heating technology. Shape dependence is usually taken into account with empirically produced correction factors, which can result in significant oversizing of heating time, energy-wasting technology and material structure of insufficient fineness. In the course of our work, we investigated and compared the shape dependence of cylindrical and prismatic specimens with the same surface-to-volume ratios, which were combined with surface heat transfer analyses and geometric effect tests to formulate new approximate equations for determining heating time. As a result, we could mathematically derive a relationship between heating time, size and shape of the active surfaces, the correlation of which can shorten heating time by 20%. In addition, a shape factor (1.125) between cylinder and prismatic-shaped specimens was determined, which can be used with the new equation to calculate heating time for similar specimens. At last, a relationship is developed between the amount of heat that can be stored in the body during heat equalization and the complexity of the shape, which can be characterized through ratios depending on heating times and active surfaces in the function of total surface/volume ratio. Based on this relationship it can be determined more precisely when heat equalization occurs; therefore, shorter heating time can be achieved. In conclusion, with the help of this new method, optimal heating time for structural steel components, in the case of small cross-section and weight, can be determined.

The usage of CHT (Continuous Heating Transformations) diagrams for a given steel or equivalent grade, requires knowledge of heating temperature, average heating rate, and the heating time. Definition of these technological parameters are primarily based on the complex relationship system between the geometric, thermal parameters and the heating device. In our research, we mainly focused on those physical key parameters that can mostly influence the heating and transformation rate. These parameters provide realistic, usable data for analysing the process of thermal diffusion and FEA (Finite Element Analysis) tests. During analysis, an easy-to-use function relationship was determined for approaching the heating rate more precisely. This method allows handling the CHT charts easily, within a selected range, regarding weldable mild steels.

In case of numerical analysis of forged parts, it is important to specify the friction coefficient characterizing the lubrication conditions. In our paper we present a combined method of a known SU (Simple Upsetting) deformation with EDS (Energy Dispersive Spectroscopy), which shows the relationship between the Kudo's friction number (this friction model is applicable for metalworking processes which produces high surface pressure) and the theoretical layer thickness of the graphite film covering the sink cavity. The tests were accomplished considering the solids content of non-synthetically produced lubricant concentrates diluted to varying degrees.