Based on the failure model of building structural steels under earthquake loading, the low cycle fatigue test at constant strain, the stochastical fatigue test under real earthquake load spectrum and the structural fa...Based on the failure model of building structural steels under earthquake loading, the low cycle fatigue test at constant strain, the stochastical fatigue test under real earthquake load spectrum and the structural fatigue test are carried out. The experimental results show that microalloying of V Ti and Nb can improve the anti-seismic propersties of steel bars. In the high strain and shori life range, both the static strength and ductility of steels are very important to increasing the low cycle fatigue resistance of steels.展开更多
The experiments were carried out to measure the mechanical properties ofthree grades of structural steels (Q235A, 16Mn and Q390E steel) at low temperature. It was shownthat the strength of the steels increases while t...The experiments were carried out to measure the mechanical properties ofthree grades of structural steels (Q235A, 16Mn and Q390E steel) at low temperature. It was shownthat the strength of the steels increases while the plasticity and toughness decrease as temperaturedrops. In the transitional area the toughness drops rapidly with temperature. Among the threestructural steels, Q390E steel has the best toughness and the lowest sensitivity.展开更多
A set of evaluation indicators based on corrosion ratio in theory for assessing the extent of pitting corrosion and performance reduction are proposed. In order to quantify the morphology of pitting corrosion and extr...A set of evaluation indicators based on corrosion ratio in theory for assessing the extent of pitting corrosion and performance reduction are proposed. In order to quantify the morphology of pitting corrosion and extract the evaluation indicators,the 3D profile data obtained by pitting morphology measurement are imported into a special written program to automatically determine the location of each corrosion pit and distill any desired data pertinent to the pitting morphology. The results show that this method seems to be effective to analyze the corroded surface and characterize the pitting morphology.展开更多
The resistance to crack propagation at earlier stage for a high strength structural steel with certain ductility and its correlation to microstructures,stress states,deformation history and strain characteristics have...The resistance to crack propagation at earlier stage for a high strength structural steel with certain ductility and its correlation to microstructures,stress states,deformation history and strain characteristics have been investigated.The resistance to crack propagation is mainly de- termined by the plastic constrain ahead of the crack tip,the elastic energy and plastic work absorbed in the stress-strain field.These are connected with the state function of triaxial stress.The deformation history and strain characteristic during deformation of material are described by the flow line in which the deformation history and strain characteristic restrain the crack initiation at stage Ⅱ and the crack propagation at stage Ⅲ.The strain hardening rate may sensitively reflect the stress distribution and micro-fracture mechanism in the interi- or of material.展开更多
The Monte- Carlo method is used to simulate the surface fatigue crack growth rate for offshore structural steel E36-Z35, and to determine the distributions and relevance of the parameters in the Paris equation. By thi...The Monte- Carlo method is used to simulate the surface fatigue crack growth rate for offshore structural steel E36-Z35, and to determine the distributions and relevance of the parameters in the Paris equation. By this method, the time and cost of fatigue crack propagation testing can be reduced. The application of the method is demonstrated by use of four sets of fatigue crack propagation data for offshore structural steel E36-Z35. A comparison of the test data with the theoretical prediction for surface crack growth rate shows the application of the simulation method to the fatigue crack propagation tests is successful.展开更多
By introducing aparameter of difference in ferrite formation temperature between binary Fe-C and multicomponent system,and referring to the thermodynamic model for Fe-C binary system,a simplified thermodynamic model f...By introducing aparameter of difference in ferrite formation temperature between binary Fe-C and multicomponent system,and referring to the thermodynamic model for Fe-C binary system,a simplified thermodynamic model for pro-eutectoid ferrite formation in Fe-ΣXiC multicomponent structural steels(Xi=Mn,Si,Mo,Cr,Ni or Ti,etc)was suggested.The comparison of the calculated Ae3 temperatures with the measured data of steels 42 shows that the relative standard deviation and root-mean-square(RMS)error between them are only 0.71% and 8.92 K,respectively.However,the deviations between the same measured data and the values calculated from the superelement model are as high as 1.86% and 23.83 K,respectively.It can be concluded that the simplified thermodynamic model for pro-eutectoid ferrite formation in multicomponent structural steels is acceptable and the calculated Ae3 temperatures are in good agreement with the experimental data.展开更多
For the research on steel structure in fire,it is very important to determine the properties of structural steel at elevated temperature.Up to now,the high-temperature properties of material is believed to be related ...For the research on steel structure in fire,it is very important to determine the properties of structural steel at elevated temperature.Up to now,the high-temperature properties of material is believed to be related to only temperature state,which is not precise enough to simulate the behavior of steel structures under different combinations of heating,cooling,loading,and unloading.To analyze the influence of the temperature-load history on the steel properties,a series of tests were carried out under different temperature-load paths about steel Q235,which is widely used in steel structures in China.In this paper,the method to set the temperature-load paths was introduced;the variety regulation of steel properties changing with temperature was analyzed under different paths;according to experimental results,the formulas of elastic modulus and yield strength at elevated temperature were fitted,and the stress-strain-temperature 3D relationships of structural steel under different paths were presented.展开更多
To analyze the seismic response of steel structure isolation systems under long-period seismic motion,a 9-story steel frame building was selected as the subject.Five steel structure finite element models were establis...To analyze the seismic response of steel structure isolation systems under long-period seismic motion,a 9-story steel frame building was selected as the subject.Five steel structure finite element models were established using SAP2000.Response spectrum analysis was conducted on the seismic motion to determine if it adhered to the characteristics of long-period seismic motion.Modal analysis of each structural model revealed that the isolation structure significantly prolonged the structural natural vibration period and enhanced seismic performance.Base reactions and floor displacements of various structures notably increased under long-period seismic motion compared to regular seismic activity.Placing isolation bearings in the lower part of the structure proved more effective under long-period seismic motion.In seismic design engineering,it is essential to consider the impact of long-period seismic motion on structures and the potential failure of isolation bearings.展开更多
Alloying structural steel used for mechanical structures has a high requirement for cleanliness because its failures are greatly affected by non-metallic inclusions and total oxygen content in steel.It has been report...Alloying structural steel used for mechanical structures has a high requirement for cleanliness because its failures are greatly affected by non-metallic inclusions and total oxygen content in steel.It has been reported by some steelmaking plants to have some problems in controlling total oxygen content and inclusions during alloying structural steel production.For this purpose,cleanliness control in 0.2C-0.3Si-0.6Mn-1Cr-0.2Mo steel was investigated.Firstly,low melting temperature zone(≤1873 K) of CaO-Al2O3-MgO system and formation condition of low melting temperature inclusions were investigated through thermodynamic equilibrium calculation.On this basis,industrial tests were carried out.Through sampling at different stages,transformation of oxide inclusions and change of total oxygen content in steel were studied.The results show that:in order to form CaO-Al2O3-MgO system inclusions with low melting temperature,mass percent of Al2O3,MgO and CaO in inclusions should be controlled from 37.6% to 70.8%,0 to 17.4% and 25.5% to 60.6%;For the condition of 1873 K and 0.05%(mass percent) dissolved aluminum in steel,the activities of dissolved oxygen,magnesium and calcium should be controlled as 0.298×10-4-2×10-4,0.1×10-5-40×10-5 and 0.8×10-8-180×10-8 respectively.With secondary refining proceeding,average total oxygen content and inclusion amount decrease,the type of most inclusions changes from Al2O3 after tapping to Al2O3-MgO after top slag is formed during ladle furnace refining and finally to CaO-Al2O3-MgO after RH treatment.In the final products,average total oxygen content was 12.7×10-6 and most inclusions were in spherical shape with size less than 5 μm.展开更多
Lamellar tearing and crack-induced brittle failures along steel plates in the through-thickness direction seriously threaten the safety and reliability of steel thick plate structures in construction and service, espe...Lamellar tearing and crack-induced brittle failures along steel plates in the through-thickness direction seriously threaten the safety and reliability of steel thick plate structures in construction and service, especially at low ambient temperatures. Three kinds of tests, including uniaxial tensile tests, Charpy V-Notch impact tests, and three-point bending (TPB) tests were performed at normal and low temperatures to investigate the through-thickness mechanical properties, impact and fraclure toughness of Q345B structural steel plates with thicknesses from 60 to 165 mm. The test specimens were mainly sampled along the through-thickness direction of the plate, but transverse specimens along the rolling direction were also involved. The ductility index (percentage reduction of area), impact toughness index (Charpy impact energy), and fracture toughness index (critical crack tip opening displacement (CTOD) values) all decrease as the temperature declines. All the mechanical properties and the impact and fracture toughness along the through-thickness direction are worse than those along the rolling direction. The results also offer experimental support for the determination of an evaluation indicator for structural steel thick plates with through-thickness characteristics.展开更多
This article reports a new generation of Q460 multi-functional construction structural steel,which has high strength(yield strength larger than 460 MPa),excellent toughness(higher than 110 J/cm^(2) at-60 ℃),lower yie...This article reports a new generation of Q460 multi-functional construction structural steel,which has high strength(yield strength larger than 460 MPa),excellent toughness(higher than 110 J/cm^(2) at-60 ℃),lower yield ratio(lower than 0.8),good fire resistance(yield strength at 600 ℃ larger than two-thirds of its room-temperature yield strength)and better corrosion resistance.The eff ects of finish cooling temperature(FCT)on the microstructure and properties were studied by scanning electron microscopy(SEM),transmission electron microscopy(TEM),emission electron probe micro-analysis(EPMA),electron backscattering diff raction(EBSD),tensile tester,impact tester,periodic immersion cycle acceleration test and electrochemical experiment.The results show that the strength and toughness are simultaneously improved by decreasing the FCT due to more lath-like bainite with large number of dislocations,refined martensite/austenite(M/A)with higher carbon concentration and increased high angle boundaries.In addition,the fire resistance of the newly developed Q460 steel is obviously better than the conventional one,which is mainly due to non-recrystallized lath-like bainite with high dislocation density at elevated temperature.The corrosion resistance of the new Q460 steel is also improved due to the addition of Cu and Cr.展开更多
Value-added applications of niobium (Nb) microalloyed steels continue to be developed for commercial implementation to meet increased material demands and improved properties for 21st century structural applications. ...Value-added applications of niobium (Nb) microalloyed steels continue to be developed for commercial implementation to meet increased material demands and improved properties for 21st century structural applications. These applications demand Nb-bearing steels that deliver improved toughness, fracture and fire resistance and weldability. Such applications include medium and jumbo beam, boiler, bridge, container, heavy equipment, long product, pressure vessel, ship, storage tank and windtower applications. Steel producers are challenged to develop microalloyed steel grades that cost effectively meet end user demands for higher strength at thinner cross sections, better low temperature toughness to resist brittle fracture in building, pressure vessel and ship structures, sustain higher loads per unit area in earthquake and hurricane zone product applications, demonstrate improved fire-resistance in buildings, bridges and tunnels and provide overall improved weldability. Niobium is often a key element to achieve these results. This paper will discuss Nb market opportunities and key operational practices required to successfully melt, cast and roll these high strength steel grades. Niobium process metallurgy is important to leverage the ability of niobium to obtain ultra-fine grain, homogeneous structural steel microstructures with superior mechanical properties. The process metallurgy, physical metallurgy and resultant properties are significantly determined by mill capabilities, mill practices, operational understanding and the culture of the steel mill. The optimal combination and implementation aspects that are unique to each mill we call metallurgical operational integration (MOI) . MOI is the bridge that links the product requirements to mill capability and process implementation.展开更多
The effect of tempering on carbides and hydrogen embrittlement in E690 high strength marine structural steel has been investigated.The steel was tempered at 600℃ for 1–3 h.Detailed characterization was carried out t...The effect of tempering on carbides and hydrogen embrittlement in E690 high strength marine structural steel has been investigated.The steel was tempered at 600℃ for 1–3 h.Detailed characterization was carried out to characterize the microstructure,especially the dislocation density and grain size.The hydrogen permeation test and thermal desorption spectroscopy test were also implemented.The dislocation density decreases,the amount of carbide increases,and carbides(M_(23)C_(6) and MX)coarsen with the tempering time increasing.After tempered at 600℃ for 3 h,the diffusible hydrogen trapped by lattice and dislocation decreases while the non-diffusible hydrogen trapped by carbides increases,leading to the best hydrogen embrittlement resistance,although hydrogen diffuses rapidly due to the reduction of dislocation density.And the fracture mode changes from a combination of brittle cleavage and ductile dimpled fracture to fully ductile dimple fracture under hydrogen charging condition.Moreover,a phenomenon that hydrogen accelerates the dislocations movement of the steel during deformation was observed,which is related to the fact that hydrogen enhanced localized plasticity mechanism.展开更多
The influence of rare earth lanthanum and cerium on impact property of structural alloy steel with extra low sulfur and oxygen was studied by impact test and microanalysis. The results showed that rare earths increase...The influence of rare earth lanthanum and cerium on impact property of structural alloy steel with extra low sulfur and oxygen was studied by impact test and microanalysis. The results showed that rare earths increased impact power of the steel when their contents were about 0.005%. Proper addition of rare earths could purify grain boundaries and decrease amount of inclusions, and reduced the possibility of crack growth along grain boundaries and through inclusions. Therefore, such steel could absorb more crack growth energy while it was impacted. However, if the content of rare earths is excessive, the grain boundary would be weakened and brittle-hard phosphates and Fe-RE intermetallic would be formed, which worsened impact toughness of steel.展开更多
This paper introduces CBFEM (component-based finite element model) which is a new method to analyze and design connections of steel structures. Design focused CM (component model) is compared to FEM (finite eleme...This paper introduces CBFEM (component-based finite element model) which is a new method to analyze and design connections of steel structures. Design focused CM (component model) is compared to FEM (finite elements models). Procedure for composition of a model based on usual production process is used in CBFEM. Its results are compared to those obtained by component method for portal frame eaves moment connection with good agreement. Design of moment resistant column base is demonstrated by a case loaded by two directional bending moments and normal force. Interaction of several connections in one complex joint is explained in the last example. This paper aims to provide structural engineers with a new tool to effectively analyze and design various joints of steel structures.展开更多
Work-hardening behaviour of type 316 austenitic stainless steel having difFerent initial dislocation structures introduced by swaging to various levels is analysed by a simplified Kock's model which takes into acc...Work-hardening behaviour of type 316 austenitic stainless steel having difFerent initial dislocation structures introduced by swaging to various levels is analysed by a simplified Kock's model which takes into account the structural changes through the dislocation accumulation and annihilation process during deformation. The dislocation accumulation and annihilation factors show a temperature and structure dependence. The dislocation annihilation factor shows a plateau or decreasing tendency in the dynamic strain ageing (DSA) temperature range. This is attributed as either due to dislocation accumulation being more pronounced than dislocation annihilation or as due to precipitates being formed at DSA temperatures acting as obstacles to dislocation motion in the DSA temperature range.展开更多
The problem of noise has always been highlighted in assembled steel structure houses.Therefore,it is necessary to use effective soundproof measures where steel beams intersect with the reserved line pipe openings,door...The problem of noise has always been highlighted in assembled steel structure houses.Therefore,it is necessary to use effective soundproof measures where steel beams intersect with the reserved line pipe openings,doors,windows,elevator shafts,and other locations.In this paper,we will investigate the areas with subpar soundproof performance in an assembled steel structure residential project and propose suitable noise control measures to address this issue.展开更多
Because of urbanization,land resources in China’s cities has become increasingly scarce.Therefore,modern buildings are becoming taller,making high-rise steel frame structures the new favorite of the construction indu...Because of urbanization,land resources in China’s cities has become increasingly scarce.Therefore,modern buildings are becoming taller,making high-rise steel frame structures the new favorite of the construction industry.However,the construction of high-rise steel frame structures requires advanced technology.If the construction technology is effectively implemented and the welding techniques of the construction personnel align with the requirements for high-rise steel frame structures,it can help mitigate deformations in the steel structure,thus preserving the overall construction quality of high-rise steel frame structures.To enhance the applicability of steel frame structures in high-rise buildings,this paper focuses on analyzing the optimization path for the construction process of high-rise steel frame structures.It introduces a tailored approach to control welding-induced deformations in steel frame structures,aiming to make a valuable contribution to the advancement of China’s construction industry.展开更多
Shear-type structures are common structural forms in industrial and civil buildings,such as concrete and steel frame structures.Fault diagnosis of shear-type structures is an important topic to ensure the normal use o...Shear-type structures are common structural forms in industrial and civil buildings,such as concrete and steel frame structures.Fault diagnosis of shear-type structures is an important topic to ensure the normal use of structures.The main drawback of existing damage assessment methods is that they require accurate structural finite element models for damage assessment.However,for many shear-type structures,it is difficult to obtain accurate FEM.In order to avoid finite elementmodeling,amodel-freemethod for diagnosing shear structure defects is developed in this paper.This method only needs to measure a few low-order vibration modes of the structure.The proposed defect diagnosis method is divided into two stages.In the first stage,the location of defects in the structure is determined based on the difference between the virtual displacements derived from the dynamic flexibility matrices before and after damage.In the second stage,damage severity is evaluated based on an improved frequency sensitivity equation.Themain innovations of this method lie in two aspects.The first innovation is the development of a virtual displacement difference method for determining the location of damage in the shear structure.The second is to improve the existing frequency sensitivity equation to calculate the damage degree without constructing the finite elementmodel.Thismethod has been verified on a numerical example of a 22-story shear frame structure and an experimental example of a three-story steel shear structure.Based on numerical analysis and experimental data validation,it is shown that this method only needs to use the low-order modes of structural vibration to diagnose the defect location and damage degree,and does not require finite element modeling.The proposed method should be a very simple and practical defect diagnosis technique in engineering practice.展开更多
The paper discusses the structural design of a futuristic 700℃ MS(Molten salt)Storage Shell,which considers many elements in providing an adequate and comprehensive design.In designing the structural carbon steel for...The paper discusses the structural design of a futuristic 700℃ MS(Molten salt)Storage Shell,which considers many elements in providing an adequate and comprehensive design.In designing the structural carbon steel for the tank,temperature is an important consideration because steel has a yield strength at 700℃,that is 33%of its nominal yield,while the Young’s Modulus at 700℃ is 50%of its nominal Young’s Modulus.At this temperature,thermal stresses can yield or tear the structural steel unless free expansion of the structure is allowed.This is accomplished with sand layers below each layer of steel and by including a small gap behind the side carbon steel layer.A roof shell design for the tank is also presented in this paper,comparing various roof shell types and their designs.All designs include thermal insulation and an inner stainless steel corrosion layer to protect the structural and thermal insulation elements of the tank from the MS.展开更多
文摘Based on the failure model of building structural steels under earthquake loading, the low cycle fatigue test at constant strain, the stochastical fatigue test under real earthquake load spectrum and the structural fatigue test are carried out. The experimental results show that microalloying of V Ti and Nb can improve the anti-seismic propersties of steel bars. In the high strain and shori life range, both the static strength and ductility of steels are very important to increasing the low cycle fatigue resistance of steels.
基金This work was financially supported by the National Natural Science Foundation of China (No. 50078029).
文摘The experiments were carried out to measure the mechanical properties ofthree grades of structural steels (Q235A, 16Mn and Q390E steel) at low temperature. It was shownthat the strength of the steels increases while the plasticity and toughness decrease as temperaturedrops. In the transitional area the toughness drops rapidly with temperature. Among the threestructural steels, Q390E steel has the best toughness and the lowest sensitivity.
基金Sponsored by the National Natural Science Foundation of China(Grant No.51378417)Program for Changjiang Scholars and Innovative Research Team in University(IRT13089)PhD Innovation Fund of Xi'an University of Architecture and Technology
文摘A set of evaluation indicators based on corrosion ratio in theory for assessing the extent of pitting corrosion and performance reduction are proposed. In order to quantify the morphology of pitting corrosion and extract the evaluation indicators,the 3D profile data obtained by pitting morphology measurement are imported into a special written program to automatically determine the location of each corrosion pit and distill any desired data pertinent to the pitting morphology. The results show that this method seems to be effective to analyze the corroded surface and characterize the pitting morphology.
文摘The resistance to crack propagation at earlier stage for a high strength structural steel with certain ductility and its correlation to microstructures,stress states,deformation history and strain characteristics have been investigated.The resistance to crack propagation is mainly de- termined by the plastic constrain ahead of the crack tip,the elastic energy and plastic work absorbed in the stress-strain field.These are connected with the state function of triaxial stress.The deformation history and strain characteristic during deformation of material are described by the flow line in which the deformation history and strain characteristic restrain the crack initiation at stage Ⅱ and the crack propagation at stage Ⅲ.The strain hardening rate may sensitively reflect the stress distribution and micro-fracture mechanism in the interi- or of material.
文摘The Monte- Carlo method is used to simulate the surface fatigue crack growth rate for offshore structural steel E36-Z35, and to determine the distributions and relevance of the parameters in the Paris equation. By this method, the time and cost of fatigue crack propagation testing can be reduced. The application of the method is demonstrated by use of four sets of fatigue crack propagation data for offshore structural steel E36-Z35. A comparison of the test data with the theoretical prediction for surface crack growth rate shows the application of the simulation method to the fatigue crack propagation tests is successful.
基金Item Sponsored by National Natural Science Foundation of China(50075053)
文摘By introducing aparameter of difference in ferrite formation temperature between binary Fe-C and multicomponent system,and referring to the thermodynamic model for Fe-C binary system,a simplified thermodynamic model for pro-eutectoid ferrite formation in Fe-ΣXiC multicomponent structural steels(Xi=Mn,Si,Mo,Cr,Ni or Ti,etc)was suggested.The comparison of the calculated Ae3 temperatures with the measured data of steels 42 shows that the relative standard deviation and root-mean-square(RMS)error between them are only 0.71% and 8.92 K,respectively.However,the deviations between the same measured data and the values calculated from the superelement model are as high as 1.86% and 23.83 K,respectively.It can be concluded that the simplified thermodynamic model for pro-eutectoid ferrite formation in multicomponent structural steels is acceptable and the calculated Ae3 temperatures are in good agreement with the experimental data.
文摘For the research on steel structure in fire,it is very important to determine the properties of structural steel at elevated temperature.Up to now,the high-temperature properties of material is believed to be related to only temperature state,which is not precise enough to simulate the behavior of steel structures under different combinations of heating,cooling,loading,and unloading.To analyze the influence of the temperature-load history on the steel properties,a series of tests were carried out under different temperature-load paths about steel Q235,which is widely used in steel structures in China.In this paper,the method to set the temperature-load paths was introduced;the variety regulation of steel properties changing with temperature was analyzed under different paths;according to experimental results,the formulas of elastic modulus and yield strength at elevated temperature were fitted,and the stress-strain-temperature 3D relationships of structural steel under different paths were presented.
基金Anhui Province Young and Middle-aged Teacher Training Action Excellent Young Teacher Cultivation Project(YQYB2023162)Anhui University Natural Science Research Key Project(KJ2021A1410)Special Topic of the Higher Education Institution Scientific Research Development Center of the Ministry of Education(ZJXF2022080)。
文摘To analyze the seismic response of steel structure isolation systems under long-period seismic motion,a 9-story steel frame building was selected as the subject.Five steel structure finite element models were established using SAP2000.Response spectrum analysis was conducted on the seismic motion to determine if it adhered to the characteristics of long-period seismic motion.Modal analysis of each structural model revealed that the isolation structure significantly prolonged the structural natural vibration period and enhanced seismic performance.Base reactions and floor displacements of various structures notably increased under long-period seismic motion compared to regular seismic activity.Placing isolation bearings in the lower part of the structure proved more effective under long-period seismic motion.In seismic design engineering,it is essential to consider the impact of long-period seismic motion on structures and the potential failure of isolation bearings.
基金Item Sponsored by National Basic Research Program of China(2010CB630806)
文摘Alloying structural steel used for mechanical structures has a high requirement for cleanliness because its failures are greatly affected by non-metallic inclusions and total oxygen content in steel.It has been reported by some steelmaking plants to have some problems in controlling total oxygen content and inclusions during alloying structural steel production.For this purpose,cleanliness control in 0.2C-0.3Si-0.6Mn-1Cr-0.2Mo steel was investigated.Firstly,low melting temperature zone(≤1873 K) of CaO-Al2O3-MgO system and formation condition of low melting temperature inclusions were investigated through thermodynamic equilibrium calculation.On this basis,industrial tests were carried out.Through sampling at different stages,transformation of oxide inclusions and change of total oxygen content in steel were studied.The results show that:in order to form CaO-Al2O3-MgO system inclusions with low melting temperature,mass percent of Al2O3,MgO and CaO in inclusions should be controlled from 37.6% to 70.8%,0 to 17.4% and 25.5% to 60.6%;For the condition of 1873 K and 0.05%(mass percent) dissolved aluminum in steel,the activities of dissolved oxygen,magnesium and calcium should be controlled as 0.298×10-4-2×10-4,0.1×10-5-40×10-5 and 0.8×10-8-180×10-8 respectively.With secondary refining proceeding,average total oxygen content and inclusion amount decrease,the type of most inclusions changes from Al2O3 after tapping to Al2O3-MgO after top slag is formed during ladle furnace refining and finally to CaO-Al2O3-MgO after RH treatment.In the final products,average total oxygen content was 12.7×10-6 and most inclusions were in spherical shape with size less than 5 μm.
基金the National Natural Science Foundation of China,the Specialized Research Fund for the Doctoral Program of Higher Education of China
文摘Lamellar tearing and crack-induced brittle failures along steel plates in the through-thickness direction seriously threaten the safety and reliability of steel thick plate structures in construction and service, especially at low ambient temperatures. Three kinds of tests, including uniaxial tensile tests, Charpy V-Notch impact tests, and three-point bending (TPB) tests were performed at normal and low temperatures to investigate the through-thickness mechanical properties, impact and fraclure toughness of Q345B structural steel plates with thicknesses from 60 to 165 mm. The test specimens were mainly sampled along the through-thickness direction of the plate, but transverse specimens along the rolling direction were also involved. The ductility index (percentage reduction of area), impact toughness index (Charpy impact energy), and fracture toughness index (critical crack tip opening displacement (CTOD) values) all decrease as the temperature declines. All the mechanical properties and the impact and fracture toughness along the through-thickness direction are worse than those along the rolling direction. The results also offer experimental support for the determination of an evaluation indicator for structural steel thick plates with through-thickness characteristics.
基金financially supported by the Key Research and Development Program of Hebei Province of China(Grant No.18211019D)the"333 Talent Project"of Hebei(Grant No.A201803007)the Technical Development Program between HBIS Company Limited and NEU(Contract No.2019040200044)。
文摘This article reports a new generation of Q460 multi-functional construction structural steel,which has high strength(yield strength larger than 460 MPa),excellent toughness(higher than 110 J/cm^(2) at-60 ℃),lower yield ratio(lower than 0.8),good fire resistance(yield strength at 600 ℃ larger than two-thirds of its room-temperature yield strength)and better corrosion resistance.The eff ects of finish cooling temperature(FCT)on the microstructure and properties were studied by scanning electron microscopy(SEM),transmission electron microscopy(TEM),emission electron probe micro-analysis(EPMA),electron backscattering diff raction(EBSD),tensile tester,impact tester,periodic immersion cycle acceleration test and electrochemical experiment.The results show that the strength and toughness are simultaneously improved by decreasing the FCT due to more lath-like bainite with large number of dislocations,refined martensite/austenite(M/A)with higher carbon concentration and increased high angle boundaries.In addition,the fire resistance of the newly developed Q460 steel is obviously better than the conventional one,which is mainly due to non-recrystallized lath-like bainite with high dislocation density at elevated temperature.The corrosion resistance of the new Q460 steel is also improved due to the addition of Cu and Cr.
文摘Value-added applications of niobium (Nb) microalloyed steels continue to be developed for commercial implementation to meet increased material demands and improved properties for 21st century structural applications. These applications demand Nb-bearing steels that deliver improved toughness, fracture and fire resistance and weldability. Such applications include medium and jumbo beam, boiler, bridge, container, heavy equipment, long product, pressure vessel, ship, storage tank and windtower applications. Steel producers are challenged to develop microalloyed steel grades that cost effectively meet end user demands for higher strength at thinner cross sections, better low temperature toughness to resist brittle fracture in building, pressure vessel and ship structures, sustain higher loads per unit area in earthquake and hurricane zone product applications, demonstrate improved fire-resistance in buildings, bridges and tunnels and provide overall improved weldability. Niobium is often a key element to achieve these results. This paper will discuss Nb market opportunities and key operational practices required to successfully melt, cast and roll these high strength steel grades. Niobium process metallurgy is important to leverage the ability of niobium to obtain ultra-fine grain, homogeneous structural steel microstructures with superior mechanical properties. The process metallurgy, physical metallurgy and resultant properties are significantly determined by mill capabilities, mill practices, operational understanding and the culture of the steel mill. The optimal combination and implementation aspects that are unique to each mill we call metallurgical operational integration (MOI) . MOI is the bridge that links the product requirements to mill capability and process implementation.
基金The authors acknowledge the generous financial support from National Key R&D Program of China(No.2016YFB0300601)the National Natural Science Foundation of China(Nos.U1564203,51831002 and 51571141)+2 种基金The authors also gratefully acknowledge the support sponsored by Program of Shanghai Academic Research Leader 18XD1402200provided by Shanghai Key Laboratory of Materials Laser Processing and Modification,Shanghai Jiao Tong UniversityBesides,this research was supported by the TESCAN CHINA.
文摘The effect of tempering on carbides and hydrogen embrittlement in E690 high strength marine structural steel has been investigated.The steel was tempered at 600℃ for 1–3 h.Detailed characterization was carried out to characterize the microstructure,especially the dislocation density and grain size.The hydrogen permeation test and thermal desorption spectroscopy test were also implemented.The dislocation density decreases,the amount of carbide increases,and carbides(M_(23)C_(6) and MX)coarsen with the tempering time increasing.After tempered at 600℃ for 3 h,the diffusible hydrogen trapped by lattice and dislocation decreases while the non-diffusible hydrogen trapped by carbides increases,leading to the best hydrogen embrittlement resistance,although hydrogen diffuses rapidly due to the reduction of dislocation density.And the fracture mode changes from a combination of brittle cleavage and ductile dimpled fracture to fully ductile dimple fracture under hydrogen charging condition.Moreover,a phenomenon that hydrogen accelerates the dislocations movement of the steel during deformation was observed,which is related to the fact that hydrogen enhanced localized plasticity mechanism.
基金Project supported bythe Ministry of Science and Technology of China (2002BA315A-5)
文摘The influence of rare earth lanthanum and cerium on impact property of structural alloy steel with extra low sulfur and oxygen was studied by impact test and microanalysis. The results showed that rare earths increased impact power of the steel when their contents were about 0.005%. Proper addition of rare earths could purify grain boundaries and decrease amount of inclusions, and reduced the possibility of crack growth along grain boundaries and through inclusions. Therefore, such steel could absorb more crack growth energy while it was impacted. However, if the content of rare earths is excessive, the grain boundary would be weakened and brittle-hard phosphates and Fe-RE intermetallic would be formed, which worsened impact toughness of steel.
文摘This paper introduces CBFEM (component-based finite element model) which is a new method to analyze and design connections of steel structures. Design focused CM (component model) is compared to FEM (finite elements models). Procedure for composition of a model based on usual production process is used in CBFEM. Its results are compared to those obtained by component method for portal frame eaves moment connection with good agreement. Design of moment resistant column base is demonstrated by a case loaded by two directional bending moments and normal force. Interaction of several connections in one complex joint is explained in the last example. This paper aims to provide structural engineers with a new tool to effectively analyze and design various joints of steel structures.
文摘Work-hardening behaviour of type 316 austenitic stainless steel having difFerent initial dislocation structures introduced by swaging to various levels is analysed by a simplified Kock's model which takes into account the structural changes through the dislocation accumulation and annihilation process during deformation. The dislocation accumulation and annihilation factors show a temperature and structure dependence. The dislocation annihilation factor shows a plateau or decreasing tendency in the dynamic strain ageing (DSA) temperature range. This is attributed as either due to dislocation accumulation being more pronounced than dislocation annihilation or as due to precipitates being formed at DSA temperatures acting as obstacles to dislocation motion in the DSA temperature range.
文摘The problem of noise has always been highlighted in assembled steel structure houses.Therefore,it is necessary to use effective soundproof measures where steel beams intersect with the reserved line pipe openings,doors,windows,elevator shafts,and other locations.In this paper,we will investigate the areas with subpar soundproof performance in an assembled steel structure residential project and propose suitable noise control measures to address this issue.
文摘Because of urbanization,land resources in China’s cities has become increasingly scarce.Therefore,modern buildings are becoming taller,making high-rise steel frame structures the new favorite of the construction industry.However,the construction of high-rise steel frame structures requires advanced technology.If the construction technology is effectively implemented and the welding techniques of the construction personnel align with the requirements for high-rise steel frame structures,it can help mitigate deformations in the steel structure,thus preserving the overall construction quality of high-rise steel frame structures.To enhance the applicability of steel frame structures in high-rise buildings,this paper focuses on analyzing the optimization path for the construction process of high-rise steel frame structures.It introduces a tailored approach to control welding-induced deformations in steel frame structures,aiming to make a valuable contribution to the advancement of China’s construction industry.
基金the Zhejiang Public Welfare Technology Application Research Project(LGF22E080021)Ningbo Natural Science Foundation Project(202003N4169)+2 种基金Natural Science Foundation of China(11202138,52008215)the Natural Science Foundation of Zhejiang Province,China(LQ20E080013)the Major Special Science and Technology Project(2019B10076)of“Ningbo Science and Technology Innovation 2025”.
文摘Shear-type structures are common structural forms in industrial and civil buildings,such as concrete and steel frame structures.Fault diagnosis of shear-type structures is an important topic to ensure the normal use of structures.The main drawback of existing damage assessment methods is that they require accurate structural finite element models for damage assessment.However,for many shear-type structures,it is difficult to obtain accurate FEM.In order to avoid finite elementmodeling,amodel-freemethod for diagnosing shear structure defects is developed in this paper.This method only needs to measure a few low-order vibration modes of the structure.The proposed defect diagnosis method is divided into two stages.In the first stage,the location of defects in the structure is determined based on the difference between the virtual displacements derived from the dynamic flexibility matrices before and after damage.In the second stage,damage severity is evaluated based on an improved frequency sensitivity equation.Themain innovations of this method lie in two aspects.The first innovation is the development of a virtual displacement difference method for determining the location of damage in the shear structure.The second is to improve the existing frequency sensitivity equation to calculate the damage degree without constructing the finite elementmodel.Thismethod has been verified on a numerical example of a 22-story shear frame structure and an experimental example of a three-story steel shear structure.Based on numerical analysis and experimental data validation,it is shown that this method only needs to use the low-order modes of structural vibration to diagnose the defect location and damage degree,and does not require finite element modeling.The proposed method should be a very simple and practical defect diagnosis technique in engineering practice.
文摘The paper discusses the structural design of a futuristic 700℃ MS(Molten salt)Storage Shell,which considers many elements in providing an adequate and comprehensive design.In designing the structural carbon steel for the tank,temperature is an important consideration because steel has a yield strength at 700℃,that is 33%of its nominal yield,while the Young’s Modulus at 700℃ is 50%of its nominal Young’s Modulus.At this temperature,thermal stresses can yield or tear the structural steel unless free expansion of the structure is allowed.This is accomplished with sand layers below each layer of steel and by including a small gap behind the side carbon steel layer.A roof shell design for the tank is also presented in this paper,comparing various roof shell types and their designs.All designs include thermal insulation and an inner stainless steel corrosion layer to protect the structural and thermal insulation elements of the tank from the MS.