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In high-strength steel (HSS), shear edge failure due to stretch flangeability is a serious problem. Shear edge failure is strongly affected by the cutting methods. As countermeasures, cut-off punching and double punching of the entire circumference have conventionally been considered. However, it has not been shown whether these processes can be applied to the stretch-flange-forming part of the outer circumference of automotive parts. In this study, the effect of the punching allowance and the method of improving the double punching process on the outer circumferences of automotive parts were investigated using hot-rolled HSS sheets. The results of hole expansion tests and observations of shear edge faces and metal flow show that partial double punching reduces the rigidity of the cut-off side and increases the collapse probability. Also, the crack propagation caused by high tensile stress near the upper cutting edge is accelerated. In comparison with double punching of the entire circumference of a 590 MPa-class or 780 MPa-class HSS sheet, in partial double punching, the stretch flangeability is improved and the hole expansion test value is 1.5 times that of double punching when the cut off amount is greater than the thickness. However, it is considered that the stiffness of the cut-off side varies depending on the curvature and the thickness of the plane, and the effect of such variations will be confirmed in a wide range of curvature and thickness in the future. [ABSTRACT FROM AUTHOR]

Advanced high‐strength steels (AHSS) have been extensively studied to develop its third generation from relatively low‐cost alloys, but seeking optimized mechanical properties. In this context, the effects of quenching heat treatments are evaluated in this work after intercritical austenitizing (IA) on microstructure, alloying elements partitioning, and Ms temperature for a commercial CMnSi alloy. Applying dilatometric data and microstructural characterization, different heat cycles are evaluated. The obtained experimental results are compared with those ones obtained by computer simulations at equilibrium conditions. Based on this characterization, an optimized one‐step quenching and partitioning (Q&P) cycle (after IA) is proposed and applied to tensile test specimens. Then, the specimen microstructure is characterized by scanning and transmission electron microscopy as well as by X‐ray diffraction. Using the proposed methodology, it is possible to produce a Q&P steel with a product of tensile strength and elongation of 29.5 GPa% and a 7% volumetric fraction of retained austenite. It is concluded that the precise knowledge about the IA effects on the phase transformations and microstructure evolution in a commercial CMnSi alloy has great potential to be applied in defining a one‐step Q&P heat treatment that favors a multiphase microstructure, which meets mechanical properties requirements for a third‐generation AHSS. [ABSTRACT FROM AUTHOR]

High-strength steel (HSS) can effectively and economically design structural members that withstand large forces induced by extreme events such as earthquakes. To evaluate the seismic performance of HSS members and structures using nonlinear finite element (FE) analyses, using an accurate material model is important, which can simulate the inelastic cyclic behavior of the HSS. The peculiar material behavior of HSS needs to be considered in the model. This study used a combined hardening model to construct the material model. The configuration of the model and the constituent model parameter values are determined to precisely simulate the low-cycle fatigue (LCF) behavior of HSS. An efficient particle swarm optimization (PSO) algorithm is used to determine parameter values with LCF test data of 54 individual HSS coupons. In additions, to conveniently determine the model parameter values with only monotonic tensile test data instead of conducting expensive LCT tests, empirical equations are proposed. It is shown that the LCF curves of HSS can be accurately simulated using the constructed material model with the proposed equations. [ABSTRACT FROM AUTHOR]

Faced with the rapid development of large-scale pumped-storage power stations, the trade-off between the strength and toughness of hydropower steels in extreme environments has been limiting their application. The effects of Nb micro-alloying and direct quenching and tempering processes on the strengthening–toughening mechanism of 1000 MPa grade high-strength hydropower steel are studied in this paper, and the precipitation behavior of Nb is discussed. The results showed that only the 0.025Nb steel using the DQT process achieved a cryogenic impact energy of more than 100 J at −60 °C. Under the DQT process, a large number of deformation bands and dislocations were retained, refining the prior austenite grains and providing more nucleation sites for the precipitation of NbC during the cooling process. The DQT process has a more obvious local strain concentration, mainly focusing on the refined lath boundary, which indicates that the refinement of the microstructure also promotes the stacking of dislocations. The improvement in fine grain strengthening and dislocation strengthening by the DQT process jointly led to an increase in strength, resulting in a better combination of strength and toughness. [ABSTRACT FROM AUTHOR]

Nature has long inspired technological innovations, fostering the rapidly developing field of bionics. Inspired by the microstructure of bamboo, we have developed a bamboo-like structure for steel. This novel steel achieves a tensile strength exceeding 1200 MPa and a uniform elongation nearing 68%, resulting in a product of strength and uniform elongation up to 83 GPa·%. The high strength of the steel is primarily attributed to its ultra-fine lamellar grains. Additionally, the graded occurrence of multiple deformation mechanisms collectively maintains its exceptional work-hardening capability. This study presents a new approach to enhancing the performance of medium-Mn steels. Impact Statement: A bamboo-like steel consisting of lamellar ferrite and austenite alternating along the rolling direction, providing a new path to produce medium-Mn steels with outstanding mechanical properties. [ABSTRACT FROM AUTHOR]

Martensitic steels, engineered to meet automotive weight reduction and crashworthiness requirements, are highly susceptible to hydrogen embrittlement (HE). Despite extensive research to improve HE resistance, these steels remain vulnerable to HE after undergoing resistance spot welding (RSW). HE in spot-welded steels has been largely unexplored, and its underlying mechanism remains unclear. This study investigates the HE mechanism in RSWed steel sheets by examining microstructural alterations and hydrogen trapping sites before and after RSW. Additionally, the study analyzes variations in tensile-shear test (TST) properties relative to increasing hydrogen content. In spot-welded steels, the tensile-shear strength and fracture displacement decline as diffusible hydrogen levels increase. Specifically, fracture displacement sharply declines within the first 3 h of hydrogen charging, but this loss rate significantly decreases thereafter. This slope shift is attributed to a transition in the crack propagation path. Initially, cracks propagate along the fusion zone line, featuring transgranular failure. However, beyond a critical hydrogen content, crack propagation shifts to the prior austenite grain boundary (PAGB) in the upper critical heat-affected zone (UCHAZ), exhibiting intergranular failure. Consequently, when hydrogen content surpasses this critical threshold, the PAGB in the UCHAZ is weakened due to hydrogen-enhanced decohesion (HEDE) and hydrogen-enhanced localized plasticity (HELP). Cracks then propagate along the PAGB in the direction of maximum stress during the tensile-shear test (TST), leading to a change in the crack propagation path. [Display omitted] • The resistance to hydrogen embrittlement for spot-welded advanced high strength steel is evaluated by tensile-shear test. • The difference in the behaviors of hydrogen embrittlement between steel matrix and welded part is compared. • The phenomenon of crack propagation path transition is observed over certain hydrogen content. • The mechanism of crack propagation path transition is discussed. [ABSTRACT FROM AUTHOR]

Considering the advantages of hybrid steel I-section beams in reducing engineering costs and fully utilizing the mechanical properties of steel, and the lack of research on their ductility, hybrid steel I-section beams were tested to analyze the effects of the plate width–thickness ratio and steel strength matching on the flexural bearing capacity and ductility. The steel strength matching of the hybrid steel I-section beam with a high steel strength utilization rate and good ductility was related closely to the section size. Additionally, a parametric analysis based on the finite- element method was performed for further study. The steel strength ratio φ of the web to the flange with the best ductility was less than 1, and φ decreased with an increase in flange steel strength. The steel strength utilization rate and ductility decreased with an increase in φ. Based on the parametric analysis results, the optimal range of φ in hybrid-steel I-section beams with flange steel strength of 460–690 MPa was 0.56–1. The plate width–thickness ratio limit of the ductile section decreased with the decrease of φ. Considering the plate interaction and steel strength matching, a sectional ductility design method is proposed that is more applicable to hybrid steel I-section beams than existing methods. [ABSTRACT FROM AUTHOR]

The expanded web depth of steel beams leads to improved strength and stiffness. In some design scenarios, such as cellular, castellated, or expanded steel beams, increasing the depth of the web improves the strength and performance of the steel beam. The expanded web of steel beams can be accomplished by creating a horizontal cutting in the web and then adding a plate between the two web section halves, which are called spacer plates. This method leads to improved stiffness and strength. Numerical models have been developed to accurately predict the properties of these beams. This study investigates the use of incremental plates to increase the depth of hot-rolled wide-flange steel beams. The experimental results were validated first with the Finite Element (FE) numerical model created by ABAQUS software, and then Finite Element Analysis (FEA) methods were used to create and analyze new numerical models by considering parameters that provided more models at a lower cost. The load-mid-span deflection curve behavior of both models (experimental and theoretical) was similar. Also, the load-deflection behavior of steel beams with two types of openings was studied. For the first type of opening (B1 NUM), with a smaller opening width of 30 mm and a higher hole number (24), the ultimate load increased by 53%, 111%, and 184%, the deflection at 0.95 Pu increased by 160%, 293%, and 81% of beams with ratio 150%, 200%, and 250% compared with the reference beam. For the second type of opening (B2 NUM), with a larger opening width of 60 mm and smaller hole number (12), the ultimate load capacity increased by 51%, 147%, and 177%, for beams with a ratio of 150%, 200%, and 250%, compared with the reference beam. The deflection at 0.95 Pu increased by 46% and 15% for beams with a ratio of 150%, and 200%, and decreased by 8% for beams with a ratio of 250%. Accordingly, for the first type of opening, the expanded ratios of 150% and 200% performed best with a reduction of only 1%-12% in the ultimate load capacity. However, for the second type of opening, the beam with a ratio of 250% performed better than the first type. Using prestress strands may highly improve steel beams' performance with the expanded webs containing openings by creating a stronger section that can withstand higher loads and exhibit improved structural performance, especially from beams with a ratio of 150%. [ABSTRACT FROM AUTHOR]

A systematic study is performed on the development of hot-dip galvanized coatings on a Mn-containing high-strength steel sheet by varying the dew point (− 50, − 10, and + 10 °C) during inter-critical annealing of the steel strip at 800 °C. It also studies the effect of dew point on the corrosion behavior of the coatings in freely aerated 3.5 wt% NaCl solution. The reducing gas atmosphere consists of 95% N2 and 5% H2, where inter-critical annealing is carried out. Surface oxidation of the steel has a strong effect on the development of sound coating. A defect-free adherent galvanized coating is obtained on the annealed steel surface at a fixed dew point of + 10 °C, and it is attributed to the fine and continuous compact Fe-Al crystals compared to galvanized coatings produced at other dew points as well as the highest atomically dense (0002) basal plane. This also leads to the lowest corrosion rate (~ 0.164 mm y−1, where mm and y stand for millimeter and year, respectively) of the galvanized coating produced at a dew point of + 10 °C when compared with galvanized coatings produced at dew points of − 50 °C (~ 0.279 mm y−1) and − 10 °C (~ 0.259 mm y−1). The lowest corrosion rate of the galvanized specimen developed at + 10 °C dew point can be attributed to the uniform and defect-free coating surface, together with the dominance of the more atomically dense (0002) basal plane. [ABSTRACT FROM AUTHOR]

In this article, the effect of Ce element on the microstructure and mechanical properties was studied by Ce addition to the hot‐formed steel. Scanning electron microscope and energy dispersive spectrometer (SEM‐EDS) was used to analyze the improvement effect of Ce on inclusions and the effect of inclusions on fracture behavior; Electron back scattering diffractometer (EBSD) was used to analyze the refinement and strengthening effect of Ce on martensitic grains; transmission electron microscope (TEM) and high resolution transmission electron microscope (HRTEM) was used to analyze the microstructure strengthening effect and microalloying effect of solid solution Ce in hot‐formed steel. Through a systematic analysis of mechanical properties and microstructure, the mechanism of Ce enhances the strength and elongation of hot‐formed steel was clarified. Besides, this work provides a research basis for further improving the safety and machinability of hot‐formed steel. [ABSTRACT FROM AUTHOR]

One of the efficient and cost-effective structural elements is the castellated steel beam (CSB) which can significantly lower building costs. This fact encourages studying the structural behavior of such beams and determining the castellation ability to maximize flexural stiffness while avoiding shear failure. For this purpose, experimental and theoretical investigations were carried out. The experimental work consisted of fabricating and testing six beams with span lengths of 2000 and 1038 mm and expansion ratios of 1.0, 1.25, and 1.50. Meanwhile, the theoretical part included an adopted analytical procedure that produced an unprecedented theory-based formula giving the maximum expansion ratio ( ψ m ), thus determining the nominal flexural strength of any castellated section. On the other hand, the experimental results, which covered a variety of mechanisms and failure modes, including overall flexural failure, shear and compression buckling of the web posts, tearing and inelastic local buckling, and compression buckling of the top tee, confirmed that ψ m should not be exceeded to fully utilize the flexural capacity of CSBs. The formula for ψ m was then graphed for design purposes, and it was found that it relies on three major parameters: loading type factor (Cc), span length (L), and properties of the root section, upon which any castellated section has a distinct ultimate flexural strength. Furthermore, the ultimate flexural strength increases as the loading type factor decreases and the span length increases. [ABSTRACT FROM AUTHOR]

The formation and growth of different types MnS inclusions were in situ observed and confirmed by CLSM and FESEM in high-Al medium-Mn steel. Type II, IIS, and III MnS are mainly determined by the solidification route of steel and the change of degrees of supersaturation of S and Mn elements. The sintering of type III and II is key factor leading to an increase in the size of MnS inclusions. [ABSTRACT FROM AUTHOR]

The derived diagram defines three main ranges of hydrogen concentration in the metal, which have their own specific mechanisms of hydrogen influence on the characteristics of strength and ductility of the pipeline steel. It has been demonstrated that the nature of the hydrogen effect mechanism depends on the ratio of diffusible C H dif and residual (trapped) hydrogen C H res in the steel. A specific effect has been found, namely: at the hydrogen concentration C H ≅ 0.01 - 0.2 ppm where all hydrogen is practically diffusible, the plastic deformation of the steel is facilitated, i.e., the deforming of the material takes place more easily. At the concentration range C H ≅ 0.8 - 10 ppm , where the trapped hydrogen prevails, the mechanism of hydrogen embrittlement of the steel is completely dominated. Therefore, the hydrogen concentration range beginning from C H ≅ 0.8 ppm can be considered as critical. The range of values of hydrogen concentration in the metal C H ≅ 0.2 - 0.8 ppm is a transition zone where the simultaneous coexistence of these two mechanisms is possible. The constructed diagram can be applied for the interpretation of the inspection results of long-term operated pipelines, and also for the choice of materials for the construction of new networks for hydrogen transportation. [ABSTRACT FROM AUTHOR]

High-carbon hardline steels are primarily used for the manufacture of tire beads for both automobiles and aircraft, and vanadium (V) microalloying is an important means of adjusting the microstructure of high-carbon hardline steels. Using scanning electron microscopy (SEM), X-ray diffraction (XRD), and transmission electron microscopy (TEM), the microstructure and precipitation phases of continuous cooled high-carbon steels were characterized, and the vanadium content, carbon diffusion coefficient, and critical precipitation temperature were calculated. The results showed that as the V content increased to 0.06 wt.%, the interlamellar spacing (ILS) of the pearlite in the experimental steel decreased to 0.110 μm, and the carbon diffusion coefficient in the experimental steel decreased to 0.98 × 10−3 cm2·s−1. The pearlite content in the experimental steel with 0.02 wt.% V reached its maximum at a cooling rate of 5 °C·s−1, and a small amount of bainite was observed in the experimental steel at a cooling rate of 10 °C·s−1. The precipitated phase was VC with a diameter of ~24.73 nm, and the misfit between ferrite and VC was 5.02%, forming a semi-coherent interface between the two. Atoms gradually adjust their positions to allow the growth of VC along the ferrite direction. As the V content increased to 0.06 wt.%, the precipitation-temperature-time curve (PTT) shifted to the left, and the critical nucleation temperature for homogeneous nucleation, grain boundary nucleation, and dislocation line nucleation increased from 570.6, 676.9, and 692.4 °C to 634.6, 748.5, and 755.5 °C, respectively. [ABSTRACT FROM AUTHOR]

Although research has shown a considerable influence of the pre-cracking phenomenon on steel-congested concrete members, only normal concrete (NC) has been considered in the literature. The intention in this paper is thus to study the effect of the pre-cracking phenomenon on the bond response of pre-cracked NC with different slump flow values and self-consolidating concrete (SCC). Initial crack widths ranging from 0.0 to 0.5 mm are studied. Results show that initial crack widths larger than 0.10 mm have a significant influence on bond properties, such that reduction factors greater than 30% and 50% are obtained for the maximum bond strength of concrete specimens exposed to initial crack widths of 0.2 mm and 0.4 mm, respectively. Results show that concrete mixtures with higher workability are less sensitive to the pre-cracking phenomenon as compared to NC mixtures. The average bond stress of steel rebar in the pre-cracked SCC is found to be similar to that of the NC with a slump flow of 200 mm, which is considerably better than for NC with a slump flow of 97 mm. Moreover, results show that 65.8, 80.6, 88.5 and 93.1% fracture energy reductions are obtained for crack widths of 0.20, 0.30, 0.40 and 0.50 mm, respectively, as compared to the small crack width of 0.15 mm. [ABSTRACT FROM AUTHOR]

The influence of varying the manganese (Mn) contents of high-strength copper-containing hull steel on its microstructural evolution and mechanical properties was investigated. With increasing Mn content from 2 to 5%, the tensile strength of the steel increased by ~100 MPa, while the elongation of steel remained at ~23.5%, indicating good plasticity. However, the 2Mn sample had 128 J higher low-temperature (−84 °C) impact work than the 5Mn sample. The microstructures of different Mn steels were composed of fresh martensite (FM), ferrite/tempered martensite (F/TM), and reversed austenite (RA). The increase in Mn content markedly increased the presence of RA and intensified the work hardening caused by the transformation-induced plasticity (TRIP) effect during the tensile process. However, as the phase transformation in different Mn steels occurred in the early stage of strain and did not extend throughout the entire plastic deformation process, increasing plasticity via phase transformation was difficult. In addition, although the volume fraction of RA increased significantly in 4Mn and 5Mn steels, the stability of RA significantly decreased. The presence of numerous metastable blocks and coarse lath-like RA contributed little to low-temperature impact work and was even detrimental to toughness. The substantial fresh martensite resulting from phase transformation facilitated microcrack generation, owing to rapid volume expansion and mutual impacts, thus reducing the work required for crack formation. Additionally, the abundance of deformation twins significantly reduced the work needed for crack propagation. These combined actions significantly reduced the low-temperature toughness of 4Mn and 5Mn steels. [ABSTRACT FROM AUTHOR]

Process maps were developed using a combination of microstructural analysis and DICTRA-based modeling to predict the austenite vol.% as a function of the intercritical annealing parameters and starting microstructure. The maps revealed a strong dependence of the calculated austenite fraction (vol.%) on the Mn content (4–12 wt.%) and intercritical annealing temperatures (600 °C to 740 °C). The calculations were carried out for constant carbon, Al, and Si contents of 0.2 wt.%, 1.5 wt.%, and 1.0 wt.%, respectively. A modified empirical equation proposed by Koistinen and Marburger was employed to calculate the room-temperature retained austenite vol.% as a function of the intercritical annealing temperature, including the effect of the austenite composition. The process maps offer valuable insights for designing intercritical treatments of medium-Mn steels, aiding in the optimization of steel properties for automotive applications. [ABSTRACT FROM AUTHOR]

Owing to the non-uniform distribution of chemical composition and temperature during the heat treatment process, the residual stress and deformation of the workpiece emerge as crucial factors requiring consideration in managing the service performance and lifespan of shield machine cutter rings crafted from H13 steel. Considering H13 steel with titanium microalloying as the research object for the shield machine cutter ring, we simulate the quenching process using Deform-3D. The temperature field, phase transformation, stress evolution, and deformation amount after quenching are analyzed. The results demonstrate a strong agreement between the simulation and experimental results, offering valuable insights for optimizing the heat treatment process and enhancing the overall performance of shield machine cutter rings. [ABSTRACT FROM AUTHOR]

Circular design strategies such as adaptivity, detachability, and reusability represent new challenges and increased demands on the future‐proof buildings sector. To contribute to the circularity and sustainability of the steel construction sector, an innovative solution of beam‐column moment‐resisting joints with long bolts and short steel elements (links) is proposed, enabling an extension in the service length of existing steel members. This paper assesses the influencing connection parameters (e.g. bolt preload, bolt length and diameter, end plate thickness, etc.) on the moment (flexural) resistance, stiffness, rotation, ductility, and failure modes of base configurations of these joints. [ABSTRACT FROM AUTHOR]

Fire is generally aftermath of an earthquake because of damaged gas pipelines, electrical short circuits, etc. This increases the vulnerability for greater damage to structures and human. In order to mitigate the damage, authors designed and developed an earthquake-resistant high strength steel with fire resistance using Thermo-Calc software. The designed micro-alloyed steel was produced in vacuum induction furnace and casted into ingots. Subsequently, the ingots were rolled to the preferred size in 2/4 high rolling mill. From the rolled plates, desired UTM samples were fabricated. The fabricated samples were quenched in different quench media like brine, water and forced air after preheating to 1050 °C in order to obtain TEMPCORE properties (martensite at the outer ring and ferrite plus pearlite at the core) in the final product. Though various quenching media were used, water quenched samples were giving desired results and hence these samples were used for further fire resistance studies. SEM and TEM studies were performed on these samples at various stages. It was observed that pearlite formed at the core and martensite at the outer ring transformed from the ferrite and the same was confirmed by EBSD. From the TEM studies, it was observed that there is formation of tempered martensite laths and nano-sized nodular carbides of V, Nb and Mo resulting in high yield strength of 715 and 477 MPa at room temperature as well as at elevated temperature of 650 °C, respectively. [ABSTRACT FROM AUTHOR]

Herein, the microstructure and mechanical properties of a low‐alloy Cu‐bearing transformation‐induced plasticity (TRIP) steel and their dependence on the processing history are investigated. The distributions of the retained austenite and bainite are found to be dependent on the initial cold‐rolled microstructure, which can be tailored by the preceding hot‐rolling route (unidirectional/cross rolling) and the subsequent cooling rate (furnace/air cooling). Mechanical properties and TRIP effect strongly depend on the initial microstructure, where the air‐cooled sheet shows remarkable mechanical properties; while the cross‐rolled sheet shows isotropic properties. The addition of copper results in an increase in the amount of the retained austenite, enhancement of strength‐ductility balance, and improvement of the hardening behavior of TRIP‐assisted high‐performance steel. [ABSTRACT FROM AUTHOR]

Herein, the effects of Chromium–Molybdenum (Cr–Mo) addition on the microstructural evolution and mechanical properties of medium‐carbon steel after spheroidization annealing are systematically studied through scanning electron microscopy, electron backscatter diffraction, and tensile testing. Cr–Mo addition hinders the proeutectoid ferrite + pearlite transformation, thereby promoting the bainite transformation. Moreover, it refines the pearlite lamellar spacing as well as decreases the average carbide diameter, increases the number of carbides per unit area, and hinders ferrite recrystallization. Compared with those in the B1 steel annealed for 8 h, the size of carbides and their number per unit area in the CM1 steel are 30% lower and 2.2‐fold higher, respectively. Due to finer ferrite grains, smaller carbides, and a higher amount of carbides, the strength of steel improves, and the plasticity slightly reduces after Cr–Mo addition. After 2 h of annealing, the yield strengths of Cr–Mo steels are 77.5–109.5 MPa higher than those of base steels; the elongations are above 20%. The contributions of the strengthening mechanism of steel to the yield strength are as follows (from high to low): grain boundary, precipitation, solid solution, and dislocation strengthening. [ABSTRACT FROM AUTHOR]

Nb-Ti high-strength low-alloy pipeline steel was subjected to a six-pass rolling process followed by the coiling process at different temperatures between 600 and 650 °C using the thermo-mechanical testing system Gleeble 3500 (Gleeble, New York, NY, USA). This experimental steel was subjected to 72% heavy reduction through a thermos-mechanical controlled process. Thereafter, the microstructures were observed using optical microscopy, scanning electron microscopy, electron backscatter scanning diffraction, and transmission electron microscopy coupled with energy dispersive spectrometry and selected area electron diffraction. For the selected three coiling temperatures of 600, 625, and 650 °C, acicular ferrite, polygonal ferrite, and pearlite were observed, and morphology and statistical analysis were adopted for the study of precipitates. Based on the estimation by the Ashby–Orowan formula, the incremental strength through precipitation strengthening decreases with coiling temperatures and reaches 26.67 Mpa at a coiling temperature of 600 °C. Precipitation-time-temperature curves were obtained to explain the transformation of precipitates. The (Nb, Ti)(C, N) particles tended to precipitate in the acicular ferrite with [011](Nb, Ti)(C, N)//[011]α-Fe orientation. The lower coiling temperature provided enough driving force for the nucleation of precipitates while inhibiting their growth. [ABSTRACT FROM AUTHOR]

In order to find out the deformation behavior and mechanical properties of 42CrMo steel under warm upsetting conditions, the Gleeble-3500 thermal simulation testing machine was used to carry out a warm upsetting physical simulation experiment on 42CrMo steel. By controlling deformation temperature, strain rate, and constant temperature deformation pass, the microstructure evolution rule under different warm upsetting conditions was analyzed, and its hardness value was measured. Then, the simulation experiment is carried out based on the Deform-3D finite element platform. The results show that, with the increase in deformation temperature, 42CrMo steel has a temperature rise softening effect, which significantly reduces the peak value of rheological stress. At 650 °C, the maximum peak value of rheological stress is only 45.3% of that of cold upsetting deformation at room temperature, and the stress-strain curve tends to be gentle at the plastic deformation stage, which is the most suitable temperature for warm upsetting deformation. The maximum peak flow stress of 42CrMo steel increases with the increase in strain rate, but the number of deformation channels has little influence on the stress-strain curve. The warm, upsetting deformation can refine the internal grain structure significantly, and the grain refinement mechanism is mechanical crushing. When the temperature is slightly higher, the broken grain will recover, and the grain size will grow. During the process of warm upsetting, the strain rate has a great influence on the microhardness of the sample. The deformation pass has little influence on the hardness, and the hardness increases slightly with the increase in the deformation pass. Through the Deform-3D simulation, the correlation coefficient R and the average absolute relative error (AARE) between the simulation value and the experimental value were calculated, and the correlation coefficient R-value was 0.9948, and the average absolute relative error (AARE) was 2.05%, indicating that the simulation can accurately reflect the relationship between displacement and applied load. [ABSTRACT FROM AUTHOR]

Background: Failure of the structure may be avoided if, the damage is noticed at an early stage and proper remedial work is performed. In this context, this paper presents a detection of structural damage in steel beams, which are major load carrying members in bridges and buildings. Method: In the present study, the Generalized Flexibility Energy Quotient Difference Index (χ) is determined at various locations of the beam by introducing the damage by means of a cut by 0.5 mm to 2.5 mm at an interval of 0.25 mm. In practice, it is very difficult to capture all the modes of vibration. Hence, the method followed uses the first mode of vibration only for quantifying the magnitude of damage and its location. The validation is done between numerical simulations and experimental works for the estimation of first frequency. The efficiency of the method is tested by inducing the damage very close to the support. In ANN, the depth of cut at various locations of the beam and χ is utilized in the input layer. Results: The predicted depth of cut or severity of damage from the output layer of ANN model is compared with the actual depth of cut induced in the beam. Finally, the polynomial equations are formulated for the damaged elements, which are the major contribution of the present study. These equations can be used as a ready reckoner to estimate the actual depth of cut in the beam. This approach is validated through a beam with fixed ends and two-span beam, and the results indicate that this method is very much beneficial in preventing the structural failure. [ABSTRACT FROM AUTHOR]

The performance of carbon fiber reinforced polymer (CFRP) composite materials under quasi-static and high strain rate loading can be predicted with a high level of accuracy using the non-linear finite element analysis (FEA) method. Experimental validation tests under uniaxial tensile loading have shown a good correlation with FEA predictions for thermoset polymer composites, using commercially available epoxy resin MTM710 with carbon fiber reinforcement and for comparative tests on DP600 steel and aluminum alloys (AC170 and 5754 series). The physical and numerical results comparison of composite, aluminum, and high-strength steel indicates that the composite may be used as an alternative to aluminum and high-strength steel since the composite was shown to have almost the same strength as steel and higher strength than aluminum with the advantage of being lightweight and possessing similar mechanical behavior under quasi-static conditions. The results demonstrated that the strain rate range used did not significantly affect the strength of the composite materials. The selection of materials can be optimized reliably by FEA based on mechanical properties, cost, and weight. This will significantly reduce the new product introduction timescale, which is essential for the wider use of polymer composites for structural applications, especially in the automotive industry. [ABSTRACT FROM AUTHOR]

Landslides due to catastrophic weather events, especially heavy rainfall, have risen significantly over the last several decades, causing significant damage and affecting the health and livelihoods of millions of people. Using tree roots to bio-engineer shallow slopes has been proven to be a cost-effective, sustainable measure and thus has gained increasing popularity. As slope failure often occurs under heavy precipitation, it is important to understand the mechanical interactions in the soil matrix surrounding a root to better estimate the reinforcement capacity of a root system, especially as the soil undergoes wetting from drier conditions. However, very few studies of root reinforcements have considered the effects of degree of saturation on behaviour. In this study, steel wires are used as a root analogue to explore the impact of root geometry, soil dilation and soil saturation on the pull-out behaviour of a root and three commonly used unsaturated soil strength models have been used to interpret the pull-out results. It was found that roots with larger diameter did not contribute to additional resistance. Also, a linear relationship between degree of saturation and pull-out strength was identified over a large range of suctions and one of the unsaturated soil strength models seemed to provide a more reasonable interpretation. The results will help future bioengineering slope design by improving the understanding of soil-root interface behaviour, including the effect of root diameter in slippage failure and greater emphasis on the importance of taking degree of saturation into account in unsaturated soil strength models. [ABSTRACT FROM AUTHOR]

We investigated the influence of steel surface properties on the wettability of zinc (Zn). Our main objective is to address the selective oxidation of solute alloying elements and enhance the wetting behavior of Zn on advanced high strength steel (AHSS) by employing an aluminum (Al) interlayer through the physical vapor deposition technique. The deposition of an Al interlayer resulted in a decrease in contact angle and an increase in spread width as the molten Zn interacted with the Al interlay on the steel substrate. Importantly, the incorporation of an Al interlayer demonstrated a significant improvement in wettability by substantially increasing the work of adhesion compared to the uncoated AHSS substrate. [ABSTRACT FROM AUTHOR]

Fe-C-Cr-Nb alloy steel surfacing layers with different contents of C and Cr were prepared on 45 steel base metal by selfshielded flux-cored wires with distinct amounts of high carbon chromium iron addition and melt arc surfacing. The composition and microstructure changes of the surfacing layer were tested and analyzed. The surfacing test plate was processed into a pulling specimen, and the bonding strength between the surfacing layer and the 45 steel base metal was tested with a self-designed pulling test method. The fracture location of the pulling specimen and fracture characteristics were observed by a metallurgical microscope and a scanning electron microscope. The result shows that with the increase of the amount of high carbon chromium iron added to flux-cored welding wire, the content of C and Cr in the surfacing layer increases, and the NbC hard phase disperses. The microstructure of the steel matrix changes from mixed martensite + residual austenite to high carbon martensite + residual austenite, and then independent austenite appears. The hardness of the surfacing layer first increases and then decreases. The bonding strength between the surfacing alloy and the 45 steel base metal first decreases and then increases, and the fracture location is at the bottom of the surfacing layer or the fusion zone with mostly quasi-cleavage characteristics. When the additional amount of high carbon chromium iron reaches 13%, thee pulling specimen exhibits significant deformation with the highest bonding strength, and the fracture is close to the fusion line, where there are numerous tearing edges and shallow dimples. [ABSTRACT FROM AUTHOR]

This article uses scanning electron microscopy (SEM) and electron back-scattering diffraction (EBSD) to study the effect of C and Mn segregation on the microstructure and mechanical properties of high-strength steel with 20 mm thickness used for wind power before and after simulated welding. A Gleeble-3500 (GTC, Dynamic Systems Inc., Poestenkill, NY, USA) was used to study the microstructure evolution of the simulated coarse-grained heat-affected zone (CGHAZ) of experimental steel under different welding heat inputs (10, 14, 20, 30 and 50 kJ/cm) and its relationship with low-temperature impact toughness (−60 °C). The results indicate that alloy element segregation, especially Mn segregation, significantly affects the impact toughness scatter of the steel matrix, as it induces the formation of low-temperature martensite or hard phase, such as M/A (martensite/austenite) constituent. In addition, segregation also reduces the low-temperature impact toughness of the simulated welding samples and increases the fluctuation range. For high-strength steel with yield strength higher than 460 MPa used for wind power generation, there is an optimal welding heat input (~20 kJ/cm), which enables the simulated coarse-grained heat-affected zone (CGHAZ) to obtain the highest impact toughness due to the formation of lath bainite (LB) and the finest crystallographic block units. Excessive or insufficient heat input can induce the formation of coarse granular bainite (GB) or lath martensite (LM), leading to a larger size of crystallographic block units, reducing the hindering effect of brittle crack propagation and deteriorating low-temperature impact toughness. [ABSTRACT FROM AUTHOR]

The production reality of sheet steels from casting to the end product is such that in the cases of ultra- and advanced high-strength steels, we have to deal with the segregation of elements on macro- and microlevels. Both can have a significant impact on the microstructure formation and resulting properties. There are several production stages where it can influence the transformations, i.e., casting, hot rolling process and annealing after cold rolling. In the present work, we focus on the latter, and more specifically, the transformation from ferrite–cementite to austenite, especially the nucleation process, in cold-rolled material. We vary the levels of two substitutional elements, Mn and Si, and then look in detail at the microsegregation and nucleation processes. The classical nucleation theory is used, and both the chemical driving force and strain energy are calculated for various scenarios. In the case of a high Mn and high Si concentration, the nucleation can thus be explained. In the cases of high Mn and low Si concentrations as well as low Mn alloys, more research is needed on the nuclei shapes and strain energy. [ABSTRACT FROM AUTHOR]

To analyze various types of cold formability in TRIP-aided polygonal ferrite (TPF), annealed martensite (TAM), and bainitic ferrite (TBF) steels, the effects of the mean normal stress on the strain-hardening, strain-induced martensite transformation, and void-formation behaviors were investigated. The strain-hardening behavior was influenced by positive mean normal stress and was hardly influenced by zero and negative mean normal stresses in all steels. Positive mean normal stress promoted the strain-induced martensitic transformation behavior, especially in TBF steel due to the high mechanical stability of the retained austenite. The void-formation behavior was also promoted by positive mean normal stress, especially in TPF steel. These behaviors were also related to the microstructural properties, such as the matrix structure, retained austenite characteristics, and second phase. [ABSTRACT FROM AUTHOR]

In this study, X80 pipeline steel is prepared with different Nb contents through the thermo-mechanically controlled rolling process. The effects of using two different Nb contents on the impact toughness and microstructure of the pipeline steel are examined using various experimental techniques. The results show that with the increase in Nb content, the transformation temperature Ar3 decreases, and the nucleation and growth of bainitic ferrite with lath features (LB) are promoted, while those of granular bainite (GB) are inhibited. In addition, the stability of the austenite phase increases with the increase in Nb content. Therefore, the volume fractions of LB and martensite–austenite (M/A) constituents increase, while the proportion of high-angle grain boundaries (HAGBs) decreases. The impact energy of pipeline steel at −45 °C is closely related to the Nb content. Specifically, the impact energy decreases from 217 J at 0.05 wt.% Nb to 88 J at 0.08 wt.% Nb. The cracks are preferentially formed near the M/A constituents, and the HAGBs significantly inhibit the crack propagation. The steel with 0.05 wt.% Nb has a lower content of M/A constituents and a higher proportion of HAGBs than the one with 0.08 wt.% Nb. In addition, as the Nb content increases, the crack initiation energy and the crack propagation energy decrease. Thus, the 0.05 wt.% Nb steel has a higher low-temperature impact energy. [ABSTRACT FROM AUTHOR]

High‐strength steels can be used in civil structures that demand high strength/weight ratios, but their advantages may be weakened by fire. For this reason, this study has been concerned with the mechanical properties of a type of quenched‐and‐tempered high‐strength steel at elevated temperatures up to 800°C, the steel grade is S690. A standard axial tensile test was conducted on plate specimens with a reduced section. The test results demonstrated that the stress–strain curves of S690 steel at elevated temperatures had no distinctive yield plateau but post‐yield hardening, the effective yield strengths and elastic modulus deteriorated dramatically with the increasing temperature due to microstructure changes. Besides, this study also investigated the effects of steel plate thickness on said temperature‐dependent mechanical properties. The plate thicknesses are 8 and 12 mm nominally. The comparisons showed that, different from the trend at room temperature where the thinner steel plates usually have higher strength than their thicker counterparts, the thinner plates exhibited lower strengths at elevated temperatures, this implies that with the same cross‐sectional area, a steel member formed by thinner plates would have a lower cross‐sectional load‐carrying capacity under fire. [ABSTRACT FROM AUTHOR]

At present, the heat treatment process tends to focus on the strength and toughness of high strength steel, while ignoring the softening behavior of welding heat-affected zone (HAZ). The effect of austenitizing temperature and tempering temperature on mechanical properties and HAZ softening behavior of ultra-high strength steel (UHSS) are investigated. The results indicate that the optimum combination of strength, toughness and degree of HAZ softening can be achieved by quenching at 950 °C and tempering at 650 °C. With the increase of austenitizing temperature from 890 to 980 °C, more carbides dissolved in the matrix and the prior austenite grain size (PAGS) increased. Therefore, after tempering at 650 °C, the strength increases first and then decreases slightly under the combined effect of the enhancement of precipitation strengthening and the decline of grain boundary strengthening. When the tempering temperature increases from 350 to 650 °C, the toughness of the samples quenched at 950 °C increases from 27.3 to 73.1 J, attributed to the decrease of carbon content and dislocation density of the matrix, and the increase of high-angle grain boundary (HAGBs) density. The austenitizing temperature has a great influence on the degree of HAZ softening. With the austenitizing temperature increasing from 920 to 980 °C, the degree of HAZ softening becomes more serious due to the over-grown recrystallized grains and coarsened carbides. [ABSTRACT FROM AUTHOR]

Materials with good mechanical and chemical properties (materials should be resistant to various types of corrosion) are proposed for the various structures of means of transport. For this reason, high-alloy steels, including duplex steels, are increasingly used in the automotive industry. The 1.4462 duplex steel used in means of road transport steel could be treated as an interesting high-strength stainless material used in the automotive industry. Generally, duplex steels have a high resistance to localized and uniform corrosion. The duplex and superduplex steels are assumed to be rather proper weldable materials; however, cracks could be observed both in the heat-affected zone (HAZ) and in the weld. The article analyses the influence of tubular cored metal arc (136) with active gas shield welding (process 136) parameters on the arrangement of correct joints used in tanker truck elements, as an example of welding in the automotive sector. Various mechanical tests checking the properties of joints were realized. The goal of the paper is to choose the correct welding parameters for elements of 1.4462 steel. The construction elements of a tanker truck are made by the 136 method of welding. [ABSTRACT FROM AUTHOR]

The present study systematically investigated the effects of a laser welding speed and a defocusing amount on the microstructure and mechanical properties of low alloy high strength Q345 steel joints. The macro-morphology, microstructure, Vickers microhardness, and tensile properties of as-welded joints were analyzed. The results indicated a significant correlation between the laser welding speed and the size of individual zones within the welded joint. As the laser welding speed increased, the size of each zone decreased noticeably. The microstructure of the fusion zone was composed of proeutectoid ferrite, ferrite side-plate, and acicular ferrite. An increase in welding speed and defocusing amount facilitated microstructural changes towards formation of ferrite side-plate and acicular ferrite. Maximum tensile strength and maximum elongation of as welded joints were measured to be 669 MPa and 21.8%, respectively. The joints with maximum tensile strength tended to fracture within the fusion zone. The increase in welding speed and defocusing amount caused a significant decrease in normalized enthalpy and volumetric energy density. [ABSTRACT FROM AUTHOR]

Medium Mn steels are an emerging class of 3rd generation advanced high-strength steels. These steels have received significant attention due to their high strengths, large ductilities and also lower cost compared to their predecessor high Mn Twinning Induced Plasticity (TWIP) steels. Additionally, medium Mn steels have been found to exhibit TWIP and/or Transformation Induced Plasticity (TRIP) effects which can be harnessed to give a high strain hardening rate. Many thermomechanical processing concepts in the literature have been developed, producing multiple microstructure types with differentmechanical properties. The present review therefore aims to summarise the current knowledge of medium Mn steel alloy design especially on the processing, microstructure and property relationships in medium Mn steels. It complements the review of Sun et al. [Physical metallurgy of medium-Mn advanced high-strength steels, Int Mater Rev. 2023.], written independently and in parallel, which focusses more on the phase interfaces and thermodynamics. [ABSTRACT FROM AUTHOR]

Using X-ray computed tomography and focused ion beam-scanning electron microscopy (FIB-SEM) serial sectioning, this study investigated the three-dimensional propagation behavior of hydrogen-related intergranular cracks in martensitic steel with a tensile strength of 1.2 GPa, focusing on segments of prior austenite grain boundaries (PAGB segments). X-ray computed tomography revealed that the crack morphology was more continuous in the hydrogen-charged specimens. Through FIB-SEM serial sectioning, we found that crack-tip blunting and ductile rupture of un-cracked ligaments were associated with specific PAGB segments in the uncharged specimen. In the case of hydrogen-related intergranular crack propagation, even very fine, low-angle PAGB segments (sub-micrometer size) can act as obstacles for crack propagation. Based on these results, we propose that the misorientation of each PAGB segment has a large influence on the local arrestability of intergranular crack propagation. [Display omitted] • 3D crack morphology is more continuous in the hydrogen-related fracture. • Un-cracked ligaments tend to form at low-angle boundary segments. • Low-angle boundary segment can arrest intergranular crack. • Crystallographic feature of boundary segment influences local crack-arrestability. [ABSTRACT FROM AUTHOR]

The Fe–0.44%C–1.8%Si–1.3%Mn–0.82%Cr–0.28%Mo steel treated by the quenching–partitioning process showed a product of strength and elongation of 30 GPa % with yield stress of 1350 MPa. Such a combination of high ultimate tensile strength and good ductility is attributed to a high portion of retained austenite (≥20%) transforming to martensite under tension. The high yield stress is provided by carbon supersaturation of austenite and a high dislocation density in this phase. [ABSTRACT FROM AUTHOR]

Certain medium-manganese (6–12 wt% Mn) steels can be heat-treated to produce single-phase (austenite) or multi-phase (ferrite, austenite, bainite, martensite, and/or iron carbide) microstructures. With the proper amount of silicon and aluminum, both transformation-induced plasticity (TRIP) and/or twinning-induced plasticity (TWIP) can be the active deformation mechanism. In this study, two steel heats with compositions of Fe–7.53Mn–2.01Al–1.94Si–0.74C and Fe–7.71Mn–1.57Al–1.51Si–0.50C were investigated. The lower-carbon steel had a wider heat treating range but did not achieve as high of a hardness as the higher-carbon steel. Multi-phase microstructures were produced in both of these steels, and the multi-phase microstructures had higher yield strength compared to single-phase (austenite) microstructures. A high iron and manganese content skull adhered to the sides of the furnace after induction melting. This skull was difficult to remove from the furnace lining. [ABSTRACT FROM AUTHOR]

Quenching and self-tempering (QST) is an advanced thermo-mechanical process for "H" shaped steel beams. QST is an intensive surface cooling and self-tempering process that provides the grain refinement needed for high strength of low-carbon steels. However, the application of quenching often results in substantial deformation due to the formation of the martensitic microstructure at a high cooling rate. Quench deformation has been a complex metallurgical phenomenon that is difficult to accurately control in the beam-making process. A correlation between shape distortion and temperature distribution was therefore investigated through a lab-scale test. The thermal deformation was also analyzed numerically by using a commercial finite element program ANSYS APDL to explain the thermal expansion and contraction mechanisms of quenched steel beams. A metallurgical effect was sub-coded to follow a phase transformation in the quenching simulation. The theoretical approach and numerical simulation of the H-beam quenching are compared to the experimental findings. [ABSTRACT FROM AUTHOR]

Punching is an important process of the production for ultra-high-strength steel automobile components. By selecting the appropriate punching parameters, the punching quality can be effectively improved and the punching force can be reduced. In this study, several typical fracture damage models applicable to the punching process of high strength steel were compared, where the critical damage values were calculated through an iterative predictor–corrector approach. Meanwhile, the effects of punching parameters on maximum punching force (MPF) and punched face quality for hot stamped ultra-high strength steel Usibor1500P were investigated experimentally. The results show that the Oyane damage model is the most suitable one in simulating the punching process of Usibor1500P, which can better predict the punched profile features and the variation of punching force within one stroke. The increase in die clearance decreases the MPF, while the plate thickness, punch diameter and punch corner radius increase the MPF. The change of the punch corner radius has the most significant effect on the improvement of the punched face quality. [ABSTRACT FROM AUTHOR]

The new DUNE experimental facility for the study of neutrinos, hosted by the U.S. Fermilab, includes a massive steel cage fabricated out of S460 HL1100M profiles, where the corner joint between beams and columns is solved with a bolted flushed end plate. Although this joint typology is well described in the Eurocode, the size and internal forces of this case are out of the common experimental range. Thus, a real‐scale test of the joint has been carried out at the University of Coimbra. The results were used to validate high‐quality FEA models, which accurately reproduced the behavior and allowed further insight into the joint component characterization. Comparison with the Eurocode design values show a good agreement, validating the application of the component method to very large joints. [ABSTRACT FROM AUTHOR]