Types Of High-strength Steels Research Articles

Optimizing Fatigue Performance in Gradient Structural Steels by Manipulating the Grain Size Gradient Rate.

As a new type of high-performance material, gradient structural steel is widely used in engineering fields due to its unique microstructure and excellent mechanical properties. For the prevalent fatigue failure problem, the rate of change in the local grain size gradients along the structure (referred to as the gradient rate) is a key parameter in the design of gradient structures, which significantly affects the fatigue performance of gradient structural steel. In this study, a new method of 'Voronoi primary + secondary modeling' is adopted to successfully establish three typical high-strength steel models corresponding to the convex-, linear-, and concave-type gradient rates for gradient structures, focusing on the stress-strain response and crack propagation in structural steel with different gradient rates under cyclic loading. It was found that the concave gradient rate structural model is dominated by finer grains with larger volume fraction, which is conducive to hindering fatigue crack propagation and has the longest fatigue life, which is 16.16% longer than that of the linear gradient rate structure and 23.66% longer than that of the convex gradient rate structure. The simulation results in this study are consistent with the relevant experimental phenomena. Therefore, when regulating the gradient rate, priority should be given to increasing the volume fraction of fine grains and designing a gradient rate structure dominated by fine grains to improve the fatigue life of the material. This study presents a new strategy for designing engineering materials with better service performance.

Quantification of static softening process and its effects on work hardening characteristics of a typical high strength steel during multi-pass deformation

Heavy components of 300 M steel are usually manufactured by multi-pass forging. It is necessary to study the flow characteristics of 300 M steel during multi-pass deformation, which helps to regulate the flow behaviors during the actual forging process. In the study, multi-pass compression experiments are conducted on the Gleeble-3500 device to mimic the forging process of 300 M steel. Results show that the deformation parameters and inter-pass holding parameters can affect the work hardening rate significantly. It can be ascribed to coupling effects of dynamic softening and static softening behaviors. A unified static softening kinetics model is established to evaluate the coupling effects of static recovery, static recrystallization, and metadynamic recrystallization on the static softening behaviors. The established static softening kinetics model shows high prediction accuracy with a reliability of 0.99605. Furthermore, a new constitutive model is established to describe the effects of dynamic softening and static softening on the flow stress during multi-pass deformation. The prediction accuracy of the new constitutive model is 0.98897 with a mean absolute error of 4.075%, which demonstrates that the established constitutive model is reliable.

Seismic behavior of Q620 high-strength steel welded Box-section columns: Experimental tests, analysis, and model

This study experimentally and numerically investigates the seismic behavior of high-strength steel (HSS) welded Box-section columns. The HSS structures have made rapid development in various types of building structures. However, the high yield-to-tensile ratio of HSS limits its application in seismic design. To address this gap, a new type of HSS called Q620 has been developed by Hebei Iron and Steel Co., Ltd. (HISCO). A total of three specimens were designed by this seismic-resistant Q620 HSS material and tested under cyclic load. The main failure modes included local buckling of the bottom section of the column, and obvious flexural deformation led to fracture of the specimen. Additionally, the nonlinear kinematic hardening model was utilized to accurately establish the finite element (FE) model for the HSS welded Box-section columns. Based on the validated FE model, an extensive parametric analysis (e.g., width-to-thickness ratio, axial compression ratio, and slenderness ratio) was conducted to evaluate the seismic behavior of the Q620 HSS welded Box-section columns. The results indicated that the Box-section columns exhibited favorable hysteretic behavior and notable plastic deformation capacity. A higher width-to-thickness ratio resulted in a faster decline in stiffness and a more pronounced advancement of damage. The ductility and energy dissipation capacity of Box-section columns were generally decreased with increasing axial compression ratio or slenderness ratio. A newly simplified hysteretic model was proposed, which was in good agreement with the experimental results.

Experimental Study on Seismic Fatigue Capacity of High- and Mild-Strength Structural Steels with and without Corrosion

The test results on hourglass specimens of steel under repetitive sine loads provide graphs that indicate the stress range in terms of the number of cycles to failure and are known as S-N curves. Using this curve, it is determined that if the applied stress is less than a certain level, failure will not occur as the number of load cycles increases. The S-N curve can be affected by several factors such as yield stress, temperature, surface properties, and corrosion. In this research, the S-N curve has been investigated for two types of high-strength steels, S690 and S460, as well as two types of mild-strength steels, S235 and S355, at 25°C, and S355 with corrosion. The numbers of samples used for S235 and S460 steels were 45 each while S355 and S690 steels were 36 each and for S355 with corrosion was 15 with the high cycle fatigue curve obtained for them. To investigate the effect of plate thickness on the high cycle fatigue of the samples, four sets of 24-piece S235 steel samples, being 96 samples in total, were made of plates with different thicknesses of 8, 12, 15, and 20 mm and tested. Finally, a four-story three-span steel moment frame was designed, and under the Northridge earthquake record, the high cycle fatigue was investigated. It was observed that the high cycle fatigue was not effective for the mentioned structure under the Northridge earthquake record, but in the corroded structure, damage from high cycle fatigue occurs under this record.

Analysis and simulation of impact tests on automotive elements using two types of high-strength steels

This research, the main objective is to study and analyze the behavior of the automobile part called front bumper reinforcement, subjected to impact; For this, two types of materials belonging to the family of ultra-high strength steels will be used, since they are two materials that have excellent mechanical properties. To carry out the studies, a simplified model of said piece was increased; likewise, the analyzes will be developed with the help of CAE software. To carry out the process, a series of stages will be developed, ranging from the development of the model to be analyzed, considering its geometric study characteristics, as well as the knowledge of the mechanical properties of the materials to be worked on. In the same way, the conditions to which the element is subjected at the moment of impact will be known and applied. The force applied to the element will be subject to the speeds according to the standards used for this type of parts in impact tests. This research contributes to the studies of parts that are part of the safety of the vehicle, as well as knowing the mechanical advantages that 38MnB5 steel has compared to 22MnB5 steel.

Study on Corrosion Behavior and Mechanism of Ultrahigh-Strength Hot-Stamping Steel Based on Traditional and Compact Strip-Production Processes.

Hot-stamping steel is a type of high-strength steel that is mainly used in key safety components such as the front and rear bumpers, A-pillars, and B-pillars of vehicles. There are two methods of producing hot-stamping steel, i.e., the traditional process and the near net shape of compact strip production (CSP) process. To assess the potential risks of producing hot-stamping steel using CSP, the microstructure and mechanical properties, and especially the corrosion behavior were focused on between the traditional and CSP processes. The original microstructure of hot-stamping steel produced by the traditional process and the CSP process is different. After quenching, the microstructures transform into full martensite, and their mechanical properties meet the 1500 MPa grade. Corrosion tests showed that the faster the quenching speeds, the smaller the corrosion rate of the steel. The corrosion current density changes from 15 to 8.6 μA·cm-2. The corrosion resistance of hot-stamping steel produced by the CSP process is slightly better than that of traditional processes, mainly since the inclusion size and distribution density of CSP-produced steel were both smaller than those of the traditional process. The reduction of inclusions reduces the number of corrosion sites and improves the corrosion resistance of steel.

Hydrogen permeation and hydrogen damage behavior of high strength casing steel in acidic environment

To explore the effect of hydrogen permeation on pipes in an acidic environment, the tensile mechanical properties of three types of high strength steels were evaluated before and after hydrogen filling. The hydrogen damage behavior of three kinds of high-strength steels was studied by electrochemical hydrogen permeation test, MTS tensile test, and fracture morphology analysis. First, the basic physical and chemical properties of the materials were analyzed, and then the D-S double electrolytic cell technology was used for hydrogen permeation experiment. Finally, the influence of hydrogen loading on the tensile mechanical properties of the steel was determined by MTS tensile test and fracture morphology analysis. As the hydrogen filling current increases, the system temperature rises and the pH decreases, the hydrogen diffusion coefficient increases and the sensitivity of the steel to hydrogen embrittlement increases. The higher the steel strength, the higher the hydrogen diffusion coefficient, the higher the diffusible hydrogen concentration, the higher the hydrogen embrittlement sensitivity. The hydrogen damage evaluation method of high-strength steel used in this paper can provide a reference for the applicability evaluation of oil well pipe under acidic environment and provide theoretical guidance for the selection of oil well pipe in the field.

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

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

Numerical analysis of high-strength reinforcing steel with conventional strength in reinforced concrete beams under monotonic loading

Abstract This work presents finite element (FE) modeling using the ABAQUS program to investigate the effect of steel reinforcement with three different types of high-strength steels, grades 420, A1035, and SD685 on the flexural behavior of RC beams under monotonic loading. Experimental findings from the literature have been used to validate the proposed model. The numerical load, deflection, mode of failure, failure concrete strain, and bottom steel strain at failure of 24 numerical specimens with collapsed conditions of tension-controlled, balanced, and compression-controlled are recorded. Also, the effect of compression reinforcement is being investigated. The results reveal that the flexural behavior of the experimental test for the three steel grades is well validated by FE analysis. The ductile and brittle behavior features of yield strength (YS) larger than 420 can be predicted for specimens designed according to current standards ACI-318M-19. Also, the compression reinforcement improves load capacity while reducing displacement. It may be argued that when YS decreases, tensile stress and strain of flexural rebar rise, causing the beam to become more ductile. When the YS increased, the brittle behavior was induced.

Fatigue performance of transverse welded attachment of high-strength structural steel series

This study presents an experimental investigation of the fatigue performance of non-load-carrying transverse fillet-welded attachments made of high-strength steel (HSS). Four typical HSSs were selected, with steel yield strength of 460 MPa, 550 MPa, 690 MPa, and 960 MPa. A total of 88 high-cycle fatigue tests were conducted. Based on the analysis of the morphological details of the fracture surfaces and the failure modes, three different methods for fatigue assessment, such as the nominal stress method, the effective notch stress method and the strain energy density method, were applied to directly compare the fatigue performance of HSS and conventional strength steel (CSS, with a yield strength of approximately 235–355 MPa). HSS transverse fillet-welded attachments have demonstrated excellent fatigue resistance compared with specifications (FAT 80) in the design codes by using the nominal stress method, the natural slope of the S–N curves is nearly 4.0, rather than 3.0 prescribed in the current design codes for fatigue assessment of welded structures. For the notch stress method, HSS transverse fillet-welded attachments show a greater increase in fatigue life for low notch stress ranges (approximately Δσk≤ 400 MPa). However, for high notch stress ranges (approximately Δσk > 400 MPa), the increase in fatigue life is limited. The results with the strain energy density method are similar to those with the notch stress method.

Tensile stress-strain models for high strength steels

In recent years, high strength steels (HSSs) with a minimum nominal yield stress of 460 MPa have been increasingly used in structural applications. An HSS may exhibit continuous or discontinuous yielding, depending on the chemical composition and manufacturing process and procedure. However, no criterion has been proposed in the literature to predict the occurrence of a yield plateau. Meanwhile, the ductility of HSSs is often limited, making it essential to predict their fracture for a safe design. However, existing stress-strain models used for HSSs cannot meet this need. To develop versatile stress-strain models for HSSs, 212 test curves are collected from open literature. In addition, four curves are obtained from tensile tests of two types of HSS produced in Australia (Bisalloy 80 and 400). By analysing the collected test data, a criterion is proposed to determine the occurrence of the yield plateau according to the yield stress of the steel and its carbon content. Two stress-strain models are then proposed for HSSs exhibiting continuous and discontinuous yielding, respectively. Moreover, predictions from the discontinuous model are also compared with the test data of conventional mild steel, proving that the model can also capture the stress-strain response of the conventional mild steel. Finally, the proposed models are used in the simulation of HSS coupons and beams, which proves the feasibility of the proposed HSS models for structural analysis.

Effects of the Arctic low temperature on mechanical properties of Q690 and Q960 high-strength steels

Mechanical properties of high strength steel (HSS) are fundamental information to analyse and design HSS structures. This study extends the applications of HSS Q690 and Q960 to the Arctic infrastructures. The mechanical properties of HSS Q690/Q960 at the low temperature range of −80~20℃ were studied through performing standard tensile tests on 20 HSS Q690 coupons and 19 Q960 coupons in cooling chamber with LNG, which simulated the Arctic low-temperature environment. The influences of low-temperature levels, thickness of HSS plate, and HSS type on mechanical properties of HSS Q690/Q960 were in-depth investigated. The test results showed that the Arctic low temperature increased the modulus, yield and ultimate strength of HSS Q690/Q960, but did not reduced the ductility of these two types of HSS. In addition, all the tensile coupons of HSS failed in ductile mode without brittle fracture. This paper also developed constitutive models for HSS Q690/Q960 at low temperatures of −80~20℃. Validations showed that the developed constitutive models estimated reasonably well mechanical properties of HSS Q690/Q960 at low temperatures of −80~20℃.

Assessment of thermal properties of various types of high-strength steels at elevated temperatures

Accurate assessment of the thermal properties of steel is a key issue in the fire simulation and design of steel structures. Thermal property tests were conducted for seven types of high-strength steels (HSSs), namely Q460, Q500, Q550, Q620, Q690, Q890, and Q960 steels, along with conventional mild steel Q345. The thermal expansion, specific heat, and thermal conductivity of various steels at a temperature range of 25–1000 °C were obtained and compared to the results proposed by Eurocode 3 and ASCE to validate the applicability of these codes to HSSs. The test results showed that the phase transition temperature of HSS was lower than that of mild steel, and HSS experienced substantial thermal expansion at elevated temperatures. Eurocode 3 and ASCE can be used to approximate the thermal expansion of the HSS only before the phase transition temperature. The endothermic capacity of HSS was weaker than that of mild steel at elevated temperatures. The specific heat of the various types of HSSs could only be effectively predicted by Eurocode 3 and ASCE up to 600 °C, whereas their thermal conductivity could not be reasonably predicted by these codes in temperature range of 25–1000 °C. New equations for thermal expansion, specific heat, and thermal conductivity were proposed to accurately assess the thermal properties of HSS.

Analysis of fracture behavior of high-strength steels in tension after fire exposure

High-strength steels have been widely applied in high-rise and long-span structures. Exposure to high temperatures due to fire may lead to reduction in material properties and fracture behavior of high-strength steels, greatly affecting the post-fire behavior of high-strength steel structures. This paper investigates the post-fire fracture behavior of high-strength steels in tension to pave the way for safety assessment of high-strength steel structures after fire. The fracture models of Chinese high-strength steels (Q460, Q550, Q690, Q890) and European high-strength steels (S460, S690 and S960) are calibrated and validated against limited experimental results of tensile coupon tests in an exposure temperature range of 200 °C to 1000 °C. The effect of air-cooling and water-cooling methods on the post-fire fracture behavior of high-strength steels is investigated. The fracture behavior is represented by the post-necking true stress-strain curve, toughness index (resistance to fracture initiation) in the stress modified critical strain model (SMCS) and damage evolution law. It is found that different types of high-strength steels with similar yield strength may exhibit quite different fracture behavior after exposure to high temperatures. The maximum exposure temperature and cooling method are two critical factors influencing the post-fire fracture behavior of high-strength steels. The true stress-strain curves after onset of necking can be simply expressed by a straight line with a slope, which becomes temperature dependent when the exposed temperature exceeding a critical level (e.g. 600 °C). The toughness index in SMCS model is subjected to great reduction in a temperature range of 800 °C to 900 °C for Q460-Q890 steels and 750 °C to 900 °C for S460-S960 steels. The most rapid evolution of damage occurs after being exposed to temperatures in a range of 650 °C to 900 °C. Compared to air-cooling method, the water-cooling method may lead to great reduction in the slope of post-necking true stress-strain curves (by 50%), significant reduction in toughness index (by 80%), and even change of fracture mode from ductile fracture to brittle fracture. It is recommended to choose reasonable and appropriate post-fire material properties for fracture prediction of different high-strength steels.

Description of Residual Stresses in Autofrettaged Open-Ended Cylinders Made of High-Strength Steel.

The elastic range in loading–unloading processes is often reduced with a Bauschinger effect. This material property may have a high impact on residual stresses and, as a result, on the performance of autofrettaged cylinders under service conditions. The objective of the present paper is to demonstrate this impact using a material model that accounts for the response of typical high-strength steel. The solution is semi-analytic and, therefore, can be used for fast and accurate analysis of the process of autofrettage. A numerical example illustrates the general solution. This example shows that the Bauschinger effect has a significant impact on the residual circumferential stress in the vicinity of the inner radius of the cylinder. This stress is the most significant quantity of autofrettaged cylinders. Therefore, the main result obtained suggests that even a moderate Bauschinger effect should be taken into account in analyses of the process of autofrettage.

Mechanical properties of high-strength Q960 steel at elevated temperature

This study experimentally investigates the temperature-induced deterioration in the mechanical properties of high-strength Q960 steel. High-strength steel has numerous advantages compared with conventional mild-strength steel and has gained wide applications in engineering structures, particularly in high-rise and long-span buildings. The fundamental issue in the fire-resistance design of high-rise or long-span steel buildings is the evaluation of mechanical properties under elevated temperature. There is little information on the temperature-induced mechanical-property deterioration of Q960 steel because of the limited research on this subject. To bridge this knowledge gap, a series of tensile coupon tests on Q960 steel was carried out under various temperatures from 20 to 900 °C to obtain the corresponding stress–strain relationships, yield strength, ultimate strength, and elastic modulus at elevated temperatures. The test results were compared with the results of other high-strength steel types such as Q460, Q690, and S960 steels reported in previous studies as well as the mechanical properties recommended in applicable design codes or standards. The comparison showed that the effects of temperature on the mechanical properties among different types of high-strength steels are different. New predictive equations for evaluating the material properties of Q960 steel at elevated temperatures were presented.

Experimental study to differentiate mechanical behaviours of TMCP and QT high strength steel at elevated temperatures

High strength steel (HSS) has gained its popularity in high-rise and large-span structures in which fire is one of the extreme scenarios that needs to be considered in structural design. In view of different types of HSS manufactured from different heat-treatment processes, their mechanical behaviours under fire would be different. However, previous studies and modern design codes show inadequacy of information on their temperature-dependent mechanical properties, especially their mechanical differences due to the different heat-treatment methods. With the research gap being identified, high-temperature coupon tests were conducted on two types of S690 steel respectively manufactured from thermo-mechanically controlled process (TMCP) and quenching and tempering (QT) process. Both steady- and transient-state test methods were adopted. Microstructure changes were discussed and temperature-dependent mechanical properties were compared with each other and with those of mild steel produced through hot-rolling process. The test results revealed that TMCP-S690 steel exhibited similar elastic modulus at elevated temperatures as QT-S690 steel but smaller effective yield strengths when the thermal creep was more significant above 400 °C. Through this study, the heat-treatment dependent thermal elongations, elastic moduli and effective yield strengths at elevated temperatures were recommended for fire resistant design of HSS structural elements. The stress–strain constitutive model was also provided for numerical modelling.

Karakterizacija beinitno-feritnih struktura formiranih u zoni uticaja toplote zavarenih spojeva različitih čelika visoke čvrstoće (S700MC/S960QC) i njihova zavisnost od brzine hlađenja

Modern steel structures and joints must satisfy various increasingly demanding requirements such as high yield strength, improved cross section to mass ratio, and desirable ductile-to-brittle transition properties. Consequently, joining different types of high-strength steels has become an attractive option from the cost perspective and for weight and corrosion reduction. In dissimilar welding, however, there remains a need for better understanding of discrepancies in microstructure formation resulting from asymmetric heat distribution. In this study, a characterization of the transformation of bainite, ferrite, and martensite in the microstructure of the heat affected zone (HAZ) formed by a cooling time of 10 kJ/cm of heat input was carried out for dissimilar high-strength joint steels (S700MC/S960QC). The characterization was performed by scan electron microscopy (SEM) sampling, the images of which were analyzed by ImageJ Pro and evaluated by volume fraction of block - like granular bainite (GB). The alloy elements composition close to the fusion line of both materials was then assessed using energy dispersive X-ray spectroscopy (EDS). The results showed a strong presence of GB, which had about 70% volume fraction in S700MC at 615 °C, and which comprised formations of lower bainite and retained austenite (RA) at 420 °C. The presence of 55% block GB was observed at 470 °C in S960QC, which was caused by the formation of tempered martensite (TMA) at 400 °C. Presence of 1.3Ni, 0.4Mo, and 1.6Mn in the coarse grain heat affected zone (CGHAZ) of S700MC confirmed the risk of brittle failure on the S700MC side due to the high presence of carbide and ferrite in the GB.

Finite Element Analysis of Second-order Effect of Plane High Strength Steel Frame Structures

High-strength structural steels have been gradually used in building structures and bridge structures because of their good mechanical properties and machinability. The mechanical behavior of high strength steel members is significantly different from that of ordinary steel members. Based on the approximate second-order calculation formula in the “Code for Design of Steel Structures” GB50017-2003, the non-linear increase coefficient of the material are introduced. The finite element analysis method is used to check the second-order nonlinear effect of typical high-strength steel frame. The results of the approximation second-order analysis and the second-order elastic-plastic analysis are compared. The second-order effect and the applicability of approximation method to high strength steel frame is analysed. The result of the calculation and analysis is valuable to engineering application.

Local laser softening of press-hardened steel at high feed rates

The development of hot stamped manganese–boron steels established new potentials for lightweight constructions for applications in the automotive industry. This type of high strength steel allows the usage of thin sheet thicknesses resulting in low specific weight retaining the optimized performance of passive safety. The parts have a high tensile strength of about 1500 MPa. However, this high strength is not favorable in all sections of a part, especially those which are relevant for safety or for joining. To ensure the requirements for the crash properties or the joining areas, a high ductility is required in these areas. A way to overcome this problem is a local softening of the crash and joining zones via laser heat treatment. By means of laser radiation, the brittle martensitic microstructure is either tempered or transformed into a ferrite/perlite dominated microstructure. A fiber-coupled diode laser with a maximum laser power of 12 kW and rectangular laser spot is used for the laser heat treatment. The temperature is controlled by a monochromic pyrometer integrated into the optical system. Generally, the necessary process feed rate of the heat treatment process is low (about 1000 mm/min), as a homogeneous result of the heat treatment is pursued. As the feed rates increase (up to 8000 mm/min), the temperature distribution across the thickness of the material becomes more inhomogeneous. With the topside being hotter than the backside, the material is tempered with a varying intensity resulting in a hardness distribution across the thickness. The influencing parameters for this effect are being characterized, and the mechanical properties of the anisotropic material are investigated.