High Strength Steel Plates Research Articles

Patch-loading resistance of QN1803 and S32001 high-strength stainless steel plate girders: Experimental study and numerical simulation

Patch-loading resistance of QN1803 and S32001 high-strength stainless steel plate girders: Experimental study and numerical simulation

Experimental and Numerical Characterization of Local Properties in Laser-Welded Joints in Thin Plates of High-Strength–Low-Alloy Steel and Their Dependence on the Welding Parameters

Laser welding on thin plates of high-strength steel is increasing in various industrial applications. The mechanical behavior of welded joints depends on their local properties, which in turn depend on the welding parameters applied to join the base material. This work characterizes the local properties of butt-welded joints of thin plates of high-strength–low-alloy (HSLA) steel. This study focuses on the effect of welding parameters on the microstructure, tensile response, microhardness, and weld bead profile. For this purpose, a factorial experimental design was formed, covering a heat input range from 53 to 75 J/mm. This study identified the main effects and interactions of welding speed and laser power on the weld bead profile and on its width. The microstructure, weld bead width, hardness, and tensile mechanical properties were significantly influenced by heat input. Furthermore, numerical simulations on real weld bead profiles revealed high values of the stress concentration factor and suggested a correlation with heat input.

Through-thickness Work Hardening Variation in Thick High Strength Steel Plates: A Novel Inverse Characterization Method

Due to the production process, thick high strength steel plates potentially exhibit inhomogeneous plastic material behavior through the thickness. For example, the initial yield stress and work hardening behavior might vary through the plate thickness. In order to establish a reliable plasticity model that can be used in finite element simulations to optimize forming processes or to investigate the structural integrity of large structures, this material behavior needs to be characterized. A straightforward characterization method consists of slicing the thick high strength steel plate and conducting standard tensile tests. However, this approach comes with a large experimental effort. A novel specimen is proposed enabling to inversely identify the work hardening behavior at distinct locations through the thickness of a thick steel plate. To this end, a tensile specimen with circular pockets at different depths is used. The strain fields within the pockets are captured using digital image correlation (DIC). finite element model updating (FEMU) is used to inversely identify a predefined strain hardening law for each pocket. First, the procedure is optimized and numerically verified using virtual experiments generated by a finite element model with a known variation of the work hardening behavior. Finally, the procedure is experimentally validated by characterizing the strain hardening behavior of a 10 mm thick S690QL grade.

Crystallographic Study of Transformation Products of Heat-Affected Zone and Correlation with Properties of FH690 Heavy-Gauge Marine Steel by Multi-Pass Submerged Arc Welding

In this work, the microstructure–property relationship of the heat-affected zone (HAZ) of a FH690 ultra-heavy marine steel plate was investigated based on insight of microstructure and crystallographic features. After multi-pass welding with a heat input of ~30 kJ/cm, an ~8 mm wide HAZ was obtained with a coarse grain HAZ (CGHAZ) of ~3.8 mm, fine grain HAZ (FGHAZ) of ~3.4 mm, and intercritical HAZ (ICHAZ) of ~1 mm. High impact toughness values of ~120 and 140 J at -60 °C were obtained for coarse grain HAZ and fine grain HAZ, respectively. The microstructure of the CGHAZ and FGHAZ was fine lath bainite. Although the average prior austenite grain size for the CGHAZ was ~75 μm, which was five times that of the FGHAZ (15 μm), a high density of high-angle grain boundaries (HAGBs) with misorientation higher than 45° was obtained in the CGHAZ. This is the underlying reason for the excellent low-temperature toughness of the HAZ. Thermo-dynamic calculations indicated that the high density of HAGBs in the CGHAZ was attributed to the decreased bainitic transformation temperature due to the reduced phase transformation driving force via the high nickel addition, leading to weak variant selection. In addition, the high nickel addition offered high hardenability for high hardness in the FGHAZ. The outcome of this study could provide an experimental and fundamental basis for designing high-strength ultra-heavy steel plates with excellent weldability.

Experimental study on bond-slip behaviors of CFRP sheet-Q690 high strength steel plate considering the effect of CFRP sheet thickness and bonding length

With the increasing application of carbon fiber reinforced polymer (CFRP) in steel structure engineering, the bond-slip behavior between the two has attracted much attention. Firstly, 18 sets of CFRP sheet-Q690qD high-strength steel double strap shear specimens were fabricated considering the effects of CFRP sheet thicknesses and bond length. Then, static and fatigue tests were conducted on them. Subsequently, based on the 3D-DIC acquisition technology, the bond-slip curves were obtained using the smoothing method and the fitting method respectively Finally, the three key parameters of τmax, s1and sf in the bifurcated model at each working condition were obtained. The experimental results indicated that the bond length was positively correlated with the static load ultimate strength, while the thickness of the CFRP sheet had less effect on the ultimate strength. The fatigue life of the specimen with a bond length of 40 mm under equal stress ratio fatigue loading was much higher than that of the specimens with bond lengths of 60 mm and 80 mm. It was found that the fitting method had better stability and accuracy in fitting the bond-slip curves of CFRP sheet-Q690qD high-strength steel specimens. The accuracy of the fitting maximum bond load was above 80 %, which can provide a relevant basis for the subsequent numerical simulation calculation.

Research on the Mechanism and Processability of Roll Forming.

Cold bending forming is a complex forming process, and its product quality is closely related to the forming process parameters. To mitigate issues such as bulging and waviness arising from the extension of the material at the edges during the forming process of thin-walled circular tubes, a comprehensive comparative analysis was conducted on four forming methods. This analysis determined that the combined bending method is the optimal forming technique for the equipment. For the impact of different parameters on the equivalent plastic strain distribution of the product and the force on the rollers, numerical simulations were carried out using the software COPRA (COPRA FEA RF 2023.1) after designing the pattern diagram based on the integrated bending method. The results showed that different processing speeds on the equivalent plastic strain distribution and work hardening of the plate have little effect. As the spacing between the upper and lower rollers increases, the equivalent plastic strain of the plate to a certain extent and the value of the moment of the rollers is significantly reduced. Analyzing the performance characteristics of high-strength steel materials from the aspects of the thickness strain and cross-sectional forming of the plate, this verifies the advantages of forming high-strength steel plates. The numerical simulation results of this study are in good agreement with actual production experimental results.

Investigations into mechanical properties of 50 and 70 mm thick high strength S690 butt-welded sections

A comprehensive investigation into the mechanical properties of 50 and 70 mm thick high strength S690 steel plates and their butt-welded sections under tension was presented in this paper, and a total of 40 tensile tests were conducted. Firstly, a total of 18 proportional coupons with circular cross-sections were extracted at three different layers within the plate thicknesses. Tensile tests on all of these coupons were carried out to obtain their mechanical properties, and their variations across the plate thicknesses were also examined. Secondly, submerged arc welding was adopted to prepare butt-welded sections between these thick steel plates with various heat input energy. Micrographic examinations on typical heat-affected zones of the welded sections were also performed. Standard tensile tests on a total of 22 proportional coupons with rectangular cross-sections were carried out to obtain their mechanical properties, and the full range deformation characteristics of these coupons were assessed and compared, in particular, their tensile strengths and elongations at fracture. This paper presents important experimental evidence on the mechanical properties of these high strength steel plates of practical thicknesses in construction, and also of their butt-welded sections. It is demonstrated that there is little or even no reduction in their mechanical properties of these butt-welded sections, provided that the welding processes are properly controlled according to established welding practice. Hence, full strength butt-welded sections between these thick high strength S690 steel are readily achieved in practice, similar to those of the commonly adopted S355 steel. These important findings are contrary to general understanding as many researchers and engineers consider that the mechanical properties of these high strength S690 steel are reduced significantly after welding, irrespective of their plate thicknesses.

Oblique penetration of spherical tungsten alloy projectiles on high-strength steel plates

The uniaxial tensile and dynamic compression properties of 22SiMn2TiB high-strength steel were first investigated, which shows certain strain-rate effects and obvious temperature-softening effects. Ballistic tests were carried out on 12 mm thick 22SiMn2TiB steel using ∅11 mm tungsten projectiles at 0°∼45° obliquity and a velocity of 500∼900 m/s. The study found that the ballistic limit velocity (BLV) increased monotonously with the increase of the obliquity. Based on the De Marre equation, a BLV calculation model was calibrated, which predicted experimental results well. Corresponding numerical simulation was carried out using LS-DYNA with fitted Johnson-Cook model parameters, its results are in good agreement with the test's. Additionally, the protective mechanism of the 22SiMn2TiB steel plate at an oblique angle was revealed through microscopic morphology analysis of the high-strength steel plate. It identifies adiabatic and normal shear failure, tensile and tensile-shear mixed failure, and the formation of different cracks in two groups, ultimately leading to plugging failure. The study provides a reference for the engineering design of the defensive structures using 22SiMn2TiB high-strength steel.

Advanced Waterjet Technology for Machining Beveled Structures of High-Strength and Thick Material

The bevel cutting of large-thickness plates is a key process in modern industries. However, traditional processing method such as air-arc gouging bevel cutting or laser bevel cutting may cause serious deformation and rough surface quality due to the defects of the thermal cutting method. In order to improve the quality and efficiency of bevel processing, the abrasive waterjet cutting method is used in this research to overcome the challenge for bevel machining of high-strength DH40 steel plates with a large thickness. For different kinds of beveled structures, a 3D camera is used to measure the reference points defined on the workpiece and the SVD registration algorithm is adopted to transform the theoretical coordinate system to the actual coordinate system. Furthermore, the distance between the nozzle and the workpiece surface is also measured and compensated for to ensure the consistency of the bevel width. Finally, experiments are carried out for different kinds of bevels to verify the feasibility of the proposed method for high precision processing for beveled structures. The developed method has been effectively applied in the actual shipbuilding industry.

Research on the welding process of Q355ND thick plate with narrow gap double wire submerged arc welding

Abstract Aiming at the problems of low welding efficiency and unstable quality of thick plates of marine equipment in offshore deep-water areas represented by offshore wind power, the high-efficiency welding process of narrow-gap double-wire submerged arc welding of 30 mm thick Q355ND low alloy high-strength steel plate was developed by selecting the suitable welding material and welding process parameters. The results show that the welded joint has a beautiful appearance, well-fused sides, and no defects. The structure of the heat-affected zone of the joint is mainly composed of pro eutectoid ferrite, acicular ferrite, bainite, and a small amount of pearlite. The center of the seam is composed of a large amount of massive ferrite and a small amount of bainite. The average tensile strength of the joint reaches 536.5 Mpa, and the average impact energy of the weld center at -20°C reaches 48.4 J. The average impact energy of the heat-affected zone reaches 164 J. All physical and chemical performance tests meet the standard requirements. The development of welding processes has important practical significance for improving production efficiency and product quality. It will be widely used to construct offshore wind power towers, offshore platform jackets, and other offshore deep-water engineering equipment.

Simultaneous measurement of corrosion potential and hydrogen penetration using double-head scanning Kelvin probe

High-strength steels, such as high-strength bolts or steel plates are considerably sensitive to hydrogen embrittlement. Serious safety problems in steel structures are possible, because they are exposed to atmospheric condition containing chloride ions. Embrittlement is induced by hydrogen penetration during atmospheric corrosion. We developed Double-Head Scanning Kelvin Probe (DHSKP) equipment to clarify the relationship between the corrosion process and hydrogen permeation. Each probe can simultaneously measure the corrosion potential on the corroded side and surface potential on the hydrogen-detecting side at the same time. In this study, we investigated the correlation between the corrosion potential and hydrogen permeation under changing conditions from wet to dry processes on the surface of a steel sample. During the drying process, the corrosion potential at the rust layer that precipitated in the early wetting condition showed a less noble potential locally, whereas the surface potential of the Pd film on the hydrogen detection side showed a less noble potential locally. The hydrogen permeation sites were limited to small spots in the opposite area, where the corrosion potential showed a less noble local-potential during the drying process. Hydrogen penetration by corrosion likely occurs in acidic liquids under the rust layer during the drying process.

Experimental investigation and predictive models of membrane residual stresses in S690 high strength steel welded π-shaped and cruciform sections

This paper reports an experimental investigation of the membrane residual stresses in S690 high strength steel welded π-shaped and cruciform sections. The experimental programme was performed on three π-shaped sections and two cruciform sections, fabricated from 5 mm thick S700MC high strength steel plates by means of gas metal arc welding, and included material tensile coupon tests and membrane residual stress measurements, with two measurements for each of the five S690 high strength steel welded π-shaped and cruciform sections. The measured tensile and compressive membrane residual stresses were analysed and the self-equilibrium of the measured membrane residual stresses in each constituent plate element was also verified, with the maximum unbalanced membrane residual stress to yield stress ratios of 3.3% for π-shaped sections and 3.2% for cruciform sections. The existing membrane residual stress predictive models, as given in the European convention and Swedish regulations, were assessed for their applicability to S690 high strength steel welded π-shaped and cruciform sections, revealing inaccuracy. Finally, two sets of new predictive models for membrane residual stresses in S690 high strength steel welded π-shaped and cruciform sections were proposed and shown to result in accurate predictions of the measured membrane residual stress data.

Seismic Performance Assessment of Composite Frame–High-Strength Steel Plate Wall Core Tube Resilient Structural System

Against the backdrop of China’s continuous promotion of green and low-carbon transformation and the development of construction industrialization, high-strength composite structural systems have significant development prospects. However, their research and application in the field of construction are insufficient. In response to this issue, the study proposes a new high-performance structural system, namely the composite frame–high-strength steel plate wall core tube resilient structural system, which includes a core tube composed of double steel plate concrete composite shear walls and replaceable energy dissipation coupling beams, as well as composite frames. The highest strength grades of the steel plate and concrete used in the composite walls of the core tube are Q550 and C100, respectively. Using a 200 m building as an example, this study designs and establishes models for this high-performance structure and a conventional reinforced concrete frame–core tube structure. Subsequently, the dynamic elastoplastic time history analysis and seismic resilience assessment of structures are conducted under design basis earthquakes (DBEs), maximum considered earthquakes (MCEs), and extremely rare earthquakes (EREs). Research has shown that, compared to conventional structures, the thickness of shear walls of new high-performance structures can be effectively reduced, which helps decrease the self-weight of the structure and improve the available space in buildings. Additionally, high-performance structures exhibit a better performance in controlling the story drift ratio, lower plastic damage and overall stiffness degradation of the structure, and better seismic performance. The seismic resilience of the high-performance structure has been significantly enhanced, especially in terms of minimizing casualties, thereby better ensuring the safety of people’s lives and property.

Effect of relaxation before quenching on microstructure and properties of the steel

The effect of different relaxation time before online quenching on mechanical strength and toughness of high-strength medium-thickness martensitic steel plate was analysed in this work. Increasing the relaxation time from 15 s to 135 s resulted in an increase in the impact energy at −20 °C from 33 J to 148 J. However, the yield strength was decreased from 1050 MPa to 1002 MPa. Dislocation density and martensitic lath width are the main factors causing the strength change. Moreover, the dislocation density caused by deformation drops first sharply and then gently during the relaxation, resulting in an inverse trend of martensitic lath width. Additionally, there appears to be a linear relation between impact energy at −20 °C and dislocation density−1/2.

Recrystallization during tempering of high strength steel plates

Recrystallization during tempering of high strength steel plates

Axial compressive bearing capacity of high-strength concrete-filled Q690 square steel tubular stub column

Concrete-filled high-strength steel tubular (CFHSST) column is a kind of composite structure that uses high-strength steel instead of ordinary steel to strengthen the transverse restraint of concrete. In this work, in order to investigated the axial bearing capacity of CFHSST square column, a series of 22 CFHSST square stub columns were prepared by using two kinds of Q690 high-strength steel plates with different thickness of 3 mm and 6 mm with the strength of 741–749 MPa and 819–871 MPa, respectively. The static axial compression tests were carried out to understand the confinement effect of high-strength steel tube on concrete of different strength under static axial pressure and the influence of local buckling on the specimen. The axial compressive performances of CFHSST square stub columns are analyzed, including the failure mode, the relationship between load and deformation, and the stress-strain relationship. The test results show that the core concrete strength and area are major factors which have affected on bearing capacity of CFHSST square stub columns. Furthermore, width-to-thickness ratio exhibits significantly improving the failure mode and ductility of CFHSST square stub columns, while width-to-thickness ratio, the ratio of steel or the coefficient of hoop determine confinement effect. Q690 steel tube has good confinement effects, but the confinement effects on low strength concrete is small, especially for the specimen with relatively small width-to-thickness ratio. Finally, the calculation method of the ultimate bearing capacity of CFHSST square stub columns under axial compression is proposed, which can effectively evaluate the ultimate bearing capacity of CFHSST square stub columns.

Fire-resistance design of ultimate and serviceability limit states for Q690 high-strength steel plate girders under patch loading

This study numerically investigated the serviceability and ultimate limit states of Q690 high-strength steel (HSS) plate girders exposed to fire under patch loading. A shell element numerical model of the Q690 HSS plate girder was created using Abaqus software, and its accuracy was verified through experimental results. A comprehensive parametric analysis involving 512 numerical models was conducted to examine the effects of elevated temperatures, web aspect ratio, loading length, and web depth-to-thickness ratio. Because of the absence of specific design guidance in EN 1993–1-2 for Q690 HSS plate girders exposed to fire, the accuracy of the resistance model specified in EN 1993–1-5 that was applied to steel plate girders at room temperature was verified by employing the material properties of Q690 HSS at elevated temperature. The verification results revealed that the ultimate resistance of the Q690 HSS plate girder obtained from the resistance model in EN 1993–1-5 was considerably lower than that obtained from the numerical analysis. A modified resistance reduction function that applies to the Q690 HSS plate girder at room temperature was proposed based on the resistance model in EN 1993–1-5. Comparisons indicated that the accuracy of the resistance model in EN 1993–1-5 was improved when applied with the proposed resistance reduction function. Additionally, predictive approaches were introduced to determine the ultimate resistance, effective resistance, and effective stiffness of Q690 HSS plate girders in fire. The comparison with numerical results highlighted that the proposed approaches exhibited high accuracy and provided a sound basis for the engineering design of Q690 HSS plate girders.

Component test for the assessment of delayed hydrogen-assisted cracking in thick-walled SAW joints for offshore applications

Offshore wind turbines continuously increase in size and weight and demand adequate offshore foundations concepts like monopiles, tripods, or jackets. These components are typically constructed using submerged arc welding (SAW) with high-strength thick steel plates like the S420ML. During welding, the occurrence of delayed hydrogen-assisted cracking (HAC) must be anticipated. HAC is a critical combination of the local hydrogen concentration within a susceptible microstructure under certain mechanical load, i.e., the occurring (welding) residual stresses. The welding sequence of the thick-walled plates complicates the residual stress distribution due to the necessary repeated thermal cycling, i.e., welding seam/layer deposition to fill the joint. For that purpose, SAW with two-wire-technique was used to weld a specially designed and prototype-like mock-up of a real component with a thickness of 50 mm, filled with over 20 passes and a seam length of 1000 mm. Additional welded stiffeners simulated the effect of a high restraint, to achieve critical HAC conditions. The necessity of a minimum waiting time (MWT) before the NDT can be conducted (to exclude HAC) was critically verified by the application of ultrasonic testing of the welded joint at different time-steps of the NDT of up to 48 h after the completion welding. The residual stresses were determined by a robot XRD goniometer. Tensile residual stresses up to the yield limit are found both in the weld metal and in the heat-affected zone. Numerical modeling allowed the qualitative estimation of the hydrogen diffusion in the weld. No noticeable HAC occurrence was identified and confirms the high cracking resistance of the investigated material. Finally, the applicability of the MWT concept should be critically discussed.

Shear resistance of perforated QN1803 high-strength stainless steel plate girders through experimental testing and numerical analysis

QN1803, a high-strength stainless steel, has been developed by steel industry recently. Its tensile yield strength can be approximately 40 % (or more) higher than that of the commonly-used EN1.4301, while its cost is 20 % lower due to its reduced nickel content. One obvious application for QN1803 is in plate girders, where web perforations are often required to accommodate building services. However, no research work has been reported in the literature that investigates the reduced shear buckling capacity of QN1803 plate girders as a result of web perforations. This issue is addressed herein. An experimental program comprising six plate girder tests is conducted in this study. Three different hole ratios were considered: 0.2, 0.4 and 0.6. The depths of web were selected as 700 mm and 500 mm, while the thickness of web was fixed as 4.0 mm. The initial geometric imperfections were determined from three-dimensional (3D) scanning prior to the plate girder tests. Finite element (FE) models incorporating the material non-linearity and initial geometric imperfections were then developed and validated against the experimental results. A parametric analysis including 62 FE models was performed to examine the influences of the critical parameters on the shear buckling capacity of such perforated members. The results suggest that for those members with a hole diameter - web height ratio of 0.6, the shear buckling capacity was reduced by 56 % on average due to the web perforation. The design rules for determining the shear buckling capacity of stainless steel plate girders as specified in Eurocodes (EN 1993–1–4 + A1) (2015) and American Specification (ANSI/AISC 370–21) (2021) were evaluated. Upon comparison, it was demonstrated that both EN 1993–1–4 + A1 (2015) and ANSI/AISC 370–21 (2021) cannot provide accurate and safe predictions for determining the shear buckling capacity of such members.

Re-Distribution of Welding Residual Stress in Fatigue Crack Propagation Considering Elastic–Plastic Behavior

The welding residual stress re-distribution behavior during fatigue crack propagation in butt-welded high-strength steel plates for ship construction is investigated based on experimental test results and numerical analyses. The specimens’ initial welding residual stresses are obtained from X-ray for middle tensile (MT) specimens cut from butt-welded high-strength steel plates. Then, fatigue crack propagation experiments on MT specimens are conducted, and a strain gauge is used to measure the residual stress re-distribution field around cracks. A practical fatigue crack propagation simulation procedure is developed with a dynamic update of in-situ welding residual stress, where the residual stress intensity factor Kres of the MT specimen is deduced. The stress ratio effect on Kres during fatigue crack propagation is analyzed and a good agreement between experimental and numerical results is achieved.