Properties Of Structural Steel Research Articles

Enhancing the Tensile Properties and Ductile-Brittle Transition Behavior of the EN S355 Grade Rolled Steel via Cost-Saving Processing Routes.

Structural rolled steels are the primary products of modern ferrous metallurgy. Consequently, enhancing the mechanical properties of rolled steel using energy-saving processing routes without furnace heating for additional heat treatment is advisable. This study compared the effect on the mechanical properties of structural steel for different processing routes, like conventional hot rolling, normalizing rolling, thermo-mechanically controlled processing (TMCP), and TMCP with accelerating cooling (AC) to 550 °C or 460 °C. The material studied was a 20 mm-thick sheet of S355N grade (EN 10025) made of low-carbon (V+Nb+Al)-micro-alloyed steel. The research methodology included standard mechanical testing and microstructure characterization using optical microscopy, scanning and transmission electronic microscopies, energy dispersive X-ray spectrometry, and X-ray diffraction. It was found that using different processing routes could increase the mechanical properties of the steel sheets from S355N to S550QL1 grade without additional heat treatment costs. TMCP followed by AC to 550 °C ensured the best combination of strength and cold-temperature resistance due to formation of a quasi-polygonal/acicular ferrite structure with minor fractions of dispersed pearlite and martensite/austenite islands. The contribution of different structural factors to the yield tensile strength and ductile-brittle transition temperature of steel was analyzed using theoretical calculations. The calculated results complied well with the experimental data. The effectiveness of the cost-saving processing routes which may bring definite economic benefits is concluded.

A novel method for preparing α-Al2O3 (Cr2O3)/Fe–Al composite coating with high hydrogen isotopes permeation resistance

α-Al2O3 as a preferred material for hydrogen isotopes permeation barrier (HIPB) can effectively prevent hydrogen embrittlement in structural steel and has higher thermal stability. However, its application is limited by the issue that it is hard to prepare α-Al2O3 at relatively low temperature and its formation temperature is too high (>1000 °C) to damage the mechanical properties of structural steel. To overcome this issue, this paper presents a novel method (combining Al electrodeposition, aluminizing, Cr deposition and air oxidation) for the preparation of α-Al2O3 (Cr2O3)/Fe–Al composite coating on 316 L stainless steel for the first time. The formation temperature of α-Al2O3 was successfully reduced to 800 °C. The post-oxidation samples were characterized by SEM, XPS, XRD, EDS and TEM. The results showed that the oxide film was composed of highly crystalline α-Al2O3 and Cr2O3 nanoparticles, where the later were diffusely distributed in the internal α-Al2O3 film. And there was an epitaxial growth relationship between α-Al2O3 and Cr2O3. The low-temperature formation of the α-Al2O3 film was due to the fact that the Cr2O3 nanoparticles formed during the oxidation process acted as templates and nucleation sites, which reduced the nucleation barrier of α-Al2O3. Deuterium permeation tests showed that its deuterium permeation reduction factor (DPRF) was 8892 at 500 °C, which met the standard for practical application.

About Some Properties of Structural Steel Used in the Construction of a Railway Bridge Over the Amur River in the Early XX Century

The main stages of construction in 1913–1916 of the railroad bridge across the Amur River near Khabarovsk are presented. The peculiarities of the construction of the structure in the difficult foreign policy conditions of the beginning of the last century, which caused a reduction in the pace of construction, are noted. The most honored organizers, designers and builders of the Amur Bridge are mentioned. Construction materials and places of their extraction, as well as suppliers of structural steel used in the construction of a unique transportation structure are specified. The methods of construction and assembly of the main load-bearing elements of the bridge structure are considered. Special attention is paid to the study of chemical composition, micro- and macrostructure, hardness of structural steels used in the manufacture of bridge spans. Conclusions about the conformity of the chemical composition of the investigated materials to the alloys specified in the current normative documentation, as well as the method of their smelting are formed. Modern metal materials used in the reconstruction of the bridge crossing at the beginning of the XXI century are given for comparison. The functionality of the bridge after reconstruction is reflected and the potential of its further development is given. A promising method of increasing the complex of characteristics of metal products by processing billets in solid-liquid state, which allows to reduce the metal consumption of structures, is considered.

Strength and Deformability of Structural Steel for Use in Construction

The purpose of the study is an experimental determination of the stress-related characteristics of the structural steel produced in the Republic of Kazakhstan for use in conventional and earthquake-resistive construction. Since 2015, the construction industry has been using European regulatory documents—Eurocodes—as a statutory framework. In particular, the Eurocode 1993 for steel structures and the Eurocode 1998 for the design of earthquake-resistant structures However, the study of stress-related properties of structural steel using experimental methods of ISO standards has not been performed. Therefore, in the construction industry of the Republic of Kazakhstan, steel-work structures have been used in fairly limited volume since 2015. The experimental studies were conducted on 7 types of structural steel with thicknesses of 8, 10, and 20 mm manufactured by Arcelor Mittal. The yield strength, ultimate tensile strength (breaking stress), and tensile strength at break were studied. The experimental studies were carried out on the basis of ISO standards. In each test run, 5 samples were used. In two series, 20 samples each were tested, which made it possible to estimate the yield strength and strength distribution functions. The correlation relationships between Brinell hardness and yield and strength limits have been studied. As a result of experimental studies, it was found that the strength and deformability parameters fully comply with the requirements of Eurocode 1993. Based on the application of the Student's test, it is revealed that the distribution functions of yield strength and resistance correspond to the normal law (Gaussian function). The calculation of a three-story, two-span residential building with box section columns for construction in an area with a seismicity of 8 points is performed by the finite element method. The work results will significantly increase the scope of Kazakhstani structural steel use in seismic and conventional areas of the Republic of Kazakhstan. Doi: 10.28991/CEJ-2024-010-03-09 Full Text: PDF

Effect of tempering conditions on the structure and strength properties of structural steels

The structure and mechanical properties of low- and medium-carbon steels quenched and tempered with different isothermal holding times at temperatures ranging from 250 to 650 °C are studied. It is shown that, for the steels under study, three stages can be distinguished on the curves of hardness as a function of isothermal holding at different temperatures. Hardness testing is used to determine tempering conditions leading to a comparable level of hardness. To calculate the tempering parameter, the constant C in the Hollomon–Jaffe equation is determined for the steels in question.

Evaluation of fatigue crack initiation and propagation properties of structural steels with different cyclic softening behavior based on local strain

Evaluation of fatigue crack initiation and propagation properties of structural steels with different cyclic softening behavior based on local strain

Applying the Hollomon-Jaffe parameter to predict changes in mechanical properties of irradiated austenitic chromium-nickel steels during isothermal exposure

<abstract> <p>The Hollomon-Jaffe parameter is widely used in metallurgy and materials science to characterize the behavior and predict the various metals' physical-mechanical properties under different temperature and time modes. The possibility of predicting changes in the mechanical properties of structural steels due to thermal influences has been studied. The paper presents the results of a study of the mechanical properties of the materials of the core components of the BN-350 reactor facility (RF) made of austenite chromium-nickel steel 12Cr18Ni10Ti (a spent fuel assembly's jacket) and 09Cr16Ni15M3Nb (an intro-channel displacer). The samples were studied both before and after radiation annealing. Annealing of steel samples at 550 ℃ reduced the yield strength and significantly restored the plasticity and ability of the material to strain hardening. The efficiency of post-radiation annealing of the materials increases with annealing temperature and leads to a transition to the reduction process. It was established that medium of high temperature annealing during heat treatment does not lead to significant changes in the mechanical properties of irradiated materials. The microstructure studied using a scanning electron microscope reasonably correlates with the results of mechanical tests. The possibility of using the Hollomon-Jaffe parameter to predict the properties of austenite chromium-nickel steel, which received damaging doses in the range from 12 to 59 dpa, was shown for the first time. Thus, for the first time, the unique coefficient (<italic>C</italic>) of the Holloman-Jaffe parameter for irradiated materials of chromium-nickel steel was experimentally determined, and dependencies characterizing the change in hardness of chromium-nickel steel on temperature and duration of post-radiation thermal exposure were established.</p> </abstract>

Mechanical Properties of Structural Steel after Diamond Burnishing

Mechanical Properties of Structural Steel after Diamond Burnishing

Numerical study and design of ultra-high-strength steel plate girders subjected to patch loading after elevated temperature

When a steel structure does not collapse after a fire, it is meaningful to study its residual resistance after exposure to elevated temperatures to evaluate its post-fire service capacity. The elevated temperatures of a fire change the residual mechanical properties of structural steel, which influences the patch-loading resistance performance of steel plate girders. However, the effects of temperature on the residual resistance performance of Q960 ultra-high-strength steel (UHSS) plate girders subjected to patch loading remain unclear. This study aims to determine the variation trends of the post-fire bearing performance of Q960 UHSS plate girders subjected to patch loading based on their mechanical properties after exposure to elevated temperature and natural cooling. The effects of the web width-to-height ratio, web height-to-thickness ratio, load length, and exposure temperature were considered in the parametric study; a total of 400 numerical models were included. Additionally, the influence of the exposure temperature on the serviceability limit state of Q960 UHSS plate girders was considered. The applicability of EN 1993-1-5 was verified based on the finite element analysis results, which showed that the design methods in EN 1993-1-5 significantly underestimated the ultimate resistance of Q960 UHSS plate girders exposed to elevated temperatures. Thus, the strength reduction function in EN 1993-1-5 was revised to improve the accuracy of the statistical analysis.

Influence of Thermal Loads on the Microstructure and Mechanical Properties of Structural Steel

Influence of Thermal Loads on the Microstructure and Mechanical Properties of Structural Steel

Finite element modelling of lattice angle steel structures exposed to wildland fires

Essential civil infrastructure such as transmission line supporting towers and communication base towers that are traditionally formed from lattice angle steel structures are critical global assets, since their development promotes the establishment of electric power supply systems and modern telecommunication networks. Because this infrastructure is commonly located in rural and urban wildland areas, such towers may be prone to wildland fire attack, particularly in the current climate of severe heatwaves and droughts. Accordingly, a comprehensive study of the behaviour and response of lattice angle steel structures under fire loading is needed to assist in structural design to resist fire loading. In this paper, a finite element (FE) model of lattice angle steel structures is constructed using ABAQUS software. Several aspects that include material and geometric non-linearities, load eccentricities on component members, bolted joint slippage, and the use of the explicit dynamic analysis technique for a quasi-static loading procedure, are considered and applied in the FE model. The accuracy and reliability of the FE representation are validated by comparing its predictions with relevant existing experimental results. By incorporating the codified temperature-dependent material properties of structural steel as well as a calibrated load-slip relationship for bolted connections at elevated temperatures, the FE model is extended for performing structural fire analysis. The variations of the steelwork temperatures in wildland fires can be calculated based on representative temperature-time wildland fire curves and is adopted in the fire analysis. By invoking the FE model, an example of lattice angle steel structures is contrived to elucidate the fundamental behaviour of these structures in wildland fires, through both steady and transient state fire analyses. Parametric studies are also undertaken to evaluate the effects of the changes in the wind load direction, bolt pretension and the protection of critical panel sections on the behaviour of lattice structures when exposed to wildland fires.

Effect of Heat Treatments and Carbon Content on the Damping Properties of Structural Steel

Low- and medium-carbon structural steel components face random vibration and dynamic loads (like earthquakes) in many applications. Thus a modification to improve their mechanical properties, essentially damping properties, is required. The present study focuses on improving and developing these properties, significantly dampening properties, without losing the other mechanical properties. The specimens used in the present study are structural steel ribbed bar ISO 6935 subjected to heating temperatures of (850, 950, and 1050) ˚C, and cooling schemes of annealing, normalizing, sand, and quenching was selected. The damping properties of the specimens were measured experimentally with the area under the curve for the loading and unloading paths experienced from the tensile test. Considering the effect of different parameters on the damping properties, such as heat treatment temperatures, cooling rates, and carbon content, the results show that the damping properties in the annealing process at different temperatures have interesting damping properties, among other processes. Also, the highest damping energy for the annealing cooling scheme was attained at a heating temperature of 1050 ˚C, irrespective of the carbon content. Finally, better damping properties for the medium carbon content of (0.299%C) is achieved for all types of heat treatment process compared with a low carbon content of (0.188% C); and, in general, with increasing carbon content from medium to low, steel response to heat treatment increases and better damping properties are obtained.

Low-cycle fatigue behavior of differently matched welded joints of quenched and tempered steel

The appropriate matching of base and filler material is a complex task, where yield strength matching is the most general aspect. As the strength properties of structural steels have significantly improved in the past decades, the matching problem has become more relevant today. The mismatch phenomenon significantly affects the behavior of welded joints under dynamic and cyclic loading. Among cyclic loading, low-cycle fatigue (LCF) often occurs in welded steel constructions; furthermore, the LCF resistance of these advanced steels and their welded joints is limitedly known. In this paper, welding experiments are presented for the analysis of the LCF behavior of differently matched butt-welded joints made from two grades of quenched and tempered (Q + T) high-strength steels. For S690QL steel, matched and overmatched consumables were applied, while for S960QL steel, matched and undermatched filler materials were used. Material tests were performed to determine the mechanical properties of the different welded joints. In both examined steel grades, the welded joints tolerated a smaller number of cycles until failure than the base materials. In the case of S690QL, the LCF resistance of the matched welded joints was higher than the overmatched filler material. At S960QL in the higher strain amplitude range, the number of cycles to failure was higher at the same total and plastic strain amplitudes when undermatched filler material was used; however, an opposite ratio can be observed at lower strain values, compared to the matching filler material.

Microstructure and Mechanical Properties of Gradient Nanostructured Q345 Steel Prepared by Ultrasonic Severe Surface Rolling

In this work, ultrasonic severe surface rolling (USSR), a new surface nanocrystallization technique, is used to prepare gradient nanostructure (GNS) on the commercial Q345 structural steel. The microstructure of the GNS surface layer is characterized by employing EBSD and TEM, and the result indicates that a nanoscale substructure is formed at the topmost surface layer. The substructures are composed of subgrains and dislocation cells and have an average size of 309.4 nm. The GNS surface layer after USSR processing for one pass has a thickness of approximately 300 μm. The uniaxial tensile measurement indicates that the yield strength of the USSR sample improves by 25.1% compared to the as-received sample with slightly decreased ductility. The nanoscale substructure, refined grains, high density of dislocations, and hetero-deformation-induced strengthening are identified as responsible for the enhanced strength. This study provides a feasible approach to improving the mechanical properties of structural steel for wide applications.

Effect of Controlled Rolling on the Structural and Phase Transformations

The development of ferrous metallurgy is mainly due to the requirements of the leading metal-consuming industries to improve the performance properties of structural steels to increase the permissible loads, to reduce metal consumption and to improve the reliability of machines, structures, main gas pipelines, etc. With significant volumes of rolled metal production, reducing energy consumption and consuming raw materials during its production also come to the fore. In this regard, important and relevant works are the works aimed at creating the fundamentals of metals science and the development of new technologies that allow manufacturing the products with the required combination of properties directly in the rolling mill stream (excluding subsequent heat treatment) by purposefully controlling the processes of structure formation, as well as expanding the areas of the practical application of such technological schemes (in terms of brand and size assortment, rental destination, etc.). Such an approach makes it possible to increase the competitiveness of metal products determined by the achieved combination of metal characteristics, while reducing the cost of its production.

APPLICATION OF EXPERT AND FRACTAL ASSESSMENTS IN FORECASTING THE QUALITY OF CONSTRUCTION STEEL

Introduction. Different approaches are used to study the structure and properties of structural steels. The properties of steels are determined using traditional methods (physical methods, field tests, X-ray analysis, microscopy, etc.). Structure studies are also carried out using traditional methods based on Euclid's integer geometry. A similar approximation of structural elements by Euclid's figures leads to a decrease in the accuracy of forecast models due to the complex shape of its elements. The reason for this is the fractality (fine dimensionality) of most elements of the material structure. The paper proposes an approach based on a combination of expert and fractal assessments when creating a forecast model for the quality of construction steel. Materials and methods. Construction steel 20 in the mode of factory delivery was studied. The steel had a ferrite-pearlite structure. Mechanical tests and determination of chemical composition were carried out in accordance with the existing regulatory documents (DSTU 7809). The content of pearlite in steel ranged from 10 to 18 %, depending on the amount of carbon. Ferrite occupied the entire other part of the area of the slide examined under the Neophot-2 optical microscope. The results of the experiment. Expert assessment was used to predict mechanical indicators of strength with the aim of reducing material and time costs for conducting field tests with metal samples. The effect of the ferrite-pearlite structure on the mechanical characteristics of strength was investigated by comparing the fractal evaluations of the structure with the indicators of mechanical tests. It has been established that an increase in the fractal dimension of pearlite has a positive effect on the growth of strength indicators of steel 20. A similar effect is, in a certain way, associated with the change in the shape of pearlite grains in the process of changing the amount of carbon in steel within the limits of regulatory documents. Conclusions. For structural steel 20, models for assessing its mechanical characteristics were obtained using the fractal dimensions of structural elements and expert assessments. Coefficients of pairwise correlation of regression equations are recorded in the range of 0.65...0.85. The obtained results can be used to forecast strength indicators of steel, which is especially relevant when assessing its residual resource during operation.

Study of the corrosion properties of structural steels using magnetic characteristics

Heterogeneities of the crystal structure and chemical composition, as well as the impurity elements forming inclusions cause deviations of the properties of test object from the required physical and mechanical parameters which significantly affects the reliability and service life of the product. We present the results of studying the susceptibility of structural steels to corrosion in aggressive environment using their magnetic characteristics. Structural-phase transformations occurred in steels under the effect of heat treatment change their properties, including magnetic and corrosion ones. Heat-treated 09G2S, St3, 15XSND steel samples were studied. In addition to the main magnetic parameter — coercive force, we also used spectral characteristics of the samples obtained using a remagnetization curve, magnetic hysteresis loop. The multi-parameter approach with harmonic components was used to identify the corrosion rate and coercive force correlation. Determination of the corrosion rate in this case can be reduced to classical problems of technical diagnostics. It is shown that a complex parameter based on harmonic components obtained using a magnetic hysteresis loop and the corrosion rate exhibit a pronounced correlation which provide developing a non-destructive method for predicting the corrosion resistance of structural steels. The results obtained can be used to improve the rapid method for determining the corrosion-hazardous zones of steels using the magnetic parameters.

Experimental study on the properties of Q960 ultra–high–strength steel after fire exposure

The Q960 ultra–high–strength steel (UHSS) has broad application prospects in engineering structures owing to its superior mechanical properties. Elevated temperatures caused by fire have lasting effects on the mechanical properties of structural steel. Therefore, to accurately evaluate the service performance of the UHSS structure after fire, the post–fire mechanical properties of Q960 UHSS were investigated experimentally in this study. Different exposure temperatures and cooling methods were used in the experiments. The changes in apparent features and microstructures of Q960 UHSS exposed to elevated temperatures were discussed. A mechanical test was also conducted to clarify the effects of exposure temperature and cooling method on mechanical properties of Q960 UHSS. The post–fire mechanical properties of mild steels (Q235, Q345, and Q420), high–strength steels (Q460, Q620, and Q690), UHSSs (Q960 and S960), AL 6082–T6 aluminum alloy, and bimetallic steels were investigated to comprehensively clarify the effects of exposure temperature and cooling method. A detailed discussion on the differences in stress–strain curves between the S960 and Q960 UHSSs after fire exposure was conducted. Based on the test results, the predictive equations for the key mechanical parameters of Q960 UHSS exposed to elevated temperatures were derived. The reliability analysis on the predictive model for key mechanical parameters was performed, where the resistance factor was suggested for Q960 UHSS after fire exposure. In the end, the predictive model was proposed to quantify the residual stress–strain curve of Q960 UHSS with different exposure temperatures and cooling methods.

Experimental study on the post-fire mechanical behaviours of structural steels

The high temperature of fire has an impact on the mechanical properties of structural steel, hindering its use. Q345, Q460, Q550 and Q690 structural streels were chosen to investigate their mechanical behaviours after fire treatment at temperatures from 300 °C to 800 °C and air cooling. The mechanical parameters (yield stress, elastic modulus, yield plateau size, ultimate strength and necking strain) were analysed by considering the fire temperature, and the residual factors of the parameters for the Q345, Q460, Q550 and Q690 steels were compared with the results obtained at an ambient temperature. The results showed that the mechanical parameters for each steel began to reduce when the target temperature exceeded 600 °C, and the residual factor was a descending exponential function or a linear function of the target temperature. The predictive equations of residual factors in the literature, about Q460 and Q690 steels, were collected and analysed, and the new equations were predicted depending on all available experimental data. Finally, a stress–strain model incorporating fire temperature was proposed by a piecewise function to describe the stages of the stress–strain curve (elasticity, yielding and plasticity), and the model can represent the experimental results accurately.

Bending fatigue properties of structural steel fabricated through wire arc additive manufacturing (WAAM)

Wire arc additive manufacturing (WAAM) has become an essential production method with advantages such as ease of application and economic benefits, along with high material savings and its ability to produce large parts close to their final form in a short time. In recent years, many studies have been carried out on WAAM, most of which have investigated the properties of the manufactured parts. Among these properties, the topic of fatigue was less frequently examined. The reasons for this may include difficulties such as the long duration of fatigue tests and the large number of test specimens required. However, since fatigue is responsible for most of the damage in metal components, it is important to determine the fatigue strength of the parts produced using WAAM. In this study, the WAAM process was applied to low alloy ER70S-6 steel, which is widely used in the metal industry and is also one of the most common materials used in WAAM processes. After the fabrication, horizontal and vertical specimens were obtained from the manufactured part and mechanical and metallurgical tests were applied, including, fatigue tests, with the fatigue properties of the produced WAAMed part determined using a specially designed and produced bending stress fatigue testing machine. Results demonstrated that the fatigue limits of the horizontal and vertical fatigue specimens at 107 cycles were very close to each other, as approximately 180 MPa. The fatigue strength values of the vertical and horizontal specimens were quite similar. However, the fatigue strength of the vertical specimens up to 106 cycles was found to be slightly higher.