Behavior Of High Strength Steel Research Articles

Effect of Welding Process Parameters on the Mechanical Properties of TIG and MIG Welds in HSS X65 Pipe-A Review

The study focused on the importance of the different welding parameters on the mechanical behavior of High Strength Steel (HSS) X65 steel pipes by reviewing the advantages of parameter optimization for the Tungsten Inert Gas (TIG) - Metal Inert Gas (MIG) welding processes. The parameters considered in the study include welding speed, welding current, welding voltage and gas flowrate of the welding. The effects of improper selection and parameter optimizations were highlighted and illustrated using different metallurgical and mechanical instances. The outcome of the study indicates that adequate parameter optimization aids in obtaining good weld quality with adequate mechanical and microstructural properties. Furthermore, it helps in the determination of variation in hardness in the heat affected zone as well as the base metal. Thus, this study provides insight to welding engineers on the importance of parameter optimization in the welding of steel pipe.

Fatigue behavior of high strength steels under various levels of corrosion

Propagation of a short fatigue crack directly from a corrosion pit is investigated within this work. A corroded rectangular specimen subjected to remote tensile cyclic loading is modelled via finite element method. Propagation of the angled crack is then controlled by both loading modes (I + II). A parametric study is performed to estimate the directions of further crack propagation for various geometrical configurations. Corrosion pit size is varied to simulate various levels of corrosion, and the analysis is carried out for a range of crack lengths and different initial crack inclination angles. Assumptions of linear elastic fracture mechanics are accepted, and classical maximum tangential stress criterion is applied to calculate the angles of crack deflection. Results obtained are discussed and are prepared to mutual comparison with observations of decrease of fracture mechanical/fatigue properties on real specimens subjected to relevant experiments.

Behaviour of high strength steel butt joints exposed to arctic low temperatures

The present study investigated the tensile behaviour of high strength steel (HSS) butt joints exposed to arctic low temperatures. Two HSS grades, namely Q890 and Q960, with thicknesses of 6 mm and 8 mm, were employed. Single-V-groove butt joint specimens were fabricated by means of robotic gas metal arc welding using 1.2 mm-diameter ER100S-G and ER120S-G feedstock wires. The single-V-groove and butt joint tensile specimens were designed according to the Structural Welding Code-Steel AWS D1.1. Metallographic observations and Vickers hardness tests were performed on five series of HSS butt joint. Moreover, a total of 25 butt joint specimens were tested under uniaxial tension in a liquid nitrogen cooling chamber, with temperatures ranging from -75 °C to 25 °C. The stress-strain histories, tensile strengths and failure modes of the HSS butt joints exposed to arctic low temperatures are fully reported. The influence of low temperature exposure, parent steel grade and weld material selection on the tensile behaviour of the HSS butt joints is discussed. Based on the test results, recommendations for weld material matching for Q890 and Q960 HSS butt joints are provided. Additionally, prediction equations for HSS butt joint strengths exposed to arctic low temperatures are proposed using the best subset regression analysis. The findings from this study contribute to a better understanding of the behaviour of HSS butt joints under arctic low temperatures, and can be used to inform design and fabrication practices of HSS structures in cold environments.

Local buckling behaviour of high strength steel and hybrid I-sections under axial compression: Numerical modelling and design

This paper presents a numerical investigation on the local buckling behaviour of high strength steel (HSS) and hybrid I-sections under axial compression, which has not been comprehensively discussed in previous literature. Three sectional steel combinations, featuring different web strength grades (Q690, Q460, and Q355) and using HSS Q690 flange plates, were studied. Through the validated numerical method, parametric studies on the effect of web strength grade, boundary condition and plate slenderness were carried out. The design specifications in European, Australian, and American codes were evaluated using the results of 243 numerical models and collated test data. In addition, the continuous strength method (CSM), direct strength method (DSM), and Kato’s method, which can account for element interaction were extended to design for the local buckling behaviour of HSS and hybrid I-sections subjected to axial compression. Assessment results showed that ANSI/AISC 360-16 provides more accurate results than Eurocode 3 and AS 4100. Statistical and reliability results demonstrated the satisfactory reliability level of the proposed design expressions for CSM, DSM, and Kato’s design methods. This paper provides insight into the local buckling behaviour and mechanism behind plate interaction of hybrid I-sections.

Nonlinear analysis on mechanical behaviour of high strength steel extended endplate connections and equivalent T-stubs in fire considering axial force

In fire, ignoring the axial force acting on the high strength steel (HSS) beam-column endplate connections when considering catenary action may lead to a safety risk for the whole steel structure. Hence, a nonlinear analysis is conducted to reveal the actual performance of HSS T-stubs and HSS extended endplate connections in fire using the software ABAQUS. The ultimate displacement, failure mode and bearing capacity of HSS T-stubs under tension-shear combined action are investigated. The failure modes and moment–rotation curves of HSS endplate connections obtained by the numerical study are verified with test results in fire. Furthermore, the effects of bolt diameter, endplate thickness, endplate strength, the combination of endplate thickness and endplate strength, as well as temperature on the mechanical behaviour of HSS endplate connections considering axial force are studied. The results of nonlinear analysis are verified against Eurocode 3 Part 1–8 in various situations. The results indicate that when the shear-to-tension ratio is 2.0, the tensile bearing capacity and ultimate displacement of HSS T-stubs at 600 °C decreased to 38% and 31% of the pure tension, respectively. The parametric analysis shows that when the temperature is 600 °C, the initial stiffness and ultimate flexural capacity of connections are only about 40% and 31% of that at 20 °C.

Effect of Nb, Ti microalloying on hot deformation behavior of high strength steel

The deformation resistance would be increased with the addition of Nb and Ti, which makes it difficult to accurately control the rolling process, resulting in mixed grains and cracks. The hot deformation behavior of Nb–Ti microalloyed high strength steel was investigated in the temperature range of 900–1100 °C with the strain rate between 0.1 and 5 s−1. The recrystallization active energy was obtained by regression calculation, and the thermal deformation equation was established. The dynamic recrystallization critical strain model was established by changing the work hardening rate. The results show that a higher deformation temperature and lower strain rate are conducive to dynamic recrystallization. The active energy of dynamic recrystallization is 386.30 kJ mol−1, εp = 1.23 × 10−2Z0.087, and εc = 1.95 × 10−3Z0.111. The high strength steel is strengthened by the strengthening of grain refining and precipitation of Nb–Ti microalloys. The second phase particles are TiN with a size of about 100 nm, (Nb, Ti)C with the size between 50 and 80 nm, and NbC with the size between 10 and 20 nm.

Experimental and numerical studies on the behavior of high strength steel shear connections at elevated temperatures

This paper presents experimental and numerical studies to investigate the fire behavior of high strength steel (Q690 and Q960) shear connections. The load-displacement curves, failure modes, and load capacities, including the slip load and ultimate load of the specimens at elevated temperatures were obtained from experiments. A finite element model was established by ABAQUS software and validated by the test results to investigate the effect of the friction coefficient and the assembly form of the bolt on the shear behavior. The numerical results of load capacity were compared with that predicted by EC3, AISC 360–16, and GB50017. Parametric studies were conducted to investigate the effect of the slip load on the ultimate load at ambient temperature, and design methods were proposed considering the friction coefficient and preload values. The research shows that the slip load decreases more rapidly than the ultimate load at elevated temperatures. The critical temperature from brittle failure to ductile failure is approximately 500 °C. The load capacity predicted by AISC 360–16 is accurate, while EC3 and GB50017-2017 predict conservative load capacity. The effect of the bolt load and friction coefficient cannot be ignored for high strength steel shear connections.

Testing and design on local-biaxial flexural interactive buckling behavior of high strength steel welded box beam-columns subjected to biaxial bending

A testing research on the local-biaxial flexural interactive buckling of high strength steel Q460C, Q550D and Q690D welded box slender section beam-columns subjected to combined compression force and biaxial bending is reported. A total of thirteen median long steel columns, of which four manufactured from Q460C steel, five from Q550D steel and four from Q690D steel, were loaded until failure under biaxial eccentric compression forces. The local-biaxial flexural interaction buckling behavior is investigated by analyzing the test results. As an addition to the test data, the finite element parameter analyses are performed. The ultimate bearing capacities obtained from the test in this study and the numerical results presented in this study or in the existent literatures are compared with the calculation results in accordance with the design methods recommended in the American Specification ANSI/AISC 360–16, Eurocodes BS EN 1993-1-1 and BS EN 1993-1-5, and the newly proposed Effective Yield Strength Method (EYSM) and Effective Section Method (ESM) to check whether the current technical provisions and the new methods are suitable to the high strength steel beam-columns examined in this paper. The experimental and numerical results show that after taking the resistance factor into account, the ANSI/AISC 360–16, EN 1993-1-1 and BS EN 1993-1-5 are very conservative for the high strength steel beam-columns with greater member slenderness ratios (λ = 80, 90, 100) or with smaller plate width-to-thickness ratios (square box sections with b/t = 40, or rectangular box sections with h/t = 40 or b/t = 17); the new proposed EYSM provides an excellent prediction of the ultimate bearing capacities of the beam-columns and thus suitable for the high strength steels; but the new proposed ESM gives a very conservative estimate, over the range of steel nominal yield stress fy = 460 MPa ∼ 690 MPa, plate width-to-thickness ratio b/t = 40–80, member slenderness ratio λ = 40–100.

Numerical investigation and design for the local buckling behaviour of high strength steel hexagonal hollow section stub columns under axial compression

The local buckling behaviour of high strength steel (HSS) hexagonal hollow section (HexHS) stub columns encompassing three different fabrication routes under axial compression is numerically investigated in this study. Finite-element (FE) models were developed and validated against the experimental results. The validated FE models were subsequently employed to carry out parametric studies to expand structural performance data covering a wider range of geometries and cross-section slenderness as well as two different steel grades. The obtained results from FE models in line with the experimental data were used to evaluate the applicability of the existing design codes and the design approaches in literature to HSS HexHS under pure compression. The comparison indicates that the current slenderness yield limiting values in design codes cannot be simply extended to HSS HexHS stub columns. All the design codes exhibit a high degree of conservatism due to the lack of consideration for strain hardening whereas the Continuous Strength Method (CSM) was found to provide more accurate predictions than the Direct Strength Method (DSM). Modified design approaches are proposed to improve the accuracy of the strength predictions for HSS HexHS stub columns.

Optimization of Thick 22MnB5 Sheet Steel Part Performance through Laser Tempering

Press Hardening offers the possibility to obtain a wide range of mechanical properties through microstructural tailoring. This strategy has been successfully applied in thin sheet components, for instance, through differential cooling strategies. The application of these added value features to truck components implies adapting the process to the manufacture of thick sheet metal. This introduces an additional layer of complexity, but also opportunity, in a process where the final microstructure and, thus the mechanical performance is generated in the press shop. This work presents a study on optimizing the crash worthiness and impact energy absorption on a press hardened thick 22MnB5 steel sheet. Different microstructure design strategies have been studied, including ferrite-Pearlite (representative of a differential heating and austenitization strategy), in-die generated Bainite (representative of differential cooling) and Tempered Martensite (generated through laser tempering), keeping a fully hardened martensite as a reference condition. The material performance has been compared in terms of the monotonic properties, useful for anti-intrusion performance, and Essential Work of Fracture, a well-suited parameter to predict the crash failure behavior of high strength steels. The results show that laser tempering offers properties similar to Bainite-based microstructures and can be a successful replacement in components where the sheet thickness does not allow for the fine control of the in-die thermomechanical evolution.

Electrochemical corrosion behavior of high strength steel in simulated deep-sea environment under different hydrostatic pressure

The corrosion behavior of Ni-Cr-Mo-V high strength steel in the simulated deep-sea environment under different hydrostatic pressure and immersion time is investigated using electrochemical techniques, microscopic morphology observation and Raman spectrometer. During the first 10 days immersion, the corrosion rate presents wave-like changes. The corrosion rate under different hydrostatic pressure tends to be stable after 10 days immersion. The area with uneven composition will preferentially dissolve and form corrosion pits. The local corrosion takes the corrosion pit as the center, expands and fuses around, and finally forms uniform corrosion. High hydrostatic pressure promotes β-FeOOH transforming into other corrosion products. The anode of the steel tends to active dissolution and the cathode show oxygen diffusion control characteristics at the initial stage of corrosion. Under 20 MPa, step-shape passivation appears in the anode region. Due to the rapid reaction, the corrosion product film has poor protection performance and dissolves, which resulting in not obvious passivation phenomenon.

Experimental and numerical investigation of 800 MPa HSS welded T-section column strengthened with CFRP

Carbon Fiber Reinforcement Polymer (CFRP) has been widely utilized in repairing and retrofitting engineering. The purpose of this work is to study the buckling behavior of high strength steel (HSS) welded T-section column strengthened with CFRP using experimental and numerical method. The experiment of six specimens of 800 MPa HSS welded T-section column strengthened with CFRP under axial compression is performed. The influences of three main parameters (i.e., the number of CFRP layers, the slenderness of columns, and the width-to-thickness of plates) are observed in this work. All columns fail by the debonding of CFRP layers and the flexural–torsional buckling of specimens. CFRP layer can effectively delay the local buckling of plate or the torsional buckling of specimen. CFRP layer and slenderness has significant influences on the bearing capacity of specimens. The flexural and torsional displacement of columns strengthened with CFRP is much smaller than that of columns without CFRP. A finite element (FE) method for estimating the bearing capacity of HSS welded T-section column strengthened with CFRP is developed using ANSYS software. It is found that the confining effect of CFRP is more effective for stub columns. A more accurate model modified from Cadei et al.’s model for estimating the bearing capacity of 800 MPa HSS welded T-section column strengthened with CFRP under compression is proposed.

Corrosion Behavior of High Strength Steel Welded Joint in Seawater: A Combinatorial Study Based on General and Localized Electrochemical Methods

Corrosion Behavior of High Strength Steel Welded Joint in Seawater: A Combinatorial Study Based on General and Localized Electrochemical Methods

Experimental investigations on material properties and stub column behaviour of high strength steel irregular hexagonal hollow sections

Comprehensive experimental investigations into the material properties and stub column behaviour of cold-formed high strength steel (HSS) irregular hexagonal hollow sections (IHexHS) are presented in this paper. Apart from the tensile coupons taken from the parent plates, tensile coupons extracted from the flat and corner portions from the cross-sections were also tested in order to measure the effect of the fabrication process on material properties. The strength enhancement predictive models proposed by previous studies were compared with the obtained test results from corner coupons with increased strength due to the cold-forming effect. A total of 20 HSS IHexHS stub column specimens were tested under axial compression and the cross-section classification from the existing structural steel design codes of EN 1993-1-12, ANSI/AISC 360–16, AS 4100, AISI S100–16 and design approaches of DSM and CSM were compared and assessed against the obtained results. It was found that the design provisions of cross-section classification in current design codes cannot be extended to the HSS IHexHS stub columns. Based on current codified yield slenderness limits, the strength predictions from design codes exhibit conservatism without the consideration of strain hardening and beneficial effect of element interaction whereas cross-sections with intermediate slenderness values were over-predicted.

Study on Intrinsic Influence Law of Specimen Size and Loading Speed on Charpy Impact Test.

Charpy impact energy/impact toughness is closely related to external factors such as specimen size. However, when the sample size is small, the linear conversion relationship between the Charpy impact energy of the sub-size and full-size Charpy specimens does not hold; the Charpy impact toughness varies with the size of the specimen and other factors. This indicates that studying the internal influence of external factors on impact energy or impact toughness is the key to accurately understanding and evaluating the toughness and brittleness of materials. In this paper, the effects of strain rate on the flow behavior and the effects of stress triaxiality on the fracture behavior of 30CrMnSiNi2A high-strength steel were investigated using quasi-static smooth bar and notched bar uniaxial tensile tests and Split Hopkinson Tensile Bar (SHTP). Based on the flow behavior and strain rate dependences of the yield behavior, a modified JC model was established to describe the flow behavior and strain rate behavior. Charpy impact tests were simulated using the modified JC model and JC failure model with the determined parameters. Reasonable agreements between the simulation and experimental results have been achieved, and the validity of the model was proved. According to the simulation results, the impact energy was divided into crack initiation energy, crack stability propagation energy and crack instability propagation energy. On this basis, the effects of striker velocity and specimen width on the energy and characteristic load of each part were studied. The results show that each part of the impact energy has a negligible dependence on the hammer velocity, but there is a significantly different positive linear relationship with the width of the sample. The energy increment of each part also showed an inverse correlation with the increase in the sample width. The findings reveal that the internal mechanism of Charpy impact toughness decreases with the increase in sample width; to a certain extent, it also reveals the internal reason why the linear transformation relationship of Charpy impact energy between sub-size specimens and standard specimens is not established when the specimens are small. The analytical method and results presented in this paper can provide a reference for the study of the dynamic behavior of high-strength steel, the relationship between material properties and sample size, and the elastic–plastic impact dynamic design.

Plane bending fatigue behavior of interstitial-free steel at room temperature

Abstract Interstitial-free steels are widely used as thin sheet for automobile external panels. For this type of application, essential properties of the steel are deep-drawability and stretch-formability. However, low-strength interstitial-free steel is nearly pure iron and work on fatigue fracture behavior of this steel might be adopted as a basic study to understand the behavior of high-strength steels used for structural components. In this study, the fatigue fracture behavior of low-strength interstitial-free steel has been studied at room temperature in air and in an argon atmosphere. Fractographic observations on fatigue fracture surfaces reveal a mixed type of fracture mode (intergranular and transgranular cracking) for all specimens. The major portion of intergranular fracture has been found at the regions of low and medium crack lengths. Further increase in the crack length causes a decrease in the proportion of intergranular cracking and, finally, the fracture mode becomes completely transgranular. At the same test temperature, the proportion of intergranular fracture drastically decreased when the test was carried out in the argon atmosphere.

Local buckling behaviour of high strength steel welded box-section columns under axial compression

High strength steel (HSS) with superior strength and remarkable toughness has been widely utilised in large-scale structures. The application of HSS in engineering may result in slender plates in compression members, which are susceptible to local buckling. To investigate the local buckling behaviour of HSS columns, experiments are carried out on 800 MPa HSS welded box-section columns under axial compression in this study. Finite element analysis is performed to investigate the local buckling behaviour of welded box-section columns. Several parameters such as initial geometric imperfections, residual stresses of plates, and steel grade are considered in the analysis. The influences of the initial geometric imperfections and residual stresses on the local buckling of HSS welded box-section column are less effective than that for normal strength steel (NSS) welded box-section columns. The difference between the local buckling and post-buckling strengths of HSS increases compared with that for NSS. Present specifications for estimating the local buckling load and ultimate load of HSS welded box-section columns are evaluated. GB50017-2017 is a little overestimated for predicting the local buckling load. AISC360-16 is slightly overestimated for predicting the ultimate load. GB50017-2017 and Eurocode 3 are marginally underestimated for predicting the ultimate load of box-section columns. More accurate empirical formulas are recommended for determining the local buckling load and ultimate load of HSS welded box-columns under axial compression. Reliability analysis of various formulas for estimating the local buckling load and ultimate load of HSS welded box-section columns is performed.

Experimental study of flexural behaviour of high strength steel (HSS) ‐ Engineered Cementitious Composites (ECC) composite beam with profiled steel sheeting

AbstractDue to its high compressive strain of at least 0.5%, which is higher than both the yield strain (0.35%) of high strength steel (HSS) and the compressive strain (0.23%) of normal strength concrete (NSC), Engineered Cementitious Composites (ECC) is a material with high potential to replace NSC in HSS composite beam construction. This study reports an experimental investigation on the flexural behaviour of HSS‐ECC composite beam fabricated by using HSS I‐section in conjunction with hybrid polyethylene‐steel fibers (PE‐ST) ECC slab. Shear connection between the HSS I‐section and the top PE‐ST ECC slab was constructed by using normal profiled steel sheeting and headed shear studs. A HSS‐ECC composite beam and a HSS‐NSC composite beam were cast and tested under four‐point bending. The test results revealed that a large area of HSS I‐section in HSS‐ECC composite beam yielded compared to only a small yielded area of which in the HSS‐NSC counterpart despite the fact that both composite beams have identical configuration and silimar mechanical properties. The HSS‐NSC beam underwent longitudinal shear failure while in contrast, the HSS‐ECC beam failed by flexure and exhibited great ductility.

Effect of bending process on the fatigue behaviour of high strength steel

Integrating forming in the fatigue analyses of cold-formed High Strength Steel parts significantly increases predictive accuracy. In this study, the effect of cold-bending is modelled through a coupled forming-fatigue simulation of a bent specimen, made from a 12 mm thick S500MC grade. Different strain hardening models were studied, where a Voce law led to an increase in prestrain of about 10% and a decrease in fatigue life of 20% compared to the reference hardening behaviour. Three bending radii were investigated and a 25% decrease in radius led to a 30% increase in plastic strain. Fatigue tests were performed and a local strain approach resulted in a 76% correspondence with experimental data.

Testing, finite element analysis and design of high strength steel RHS T-joints

This paper investigates the structural behaviour of high strength steel (HSS) rectangular hollow section (RHS) T-joints under brace axial compression. Seven fabricated RHS T-joints which were composed of built-up steel tubes with a measured yield stress of 907 MPa were tested. Extensive finite element simulations on the fabricated RHS T-joints covering a wide range of geometric parameters and steel grades ranging from S460 to S960 were conducted. The chord face plastification, chord side wall failure and a combination of these two failure modes in the fabricated RHS T-joints were examined. The effects of material softening in the heat affected zones (HAZ) on the joint behaviour and influences of the steel grade, brace to chord width ratio (β) and chord width to wall thickness (2γ) on the suitability of the CIDECT strength equations for the fabricated RHS T-joints were evaluated. The deformation capacity and ductility of test specimens are shown to be reasonably sufficient. The effect of HAZ on the initial stiffness of the fabricated RHS T-joints is insignificant. The HAZ can lower the joint strength more significantly for medium β ratio; however, the joint strength reduction is less pronounced than the material strength reduction. The CIDECT strength prediction for chord face plastification is more unconservative for higher steel grade, larger 2γ ratio and smaller β ratio and becomes unduly conservative for the combined failure modes and chord side wall failure. It is suggested that 0.4 ≤ β ≤ 0.85 and 2γ ≤ 60β-1 for chord face plastification to allow for more effective use of HSS and corresponding reasonably conservative strength equations were proposed. Simplified strength equations which are based on an analytical model of plate buckling were proposed for chord side wall failure in the fabricated RHS T-joints with β = 1.0 and are also applicable for cold-formed steel RHS T-joints. A linear interpolation approach using the proposed strength equations at β = 0.85 and β = 1.0 is recommended for the combined failure modes in the fabricated RHS T-joints with 0.85 < β < 1.0.