Papers by Keyword: Structural Steel

Abstract: During underwater wet welding, the environment has a corresponding effect on the mechanical properties of the weld metal. The use of external electromagnetic action (EEA) during welding is promising for influencing the formation of welded joints and the structure formation in physically inhomogeneous environments. Experimental studies have demonstrated the effectiveness of EEA application in reducing the tendency of weld metal to form pores, enhancing degassing, and lowering hydrogen content etc. The paper presents a metallographic study of the welded joint metal of structural steel (St3) after underwater welding with 12Kh18N9T filler wire, both without and with the use of EEA. Based on calculation methods and predictive modelling, optimal operating modes of the electromagnetic system for an experimental study of the EEA effect during underwater welding have been established and implemented. It has been established that the weld metal mainly has a ferrite-pearlite structure, while an austenitic structure with elongated grains is formed in the weld metal. When using the EEA, the grain structure of the weld metal is refined by an average of 1.5 times with an insignificant decrease in microhardness. In the heat-affected zone (HAZ), in the areas of large grain (I HAZ), recrystallisation (II HAZ) and incomplete recrystallisation (III HAZ), a bainitic structure is formed in the presence of ferrite layers. Under the influence of the EEA, the grain size is refined by 1.2 times in the I HAZ and II HAZ with a decrease in the thickness of ferrite layers and an increase in microhardness by an average of 7 ... 10%. The formation of such a structure will provide a set of strength properties and toughness of the welded joint metal. Research has proven that the technology of wet welding under water using the EEA allows for the production of high-quality welded joints with a high set of physical and mechanical properties of the metal of both welded joints and the HAZ.

Abstract: This work aimed to develop new S355-based structural steels with enhanced marine corrosion resistance while preserving mechanical properties. Two alloying strategies (Cu/Ni and Al/Cr) were investigated. Conventional and new steel samples were produced and characterized for microstructure, mechanical properties, and corrosion. The new steels showed similar or improved mechanical properties. Potentiodynamic polarization tests indicated stabilization of the oxidation process in the new steels. Laboratory accelerated corrosion tests on painted specimens revealed reduced blistering at paint film defects for some new steels compared to conventional steel. Ongoing research includes evaluating painted specimens in a real offshore environment using an advanced floating laboratory

Abstract: Corrosion fatigue is a phenomenon in which corrosion damage is superimposed on fatigue damage and can result in a significant decrease in fatigue strength. Because corrosion fatigue cracks initiate from the bottom of corrosion pits, corrosion fatigue strength evaluation methods based on the corrosion pit shape have been proposed and put into practical use. However, corrosion fatigue strength evaluation methods have not been fully investigated for cases in which only corrosion damage precedes. Therefore, the state of the corroded surface due to corrosion damage was evaluated using the arithmetic mean waviness Wa. The arithmetic mean waviness Wa is an appropriate parameter for evaluating the degree of corrosion damage in structural steel immersed in synthetic sea water for long period.

Abstract: Carbon steel is widely used in infrastructure, manufacturing, and structures due to its cost-effectiveness and robust mechanical properties. However, the susceptibility of steel structures to corrosion in various working environments has been a longstanding concern. In this study, we explored the potential of titanium-aluminum (Ti-Al) coating as a surface treatment to enhance the corrosion resistance of low-carbon steel. The coating was applied using the arc spraying technique, where two materials were melted by an arc and then distributed onto the substrate using compressed air. To evaluate the corrosion resistance of the coated samples, we conducted immersion tests following the ASTM G31 standard for durations of 625 and 1000 hours. Additionally, electrochemical technique was employed to assess the anti-corrosion performance of both the Ti-Al coating and the substrate. Surface characterization was carried out using scanning electron microscopy equipped with energy-dispersive X-ray spectroscopy (SEM-EDX), as well as measurements of hardness and roughness. The SEM-EDX analysis revealed uniform distribution of titanium and aluminum across the surface and within the coating. Moreover, the coating significantly altered the surface roughness. Electrochemical corrosion testing indicated that the Ti-Al coating exhibited lower corrosion current and corrosion potential, suggesting its potential to enhance the corrosion resistance of the substrate. The SEM-EDX revealed cracks on the coating surface and the oxidation level of the coating surface varied with immersion time. The hardness of the coating was found to be relatively lower than that of the substrate, while the surface roughness was higher. Overall, the findings suggest that Ti-Al coating holds promise for enhancing the corrosion resistance of steel structures, as evidenced by its low corrosion current density and corrosion potential in corrosive environments.

Abstract: Fires can affect both civil and industrial buildings. Following a fire affecting a building or industrial structure, inspections are normally carried out to assess how the materials used in the construction have deteriorated and the severity of this phenomena. Emphasis is put on assessing the material damage, which involves understanding the mode of degradation, the mechanical and physical characteristics of these building materials and their behaviour in the presence of a thermal source. Understanding how heat affects building materials is very useful in assessing the extent of damage to various building components. Paper presents the results of an in-depth investigation of the effect of fire on an industrial building that has suffered a fire. Conclusions are drawn on the degree of material degradation of various elements of the hall structure.

Abstract: In the article the microstructure and phase composition of boride coatings deposited on selected structural steels were investigated. The boride coatings were produced using pack cementation method using commercial EKABOR-2 mixture containing of 50 wt. % of new and 50 wt. % of used powder. Boride coatings were deposited on alloyed structural steels grades (PN/EN 10084 standard): 16MnCr5, 18CrNiMo7-6, 41CrAlMo7 42CrMo4. Cylindrical samples with a diameter of 30 mm and a height of 30 mm were boronized in powder at 1000°C for 2, 4 and 6 hours in an argon atmosphere. The process was carried out in an industrial CVD Bernex BPX 325S device. The microstructure was analyzed using scanning electron microscope Phenom XL equipped with EDS spectrometer. The XRD phase analysis was conducted using XTRa diffractometer (ARL). The thickness as well as phase composition was analyzed on coatings formed on each grades of steels. The most of obtained boride coatings were characterized by single-phase structure (Fe₂B). The formation of brittle FeB phase was detected only on 16MnCr5 steel grades steels.

Abstract: This work presents a comparative finite element analysis of a 3-wheeler novel robot chassis used for uneven terrain robot applications. The chassis was modeled using SolidWorks and further analyzed in Ansys for its total deformation, equivalent stress, equivalent elastic strain and thermal strain. Two materials were taken into consideration for comparative analysis: Aluminium alloy and Structural steel. A load (force) of 500 N was distributed on the chassis uniformly and an acceleration of 5 mm/sec² was given. Thermal conditions were added by raising the temperature from 22°C to 50°C in 1 sec. The analysis performed was majorly divided into three parts: a) Only considering force, b) Considering force as well as acceleration, c) Considering force, acceleration and thermal conditions. Total deformation in Aluminium alloy was observed 1.51 to 2.79 times that of structural steel in all the cases. Both metals exhibited almost identical equivalent stress in absence of thermal effect and structural steel exhibit 1.5 times that of Aluminium alloy at elevated temperature. Aluminium alloy possess relatively more (1.86-2.63 times) equivalent elastic strain compared to structural steel. Although, distribution of thermal strain remained constant throughout the chassis for both the materials, its magnitude was 1.91 times high in Aluminium alloy. This type of analysis helps in evaluating the current design and decide whether it will sustain the required load and acceleration under given thermal conditions

Abstract: Flatness is an important quality parameter of heavy plates and it is generally achieved through cyclic elastoplastic deformation of the plate in a hot roller leveller following the rolling and cooling processes. To investigate and optimize the hot plate levelling (straightening) process, Finite Element (FE) simulations are widely used. Generally, flow curves with isotropic hardening are used for hot plate levelling simulations. However, the plate material might exhibit kinematic hardening, due to the load reversal that is seldom considered due to laborious high temperature cyclic material characterization. The current work aims at understanding the implications of considering kinematic hardening within hot heavy plate levelling simulations. Hot uniaxial and cyclic material characterization of S355 steel at 1000 °C is performed and the corresponding stress-strain curves are extracted. Using an inverse modelling technique, the associated isotropic and kinematic hardening models are calibrated. The cyclic data showed that the S355 steel exhibits kinematic hardening and the Chaboche kinematic hardening model is suitable to model this behaviour. Hot levelling simulations of plates with isotropic and kinematic hardening models showed a noticeable difference in the roll reaction forces and local curvature of the plate during the process while the resulting flatness of the final plate is not very sensitive to the material model for the investigated scenarios.

Abstract: The paper is focused on the effects of air gap size to mechanical properties of laser welded lap joints. Structural steel plates of 3 mm thickness were used in the laser welding experiments. The laser welding experiments were conducted at two very different energy inputs (EI) of 60 and 320 J/mm. The weld geometries were investigated using optical microscopy. The shear strength of the lap joints was evaluated by uniaxial tensile tests. Results showed that with low EI of 60 J/mm the size of air gap had significant effect on the width of the interface as the larger air gap size increased the width of the interface. At high EI of 320 J/mm, the width of the weld at the interface did not change significantly as the air gap increased. The hardness of the weld metal was greater than the hardness of the base material at both EIs. The shear strength of the joint increased significantly with low EI of 60 J/mm, as air gap size increased. The size of the air gap did not have a large effect on the shear strength of the joint with higher EI of 320 J/mm.

Abstract: During operation many metal structures are under conditions of combined impact of aggressive media (natural and/or technological) and mechanical loads. At the same time, the damage caused by the combined effect of corrosion and stress is often more significant than with simple "superimposing" of damage caused by mechanical load and influence of aggressive medium acting separately. When carrying out destructive tensile tests of equipment materials, there is a possibility of inaccuracy of results for determination of mechanical characteristics of this material due to actual operation of the material under conditions of aggressive environment. This, in turn, can lead to an erroneous calculation of the strength and life of the equipment. In this regard, it is particularly relevant to study the behavior of materials under the influence of various mechanical loads in aggressive media, as well as to determine the limit state of the metal based on the results of measurement of its electrode potential.