Mechanical Properties Of Structural Steels 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.

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

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.

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.

Experimental and neural networks analysis on elevated-temperature mechanical properties of structural steels

This study presents the possibility of using artificial neural network (ANN) for describing and predicting the high temperature mechanical behavior of structural steel. For this reason, a series of steady-state tensile tests were performed on two representative structural steels Q345B and Q460GJ in temperature range of 20 ℃ to 800 ℃, in the forms of steel bars with diameters of 8, 10 and 12 mm. The high-temperature mechanical properties were evaluated and compared, revealing the necessity of a general and reliable prediction model on the elevated-temperature mechanical properties of different structural steels. Furthermore, the experimental results could be well predicted by using the Ramberg-Osgood model only in a limited temperature range. Therefore, the application of back-propagation neuron network (BPNN) was proposed to predict the yield stress and ultimate stress. In order to model flow property, a long short-term memory recurrent neural network (LSTM-RNN) was first adopted in strength of mechanics. Two preprocessing methodologies including one-hot encoding and polynomial feature function were used in the models. The satisfactory agreements indicate that the trained BPNN and LSTM-RNN models are efficient and accurate in predicting the mechanical properties of structural steels.

Research on high-temperature resistant resin matrix composites of hypersonic aircraft structure

The aircraft structure would be suffered high temperature during the hypersonic flight. To solve the problem of high temperature resistance of hypersonic aircraft, the mechanical properties of different structural materials at different temperatures are studied. The tensile strength and tensile modulus of structural steel, aluminum alloy, titanium alloy, resin matrix composites and polyimide composites are analyzed, and the performance of the materials at high temperature is compared. The results show that the properties of typical materials will decrease with the increase of temperature. The high-temperature mechanical properties of structural steel and aluminum alloy are poor, and the titanium alloy can withstand higher temperature. Polyimide resin composites can work at higher temperature for a long time compared with epoxy resin and bismaleimide resin composites, and it has more obvious advantages than titanium alloy at 400 °C. Polyimide resin composite has great potential to replace traditional materials as load-bearing structural material of hypersonic aircraft.

Post-fire mechanical properties of titanium–clad bimetallic steel in different cooling approaches

Titanium-clad bimetallic steel (TCBS) consisting of titanium (cladding) and carbon steel (substrate) has been proposed to reduce the effects of corrosion on the durability of steel structures. Fire is a frequent disaster in steel structures. The elevated temperature caused by a fire and the cooling method to prevent it have a long-term influence on the mechanical properties of structural steels. In this study, the post-fire mechanical properties of a TCBS were investigated experimentally to accurately predict the residual service capacity of steel structures after a fire. The post-fire appearances of TCBS specimens were examined. The bonding interface of all TCBS specimens remained intact after exposure to elevated temperatures. The deformations of the cladding and substrate metals were coordinated before necking. Based on the fractured order, three different typical failure modes were determined in the TCBS. The differences in the cooling method and the exposure temperature resulted in differences in the nonlinear properties of the stress-strain curves. The effects of the exposure temperature and the cooling method on the yield strength, ultimate strength, elastic modulus, and percentage elongation after fracture were investigated and quantified using predictive equations. To comprehensively reveal the post-fire performance of TCBS comprehensively, the residual mechanical properties of different structural steels were compared.

Study on dislocation cell structure, dislocation density-fatigue property relationship of a structural steel

In this study, the evolution of the dislocation cell structure and variation of mechanical properties of structural steel under low-cycle fatigue were studied using the indentation experiment, optical microscope, and transmission electron microscope examinations. The results indicated that the dislocation cell structure was well-formed under cyclic loading. When the strain amplitude increased, the original grains were broken more, leading to the dislocation cell size tended to decrease, while dislocation density showed an increase with the further increase of strain amplitude from 0.4% to 1.0%, respectively. Both indentation hardness and yield stress tend to increase when the cyclic loading increases. The change in the dislocation structure was responsible for the strengthening of fatigue mechanical properties, meaning that the dislocation density tended to increase, while the dislocation cell size showed a decrease with the further increase of fatigue condition, leading to the increase of both hardness and yield strength since mechanical properties were inversely proportional to the mean cell size. The results of this study can be used for the practical designs as well as to understand the microstructure changes in structural steel subjected to cyclic loading.

Mechanical properties of stainless-clad bimetallic steel bars exposed to elevated temperatures

Fire is a frequent disaster, which performs the irreversible effects on mechanical properties of structural steels. When the structure experiences a fire and does not collapse, it is important to clarify the remaining resistance accurately. The stainless-clad bimetallic steel bar (SCBSB) consisting of the S30408 stainless-steel cladding layer and the HRB400 carbon steel substrate has the wide application in reinforced concrete structures serving in corrosive conditions. To evaluate residual resistance of SCBSB-concrete structures exposed to fire, post-fire mechanical properties of SCBSB are investigated experimentally. After the heating and cooling procedures, no cracking is observed in the cladding layer. Microstructures of SCBSB specimens are discussed. The stress–strain properties of SCBSB specimens exposed to elevated temperature and cooled with various methods are studied through the tensile coupon test. The dimensionless coefficients are selected to clarify effects of exposure temperature and cooling method on mechanical performances. These effects (at exposure temperatures lower than 600 °C) are relatively small. Predictive equations are suggested to determine mechanical performances of SCBSB specimens exposed to elevated temperature. The stress–strain models are proposed based on experimental results. Various energy indexes are selected to comprehensively investigate the ductile properties of the SCBSB specimens.

Оценка влияния дисперсности структуры стали на магнитные и механические свойства

Introduction: The control of the mechanical properties of structural steels is one of the main processes that regulate the service life of equipment. In most technical processes (pressure treatment, welding, rolling, thermal exposure), structure changes both in local areas and in the entire volume. Changes in the steel structure entail changes in its properties and as a result in local areas, at various stages of operation, the likelihood of the occurrence and development of critical defects increases. Its presence significantly affects the performance of the equipment, and leads to premature aging of the material and its failure. Precisely because the control of the mechanical properties of steel remains one of the urgent problems, new control methods are being developed. It is known that all properties of steel depend on the structure of the substance, however, studies on the effect of the dispersion of the structure under consideration on the mechanical properties are presented in an insignificant amount. Purpose: to analyze from a mathematical point of view the influence of the factor of different grain size, as a parameter reflecting the dispersity of the system, on the mechanical properties of structural steel. The paper studies a heat-treated planar samples of steels 15KhSND, 09G2S and St3. Methods of research: scanning electron and optical microscopes are used to study the grain structure and grain boundaries; SIAMS 700 software package is used for finding the boundaries and average data of the grain structure; portable X-ray fluorescence analyzer of metals and alloys X-MET 7000 is used to determine the chemical composition of the test samples in percentage; tensile testing machine IR-50 is used for measuring the tensile strength of samples; Vickers hardness tester is used to determine the hardness of samples. Results and discussion: it is found that there is a satisfactory correlation for the mechanical properties of structural steels (hardness and ultimate strength) and the grain size factor, which can be used to predict the hazardous states of structures and the operating time. The analysis of variance and regression of the detected dependencies is carried out. It is noted that the dropout of some values from the general regression dependence can most likely be associated with a decrease in the value of internal stresses as a result of a decrease in the distortions of the crystal lattice of steel occurring during heat treatment. It should be noted that the processes occurring and the degree of its influence on the properties of the structural steels under consideration can be different due to the presence of different amounts of alloying elements in the composition of the studied steels.

Impact of mechanical properties of structural steel by three transfer modes in gas metal arc welding

In manufacturing, great advantages such as high resistance and reliability have been acquired through permanent bonding processes such as welding. Electric arc welding under the name of gas metal arc welding is one of the most widely used welding processes due to its high productivity index and the quality of its weld seams. The application parameterization allows three modes of metal transfer to be developed which depend on voltage and amperage. The microstructure and mechanical properties of the base material are modified with the modes of metal transfer, due to the heat input that must be made to be able to join them, without having numerically quantified the level of affectation. In this work, the application of transfer modes on structural steel was developed following the normative models that govern technology and industry. Experimental procedures of microscopy and mechanical tests were applied to determine correlations between the mechanical properties and the parameters established during the application, the microstructures were reviewed in contrast to the results obtained.

Post-fire mechanical properties of base metal and welds of Q235 steel

Fire hazard has a non-negligible impact on building structural safety. With reasonable fire resistance design, steel structures would not necessarily cause collapse when suffering fire and cooling down, but the reliability of structures after fire needs to be re-evaluated. Although there have been considerable investigations of the mechanical behaviors of structural steel in fire or at elevated temperatures, only limited study has focused on the post-fire mechanical properties of structural steel especially under different cooling conditions. In this paper, coupon tests of Chinese Q235 structural steel, including base metal and welds, were conducted and the post-fire performance, including appearance, stress-strain curve, elastic modulus, yield strength, tensile strength, percentage elongation after fracture, and percentage reduction of area, was obtained and analyzed. With the condition of cooling in air or in water, post-fire mechanical properties of base metal and welds cooling from different maximum temperatures were analyzed and compared. Based on the test results, it is concluded that cooling in air from temperatures above 600 °C increases the ductility of Q235 steel for both base metal and welds, whereas cooling in water causes a significant drop in ductility but clearly increases strength. The post-fire tensile strength of the base metal would be higher than that of welds after cooling in water from 600 °C or higher elevated temperatures. Meanwhile, welds would develop poorer ductility than base metal. Accordingly, a set of reasonable predictive formulas is proposed for the post-fire mechanical properties of Q235 steel base metal and welds.

Post-fire mechanical properties of Q620 high-strength steel with different cooling methods

To evaluate the residual resistance of steel structures after fire, it is important to clarify post-fire mechanical properties of structural steels. Considering that high-strength steel (HSS) is increasingly used in steel structures, it is meaningful and necessary to investigate its post-fire mechanical properties. Therefore, mechanical properties of Q620 HSS exposed to elevated temperatures and cooled with different methods were investigated through experiment. Q620 HSS specimens were heated to pre-determined temperatures, later cooled to ambient temperature. Considering possible cooling environments in actual fire event, three different cooling methods were selected, namely, cooling in air (CIA), cooling in water (CIW) and cooling in fire-fighting foam (CIF). Then, tensile tests were performed to obtain post-fire mechanical properties of Q620 HSS. Test results indicated that exposed temperature and cooling method had significant effects on post-fire mechanical properties. Post-fire mechanical properties of Q620 HSS with CIF were close to those of Q620 HSS with CIA, which were different with those of Q620 HSS with CIW. Moreover, effects of exposed temperature and cooling method on elastic modulus of Q620 HSS could be ignored. Necking at failure of Q620 HSS exposed to elevated temperatures and cooled with different methods was discussed. Post-fire mechanical properties of Q620 HSS were compared with those of HSSs in other strength grades, the mild steels and the stainless steel. Predictive equations were proposed to quantify the effects of exposed temperature and cooling method on post-fire mechanical properties of Q620 HSS.

Relationship Between the Parameters of Acoustic Structural Noise and the Mechanical Properties of Structural Steels

We perform the comparative analysis of the parameters of acoustic structural noise in specimens of 40G structural steel with the use of ultrasonic flaw detectors with phased arrays. It is shown that the parameter of integral density of B-scan images most completely reproduces the variations of energy of acoustic vibrations reflected from the microstructural inhomogeneities (grain-size inhomogeneity, changes in the ratios of the phase components). The relationship between the parameter of integral density of the image of acoustic structural noise Ro and the mechanical properties of 40G steel is established. We propose an improvement of the well-known method of determination of the yield limit σy of steels according to the results of measurements of the HB hardness. To do this, we added the parameter Ro to the equation used for computations. As a result, we deduced a new equation of the form σy = f (Ro, HB) for the yield strength of 40G steel within the specified range of its values.

Critical Review of Test Methods for Mechanical Characterization of Steel for Structural-Fire Engineering Applications

AbstractKnowledge of elevated-temperature mechanical properties of structural steel is essential for accurate evaluation of structural behavior in a fire. As a result, various test procedures have ...