Use Of High Strength Steels Research Articles

Hydrogen in Aluminium-Coated Steels Exposed to Synthetic Seawater

Thermally sprayed aluminium (TSA) coatings provide protection to offshore steel structures without the use of external cathodic protection (CP) systems. These coatings provide sacrificial protection in the same way as a galvanic anode, and thus hydrogen embrittlement (HE) becomes a major concern with the use of high strength steels. The effect of TSA on the HE of steel seems to remain largely unknown. Further, the location of hydrogen in TSA-coated steel has not been explored. To address the above knowledge gap, API 5L X80 and AISI 4137 steel coupons, with and without TSA, were prepared and the amount of hydrogen present in these steels when cathodically polarised to −1.1 V (Ag/AgCl) for 30 days in synthetic seawater was determined. One set of TSA-coated specimens was left at open circuit potential (OCP). The study indicates that the amount of hydrogen present in TSA-coated steel is ~100 times more than the amount found in uncoated steel, and that the hydrogen seems to be largely localised in the TSA layer.

Improving the reliability of metal structures of buildings and structures during reconstruction

Recently, the direction of prestressing metal structures, the regulation of forces in which is made by various methods without the use of high-strength steel is one of the hot spots of research. In this paper, an unconventional method for creating pre -stress in tubular elements using an expanding substance is applied. As used by a non-explosive destructive mixture (NDM).

Overview of Steel Bridges Containing High Strength Steel

The use of high strength steel has the potential to reduce the amount of steel used in bridges and thereby, facilitate a more sustainable construction. A survey of existing bridges built using high strength steel is presented in this paper with emphasis on the Swedish bridge stock. The survey aimed at identifying the steel grades that were used and where in the cross-section they have been used. A case study on the influence of fatigue shows that today’s regulations make it more difficult to use high strength steel in comparison to previous regulations.

THE USE OF STEEL ARC WELDING PIPES ON TANK FARMS OR OIL AND GAS INDUSTRY OBJECTS

Recently, the use of high-strength steels has significantly reduced the cost of pipeline materials. However, alignment, welding, inspection, and coating costs typically account for about 20 % of the total cost of the pipeline. Due to invention of new arc welding technologies, potential to reduce costs in the construction of pipelines is being created. The need to build large-diameter pipelines over long distances has led to an increase in the need to improve the performance of ring welding of the pipeline. Electric semi-automatic gas-metal welding remains the dominant technology of annular pipe welding. The article describes the processes of arc welding, control of the microstructure of the weld, welding material for pipelines in aggressive environments, the current state of welding of main pipelines in the Russian Federation, innovative welding technologies leading to a further significant increase in the performance of arc welding. The most promising method of welding in the construction and repair of pipelines is arc welding with coated electrodes. As a rule, in semi-automatic welding of joints of sections of trunk pipelines, solid wire and protective gas are used as the electrode. Improving the productivity of welding and installation works can be achieved by introduction of new energy-efficient welding methods, partial or complete replacement of existing welding equipment, the use of innovative welding materials.

Compressive performance of ECC-concrete encased high strength steel composite columns

The use of high strength steel (HSS) in the construction of concrete encased steel (CES) composite columns is often limited by the strain incompatibility issue between HSS and concrete at peak-load. This study proposes an alternative approach to confine the high strength concrete with Engineered Cementitious Composite (ECC) to improve its compatibility with high strength steel. The main purpose of this study is to experimentally evaluate the axial compressive performance of the proposed composite column cross-section configuration. Behaviours of fifteen short columns including twelve ECC-CES columns are investigated in terms of failure modes, load-deformation curves, ductility and energy absorption capacity. The test parameters included ECC and concrete strengths, ECC cover thickness, steel section shape and column section’s aspect ratio. It was found that ECC generally improved the failure behaviour of high strength steel CES columns and increased the deformation and energy absorption capacity. On average ECC-CES columns showed around 12% and 8% higher ductility and toughness than control concrete column, respectively. A detailed 3D nonlinear finite element model was developed and validated against experimental results. Applicability of current design codes to predict the ultimate strength of ECC-CES columns was also evaluated. Finally, a method to calculate the ECC-CES column’s capacity considering effective material stresses at peak-load was proposed.

Effect of Relative Humidity on Mechanical Degradation of Medium Mn Steels.

Medium Mn steels have been considered as the next-generation materials for use in the automotive industry due to their excellent strength and ductility balance. To reduce the total weight and improve the safety of vehicles, medium Mn steels look forward to a highly promising future. However, hydrogen-induced delayed cracking is a concern for the use of high strength steels. This work is focused on the service characteristics of two kinds of medium Mn steels under different relative humidity conditions (40%, 60%, 80% and 100%). Under normal relative humidity (about 40%) at 25 °C, the hydrogen concentration in steel is 0.4 ppm. When exposed to higher relative humidity, the hydrogen concentration in steel increases slowly and reaches a stable value, about 0.8 ppm. In slow strain rate tensile tests under different relative humidity conditions, the tensile strength changed, the hydrogen concentration increased and the elongation decreased as well, thereby increasing the hydrogen embrittlement sensitivity. In other words, the smaller the tensile rate applied, the greater the hydrogen embrittlement sensitivity. In constant load tests under different relative humidity conditions, the threshold value of the delayed cracking of M7B (‘M’ referring to Mn, ‘7’ meaning the content of Mn, ‘B’ denoting batch annealing) steel maintains a steady value of 0.82 σb (tensile strength). The threshold value of the delayed cracking of M10B significantly changed along with relative humidity. When relative humidity increased from 60% to 80%, the threshold dropped sharply from 0.63 σb to 0.52 σb. We define 80% relative humidity as the ‘threshold humidity’ for M10B.

The Efficiency of Utilisation of High-strength Steel in Tubular Profiles.

The use of high-strength steel (HSS) is a current trend of the construction industry. Tubular profiles are widely used in various structural applications because of their high stiffness-to-weight ratio, exceptional resistance to torsion, and aesthetic appearance. However, the increase of the strength for the same elastic modulus of the material and geometry of tubular profiles is often not proportional to the rise of the load-bearing capacity of the structural element. The obtained experimental results support the above inference. The study was based on the flexural test results of two groups of HSS and normal-strength steel (NSS) tubular specimens with a 100 × 100 × 4 mm (height × width × thickness) cross-section. Numerical (finite element) simulation results demonstrated that the shape of the cross-section influenced the efficiency of utilisation of HSS. The relationship between the relative increase of the load-bearing capacity of the beam specimen and the corresponding change of the steel strength determined the utilisation efficiency.

Structural behavior and design of high-strength steel welded tubular connections under extreme loading

The present work is motivated by the increasing need for cost-efficient solutions in offshore structural systems for wind energy production and for improvement of their structural performance. The structural behavior and design of high-strength steel welded tubular connections (yield strength higher than 700 MPa) subjected to monotonic and strong cyclic loading is investigated. In the first part of the paper, an experimental investigation is presented on high-strength steel tubular X-joints subjected to monotonic and cyclic loading far beyond the elastic limit of the material, leading to weld fracture. Two grades of weld metal material are employed in the welding process of the specimens. The experimental results indicate that the weld material grade has a significant influence on the deformation capacity of the welded connection under monotonic loading conditions, and its low-cycle fatigue life. The experimental procedure is simulated using advanced finite element models, elucidating several features of joint behavior and complementing the experimental results. Overall, a good agreement is found between numerical simulations and experimental results, in terms of both global response and local strains at the vicinity of the welds. Furthermore, the structural performance of the welded tubular joints under consideration is assessed using available design methodologies in terms of both ultimate strength and low-cycle fatigue resistance, in an attempt to validate an efficient design methodology for low-cycle fatigue. The results from this research effort are aimed at developing the necessary background for the possible use of high-strength steel in tubular steel lattice structures, particularly in offshore platforms for renewable energy production. They can also be used as a basis for the possible amendment of relevant design specifications and recommendations for including special provisions for high-strength steel structural systems.

Experimental Study on Mechanical Properties of Q345 Steel after High Temperature Cooling

Because of its advantages of light weight, high strength and convenient construction, steel structure has gradually become the first choice for large-span and high-rise structures. The use of high strength steel in building engineering can reduce the section size of components and the weight of the structure, thus increasing the building area. But steel is not fire-resistant, when the temperature reaches 600°C, steel loses most of the stiffness and strength. Therefore, it is of great significance to study the fire resistance of steel structures, and the mechanical properties of steel structures at high temperature are the foundation of the fire resistance research. The mechanical properties of steel after high temperature are the basis for the safety assessment of steel structure after fire. Therefore, this paper studies the mechanical properties of Q345 steel after high temperature cooling.

Combination of press-hardening and isothermal holding in the treatment of high-strength steels

Today, high-strength parts for the automotive industry are mainly produced by the press-hardening technology. In order to reduce costs, savings in production and optimal materials are sought. One option involves the use of high strength steels of various chemical compositions. Two high strength steels were studied in the present experiment. The first one was CMnSi steel, a typical low-alloy TRIP steel with a carbon content of 0.2 %; alloyed with manganese and silicon. The second one was 42SiCr steel, a member of the group of martensitic steels, with a carbon content of 0.42 %. In addition to manganese and silicon, this steel is also alloyed with chromium. The CMnSi steel has not proved to be very sensitive to changes in process parameters, achieving an ultimate tensile strength of more than 950 MPa and an elongation of over 10%. 42SiCr steel was found to respond to both heating temperature and deformation, showing different mechanical properties. With the right combination of process parameters, an ultimate tensile strength of over 2100 MPa was achieved.

Damage prediction of hot stamped boron steel 22MnB5 with a microscopic motivated ductile fracture criterion: Experiment and simulation

With the increasing demand of the reduction of energy consumption and enhancement of automobile safety, the steels with ultra-high strength are widely utilized in automobile industry. Because of the high achievable strength, hot stamping process can be used to supply promising automobile components. The increasing use of high-strength steels leads to great challenges to model the fracture evolution because of their high strength and low ductility. The paper is concerned with plasticity and ductile fracture modelling of hot stamped boron steel 22MnB5, where martensite phase with high yield strength, work hardening and ductility are present during the quenching process. The Lou's ductile fracture criteria which involve void nucleation, growth and coalescence in metallic materials are theoretically reviewed and extended and implanted using users’ subroutine VUMAT in ABAQUS/Explicit. Parameters of the selected fracture criterion are determined using calibration tests with various kinds of specimens. Dogbone-like uniaxial tensile specimens are tested to determine the deformation hardening parameters, and specimens with central hole, in-plane shear specimens and notched specimens, balanced biaxial tensile specimens are tested to identify the fracture behavior in various loading stresses. Digital Image Correlation (DIC) method is applied to monitor the surface pattern and record the strain evolution of the specimen surface during the experiment. Because of fully austenitized microstructure, the Mises isotropic yield function is adopted. The hybrid method is used to obtain the fracture strain in various stress directions and implemented to determine the material parameters of fracture model. The constructed ductile fracture surfaces calibrated with fracture strain using DIC calculation and hybrid method are compared in Lode parameter and triaxiality coordinate as well as the principal stress space, respectively. The comparison reveals that the fracture strain obtained by hybrid method is more reasonable. The determined ductile fracture criterion is applied to forecast the fracture onset for seven kinds of specimens and compared with the experiment data. The comparison indicates the simply extended Lou's criterion of ductile fracture can precisely describe the evolution of ductile fracture from uniaxial tensile to biaxial tensile stress state for hot stamped boron steel 22MnB5.

Sustainable steel and composite bridges through increased lifetime by fatigue treatment

To achieve sustainable long-living infrastructures such as steel and composite bridges, the improvement of the fatigue behavior is crucial. By using high frequency mechanical impact (HFMI) treatment of critical welds, the fatigue service life of welded structures can significantly be extended due to the introduction of compressive residual stresses. Particularly with the use of high-strength steels in combination with HFMI-treatment has become economic in terms of fa­tigue design, thus, leading to reduced use of material resources. Even for welding in existing structures, positive results have already been achieved with post-weld treatment. For this inno­vative method, the amount of lifetime benefit and the conditions for successful application in the view of quality assurance have sometimes become object of critical questions. In various re­search projects, these questions could successfully be answered. By means of numerical and experimental investigations, design approaches have been developed and evaluated for the ap­plication of those treatments in constructional bridge design. The paper summarizes the results of two research projects on the subject of HFMI-treatment with the focus on the use for steel and composite bridges. An insight on the improved fatigue design, the practical use, the benefits for the constructions and possible application fields is given.

Structural behaviour and design of high strength steel RHS X-joints

This paper aims to investigate the structural behaviour and static strength of high strength steel rectangular hollow section (RHS) X-joints under axial compression in the braces through tests and numerical analysis. Eight RHS X-joints which were composed of fabricated steel tubes with a measured yield stress of 907 MPa were tested. Extensive numerical simulations on the fabricated RHS X-joints in S460, S690 and S960 steel were conducted using finite element (FE) analysis. The FE model was validated against the test results. The investigated failure modes are chord face plastification, chord side wall failure and a combination of these two failure modes. The effects of the heat affected zones (HAZ) and suitability of the strength equations adopted by the CIDECT design guide for the fabricated RHS X-joints were examined. The deformation capacity and ductility of test specimens which failed by chord face plastification could be considered as reasonably sufficient. The effects of material strength reduction in the HAZ on the joint initial stiffness are minor, but could significantly lower the joint strength. In general, the CIDECT strength prediction is increasingly unconservative with increasing steel grade for the RHS X-joints failing by chord face plastification. However, the CIDECT strength prediction is generally conservative for the combined failure modes, and becomes increasingly conservative with increasing chord side wall slenderness for chord side wall failure. The suggested ranges of brace to chord width ratio (β) and chord width to wall thickness ratio (2γ) are 0.4 ≤ β ≤ 0.85 and 2γ ≤ 60β − 1 for the RHS X-joints failing by chord face plastification to allow for more effective use of high strength steel, and corresponding strength equations were proposed. An analytical model of plate buckling was proposed and the deformation-based continuous strength method (CSM) originally developed for designing non-slender stainless steel cross-sections was adopted for the design of chord side wall failure in the RHS X-joints with β = 1.0 and 2γ up to 50. The proposed design method is also applicable for designing chord side wall failure in equal-width RHS X-joints using cold-formed and hot-finished carbon steel and cold-formed stainless steel. A linear interpolation approach using the proposed strength equations at β = 0.85 and β = 1.0 is suggested for the RHS X-joints with 0.85 < β < 1.0 and 2γ ≤ 50 which failed by the combined failure modes. The proposed strength equations can produce much more accurate and consistent strength prediction than the CIDECT design guide, and were converted to design strength equations for the design of high strength steel RHS X-joints.

Experimental and Analytical Study of High-Strength Steel RHS X-Joints under Axial Compression

The use of high-strength steels for tubular structures has been forbidden or permitted with some joint-strength reduction in most representative international standards. Six rectangular hollow section (RHS) X-joint specimens were tested under axial compression to investigate inelastic joint behavior. The key test parameters included brace-to-chord width ratio and grade of steels. All high-strength steel specimens exhibited sufficient strength compared with current European standards’ strength criteria; their strengths were even higher than the standard’s prescribed unreduced nominal strength. Significantly different postyielding behavior was observed depending upon the brace-to-chord width ratio and the grade of steels. It was also observed that the formulation of sidewall buckling strength in the current European standard tends to predict overly conservative results and requires further examination. A new design formula for RHS X-joints subjected to sidewall buckling was proposed in this paper based on a more realistic buckling shape. When the normalized plate slenderness ratio newly defined in this study is used in conjunction with the column curve c of the European standard, both accuracy and consistency of strength predictions were significantly improved compared with those of the strength formulas currently available.

Enhancement of the life-cycle performance of bridges using high-strength steel

Bridges have a significant role in society but are often massive structures requiring a high amount of materials, leading to high consumption of natural resources and high costs. In this respect, the use of high-strength steel (HSS) may represent a significant advantage as it enables to reduce the quantity of materials required for a structure to fulfil its function. Notwithstanding this potential benefit, the use of slender plates allowed by HSS makes I-girders more vulnerable to local bucking phenomena and fatigue issues. Hence, this article aims to discuss the potential advantages of HSS in bridge design, in terms of structural, environmental and economic performances. The discussion is based on a comparative analysis, in which a bridge made of steel grade S355 is compared with two alternative designs made of steel grade S690. The results of the analysis showed that although the use of HSS in bridges enables to save steel, thus providing some environmental advantages, in terms of costs the differences are negligible due to the higher requirements of HSS bridges.

Blast response of beams built with high-strength concrete and high-strength ASTM A1035 bars

The work reported in this paper is aimed towards better understanding the behavior of reinforced concrete flexural members built with high-strength reinforcement (HSR) under blast loading. As part of the study, a series of high-strength concrete (HSC) beams built with ASTM A1035 Grade 690 MPa bars are tested under simulated blast loads using a shock-tube. Parameters investigated include the effect of steel type (Grade 690 MPa vs. 400 MPa), concrete strength (100 MPa vs. 50 MPa) and reinforcement ratio (ρ = 1%–2.2%). The effect of loading rate is investigated by testing a companion set of beams under slowly applied (quasi-static) loading. The results show that use of high-strength steel in HSC beams results in increased blast capacity and improved control of displacements at equivalent blasts. The use of high-strength concrete is also found to be better suited for beams reinforced with high-strength bars. The results further demonstrate the importance of ensuring beams designed with high-strength bars are under-reinforced and provided with sufficient shear reinforcement. The blast response of the beams is predicted analytically using dynamic analysis.

Numerical Analysis of RC beam with High Strength Steel Reinforcement using CDP model

The article is based on preliminary research on use of high strength steel for RC elements. A reinforced concrete beam with a span length of 5700 mm has been subjected to four-point bending test. The bottom reinforcement of the beam was made of SAS670/800 high strength steel. This type of steel has no specific yield point. The yield limit declared by the manufacturer is specified as 670 MPa and the ultimate strength is equal to 800 MPa. The aim of the research was to establish a numerical model that would render properly the real beam behaviour. The model was created in the ABAQUS software using the CDP (Concrete Damage Plasticity) material model for concrete. The paper analyses the influence of several parameters on the results of numerical computations. The author’s aim is to define values of the dilation angle that should be implemented in the model. Generally, the value of this parameter is established a priori, without any justification. The analysis reveals that in a situation when the dilation angle is greater than or equal to 25 deg, the numerical model predicts properly the damage obtained in the experiment. For lower values of the dilation angle, the failure mode is not consistent with the actual beam behaviour in the experiment. Another issue is whether and how the results from the model are influenced by the choice of specified concrete tensile behaviour. In the CDP model, this property may be set in three ways: by giving the stress - displacement relation, stress - cracking strain relation or determining the fracture energy. All three alternatives are analysed and compared. Another aspect described in the paper, is the difference in load application through force control and displacement control as well as the influence of the amount of shear reinforcement. In order to analyse mesh size sensitivity, the results obtained for models with various mesh densities were compared.

Fatigue strength of thermal cut edges—influence of ISO 9013 quality groups

The use of high strength steels has gained importance due to the interest in effective light steel constructions. Besides the well-designed weld seams, free cutting edges gain technical and economic relevance as locations for potential fatigue cracks. In this investigation, fatigue tests were carried out on 8-mm- and 20-mm-thick samples with a minimum yield strength ranging from 355 to 960 MPa at a stress ratio of R = 0.1. The cutting methods used were oxygen, plasma, and laser cutting. The surface roughness, hardness profile, and residual stresses were measured to classify the specimens into quality groups according to ISO 9013. Most of the specimens are classified in the quality groups 2 and 3. A slight tendency can be seen that the fatigue strength decreases with an increasing roughness value. Increasing local hardness values at the cut edges also have a minor negative influence on the fatigue strength. No positive impact was observed for increasing tensile strength on the fatigue strength. With higher surface roughness values, larger notches exist, the crack initiation starts early, and the fatigue strength decreases.

Fatigue response of high-strength steel bolted connections under in-plane shear and out-of-plane bending loading modes

The use of high-strength steel (HSS) permits weight reduction in heavy-duty applications such as trucks, trailers, and agricultural machinery, where significant fatigue resistance is a requirement. Fatigue cracks are often initiated at locations of stress concentration such as the joining of mechanical parts, the most widely used methods being welding and mechanical fastening. It is known that HSSs do not only have higher yield values but also perform better in terms of fatigue. Yet, the weld fatigue resistance does not improve with an increase in the base material property due to the stress concentrations and imperfections introduced by welding. The aim is to explore the possibilities of using conventional mechanical joining techniques for HSSs and assess the fatigue properties under typical loading modes. Mechanical joining introduces an additional failure mechanism called fretting fatigue resulting from the oscillatory relative displacement between the surfaces in contact. This failure mode is reproduced by the experiments and the effects of pre-tension, hole-making procedure, washer configuration, and surface condition are analyzed for steel grades S500MC, S700MC, and S960MC. Accompanying finite-element simulations are employed to develop a deeper understanding of the underlying physics. The results might lead to various guidelines with respect to design rules and best practices for HSS bolted connections subjected to fatigue loading.

Parametric Applicability Assessment of High-Strength Steel Tubes of Noise Tunnel Structures for Weight Reduction

This study addresses the material nonlinear behaviors of noise tunnel structures composed of high-strength circular steel tubes for weight reduction. A finite element elastic and plastic analysis is performed for different types of flange connections of noise tunnels. The plastic behaviors of flange connections are also investigated considering increased road widths. To reduce the weight of noise tunnel structures, this study uses four types of steel associated with various geometries of the entire structure. From an economic point of view, the parametric results obtained in this study show that the proper use of high-strength steels makes a positive contribution to the design of lighter noise tunnels. Keywords: Noise Tunnel, Nonlinear Analysis, High Strength Steel, Flange Connection