Application Of High Strength Steel Research Articles

Microstructure and mechanical properties of the laser welded air-hardening steel joint

The decrease in mechanical properties of high-strength steel after welding is an important issue affecting the wide application of high-strength steel. Air-hardening steel is a high-strength steel suitable for lower body structural parts such as subframes. Its application process involves welding, hot forming and other processes. The present work investigates the microstructure and mechanical properties of the air-hardening steel laser welded joint that is air-cooled after hot forming in the two-phase zone (800 °C). The microstructure was characterized by electron backscattered diffraction (EBSD), scanning electron microscope (SEM) and transmission electron microscope (TEM). The results show that during hot forming, the welded joint transforms from martensite to ferrite and acicular martensite, and the base metal transforms from ferrite to polygonal martensite and ferrite. The difference in martensite morphology between the welded joint and the base metal is attributed to the nucleation positions of austenite. The structural evolution of the welded joint and the base metal is accompanied with the annihilation and reproduction of dislocations, which results in significant changes in hardness. The hardness value dropped from the highest 430 HV to 271 HV in the welded joint, while increased from the lowest 184 HV to 203 HV in the base metal. After hot forming, the tensile strength of the welded sample is reduced by only 36 MPa, and the total elongation is slightly decreased by about 1.5% compared with the unwelded sample. The welded joint and the base metal have similar plastic deformation capabilities, since the acicular martensite in the welded joint displays good plastic deformation ability, and the dislocation density of the welded joint and the base metal is similar. Overall, the microstructure and dislocation density of the air-hardening steel welded joint after hot forming are similar to those of the base metal, which is responsible for the good mechanical properties of air-hardening steel welded joint.

Experiments and investigation of planar high-strength steel joints with Additive Manufacturing

This paper investigates the application of high-strength steel in planar steel joints, specifically X-joints and T-joints, which are crucial connecting components in structural engineering, ensuring structural stability in buildings, bridges, and tower cranes. Conventional steel joints, mainly constructed from low-carbon steel, encounter challenges arising from the low ductility of high-strength steel and its strict welding criteria. The Solid Isotropic Material with Penalization (SIMP) method is employed to perform topology optimization on X-joints with different brace width to chord width ratios and T-joints, enabling the manufacturing of high-strength steel components through the Additive Manufacturing method (AM). The impact of different additive manufacturing orientations on material strength is tested, with results indicating improved mechanical properties when the loading direction is perpendicular to the normal direction of the additive manufacturing layer. Compression tests are conducted using 2D/3D Digital Image Correlation methods (2D/3D-DIC) alongside traditional measurement techniques. The results indicate that the stress distribution of the optimized joint is more rational, and the strength of the optimized joint has improved compared to the tubular joint. The optimized joint exhibits a more distinct load path and apparent failure mode. This optimized joint enables a uniform stress redistribution, enhancing ductility and achieving a strong-joint and weak-component structural mechanism that satisfies the serviceability limit state (SLS). In comparison to non-penetrative tubular joints, no significant cracks are observed under identical loading conditions.

The investigation on flexural performance of prestressed concrete-encased high strength steel beams

This paper reports an experimental on the flexural performance of prestressed concrete-encased high-strength steel beams (PCEHSSBs). To study the applicability of high-strength steel (HSS) in prestressed concrete-encased steel beams (PCESBs), one simply supported prestressed concrete-encased ordinarystrength steel beam (PCEOSSB) and eight simply supported PCEHSSBs were tested under a four-point bending load. The influence of steel strength grade, I-steel ratio, reinforcement ratio and stirrup ratio on the flexural performance of such members was investigated. The test results show that increasing the I-steel grade and I-steel ratio can significantly improve the bearing capacity of PCESB. Increasing the compressive reinforcement ratio of PCEHSSB can effectively improve its bearing capacity and ductility properties, making full use of the performance of HSS in composite beams. Increasing the hoop ratio has a small improvement on the load capacity of the test beams; setting up shear connectors can improve the ductile properties of the specimens although it does not lead to a significant increase in the load capacity of the combined beams. Then, combined with the test data, the comprehensive reinforcement index considering the location of reinforcement was proposed to evaluate the crack resistance of specimens. The relationship between the comprehensive reinforcement index and the crack resistance of specimens was given.

Application of high-strength steel in the Wire Arc Additive Manufacturing (WAAM) process

Application of high-strength steel in the Wire Arc Additive Manufacturing (WAAM) process

A Summary of the Application of High-strength Steel in Bridge Engineering

A Summary of the Application of High-strength Steel in Bridge Engineering

Role of deformation on the hydrogen trapping in the pearlitic steel

Improving hydrogen embrittlement resistance is a prerequisite for expanding the application of high-strength steels. A high-strength deformed pearlitic steel exhibits excellent hydrogen embrittlement resistance presumably because strong hydrogen trapping sites induced by deformation prevent hydrogen accumulation at potential crack initiation sites. This work reports the conclusive identification of the strong hydrogen trapping site in the deformed pearlitic steels. Thermal desorption spectroscopy showed a distinct hydrogen desorption peak at high temperature of ∼ 600 K solely in the deformed pearlite. Scanning transmission electron microscopy and atom probe tomography analyses revealed that the deformation resulted in strain localization at the ferrite/cementite interfaces, together with the formation of a large number of dislocations, leading to the strong segregation of deuterium, a natural isotope of hydrogen, at the interface. Therefore, hydrogen trapping in the deformed pearlitic steels is attributed to the strained ferrite/cementite interface.

Review and outlook about the use of high strength steel in encased composite columns

AbstractThe trends of the modern construction are recognized for many years; go large span, go light structures, go sustainable, and keep it simple. In the holistic approach to construction a column remains one of the key structural elements.This article presents benefits of the application of high strength steel; namely the potential of using S500 and S550 for encased composite columns. The study shows the increase of the buckling capacity and reduction of weight and consequently reduction of the carbon footprint especially when applying XCarb® steel. The results are presented for a single member as well as for an internal column of a 156m high office building.It is assumed in the analyses that the simplified design method for composite columns defined in EN1994‐1‐1:2004 is applicable to higher steel grades and higher concrete compression classes. Different typologies of the encased steel cross sections are considered: simple H section in rectangular encasement, and cruciform section.

Investigation of Hardfacing on Ultra-High Strength Steel Base Material

The application of high-strength steels is increasing rapidly nowadays, and steels with more than 1000 MPa yield strength are usually used in welded structures. The welding of these materials has many difficulties, so very important the precise technology planning, and disciplined work during welding. The weldability of these materials is commonly investigated field in case of joining. The application of ultra-high strength steels expands rapidly, and in the last years, it started to use them as a base material for hardfacing. Besides the wearing, there is a claim about higher strength of base materials in case of relatively extremely loaded machines. Because this ultra-high strength steel appears as a base material for hardfacing and it brings new challenges for welding technologists. In case of joining, the welding technology is complicated, usually need preheating before welding, is important to calculate and to use the right t8/5 cooling time, and basically necessary to decrease the heat input as much as possible. The bad effect of welding heat input can be compensated by the filler material too in some cases. In contrast in case of hardfacing the base material itself usually has a big thickness, and no joint preparation, additionally important to reach deep fusion on the surface. It basically determines the heat input which has a different heat cycle as in case of joining. Therefore, the heat affected zone (HAZ) differs from the HAZ in case of joining application. In this investigation, four different hardfacing were made with four different technological parameters by robotic gas metal arc welding on S1100QL steel. During the welding parameter determination, we try to find a series of heat inputs from the lowest to the practically usable highest heat input. For the experiments, two filler materials used, one for the buffer zone, and for the hardfacing itself. Microstructural evaluation and hardness tests were made on the specimens which can show the differences between the heat affected zones.

Cyclic loading tests and numerical modeling of concrete-filled 700 MPa high-strength steel tubes incorporating deep plasticity

Concrete-filled high-strength steel tubes (CFHST) could improve structural efficiency with lighter weight and higher capacity. However, the relative lower ductility and higher yield-to-tensile strength ratio of high-strength steel arouse worries about seismic performance of CFHST. In order to reveal the influence of high-strength steel on the elastoplastic hysteretic behavior of CFHST, 8 cantilever columns with Q550 and Q690 steel were subjected to constant axial load and cyclic top displacement. The actual yield strength of the steel was over 700MPa and the maximum axial load ratio was over 0.5. Based on the experimental observations, a finite element model was developed in ABAQUS that could consider deep plasticity behavior of CFHST members more precisely by introducing full-range elastoplastic constitutive model of high-strength steel and damaging–crushing behavior of infill concrete. The model was validated by the 8 tests of this study and other 34 cyclic-loaded CFST specimen from different researchers. 288 cyclic-loaded CFHST models were simulated by the effective numerical model in the parametric study on the elastoplastic deformation capacity of CFHST columns. The experimental and numerical investigations show that the CFHST could still have considerable deformation capacity if the local deformation of the steel tubes develop moderately. For heavy loaded CFST columns, high-strength thin-walled steel tubes have satisfying elastoplastic deformation capacity and ductility that are not worse than CFST with thick conventional steel tubes. The application of high-strength steel could delay the steel yield and control the damage of the concrete, leading to larger pre-peak deformation capacity. Finally, the empirical formulas were proposed to roughly yet efficiently estimate the ultimate drift θu of cyclic-loaded CFSTs with fy=345∼ 690 MPa, fc’=24∼72 MPa, ξ=1.0∼6.0 and n=0.20∼0.80, which is fairly practical in plastic inter-story-drift check and seismic design of CFHST structures.

Numerical Study on the Buckling Resistance of High Strength Steel Columns and Beam‐columns

AbstractThe rising interest in the use of high strength steel (HSS) materials is justified by several advantages that they provide. In the field of construction, their benefits range from streamlined and elegant structures to lower CO2 emissions and energy consumption. High‐rise buildings and large span bridges can be designed with smaller foundations and less structural weight, since the application of HSS makes the design with slender steel sections possible. However, special attention should be given to the stability of the compressive members since the buckling resistance generally governs their design. The existing codes to evaluate the capacity of HSS columns and beam‐columns are based on rules from experimental tests related to normal strength steel (NSS) materials, which is responsible for inconsistencies. Therefore, this current work aims to present a numerical model created and validated to evaluate the major‐ and minor‐axis flexural buckling of HSS welded I‐section columns and the combined flexural and lateral‐torsional buckling of HSS welded I‐section beam‐columns. In the following, a parametric study is also conducted, in which different cross‐sections, normalized slenderness, steel grades (from S460 up), bending moment distributions and application of restraints are considered. Finally, a comparison between the European design rules and the resistances from the Finite Element model is led, evidencing the underrating expressed by the code with a level of safety even higher when superior steel grades are evaluated.

Study on corrosion behavior and mechanism of AISI 4135 steel in marine environments based on field exposure experiment

The application of high-strength steels in marine engineering is gaining importance because of their high performance and ability to help save resources. However, detailed and systematic information about the corrosion behavior of high-strength steels in different marine corrosion zones is still limited. This study aimed to investigate and compare the corrosion behavior of AISI 4135 high-strength steel in marine atmospheric, splash, tidal, and immersion zones, focusing on rust layer characteristics, corrosion form and electrochemical corrosion behavior. Corrosion exposure experiments were performed in a specific sea area, and the recovered steel samples were characterized by Raman spectroscopy, confocal laser scanning microscopy, nitrogen adsorption analysis, etc. Results showed that the rust layer formed on the surface of the steel in all corrosion zones had component delamination. The steel samples in the atmospheric, splash, and tidal zones were characterized by pitting corrosion, where the average depths of the corrosion pits were 56.1 ± 4.7 μm, 199.5 ± 12.6 μm, 108.1 ± 11.0 μm, respectively, whereas those in the immersion zone were characterized by general corrosion. Meanwhile, electrochemical tests were performed on the electrode samples during exposure. Results showed that the corrosion of the steel progressed from slow to fast in the atmospheric, splash, and tidal zones, whereas it was relatively steady in the immersion zone. Differentiated models of the corrosion evolution of steel under wet–dry cycle and immersion conditions were presented. This discrepancy is related to the varying degrees of accumulation of ionic corrosion products at the metal/oxide interface, which are determined by the mean pore access diameter of the rust layer and the corrosion environment. This study is highly significant for the design of marine engineering considering the safety applications of high-strength steel structures in harsh marine environments.

The effect of the yield to tensile strength ratio on stress/strain concentrations around holes in high-strength steels

Application of high-strength steels in the maritime and offshore industry is currently limited by rules governing the ratio of the yield to tensile strength (the Y/T ratio). To better understand the physical basis for these rules, the nature and extent of the plastic stress/strain field in the vicinity of a stress concentration (a circular hole) in a structure made from high-strength steel are analyzed. This is done through analytical models of the stress field and the extent of plasticity in the vicinity of a hole based on classical methods. These analytical methods are validated through FEA models that are in turn validated by published experimental data. This paper concludes that a high Y/T ratio leads to a lower plastic SCF and a higher local strain in the vicinity of a hole. The extent of the plastic zone is not affected by different values of Y/T ratio for different values of σnom/σy.

Evaluation of Hydrogen Permeation into High-Strength Steel during Corrosion in Different Marine Corrosion Zones

Hydrogen permeation into high-strength steel during the corrosion process can deteriorate their mechanical properties, thus seriously threatening the safety of steel structures. However, the hydrogen permeation behavior of steels in corrosive marine environments is not well understood. In this study, the hydrogen permeation behavior and mechanism of AISI 4135 steel in different marine corrosion zones was investigated for the first time using an in situ hydrogen permeation monitoring system via outdoor and indoor tests. The three-month outdoor hydrogen permeation test showed that the diffusible hydrogen content of the steels exposed to the marine atmospheric, splash, tidal and immersion zone was 3.15 × 10−3, 7.00 × 10−2, 2.06 × 10−2 and 3.33 × 10−2 wt ppm, respectively. Meanwhile, results showed that the hydrogen permeation current density was positively correlated with the corrosion rate of the steel in the marine environments. This research is of great significance for guiding the safe application of high-strength steel in the marine environments.

Bond behaviour of high-strength steel bars in concrete with steel fibres

Reductions in materials consumption through the use of high-strength materials is important in building construction. However, high-strength steel applications have possible challenges such as their effects on bond behaviour and structural ductility. The bond behaviour, total energy capacity and failure modes of headed and straight high-strength and normal-strength steel bars were investigated using pull-out tests. In the experimental programme, 48 concrete specimens with a compressive strength of 40 MPa, different ratios of steel fibres and embedded steel bars with different yield strengths were subject to pull-out tests. The results showed that the headed bars had far greater bond stress and total energy capacity than the straight bars. It was also found that the higher the yield strength of the bars, the higher the energy capacity and bond stress. Although increases in fibre ratios led to increases in energy capacity, they did not absolutely increase the bond stress. The specimens with both headed and straight bars failed by splitting.

A comprehensive investigation on the damage induced by the shearing process in DP780 steel

Sheared edge cracking phenomenon is a key problem limiting the application of high-strength steels. Therefore, it is very necessary to explore the cracking causes to promote the solution of this problem. In this paper, the damage in the sheared edge of DP780 steel is investigated by microstructure characterization, micro/macro mechanical property evaluation, and numerical simulation. Microvoids, microcracks, and work hardening behavior are identified as damage factors affecting the sheared edge cracking. Two types of microvoids are found based on the position of microvoids. Microvoids formed at phase interfaces have the characteristics of small size (≤ 5 μm) and large number (276–340), while microvoids generated from inclusions hold large size (> 5 μm) and small number (6–18). The damage degree of microvoids is evaluated by number, size, and distribution. The result shows the damage of microvoids becomes more serious with the increasing shearing clearance. During shearing, microvoids are split to form microcracks. These microcracks become the cracking source in the subsequent process. Therefore, microcracks are the most crucial to the formability. Reducing microcracks is an effective method to avoid sheared edge cracking. Furthermore, the shearing process is simulated in ABAQUS. A VUSDFLD subroutine is developed for implementing the constitutive model of DP780 steel. The simulated results match the experiment results very well, which indicates the damage of DP780 steel during shearing can be predicted by simulations. The research of this paper is beneficial to understand the cause of sheared edge cracking and design an optimal shearing process.

Fatigue design of mild and high-strength steel cruciform joints in as-welded and HFMI-treated condition by nominal and effective notch stress approach

According to the Recommendations for Fatigue Design of Welded Joints and Components by the International Institute of Welding (IIW), the fatigue strength of welded steel joints is in general independent of the base material strength. Post-treatment methods, such as the High Frequency Mechanical Impact (HFMI) treatment, can significantly increase the fatigue performance of welded joints especially in case of high-strength steel applications, which is already considered within the IIW Recommendations for the HFMI Treatment. This paper firstly investigates the effect of the base material strength on the fatigue resistance of welded and HFMI-treated steel joints. Therefore, mild steel S355 and high-strength steel S700 cruciform joints are cyclically tested in both conditions and the statistically evaluated S/N-curves are compared. The results reveal an increase of the high-cycle fatigue strength by the HFMI-treatment by a factor of 1.35 in case of the S355, and of 1.59 for the S700 specimens. Secondly, the test results are assessed by the fatigue design curves of the corresponding structural detail within the IIW-recommendations using the nominal stress concept. Moreover, the applicability of the procedure applying the effective notch approach is analyzed. In order to numerically evaluate the effective notch stress, the geometry of the cruciform joint is modelled according to the given guidelines within the recommendations applying a reference radius of 1 mm at the weld toe for both conditions. On the basis of the numerically computed effective notch stress, a local fatigue design is performed for all test series, which reveals sound accordance between the recommended design curves and the statistically evaluated fatigue test S/N-curves.

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.

Role of Retained Austenite in Corrosion Resistance of Si-Mn Steel

Si-Mn steels are used for many industrial applications because of their high strength. One of the most important characteristics of the microstructure of Si-Mn steels is the retained austenite embedded in the matrix of martensite or bainite. The existence of the retained austenite promotes TRIP (Transformation-Induced Plasticity) effect, and therefore, provides Si-Mn steels with their excellent strength. While the retained austenite has the beneficial effect on the mechanical properties, corrosion mechanisms of the steels with the retained austenite have been unclear. In reality, the actual application of high-strength steels almost always involves outdoor corrosion environments which can be characterized as predominantly near-neutral pH environments with chloride ions. Even if the steels are successfully protected from corrosion by coating and/or painting, pitting corrosion readily occurs at the cut edges and in coating defect areas due to the presence of chloride ions. In this research, the objective is to clarify the effect of the retained austenite on the corrosion resistance of the Si-Mn steel in near-neutral pH environments.The specimens were Si-Mn steel (0.39%C, 1.51%S, 2.01%Mn, 0.010%P, 0.002%S, 0.04%Al, 0.004%N). The metallographic inspection was performed to ascertain the characteristics of the microstructure of the specimen by using EPMA (Electron Probe Micro Analyzer). It was confirmed that the microstructure consisted of the retained austenite and the matrix of martensite. To assess the corrosion behavior of the specimen, immersion tests were performed in the boric-borate buffer solutions with NaCl (pH 7.0). It was confirmed that the pits were initiated only in the matrix and not in the retained austenite.To clarify the reason for the high corrosion resistance of retained austenite, the corrosion behavior of two types of specimens were compared: Full martensitic specimen (0.44%C, 0.20%S, 0.85%Mn, 0.008%P, 0.002%S, 0.035%Al, 0.003%N) and full austenitic specimen (0.45%C, 0.32%S, 29.40%Mn, 0.014%P, 0.002%S, 0.025%Al, 0.005%N). In the case of the austenitic specimen, higher amount of Mn was added to form full austenitic structure even at room temperature. The austenitic and martensitic specimens simulated the retained austenite and matrix phases in the Si-Mn steel. The depassivation pH values of the austenitic and martensitic specimens were measured in boric-borate buffer solutions. The pH of the solution was decreased stepwise with 0.35 M H3BO3, and the open circuit potentials were measured. It was confirmed that the depassivation pH of the austenitic specimen was lower than that of the martensitic specimen. In other words, the depassivation occurred more readily on the martensite than the austenite. AES (Auger Electron Spectroscopy) depth analysis was performed to investigate the thickness of the surface oxide films on the austenitic and martensitic specimens. It was clarified that the oxide film on the austenite was about 1 nm thicker than that on the martensite, suggesting that the protective ability of the oxide film formed on the austenite is higher than that on the martensite. According to the above results, the high corrosion resistance of the retained austenite in Si-Mn steels appeared to be related with the nature of the oxide film formed on the austenite.

Effect of microstructure on hydrogen embrittlement susceptibility in quenching-partitioning-tempering steel

Hydrogen embrittlement (HE) restricts the application of high strength steel in sustainable energy productions. As one type of efficient hydrogen trap sites, the NbC carbide precipitation is a superior approach to mitigate the HE susceptibility. The microstructure, mechanical properties and HE susceptibility were investigated in different high strength steels treated by quenching and partitioning (Q&P), quenching-partitioning-tempering (Q-P-T) and intercritical annealing quenching and partitioning (IAQP) processes in this study. The results show that the NbC particles can significantly improve the HE resistance of high strength steel treated by Q-P-T process. The NbC carbide precipitation has four different morphologies with varied sizes, which can effectively trap a large amount of diffusible hydrogen atoms. The retained austenite phases with different morphologies and locations have different hydrogen trap ability, but ferrite phase does not show strong hydrogen trap ability. Meanwhile, the NbC carbide precipitation can enhance the yield strength of steel effectively through precipitation strengthening, but has little effect on its ductility.

Effect of the Welding Thermal Cycles Based on Simulated Heat Affected Zone of S1300 Ultrahigh Strength Steel

In the automotive industry there is an increasing demand for the wider application of high strength steels due to their favourable mechanical properties. The steel producers continuously developing new generations of high strength steels to insure higher strength and toughness properties. Since in most cases these steels are joined in welded structures, great attention must be taken to their weldability. The weldability of high strength steels has still challenges which are as follows: cold cracking sensitivity; reduction of strength and toughness of heat affected zone (HAZ); filler metal selection. Because the mechanical properties of ultrahigh strength steels are provided by using various alloying elements, micro alloys, and by different metallurgical methods, the steels may lose their outstanding properties during welding. In real welded joints the critical parts of the HAZ have small extent so their properties can be limitedly analysed by conventional material testing methods. With the help of physical simulators, the different parts of the heat affected zone can be produced in an adequate size for subsequent tests. In our research work the weldability, especially the HAZ properties of an ultrahigh strength structural steel (Rp0.2 = 1300 MPa) were investigated on thermal simulated samples with the help of Gleeble 3500 physical simulator. Three relevant technological variants for gas metal arc welding (GMAW), t8/5 = 5 s, 15 s and 30 s were applied during the HAZ simulations in the selected coarse-grained (CGHAZ), intercritical (ICHAZ) and intercritically reheated coarse-grained (ICCGHAZ) zones. Both the microstructure was studied by optical microscope and the mechanical properties were analysed by Vickers hardness tests and Charpy V-notch impact tests at -40 °C. According to the results the investigated ultrahigh strength steel was softened on account of the welding heat cycles, besides that the strength of the investigated ultrahigh strength steel can be better with the application of shorter t8/5 cooling time.