Properties Of High-strength Steel Research Articles

Mechanical properties of corner material in cold-formed steel structure: From normal strength to high strength

Cold-forming effect varies from normal strength steel to high strength steel due to the different chemical compositions and mechanical properties of parent materials. To date, research studies on material characterisation of cold–formed steels have been mainly focusing on the normal strength structural steel, while systematic research on high strength structural steel remains scarce. In this paper, an experimental investigation into changes in mechanical properties of high strength steel undergoing various levels of plastic deformation is firstly presented. The test results have been combined with other available high strength steel data, and compared to the normal strength steel data. Of the analysis results indicated, unified predictive equations, modified from Karren’s model in 1967 can predict the strength enhancement behaviours of normal strength and high strength steel, utilising the ultimate-to-yield strength ratio of parent materials fu,f/fy,f and inner radius-to-thickness ratio after cold–forming ri/t. Moreover, the decreases in the Young’s modulus, ultimate strain and elongation at fracture of normal strength and high strength steel after cold-forming can be predicted with no further grouping required. Statistical evaluation results confirm the accuracy of the proposed predictive expressions. This paper extends the scope of the strength enhancement equation in current north American cold-formed steel design code AISI S100–16 to high strength steels with grade up to 960 MPa, and provides key predictive material equations that can be further used in the design or numerical modelling of cold-formed steel structures.

Application of Machine Learning to predict the mechanical properties of high strength steel at elevated temperatures based on the chemical composition

This paper presents the results obtained using Machine Learning (ML) algorithms to predict the mechanical properties, including ultimate tensile strength, yield strength, 0.2% proof strength and elastic modulus, of high strength steel plate material at elevated temperatures. High strength steels are increasingly used in several areas of construction offering efficient structural solutions with a high strength-to-weight ratio. Safe fire design of these structures relies heavily on accurate prediction of mechanical properties of the material with temperature. The data on elevated temperature mechanical properties collected from the literature experimental tests show a high degree of scatter, implying that they are influenced significantly by various factors, most notably the testing method, manufacturing process and chemical composition. However, the current methods for predicting the mechanical properties of high strength steels at elevated temperatures by using ‘reduction factors’ as adopted by the structural design codes do not consider these effects and may lead to inaccurate predictions. To overcome these deficiencies, a ML-based prediction method that uses temperature and chemical composition as input parameters is developed in this paper. Deep Neural Networks are trained and validated on the basis of elevated temperature material data collated from the literature test programmes. The analysis of the results show that the trained algorithm gives an excellent correlation coefficient with very small error value in predicting the strength and stiffness reduction factors of HSS.

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.

Application of Machine Learning to Predict the Mechanical Properties of High Strength Steel at Elevated Temperature

AbstractHigh strength steels are increasingly used in several areas of construction offering structural solutions with a high strength‐to‐weight ratio. Safe fire design of these structures relies heavily on accurate predictions of mechanical properties of the material with temperature. This paper presents the results obtained using Machine Learning (ML) algorithms to predict the mechanical properties, including ultimate tensile strength, yield strength and elastic modulus, of high strength steel plate material. The mechanical properties collected from the literature experimental tests show a high degree of scatter, implying that they are influenced significantly by various factors such as the testing method, manufacturing process and chemical composition. However, the current methods for predicting the mechanical properties of high strength steels at elevated temperatures by using ‘reduction factors’ adopted by the structural design codes do not consider these effects and may lead to inaccurate predictions. These deficiencies are overcome by using a ML‐based prediction method, where the effects of the chemical composition on these reduction factors are considered. Deep Neural Networks is trained to predict the mechanical properties with temperatures. The ML‐based method together with the obtained results are presented where it is shown that the trained algorithm gives an excellent correlation coefficient with very small error value.

Experimental study on mechanical properties of Q690D high strength steel during the cooling stage of fire

Previous studies on the mechanical properties of high strength steel (HSS) Q690 at fire were mainly focused on the heating stage and post-fire stage, while few studies have been conducted on those at the cooling stage of fire. In this paper, mechanical properties of Q690D steel at the cooling stage were experimentally studied and were compared with those at the heating stage. The results show that the differences in mechanical properties of Q690D steel between the cooling and heating stages are relatively small when the ultimate heating temperature (Tu) is within 400 °C, while the differences enlarge as Tu further increases, especially after Tu exceeds 800 °C. Moreover, the effects of both the cooling rate and holding duration at Tu on the ultimate strength of Q690D steel at the cooling stage are negligible, while these effects on Young's modulus, yield strength and ductility are not negligible and related to Tu. It is noted that different heating and cooling processes have an effect on the microstructure of the steel, especially after Tu exceeds 800 °C, which would influence the mechanical properties of the steel.

Test on post-fire residual mechanical properties of high strength Q690 steel considering tensile stress in fire

As a steel building may not fail in a fire scenario, the residual mechanical properties of steel after fire exposure are essential in evaluating the post-fire performance of the steel structure. However, the current experimental research regarding the post-fire mechanical properties neglects the stress in steel during the heating and cooling phases, which violates the fact that a steel structure still carries load during a fire hazard. In order to quantitatively assess the influence of stress level in steel structures on post-fire residual mechanical properties of high strength steels, a series of tensile tests was carried out on a typical high strength Q690 steel specimen exposed to elevated temperatures under three stress ratios, namely 0.30, 0.55 and 0.80. During the heating and cooling phases, constant stress was applied on the specimen to simulate the possible stress in steel structures in fire hazards. After cooling, tensile tests were carried out to attain the post-fire stress-strain curves of Q690 steel, and accordingly determine the residual yield strength, ultimate strength and elastic modulus of Q690 steel with different temperature exposures and stress levels. The test results show that the tension stress in steel during heating and cooling can improve the post-fire yield strength and ultimate strength of Q690 steel with the maximum 8% when the exposed temperature is lower than 700 °C, and the improvement increases as the stress level increases. However, the tension stress has adverse effect on the post-fire strengths of Q690 steel when the exposed temperature reaches 800 °C. If the exposed temperature is below 700 °C, it is safe to take the original strengths of Q690 steel to evaluate the post-fire performance of Q690 steel structures. However, the stress effect on the residual strengths should be considered if the exposed temperature reaches 800 °C to avoid unconservative evaluation. The tension stress in steel has no significant influence on residual elastic modulus of Q690 steel. By comparing the obtained test data with other post-fire tests on similar steels, it is found that the post-fire residual mechanical properties of steels are different even if those steels have the same nominal yield strength. The maximum 40% dispersion for residual yield strength and 50% dispersion for ultimate strength are found when the exposed temperature surpasses 600 °C due to rolling, quenching and tempering for high strength steels.

Advanced Trends in Metallurgy and Weldability of High-Strength Cold-Resistant and Cryogenic Steels

Thermomechanical Controlled Processing (TMCP), the initial microstructure and mechanical properties of rolled products made of high-strength steels, have a significant influence on the properties and reliability of welded structures for low temperature and cryogenic service. This paper systematizes advanced research trends in the field of metallurgy and weldability of high-strength cold-resistant and cryogenic steels. The classification and properties of high-strength steels are given and TMCP diagrams and phase transformations are considered. Modern methods of improving the viscoplasticity of rolled steel and welded joints are analyzed. The problems of the weldability of high-strength steels are reduction of impact toughness at low temperatures, hydrogen embrittlement, anisotropy, and softening of welded joints in the heat-affected zone. The authors propose a systemic concept and methods for improving the metallurgy and weldability of high-strength steels for low temperature and cryogenic service.

The Influence of Varying Aluminium and Manganese Content on the Corrosion Resistance and Mechanical Properties of High Strength Steels

The aim of this paper is to evaluate the influence of small variations in chemical composition on the corrosion resistance and mechanical properties of low-manganese and medium manganese high strength steels. Six different steels with manganese content varying from 1.5 to 4.0 wt.% and aluminium from 0.008 to 6.5 wt.% were subjected to the analysis. The other subjects for evaluation included the effect of aluminium as a replacement for silicon, niobium microalloying and the effect of heat treatment. The effect of non-metallic inclusions on localized corrosion initiation and propagation was also documented. Using potentiodynamic testing, exposure testing, tensile and impact testing, it was found that the improvement in corrosion resistance associated with increasing aluminium content is accompanied by a significant deterioration of the mechanical properties. Niobium microalloying and heat treatment was found to have no quantifiable impact on the anti-corrosion properties. The effect of aluminium content proved to be superior to the effect of nonmetallic inclusions in terms of determining the overall corrosion resistance of the experimental steels.

Finite Element Analysis on Hysteretic Behavior of H-shaped Columns of Thin-Walled Sections of 690 MPa High Strength Steel

High strength steel is widely used in engineering, especially in light steel structures. However, due to the material properties of high strength steel, its seismic performance has attracted wide attention. To study the hysteretic behavior of H-shaped members of thin-walled sections of Q690 high strength steel, a finite element model was built up by using the general finite element analysis software ABAQUS. Based on the finite element model, an extensive parametric analysis of H-shaped members of thin-walled sections of Q690 high strength steel was carried out. The results showed that the limiting flange width-thickness ratio and web height-thickness ratio for H-shaped members of Q690 high strength steel were recommended to be 11 and 65, respectively, in actual engineering. Also, an increase in web height-thickness ratio and axial compression ratio could lead to a significant decrease in the ductility of H-shaped members of thin-walled sections of Q690 high strength steel. The thinner and more flexible the section is, the larger the axial compression ratio is, further reducing the energy dissipation ability of the members.

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℃.

Hysteresis Properties of Corroded High Strength Steel

In order to study the effects of corrosion damage on the hysteresis properties of high strength steel (HSS), dry-wet cycle corrosion tests were conducted on Q690D steel to obtain 6 batches of corroded specimens, and cyclic loading tests were performed on them to analyse the degradation law of hysteresis curve, skeleton curve and hysteretic energy, and then establish the hysteresis constitutive model of corroded HSS steel. Results indicated that although the hysteresis curves of corroded specimens are still smooth and full, corrosion damage would result in the continuous decrease of peak stress, and lead to the linear reduction of hysteresis energy. Besides, the cyclic hardening coefficient K’ and cyclic hardening index n’ of HSS would also decrease linearly with corrosion degree. Based on these experimental results, a new hysteresis constitutive model for corroded HSS steel was proposed, and its validity was verified.

Analysis of Microstructure and Properties of High Strength Steel for Vehicle Axle

The vehicle axle is the main bearing part of the vehicle transmission, which needs to carry large power and torque. The axle is processed with high-strength steel. In order to verify the material properties of the axle and confirm whether it meets the design requirements, the chemical composition, mechanical properties, microstructure and metal inclusions of the axle are analyzed. The results show that the chemical composition of the material used in the axle meets the standard requirements, the parts with high hardness and tensile strength are tempered martensite, and the metal inclusions are mainly alumina inclusions, silicate inclusions and tin inclusions. Through the analysis of the performance of the axle, it is concluded that the axle material can meet the design requirements.

Effect of direct quenched and tempering temperature on the mechanical properties and microstructure of high strength steel

The effect of direct quenched (DQ) and tempering temperature on the microstructure and mechanical properties of high strength steel were studied by means of SEM, EBSD, TEM and mechanical properties test. The results showed that in DQ state, the tensile strength could reach 1420 Mpa, the yield strength could be 1050 Mpa, and the elongation was about 9.0%, impact energy at −20 °C was 59 J. High density entangled dislocation was distributed inside the lath and at the boundary. A small amount of Nb and Ti carbide was precipitated at the dislocation and lath boundary, and a small amount (about 2.15%) of residual austenite distributed between the lath. With the tempering temperature rising from 500 °C to 720 °C, the tensile strength of the experimental steel decreased from 1220 MPa to 840 MPa, the yield strength decreased from 1190 MPa to 780 MPa, the elongation increased from 10% to 13%, and the impact energy at −20 °C increased from 84 J to 153 J. When the tempering temperature rised from 500 °C to 640 °C, the structure was mainly composed of lath martensite and a large number of dislocations were still distributed inside the lath. The size of carbides precipitated inside and on the boundary of the lath was about 20–30 nm. When tempered at 680 °C, the structure was mainly composed of martensite and a small amount of polygonal ferrite. There were still a large number of entangled dislocations inside and on the boundary of martensite. The carbide precipitate at the matrix boundary and dislocation line was obviously coarsening (70–80 nm). When tempered at 720 °C, the microstructure was mainly polygonal ferrite, the dislocation density in the matrix significantly decreased, and the carbide precipitated at the matrix boundary and dislocation line significantly coarsened (about 100 nm). With the tempering temperature rising from 500 °C to 720 °C, the proportion of small-angle grain boundary was gradually decreased from 88.64% to 70.50%.

Effect of ultra-trace rare earth elements on continuous cooling transformation curve of low carbon steel * *Fund projects: Inner Mongolia Autonomous Region Natural Science Foundation (2018ms05052); Liaoning Provincial Natural Science Foundation (2019-kf-25-08); Inner Mongolia University of Technology (zd201510); Inner Mongolia University of technology science and technology innovation fund for college students. Ruifeng Dong (1972 -), female, from TUZUO banner, Inner

Two groups of low carbon steel with ultra-micro amount (less than 20 ppm) rare earth lanthanum and without rare earth element were taken as experimental objects. Continuous cooling transformation curves of two kinds of low carbon steels were drawn by Formaster-F II automatic phase transformation instrument, alloy phase method and hardness method. According to the measured CCT curve, the microstructure and hardness of low carbon steel under different cooling rates were studied and analysed. The results show that the addition of ultra-trace rare earth elements can increase the Ac1 and Ac3 points of low carbon steel by about 20 °C; the starting temperature of martensite transformation MS point decreased by 19 °C, and the end temperature Mf point decreased by 6 °C; at low cooling rate, the transformation range of ferrite is increased and that of pearlite is decreased; the starting temperature of bainite Bs point increased by 20 °C, and the end temperature of bainite Bf increased by 13 °C; at low cooling rate, the ferrite transformation range becomes larger, while at high cooling rate, the ferrite transformation range becomes smaller.

Thermo-diffusion galvanizing - an effective method of anticorrosion protection of high-strength fasteners. Methods of control

For reliable protection of bolt couplings in steel structures, it is necessary to apply a coating with increased corrosion resistance and having small thickness. In the Institute CNIIPSK the problem of increasing reliability and long life service of metal structures was solved by applying a thermos-diffusion coating on high-strength bolts. Studies of zinc coatings application methods effect on hydrogen cracking and residual physical and mechanical properties of high-strength steel showed, that thermos-diffusion galvanizing (TDG) is the most effective anticorrosion coating. Kinetic of zinc coating corrosion determined under conditions, imitating an action of a low-aggressive industrial atmosphere with SO2 and a seaside atmosphere. It was shown, that TDG coating has a higher corrosion resistance comparing with galvanized and hot dip galvanized coatings. The effect of anticorrosion protection is reached due to basic intermetalliс Srphase in the TDG coating. The results of the study allow to consider, that TDG coating provides a proper corrosion resistance and prevents corrosion cracking of high-strength bolts under conditions of low-aggressive industrial and sea-side atmosphere impact.

Experimental studies on mechanical properties of S700 MC steel at elevated temperatures

At elevated temperatures, the mechanical properties of high strength steel (HSS) reported in the literature have an observable scatter. They differ from design code values that are mainly based on experiments on mild steel. In this paper, the mechanical properties of S700 MC at elevated temperatures were investigated with steady state and transient state tensile tests. The reduction factors of yield strength started to decrease from 100 °C onwards, while the EN 1993-1-2 values have no decrease up to 400 °C. The reduction factors of proportional limit were below the code values up to 200 °C. The modulus of elasticity was consistent when using both monotonic and repeated loading but differed from the code values. Further comparisons of the mechanical properties of steels with the same strength grade with the values in the literature confirm the importance of testing HSSs produced with different manufacturing processes. The constitutive equations and representative material models proposed for S700 MC also support the implementation of a performance-based approach to structural fire safety design.

Effects of loading mode on mechanical properties of high strength steel Q690 and their application in coupon test

The coupon test methods specified in the current specifications do not satisfactorily address the strain rate effect on mechanical properties of materials, which may cause some deviations in the results. Therefore, there is a demand for alternative loading modes of coupon test. In this paper, effects of loading mode on the mechanical properties of high strength steel (HSS) Q690 were tested, considering monotonic tensile coupon test, tensile coupon test with displacement-controlled holds, and tensile coupon test with strain-controlled holds. Parameters such as pre-strain, loading rate, hold times, and hold duration were considered. Results show that the yield strength, ultimate strength, and ultimate strain of steel Q690 were hardly affected by the stress relaxation induced by holds, while increase with the increase of loading rate. The largest difference of the ultimate strength induced by loading mode was 6.2 MPa which is less than 1% of the ultimate strength of the material, and that of the ultimate strain was 5.8E-3. The stress drop during stress relaxation increases with the increase of pre-strain and strain rate. The normalized stress drop at the pre-strain of 0.04 could be 37.4% larger than that at the pre-strain of 0.01. The normalized stress drop of specimen with strain rate of 0.001/s could be 27.7% larger than that with strain rate of 0.0001/s. Tensile coupon test with two displacement-controlled holds is proposed to obtain the static mechanical properties of HSS Q690. Based on the test results, the values of parameters of the Cowper-Symonds model were calibrated to consider the effect of strain rate on the dynamic yield strength and ultimate strength, respectively, of steel Q690.

Effect of Multi-stage Heat Treatment on Microstructure and Properties of High Strength Steel for Flexible Riser

Effect of Multi-stage Heat Treatment on Microstructure and Properties of High Strength Steel for Flexible Riser

Experimental study of the effect of a slow-cooling heat treatment on the mechanical properties of high strength steels

This paper investigated a novel technique that uses a slow-cooling heat treatment to reduce the strength of existing steels to produce a regional soft area for energy dissipation. This research investigated the performance and affecting mechanism of the slow-cooling heat-treatment on the mechanical properties of high strength steels. A total of 18 heat-treating cases were applied to Q420 and Q690 steels. The relation of critical strengths and ductility of the materials versus the heat-treating parameters, such as peak temperature, cooling rate, holding time and terminate temperature, were investigated and discussed. The strength reduction from the slow-cooling heat treatment process in high strength steels and normal strength steels was discussed. The results indicated that the slow-cooling heat treatment can effectively reduce the yield and ultimate strengths of high strength steels. The Q690 steel displayed a more prominent strength reduction than the Q420 steel, especially for the yield strength. The heat treatment also improved the material ductility, especially for the Q690 steels. The peak temperature and cooling rate were two determining factors for the strength reduction performance. A heat treatment process with a 900–1000 °C peak temperature and a 1–2 °C/min cooling rate was suggested for the strength reduction of Q420 steel.

Improvement of Reliability of Fatigue Properties of High Strength Steel Applying Surface Crack Non-damaging Technology

Improvement of Reliability of Fatigue Properties of High Strength Steel Applying Surface Crack Non-damaging Technology