Steels Research Articles

Post-fire residual mechanical properties of Q460GJ steel under different pre-tensile stresses

Previous studies on the post-fire mechanical properties of steel were conducted with unstressed state, without considering the influence of pre-stress which subjected to structures in reality. In this article, the post-fire residual mechanical properties of Q460GJ steel under different pre-tensile stresses were studied. The stress-strain curve, elastic modulus, yield strength, ultimate strength and fracture elongation of Q460GJ steel after different elevated temperatures heating are analyzed in detail. The experimental results are compared with that of Q460 steel and S460 steel in the existing literatures. At last, the predictive equations of post-fire mechanical properties of Q460GJ steel under different pre-tensile stresses are established. Q460GJ steel still maintains good ductility after elevated temperature heating, which increases the possibility of reuse of Q460GJ steel element after fire. The Q460GJ steel has better post-fire ductility than that of Q460 and S460 steels. The predictive equations for the post-fire residual mechanical properties for Q460GJ steel under different pre-tensile stresses were proposed. The variation coefficients of yield strength for Q460GJ steel under different pre-tensile stresses after 20 min different elevated temperatures heating were within 0.065. The findings should have a great significance to providing theoretical support for design of reusing or restoring steel building after fire.

A Contactless Low-Carbon Steel Magnetostrictive Torquemeter: Numerical Analysis and Experimental Validation

Torque measurement is a key task in several mechanical and structural engineering applications. Most commercial torquemeters require the shaft to be interrupted to place the sensors between the two portions of the shaft where a torque has to be measured. Contactless torquemeters based on the inverse magnetostrictive effect represent an effective alternative to conventional ones. Most known ferromagnetic materials have an inverse magnetostrictive behavior: applied stresses induce variations in their magnetic properties. This paper investigates the possibility of measuring torsional loads applied to a shaft made of ferromagnetic steel S235 through an inverse magnetostrictive torquemeter. It consists of an excitation coil that produces a time-varying electromagnetic field inside the shaft and an array of sensing coils suitably arranged around it, in which voltages are induced. First, the system is analyzed both in unloaded and loaded conditions by a Finite Element Method, investigating the influence of relative positions between the sensor and the shaft. Then, the numerical results are compared with the experimental measurements, confirming a linear characteristic of the sensor (sensitivity about 0.013 mV/Nm for the adopted experimental setup) and revealing the consistency of the model used. Since the system exploits the physical behavior of a large class of structural steel and does not require the introduction of special materials, this torquemeter may represent a reliable, economical, and easy-to-install device.

Effect of Ti–Mg–Ce Complex Deoxidation on the Inclusions and Mechanical Properties of S355 Steel

Oxide metallurgy technology not only refines the microstructure but also modifies the type, density, and size of inclusions. This study examines the impact of Ti–Mg–Ce composite deoxidation on the inclusions and mechanical properties of S355 steel used for heavy‐duty H‐beams. Compared to base alloy, Ti–Mg–Ce‐added alloy features a higher presence of inclusions such as MgO, TiN (containing Ce), TiOx, and TiS, except for SiO2, Al2O3, MnS, and MnO. Following Ti–Mg–Ce composite deoxidation, the number density of inclusions increases by 16.4%, and the equivalent diameter, length, and width of the inclusions decrease by 41.0%, 41.2%, and 37.9%, respectively. The length of large‐angle grain boundaries in the same area increases by 20%, and the average grain size reduces by 12.5%, resulting in an enhancement of yield strength by 23.6 MPa, tensile strength by 37 MPa, total elongation by 2.1%, and impact energy by 92 J. By employing Ti–Mg–Ce composite deoxidation to optimize inclusions and microstructure, the strength, plasticity, and toughness of the experimental steel are significantly improved.

Tracing the dynamic ecology of microbial biofilms on steel with prolonged submersion in surface water

Amplicon sequencing is applied to monitor microbial species residing in the biofilm that formed on steel surface submerged in surface water along the Ghent Terneuzen canal, stretching 31 kms from Belgium to the Netherlands. Temporal and spatial differences in the biofilm microbiota were revealed by 16S rRNA composition analysis. The loss-of-mass from S235 steel coupons showed uniform corrosion rates ranging from 242 to 906 g/m2 after 3 months. Notably, enhanced pitting corrosion was seen at one specific location near ‘Heide’ affecting the surface with depths up to 1210 µm after 6 months. We presume the excessive steel deterioration in micro-cavities is associated with microbial activity of iron-oxidising bacteria (IOB) and sulphur-reducing bacteria (SRB), such as Shewanella spp . and Gallionella spp., respectively, as redox-active species. Indications for microbially induced corrosion (MIC) are highlighted at sites with apt microbial composition, irrespective of physico-chemical water parameters. Coupons affected by high corrosion and assumed MIC did not stand out in terms of species richness and alpha diversity did not increase, suggesting partial take-over of the microbial community by IOB or SRB.

Enhancing high-temperature chloride molten salts corrosion resistance of 310S steel with Si-added Ni–Al coating

Ni–Al based coating is one of the common high temperature and corrosion resistant protective coatings. In the present paper, the effect of Si content on the formation of Al2O3 layer and the corrosion resistance of Ni–Al coating to chloride molten salt was studied. The research results show that the Ni–Al coatings with varying Si content mainly form NiAl2O4 and Al2O3 oxide layers after pre-oxidation, and form a three-layer structure after molten salt corrosion. The appropriate amount of Si added to the Ni–Al coating can promote the formation of the α-Al2O3 layer during pre-oxidation and thermal corrosion, improving the corrosion resistance of the coating to high temperature chloride molten salt, and hindering the diffusion of Cr elements. Particularly, the Ni–Al coating with Si content of 1.2 at.% has the thickest and densest Al2O3 protective layer, showing the best corrosion resistance. The simulation results shows that compared with the Ni–Al coating without Si, the Cl atoms in the Si-added Ni–Al coating need to overcome greater energy barriers to diffusion during the molten salt corrosion process, which also indicates that the addition of Si can improve the corrosion resistance of the coating.

Deep learning coupled Bayesian inference method for measuring the elastoplastic properties of SS400 steel welds by nanoindentation experiment

Nanoindentation experiment has shown broad application prospects due to its ability to measure the mechanical properties of various materials at multiple scales. In this paper, a deep learning coupled Bayesian inverse approach is proposed for measuring the elastoplastic parameters of SS400 steel welds by nanoindentation experiment. The nanoindentation experiments were performed on the SS400 steel welds, including base metal (BM), weld zone (WZ), and heat affected zone (HAZ), and the experiment load–displacement (P-h) curves were obtained. The hyper-parameters tunable artificial neural network (ANN) was established to correlate elastoplastic parameters with indentation P-h curves. Based on Bayesian inference theory, the posterior density function for estimating the unknown material parameters was established. Transitional Markov chain Monte Carlo was used for sampling from the posterior density function, and the elastoplastic properties in different regions of SS400 steel welds were identified. The advantage of the established measuring method is that the hyper-parameters optimized ANN model can provide the very accurate forward relationship between material properties and indentation P-h curves. Besides, the inverse Bayesian framework can quantify the potential uncertainty of the identified elastoplastic parameters. The measured elastoplastic properties of the base metal of SS400 steel show good agreement with tensile experiment data, of which the maximum measuring error is less than 12%. The measured elastoplastic properties in WZ and HAZ are also proved to be effective. The uncertainty of the identified elastoplastic parameters of SS400 steel welds can be quantified by posterior marginal distribution, using Mean and Variance values. The results proved that the proposed inverse measuring method is reliable and effective.

Effect of ultrasonic impact treatment on surface residual stress, microstructure and electrochemical properties of the hot-rolled S355 steel

The effects of ultrasonic impact treatment (UIT) on the microstructure, corrosion resistance, and surface residual stress of hot-rolled S355 steel were investigated. In addition, the improving mechanism of the UIT induced corrosion resistance was discussed. The results show that the UIT can effectively improve the corrosion resistance of hot-rolled S355 steel, and corrosion current density reduction is demonstrated. Based on the corrosion morphology, it can be found that after the UIT the corrosion pits became shallower, the oxide layer becomes denser, and more flocculent structures appear on the surface as well as the appearance of dense irregular curved structures. Moreover, the residual tensile stress on the surface of the hot-rolled S355 steel is transformed into residual compressive stress after the UIT. The grains are refined, and the microhardness is increased, which implied that the significant plastic deformation has occurred on the surface of the hot-rolled S355 steel. The findings confirm that dense oxides could be generated on the surface of hot-rolled S355 steel treated by ultrasonic impact since the residual compressive stress is introduced, the plastic deformation is induced, and the grains are refined.

Chitosan and Its Derivatives as a Barrier Anti-Corrosive Coating of 304 Stainless Steel against Corrosion in 3.5% Sodium Chloride Solution

This study investigates the corrosion resistance of chitosan and its crosslinked form coatings applied on stainless steel as substrate using various analytical techniques. Fourier transform infrared spectroscopy (FTIR-ATR), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS) were employed for surface characterization. Electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PDP) techniques were used to analyze the electrochemical behavior. Four coatings were evaluated along with naked stainless steel (ss): chitosan (Chi), chitosan crosslinked with ammonium paratungstate (Chi/PTA), chitosan crosslinked with polyethylene glycol (Chi/PEG), and chitosan crosslinked with polyvinylpyrrolidone (Chi/PVP). Electrochemical measurement parameters analysis assessed the coating corrosion resistance, such as impedance modulus (|Z|) and corrosion potential (Ecorr). Results indicate varying degrees of corrosion resistance among the coatings. Chi/PTA exhibited notable characteristics in the electrochemical tests, showing promising polarization resistance (Rp) and impedance behavior trends. Conversely, Chi/PEG showed differing electrochemical responses, suggesting higher susceptibility to corrosion under the study conditions. These findings contribute to understanding the electrochemical performance of chitosan-based coatings on stainless steel, highlighting their potential in corrosion protection applications.

Analisis Karakteristik Material Baja dengan Metode Digital Image Correlation (DIC)

The use of steel materials in building construction opens new opportunities for sustainable development, as steel exhibits corrosion resistance, durability, and reliability in terms of strength and ductility. Digital Image Correlation (DIC) is non-contact technique in which digital images of the surface of a test object are captured using high-resolution cameras. This study conducted measurements of strain distribution on the specimen's surface using the DIC method throughout the entire tensile testing process. The study particularly focuses on examining changes in strain distribution during the melting phase and the local deformation phase leading to fracture. In this research, a comparison will be made between the load-displacement curves obtained from experimental laboratory testing and the results analyzed using the DIC method for SS400-grade steel material. Based on the results of the tensile test and DIC analysis that have been conducted, conclusions have been drawn in the research. The tensile test results of SS400 steel material with a thickness of 6 mm, 8 mm, 10 mm, and 12 mm meet the quality requirements in the tested specification standards, and the results of the force-displacement curve between the experimental test results and the DIC method obtained a minimum deviation with a value below 10%,. Therefore, it can be concluded that the DIC method exhibits a reasonably good level of accuracy, making it suitable for validating the results of experimental tests.

Analysis and Optimization of Kerf Width in Fiber Laser Cutting of S235 Steel

Analysis and Optimization of Kerf Width in Fiber Laser Cutting of S235 Steel

‘Robinson’ Pedestrian Bridge in Budapest, Hungary

Abstract‘Robinson’ Bridge was built as part of the National Athletic Centre project in Budapest, Hungary. The 168 m long cable‐stayed pedestrian bridge has a 65 m tall inclined pylon standing on a small island. The 12,72 m wide main girder is suspended to a monopylon with a two‐plane fan‐shaped FLC stay cable system. The landmark bridge's stunning appearance was achieved with hybrid structures. Both the pylon and parts of the slender stiffening girder were made of S460 steel tubes filled with concrete to enhance their load‐bearing and dynamic characteristics. Due to very limited construction area, a special erection process was used for the pylon involving a 200t floating crane. The stiffening girder was built with incremental launching. Cable tensioning with a curved deck proposed special design challenges. Large displacements had to be accurately predicted. To meet the strictest requirements for pedestrian comfort, TMDs were applied and dynamic load tests carried out to prove the results.

Mechanical properties and damage characterization of 310S steel using laser ultrasonic inspection under extreme temperature condition

Abstract To evaluate the mechanical properties of 310S stainless steel under extreme working conditions, and realize the damage characterization function, in this study, the longitudinal wave and Rayleigh wave of materials are measured by the method of coaxial inspection on reverse surface and ipsilateral ectopic inspection, respectively, and surface cracks and internal voids are detected by the scanning laser source technology and transmission scanning detection, respectively. The detection methods are designed based on the energy distribution characteristics of Rayleigh wave and longitudinal waves in laser ultrasound. The laser ultrasonic detection systems coupled with a temperature loading device (high temperature: vacuum chamber; low temperature: refrigerating chamber) developed by the laboratory enable on-site monitoring of laser ultrasonic technology in harsh environments. Experimental results demonstrate that the error in mechanical properties (elastic modulus, shear modulus, Poisson ratio) is less than 5% over a wide temperature range (-180-1000°C). At 1000°C, surface cracks wider than 0.5mm and deeper than 1.9mm as well as internal hole defects larger than 1.0mm can be detected with an error rate below 5%.

The Optimization of Cut Surface for Computer Numerical Control Plasma Cutting Machine

This paper discusses a system designed to process parameter settings for achieving optimum cutting quality by a Computer Numerical Control (CNC) Plasma Machine, employing the Jaya algorithm. The aim is to obtain the most optimized parameter settings for the CNC Plasma Machine, focusing on the plasma cutting method applied to commonly used metals, 304 stainless steels, and S235. The investigation centres on understanding the impacts of these parameters on surface roughness (Ra) and tapper angle. The experiments, conducted using Full Factorial Design (FFD), involved mathematical prediction models developed through a regression method with three controllable levels for each parameter on 12mm S235 steel and 304 stainless steel plates. The Jaya algorithm, known for its efficiency in engineering optimization, operates on the principle of gravitating towards positive outcomes while avoiding unfavorable ones. What sets this study apart is the utilization of the Jaya algorithm, a sophisticated optimization tool that demonstrated exceptional efficiency by converging to the optimum solution within a mere 15 iterations. The Jaya algorithm’s robust performance was highlighted through a comparative analysis, positioning it as superior to alternative techniques for delivering the best optimum solution in a remarkably reduced number of iterations.

Role of Activating Flux in Weld Bead Symmetricity during Dissimilar Metal Joining

Ferritic/martensitic steels and austenitic stainless steels are high‐strength steels, and highly recommended in high‐temperature and high‐pressure application. In general, multimetallics with different Inconel alloys are used for joining. This is quite a complex and time‐consuming procedure. The current work demonstrates the efforts made to weld 8 mm‐thick P91 steel and 316L SS plates in a single pass using activating flux tungsten inert gas (A‐TIG) welding process without any interlayers. The main challenge is to get the symmetric weld bead profile. Flux coating is optimized in terms of flux composition, coating density, and coating pattern to get the full penetration with symmetric appearance. The current work discusses the possible cause and their solution of asymmetricity during dissimilar welding. Differential flux coating density is found to be very effective in controlling the arc column shape, fluid flow, and consequently the bead geometry. High coating density is used in the P91 side compared to 316L side. Symmetric weld profile with full penetration is achieved by applying multicomponent flux (33–38% TiO2, 38–43% SiO2, 13–17% NiO, and 8–10% CuO) during A‐TIG welding.

Microstructure, corrosive wear and electrochemical properties of Al2O3 reinforced FeAl coatings by laser cladding

PurposeThis study aims to investigate the influences of Al2O3 mass fraction on the corrosive wear and electrochemical behaviors of FeAl–xAl2O3 coatings.Design/methodology/approachFeAl–xAl2O3 coatings were prepared on S355 steel by laser cladding to improve its corrosive wear and electrochemical properties.FindingsThe average coefficients of friction and wear rates of FeAl–xAl2O3 coatings are decreased with the Al2O3 mass fraction, and the Al2O3 plays a positive role in the corrosion wear resistance. Moreover, the charge transfer resistance of FeAl–xAl2O3 coatings is increased with the Al2O3 mass fraction, showing the FeAl–15%Al2O3 coating has the best corrosion resistance. The findings show the corrosion resistance of FeAl–15%Al2O3 coating is the highest among the three kinds of coatings.Originality/valueAl2O3 was first added into FeAl coatings to further improve its corrosive wear and electrochemical properties by laser cladding.

Tests, simulations and web crippling design of S690 and S960 high strength steel unlipped channel sections under end-one-flange loading

This paper presents experimental and numerical investigations into the web crippling behaviour and structural design of high strength steel unlipped channel sections under end-one-flange loading. An experimental programme including six grade S690 and four grade S960 steel test specimens was firstly carried out, and the corresponding test set-up, procedures and results were reported. The web crippling test results were subsequently used in a finite element programme to validate developed finite element models, which were then adopted to perform parametric studies to cover wider parameter ranges of the bearing length, web slenderness and inside bend radius. It is found that the ultimate web crippling strength of high strength steel unlipped channel sections increases with increasing bearing length but decreasing web slenderness and inside bend radius. Considering that relevant codified design provisions are absent, the design rules of normal strength steel unlipped channel sections, as prescribed in EN 1993-1-3, EN 1993-1-5 and AISI S100, were assessed for their suitability to high strength steel unlipped channel sections. The codified design methods provide inaccurate and scattered resistance predictions for high strength steel unlipped channel sections under end-one-flange loading. Thus, an improved AISI S100 design method and a novel slenderness-based design method were proposed, which can outperform the codified design methods.

A new method of magnetic pulse welding of dissimilar metal plates using a uniform pressure electromagnetic actuator based on pre-deformation

The magnetic pulse welding method using a uniform pressure electromagnetic actuator can effectively weld dissimilar metal plates. However, the existing uniform pressure welding method leads to serious thinning of the plate at the chamfer, lack of welding at the center, and bulging of the welded sample, which seriously affects the quality of the welded joint. To solve these problems and improve the quality of welded joints, a new uniform pressure welding method of dissimilar metal plates based on pre-deformation was developed in this work. In this study, using the welding of an AA1060 aluminum plate and an SS304 steel plate with a thickness of 1 mm as an example, it was confirmed through numerical simulation and experimental research that the pre-deformation of the flyer plate controlled the impact angle of the central area of the plate, and it effectively suppressed central non-welding and serious bulge issues. Further, the welding method also reduced the height of the cushion blocks on both sides, thus mitigating aluminum plate thinning at the chamfer, ultimately improving the tensile strength of the joint. Additionally, a microscopic observation showed that the welding interface formed a wavy composite interface, and the connection strength was good. This welding method can also be extended to welding other dissimilar metal plates.

Effects of ultrasonic impact on surface characterization of S355 steel welded joint

The effects of ultrasonic impact treatment (UIT) on the residual stress, the microhardness, the nano-hardness, the microstructure, the electrochemical corrosion resistance, the corrosion morphology, and the chemical composition of the S355 steel welded joints were investigated. In addition, the mechanism of improving the electrochemical performance of the S355 steel welded joints by the UIT was studied. The results showed that the UIT could significantly improve the electrochemical corrosion resistance of the S355 steel welded joints. The corrosion potential and impedance were increased, and the corrosion current density was decreased with the increasing of the UIT time. According to the corrosion morphology, it was observed that after the UIT, the number of corrosion pits in the welds and heat-affected zones of S355 steel welded joints significantly decreased, along with reductions in the depth and size of the pits. After the UIT, the grain size of the S355 steel welded joints was refined, and both the microhardness and the nano-hardness of the welded joint were increased, which indicated that substantial plastic deformation occurred on the S355 steel welded joint. Moreover, the UIT could significantly reduce and transform residual tensile stress into residual compressive stress in areas adjacent to the welds, and the residual compressive stress could be increased with the increasing of the UIT time. It can be concluded that the introduced compressive residual stress, the grain refinement, and the generated plastic deformation were the main factors in improving the electrochemical corrosion resistance.

Investigation on fracture resistance behaviour of dissimilar metal weld joint of modified 9Cr–1Mo steel and AISI 316LN SS

Fracture behavior of dissimilar metal weld joint consisting of mod. 9Cr–1Mo steel, AISI 316LN stainless steel, Inconel 82 butter layer and Inconel 182 weld has been investigated through experiments and FE simulations. The metallographic studies on weld joint and its interfaces have been carried out to determine the influence of microstructure on tensile and fracture properties. Tensile properties of different weld regions viz., weld metal, butter layer and HAZ have been evaluated using sub-size specimens. Fracture resistance behavior of weld joint has been studied through testing of compact type specimens with initial cracks machined at different locations. The plastic η factors for estimation of J-R curve have been obtained using FE analysis for crack in different regions viz., weld metal, butter layer and HAZ. Crack in weld metal exhibits lower fracture resistance as compared to butter layer and HAZ. Further, the constraint acting on crack and its susceptibility for deviation have been discussed in terms of stress triaxiality ahead of crack tip.

A methodology to evaluate seawater corrosion on quasi-static tensile properties of a structural steel

With the wind turbine industry growing and increasingly turning its focus to the offshore sector, it is important to grasp the challenges that come with it: the logistic challenges related to transport and maintenance, the exposure to wave and wind action and also the vulnerability to corrosion. The marine environment is a complex and aggressively corrosive environment. The S690 steel, as a structural steel of high mechanical strength, offers weight reduction advantages that are of interest to the sector. However, its behaviour in a corrosive medium is still not well known. As such, this work is part of an effort to characterize S690 steel under marine environment conditions. A methodology for inducing accelerated pre-corrosion on quasi-static tensile specimens of S690 steel, while simulating the environment, has been developed and applied. The effect of this pre-corrosion on the tensile mechanical properties is evaluated through testing in accordance with the ASTM E8 standard. It was found that the induced surface pre-corrosion, equivalent to six months of exposure, did not have a significant effect on the investigated mechanical behaviour.