High Strength Steel Plates Research Articles

EFFECT OF A MAGNETIC FIELD ON THE MICROSTRUCTURE AND PROPERTIES OF A 22MnB5-CP780 WELDED JOINT

A steady-state magnetic field-assisted laser welding test of 1-mm-thick automotive 22MnB5 and CP780 high-strength steel plates was carried out using a low-power fiber laser. The effects of different magnetic induction intensities on the microstructure and mechanical properties of welded joints were investigated under a heat input of 150 J/mm. When no magnetic field was applied, there was splashing on the welded joint surface, the width was wide and the main solid-state phase transitions in the weld center included ferrite transformation and bainite transformation. The application of a magnetic field resulted in an acceleration of the cooling rate of the molten pool due to the thermoelectric magnetic force. This, in turn, led to the predominance of the bainite transformation and martensite transformation as the primary solid-state phase transitions in the weld center. In a range of 5–25 mT, the welded joints were narrow, symmetrical, well-formed and free of defects such as splashing. The experiment proved that as the magnetic induction intensity increased, the laser energy became more concentrated. This led to an increase in the average hardness at the center of the weld, a gradual reduction of the softening in the heat-affected zone and an increase in both the yield strength and elongation of the welded joint. The optimal comprehensive mechanical properties of the welded joints were observed when B = 25 mT.

Deflection Intelligent Prediction for High-Strength Steel Saddle Plate Forming Applicable to Reducing Ship Weight.

The application of high-strength steel plates can reduce ship weight, and the saddle plate is one of the most common types of double-curved hull plates. To fill the research gap regarding high-strength steel saddle plates, two prediction models are established here to predict deformation in saddle plate forming. Deflection is a key parameter reflecting the overall deformation of a curved plate. Therefore, first of all, the influencing factors of the line heating of high-strength steel saddle plates were analyzed. The influence of plate geometric parameters and forming parameters on deflection was researched. Second, a multiple linear regression model between deflection and the geometric parameters and forming parameters of high-strength steel saddle plates was established. Finally, to solve the problem of a large error in the multivariate regression model for extrapolation, an intelligent prediction program for deflection based on a support vector machine (SVM) was developed using the Python language. The results show that the error of the multiple regression model was less than 5% for data interpolation. The error of the intelligent prediction model for deflection was less than 5% for data extrapolation. This research can provide data support for the automatic forming of marine saddle plates.

High-strength steel plate girders under patch loading: Numerical analysis and design recommendations

Systematic investigations on the patch loading resistance of plate girders with different Q460, Q550, Q690, and Q960 high-strength steels (HSSs) were numerically performed with the purpose of proposing a design method suitable for plate girders with different HSSs. A numerical modelling method was proposed to reveal the resistance performance of a steel plate girder under patch loading. 39 experimental results on HSS, stainless steel, mild steel, and aluminum plate girders were used to validate the accuracy of the proposed numerical modelling method. The different HSSs, web aspect ratios, relative load lengths, and web height-to-thickness ratios were included in the parametric study. Based on the results of 192 finite element models, the effects of the key parameters on the ultimate resistance, effective resistance, and effective resistance stiffness were revealed. Subsequently, the design methods in the Chinese standard (GB 50017-2017), European standard (EN 1993-1-5), and American standard (AISC 360-16) were validated. The results indicated that the design method in GB 50017-2017 overestimated the ultimate resistance of HSS plate girders under patch loading, whereas the design methods in EN 1993-1-5 and AISC 360-16 underestimated the ultimate resistance. Subsequently, the design equations in EN 1993-1-5 were modified to accurately predict the ultimate patch-loading resistance of plate girders with different HSSs.

Axial compression behaviour of welded high-strength H-columns experimental tests and numerical simulations

High-strength steel has been produced and utilised in construction practice in recent years. Even though experimental studies and numerical simulations have been carried out on high-strength steel columns, design methods for columns have not been fully considered in national codes. This paper describes the overall buckling resistance of welded H-columns made of high-strength steel plates. Six steel columns with varied cross-sectional dimensions and slendernesses were compressed to failure in the experimental tests. The ultimate load and failure pattern of columns were determined and compared with values calculating per different national codes. Moreover, numerical simulations were also performed for high-strength steel columns, and residual stresses and initial bendings were considered in the model. The numerical model was verified using test data, and then parametric studies were conducted on the effects of height-to-width ratios of H-sections and slendernesses of columns on ultimate load. The numerical results of the buckling coefficient were also compared with design values following different design codes, and recommendations were made for the overall buckling design of high-strength steel H-columns in accordance with experimental results and numerical simulations.

HOT-DEFORMATION BEHAVIOR AND PROCESSING MAP OF 22MnB5 HIGH-STRENGTH STEEL

In order to explore the hot formability of 22MnB5, a hot-tensile test of 22MnB5 high-strength steel plate was carried out using a Gleeble-1500 hot-tensile-testing machine. The stress-strain curves at 850 °C to 950 °C and 0.01 s–1 to 10 s–1 were obtained. The results show that 22MnB5 has an obvious positive-strain-rate sensitivity, and its peak stress decreases with the increase of temperature. The mechanical constitutive equation of 22MnB5 was established by using the improved Johnson-Cook model, and the fitting value was compared with the experimental value. Based on the dynamic material model, the hot-processing map of 22MnB5 was established and analyzed. The hot-processing process was determined as follows: deformation temperature 880 °C to 930 °C, strain rate 0.01 s–1 to 1 s–1.

A macro element of demountable bolted steel-concrete composite connections for a novel prefabricated concrete sandwich wall panel structure

A novel prefabricated concrete sandwich wall panel structure (PCSWPS) system has been proposed for low-rise buildings in rural areas in China. The wall panels are jointed using high-strength bolts and steel plates through bolted steel-concrete composite connections (BSCCs). Despite published experimental results showing promising seismic performance of the structural system, the mechanics governing the interaction between the bolts, steel plates, and concrete at the connections still need to be clarified. To this end, we carried out full-scale connection experiments and finite element (FE) analysis to investigate the uniaxial tensile characteristics of the connections to simulate their working conditions in seismically loaded structures. It is shown that the tensile load-transfer mechanism through a BSCC is closely related to two frictional sliding responses and a compressive contact behavior. Based on the experimental data and FE results, a macro element was proposed to simulate the mechanical behavior of BSCCs. The macro element is able to model the interactions between the bolts, steel plates, and concrete separately using springs, assembled in series and/or in parallel in a composite manner. In particular, the loss of bolt clamping forces and ultimate tensile capacity of the connection are well captured by the macro element. Finally, the macro element was validated against existing experimental data on bolt-connected shear walls using OpenSees. It is believed that the clear load-transfer mechanism can be beneficial for the design of PCSWPS, and the proposed macro element can facilitate seismic analysis of PCSWPS without the need of a detailed connection FE model.

Investigation of the mechanism for reduction of residual stress through magnetic-vibration stress relief treatment

This article presents a comprehensive evaluation of a new residual stress reduction method based on magnetic-vibration stress relief treatment for cold-rolled DP590 high-strength steel plate. The effectiveness of magnetic-vibration stress relief treatment is compared to that of other treatment methods such as vibration treatment alone, magnetic treatment alone, and sequential combinations of vibration and magnetic treatment. The experimental results indicate that magnetic-vibration stress relief treatment is more effective than other methods in reducing residual stress. Specifically, magnetic-vibration stress relief treatment reduces transverse residual stress by approximately 39.42% and longitudinal residual stress by approximately 54.52%. In contrast, single vibration treatment reduces transverse residual stress by approximately 19.65% and longitudinal residual stress by approximately 19.31%, and single magnetic treatment reduces transverse residual stress by approximately 18.16% and longitudinal residual stress by approximately 7.12%. Theoretical analysis based on first principles reveals that ferromagnetic materials exhibit a stress-magnetic effect that can be exploited to soften and deform the material, leading to enhanced reduction effects during magnetic-vibration stress relief treatment.

Research on the resilience model of a new prefabricated shear wall structure

Based on high-strength bolts, steel plates and other components to achieve the advantages of prefabricated shear wall assembly connection “dry connection” operation advantages, a new type of assembled shear wall with friction energy consumption function was proposed. Using a combination of model tests and numerical simulations, three shear wall specimens with a scaling ratio of 1:1.54 were designed and the corresponding seismic performance tests were carried out. The effects of axial compression ratio and longitudinal reinforcement rate of edge members on the damage mode, hysteresis performance, load carrying capacity, deformation performance, stiffness degradation and energy dissipation capacity of specimens are systematically analyzed. The test results showed that the final failure modes of the three specimens were similar, which was the bending-shear failure from the development of the oblique cracks in the wall to the concrete spalling in the compression zone; The reduction of the axial compression ratio or the reinforcement rate of the longitudinal reinforcement of the edge members will lead to the reduction of the bearing capacity of the shear wall and the increase of the ultimate displacement has a negative impact on the seismic performance of the new assembled shear wall, which is manifested by the weakening of the hysteresis performance and the reduction of the ultimate bearing capacity. Combined with the finite element simulation results, the five-fold skeleton model and restoring force model of the new assembled shear wall were established, and then the calculation formulae of unloading stiffness and loading stiffness of the hysteresis curve were obtained by regression fitting. The restoring force model proposed in this paper is in good agreement with the test results, which can provide a reference for the elastic–plastic seismic response analysis of the new fabricated shear wall structure.

Wear Properties of High-Hardness Tool Steel by Directed Energy Deposition Based Additive Manufacturing

Recently, with the increase in the application of UHSS plates in automobiles, the service life of existing molds is being shortened, and directed energy deposited type 3D printing technology is being considered as a way to extend the service life. In this study, in order to improve the service life of cold molds, the wear characteristics of the deposited parts using composition systems were analysed, and the possibility of practical application was estimated through evaluation with shear molds.</br>Since the high hardness of AM layer can be reached without additional heat treatment, it was expected to improve the service life when applied to the surface of the mold. Through the wear evaluation of the ball-on-disk method, it was confirmed the wear performance improvement of M4, and as a result of the shear mold life evaluation of 1.5 GPa class high-strength automotive steel plate for the M4 deposited, it was found that shear up to 17,000 strokes were possible. When the number of strokes was increased, a fracture layer due to deposition was observed in the cross-section of the mold surface, and it is believed that additional heat treatment research is required to improve the life of the AM mold.

On the effect of pitch and yaw angles in oblique impacts of small-caliber projectiles

A terminal ballistic analysis of the effects of 7.62 mm × 51 AP P80 rounds on inclined high-strength armor steel plates is the focus of the presented study. The findings of an instrumented ballistic testing combined with 3D advanced numerical simulations performed using the IMPETUS Afea® software yielded the conclusions. The experimental verification proved that slight differences in the pitch-and-yaw angles of a projectile upon an impact caused different damage types to the projectile’s core. The residual velocities predicted numerically were close to the experimental values and the calculated core deviations were in satisfactory agreement with the experimental results. An extended matrix of the core deviation angles with combinations of pitch-and-yaw upon impact angles was subsequently built on the basis of the numerical study. The presented experimental and numerical investigation examined thoroughly the influence of the initial pitch and yaw angles on the after-perforation projectile’s performance.

Effects of States of Carbon and Solute Nitrogen on Toughness of Ferritic Steel

To develop microstructure control concepts for ensuring the toughness of high-strength steel plates, basic research was conducted using ferrite single-phase steels with different amounts of C, and the effects of the states of C were investigated along with those of solute N. In this study, Fe-0.017C (mass%) alloy, wherein the state of C was changed to a solid solution, intragranular cementite, and intergranular cementite, were used for microstructural observation, Charpy testing, and fracture surface investigation. The results reveal that the toughness of the intragranular cementite steel was the best, followed by that of solute C steel and intergranular cementite steel. In intergranular cementite steel with significantly inferior toughness, the coarse intergranular cementite leads to dislocation pile-up, initial crack formation, and macroscopic brittle fracture. The brittle fracture of intragranular cementite steel was caused by the deformation twins. It is thought that the fine intragranular cementite only had a minor effect on the crack initiation and dislocation mobility. Twin was also confirmed at the initiation point of brittle fracture in the solute C steel. Hence, it was deduced that the deterioration of toughness caused by solute C resulted from the promotion of twinning, which replaced the dislocation movements. However, the deterioration of toughness caused by solute C was smaller compared with that caused by solute N, which partly caused intergranular fracture. This is attributed to the suppression of intergranular fracture by the presence of a small amount of solute C.

Experimental analysis of a full-scale steel frame with replaceable dissipative connections

This work presents the experimental campaign performed on a full-scale 6-storey steel concentrically braced frame equipped with the so-called Dissipative Replaceable Braced Connection (DRBrC) made with plates of mild steel and high-strength steel. Such component, constituting the brace-column joint, is capable of dissipating large amounts of energy through wide hysteretic loops, while providing the possibility of being easily replaced after the building undergoes medium-high intensity earthquakes. To reduce the costs and, at the same time to obtain a representative response of the full frame, hybrid simulation tests were employed, in which only the ground floor was physically built in the laboratory. In contrast, the remainder of the structure was numerically simulated. The innovative frame was subjected to three different natural ground motions at the Damage Limitation (DL), Significant Damage (SD) and Near Collapse (NC) limit states, respectively. The outcomes highlighted the high potential of the DRBrC component in dissipating large amounts of energy and, at the same time, in protecting the remaining parts of the structure, by exhibiting very small residual displacements that enhance self-centring and repairability capabilities. Moreover, the numerical models were calibrated by including the non-negligible effect introduced by the bolt-hole clearances. All results are thoroughly described in the manuscript.

Experimental and numerical study on tensile performance of high-strength steel plate-bolt assemblies

High-strength steel plate-bolt assemblies are proposed to solve the problem of insufficient anchorage and complicated installation of blind bolts. To tap a high-strength steel core in a tubular column, ordinary high-strength bolts can be tightened in the steel tubular column on one side and bolted to the beam. To enable tapping high-strength steel plates instead of nuts, steel plate-bolt assemblies with various steel plate thicknesses and bolt grades were studied under monotonic tensile tests. After the tests, the ultimate tensile strength, the failure modes of the assemblies, and the optimum thickness of the plates were also analyzed. The Q460C-, Q345B-, and 45-grade steel plates and the M16-, M20-, and M24-grade bolts were the variation parameters. The result shows that 45-grade steel plates can be replaced by Q460C- or Q345B-grade steel plates. Additionally, adding Q690D-, Q345B-steel and 12.9-grade high-strength bolts as research variables through a finite element allows the tensile performance of the assemblies to be studied, and a test was accordingly simulated and analyzed. The results of the two are in good agreement, which verifies the accuracy and reliability of the finite element model. The high strength of the bolts and the welding requirements of the steel core can be satisfied simultaneously. In steel plate-bolt assemblies, steel consumption will be reduced by using high-strength steel plates. The thickness should not be less than the bolt diameter d for Q460C-grade steel and d + (1 ∼ 2 mm) for Q345B-grade steel. The steel plate should not be a composite plate (i.e., two steel plates connected by welding).

Correlation of fracture toughness with microstructural parameters and standard mechanical properties of high-strength medium-alloy steel

Fracture toughness of rolled plates of high-strength medium-alloy steel with a martensitic or martensitic- bainite microstructure can vary widely depending on the parameters of their microstructure, which depends on the specific chemical composition, rolling parameters, quenching and tempering. In previous works, the authors studied the metal of various experimental smelts. The studied materials were significantly different in the size of structural components separated by large-angle boundaries (hereditary austenitic grain, martensite packages, and bainite crystallites). The continuation of these studies is the analysis of the relationship between the fracture toughness of a metal of one smelt and the general quenching parameters and, as a consequence, with the same parameters of the microstructure formed during quenching, but with different tempering parameters. A general structural state parameter based on the obtained data, and correlated with fracture toughness is proposed.

Application of Machine Learning to predict the mechanical properties of high strength steel at elevated temperatures based on the chemical composition

This paper presents the results obtained using Machine Learning (ML) algorithms to predict the mechanical properties, including ultimate tensile strength, yield strength, 0.2% proof strength and elastic modulus, of high strength steel plate material at elevated temperatures. High strength steels are increasingly used in several areas of construction offering efficient structural solutions with a high strength-to-weight ratio. Safe fire design of these structures relies heavily on accurate prediction of mechanical properties of the material with temperature. The data on elevated temperature mechanical properties collected from the literature experimental tests show a high degree of scatter, implying that they are influenced significantly by various factors, most notably the testing method, manufacturing process and chemical composition. However, the current methods for predicting the mechanical properties of high strength steels at elevated temperatures by using ‘reduction factors’ as adopted by the structural design codes do not consider these effects and may lead to inaccurate predictions. To overcome these deficiencies, a ML-based prediction method that uses temperature and chemical composition as input parameters is developed in this paper. Deep Neural Networks are trained and validated on the basis of elevated temperature material data collated from the literature test programmes. The analysis of the results show that the trained algorithm gives an excellent correlation coefficient with very small error value in predicting the strength and stiffness reduction factors of HSS.

Experiment/simulation correlation-based methodology for metallic ballistic protection solutions

A methodology is developed based on the coupling of a finite element code with an optimisation module for the design of land vehicle armouring composed of lightweight aluminium alloy and high strength steel plate. Following an experiment/simulation correlation, a numerical model has been built and calibrated considering monolithic plates and then verified considering a bi-metal protection against tungsten carbide projectile mimicking the core of a 7.62×51 AP8 ammunition. In addition, a method is proposed to obtain the vres−vi curve for the full 7.62×51 AP8 bullet from the vres−vi curve obtained from the core only.

Experimental and numerical study on residual stress distributions in welded H-sections of High-strength steel

High-strength steel (HSS) has been increasingly applied in structural engineering, while the work on residual stress of HSS sections is still insufficient. Limited research is available for welded H-sections above 690 MPa while with a plate thickness of more than 10 mm. This paper deals with the residual stress distributions of welded H-sections with flame-cut edges, which are fabricated from HSS plates with yield strength of 690 MPa and 960 MPa and thickness of 10 mm–20 mm, using both experimental and numerical method. The experiments showed that the welded tensile residual stresses in the weld region are not significantly affected by sectional dimensions and steel grade. Verified by comparing with the experimental results, three-dimensional (3D) finite element (FE) models using sequentially coupled thermal-stress analysis was adopted for parametric study of compressive residual stress of welded H-sections made of 690 MPa HSS. The results showed that the compressive tensile stress is negatively correlated with plate thickness as well as width-thickness ratio. Through regression analysis, formulae were proposed for estimation of compressive residual stress in the flange and web, respectively. Finally, residual stress distribution model was developed, which was proved effective by comparing with the experimental and FE results.

A Numerical Study on the Seismic Performance of a Horizontal Dry Connection for Precast Concrete Shear Walls

Dry connections primarily consist of high-strength bolts and steel plates. They are commonly used in precast structures as they maximise time efficiency in the assembly stage compared with conventional methods. In this study, an embedded horizontal dry connection was developed using a square-shaped ring connector, high-strength hex nuts and flat washers, and grout for assembling precast concrete shear walls. Using Abaqus CAE 6.14, a numerical study was conducted on two full-scale RC shear walls including one monolithic and one precast specimen to assess the seismic performance of the bolted connection under the combined effect of axial and fully reversed cyclic loading. The average displacement ductility ratio of the precast specimen integrating the bolted connection was three times as much as the reference specimen. However, its relative energy dissipation capacity and shear strength were 21.94% and 27.92% lower, respectively. A parametric study was also carried out on the thickness and grade of the ring connector, grade of the vertical steel bars, number of ring connectors, and diameter of the vertical steel bars at the connection joints. Results showed that the seismic performance of the bolted connection was highly dependent on the bar diameter and number of ring connectors.

Mechanical properties of high strength steels and weld metals at arctic low temperatures

This paper attempts to acquire fundamental knowledge on the mechanical properties of high strength steels and the corresponding high strength weld metals at arctic low temperatures. Two types of high strength steels (Q890, Q960) and three types of high strength weld metals (made of ER100S-G, ER110S-G, ER120S-G feedstock wires) were tested at arctic low and ambient temperatures ranging from −75 °C to 25 °C. Tensile coupon specimens for steel materials were directly extracted from high strength steel plates, whilst robotic gas metal arc welding was employed to fabricate the tensile specimens of weld metals. The tensile coupon specimens were designed as per ASTM E8M and wire-cut into shapes. Twenty-three tensile coupon tests on high strength steels and eighteen tensile coupon tests on high strength weld metals were carried out. Coupon specimens were tested in liquid nitrogen cooling chamber to mimic the arctic low temperature environment. The stress–strain responses and key mechanical properties of high strength steels and weld metals at both ambient and arctic low temperatures are presented and discussed. Prediction equations for key mechanical properties, including the Young’s modulus, yield stress and ultimate tensile strength, of high strength steels and weld metals at arctic low temperatures were proposed.

Hysteresis behavior of EQ56 high strength steel: Experimental tests and FE simulation

The probability of offshore platforms suffering to extreme cyclic loads, such as storm surges and typhoons, increases highly at deep sea. It is essential to achieve the hysteresis behavior of steel material for evaluating the dynamic response of offshore platform under cyclic load. A total of 18 coupons are fabricated from the EQ56 high strength steel (HSS) plate to investigate the monotonic and cyclic behaviors. Loading protocols include monotonic tension, constant amplitude and changing amplitude strain-controlled cyclic loadings. It is revealed that the visco-plastic behavior of EQ56 HSS is insignificant under the monotonic tension at room temperature. The EQ56 HSS presents obvious Bauschinger effect, non-masing rule, stress hardening/softening behavior and strain history memory effect under strain-controlled cyclic loading. The prior loading history at low strain-amplitude levels has little effect on the saturation stress of EQ56 HSS while stress hardening can be reactivated to a new saturation level when the applied strain-amplitude is increased. The monotonic and the cyclic hysteresis curves of EQ56 HSS were compared, and hysteretic skeleton curves are fitted using the Ramberg-Osgood model. The essential parameters of the Chaboche combined hardening model are calibrated to describe the cyclic behavior of EQ56 HSS. The comparison between FE simulation and test results demonstrates that this model cannot characterize effectively the hysteretic behavior of EQ56 HSS because the strain history memory effect and coupled behavior of cyclic stress softening and hardening are ignored in its constitutive equation.