Conceptual study of X-braced frames with different steel grades using cyclic half-scale tests

In this paper, an experimental and analytical study of two half-scale steel X-braced flames with equal nominal shear strength under cyclic loading is described. In these tests, all members except the braces are similar. The braces are made of various steel grades to monitor the effects of seismic excitation. Internal stiffeners are employed to limit the local buckling and increase the fracture life of the steel bracing. A heavy central core is introduced at the intersection of the braces to decrease their effective length. Recent seismic specifications are considered in the design of the X-braced frame members to verify their efficiency. The failure modes of the X-braced frames are also illustrated. It is observed that the energy dissipation capacity, ultimate load capacity and ductility of the system increase considerably by using lower grade steel and proposed detailing. Analytical modeling of the specimens using nonlinear finite element software supports the experimental findings.

Preparation of special silicon steel grade MgO from hydromagnesite

A preparation technology of MgO powder used in special silicon steel from hydromagnesite mineral has been developed. The preparation technology includes the following steps： （1） calcining the hydromagnesite at 700-750°C for 1.5-2 h; （2） hydrating the calcined hydromagnesite to be slurry containing the solid-liquid ratio of 15-20 g？L？1; （3） acquiring Mg（HCO3）2 solution by carbonating the slurry, the carbonation temperature, CO2 pressure, and end point PH value of carbonation are less than 40°C, 0.4-0.6 MPa, and 7 respectively during the carbonation process; （4） preparing precipitated basic magnesium carbonate by thermally decomposing the Mg（HCO3）2 solution at 90-100°C; （5） obtaining the MgO product by calcining the precipitated basic magnesium carbonate at 850-950°C for 30-60 min, and adopting flowing nitrogen during the cooling process. By using this technology, more than 80wt% magnesium in hydromagnesite mineral can be extracted, and high-performance MgO products used in special silicon steel can be ob- tained.

Metallurgical analysis of a failed maraging steel shear screw used in the band separation system of a satellite launch vehicle

Maraging steels have excellent combination of strength and toughness and are extensively used for a variety of aerospace applications. In one such critical application, this steel was used to fabricate shear screws of a stage separation system in a satellite launch vehicle. During assembly preparations, one of the shear screws which connected the separation band and band end block has failed at the first thread. Microstructural analysis revealed that the crack originated from the root of the thread and propagated in an intergranular mode. The failure is attributed to combined effect of stress and corrosion leading to stress corrosion cracking.

Development history and technological progress of non-oriented electrical steel sheets at Baosteel

This paper briefly summarized the development history, product catalogue and magnetic properties of non- oriented electrical steel sheets at Baosteel, as well as the development and application of high-value-added steel grades. Recent advances in manufacturing electrical steel sheets were also introduced, including technologies for controlling inclusion,for producing high-grade steel strips by a tandem rolling mill and for controlling the transverse thickness difference of steel sheets, and the development of environmentally friendly coatings.

An Investigation of Creep Resistance in Grade 91 Steel through Computational Thermodynamics

This study was conducted to understand the relationship between various critical temperatures and the stability of the secondary phases inside the heat-affected-zone(HAZ)of welded Grade 91(Gr.91)steel parts.Type IV cracking has been observed in the HAZ,and it is widely accepted that the stabilities of the secondary phases in Gr.91 steel are critical to the creep resistance,which is related to the crack failure of this steel.In this work,the stabilities of the secondary phases,including those of the M23C6,MX,and Z phases,were simulated by computational thermodynamics.Equilibrium cooling and Scheil simulations were carried out in order to understand the phase stability in welded Gr.91 steel.The effect of four critical temperatures—that is,Acl(the threshold temperature at which austenite begins to form),Ac3(the threshold temperature at which ferrite is fully transformed into austenite),and the M23C6 and Z phase threshold temperatures—on the thickness of the HAZ and phase stability in the HAZ is discussed.Overall,the simulations presented in this paper explain the mechanisms that can affect the creep resistance of Gr.91 steel,and can offer a possible solution to the problem of how to increase creep resistance at elevated temperatures by optimizing the steel composition,welding,and heat treatment process parameters.The simulation results from this work provide guidance for future alloy development to improve creep resistance in order to prevent type IV cracking.

Efect of residual Al content on microstructure and mechanical properties of Grade B+Steel for castings for locomotives

The bogie made of Grade B＋ steel is one of the most important parts of heavy haul trains. Some accidents were found to be the result of fracture failure of the bogies. It is very important to find the reason why the fracture failure occurred. Because AI was added for the final deoxidation during the smelting process of the Grade B＋Steel, residual AI existed to some extent in the castings. High residual AI content in the bogie casting was presumed to be the reason for the fracture. In this work, the influence of residual AI content in the range of 0.015wt.% to 0.3wt.% on the microstructure and mechanical properties of the Grade B＋ Steel was studied. The experimental results showed that when the residual AI content is between 0.02wt.% and 0.20wt.%, the mechanical properties of the steel meet the requirements of technical specification for heavy haul train parts, and the fracture is typical plastic fractures. If the residual AI content is less than 0.02wt.%, the microstructures are coarse, and the mechanical properties can not meet the demand of bogie steel castings. When the residual AI content is more than 0.2wt.%, the elongation, reduction of area, and low-temperature impact energy markedly deteriorate. The fracture mode then changes from plastic fracture to cleavage brittle fracture. Therefore, the amount of AI addition for the final deoxidation during the smelting process must be strictly controlled. The optimum addition amount needs to be controlled within the range of 0.02wt.% to 0.20wt.% for the Grade B＋Steel.

Effect of Effective Grain Size and Grain Boundary of Large Misorientation on Upper Shelf Energy in Pipeline Steels

X65, X70, and X80 belong to high grade pipeline steels. Toughness is one of the most important properties of pipeline steels when the pipeline transports the gas or oil, and the means to control toughness is very important for exploring even higher grade pipeline steels. We established the relationship between toughness and crystallographic parameters of high grade pipeline steels by studying the crystallographic parameters of X65, X70, and X80 using EBSD and analyzing Charpy CVN of X65, X70 and X80. The results show that the effective grain size, the frequency distribution of grain boundary misorientation and the ratio of high angle grain boundary to small angle grain boundary are important parameters. The finer the effective grain size, and the higher the frequency distribution of grain boundaries （〉 50~）, the more excellent toughness of high grade pipeline steels will be.

Application of cluster analysis on optimization of rolling force learning

The rolling force learning function is an important part of the hot strip parameter calculation process, and the steel classification is the basis of the model parameter calculation,which has a direct impact on the model calculation precision,and the classification of steel quality will directly affect the accuracy of the model calculation.This paper is for the classification of a certain type of steel,in order to find the optimal classification of steel model to achieve greater precision of the rolling force set.Cluster analysis is a method for the study of affinities between samples or variables,in which Distance Coefficient method can be used to demonstrate the differences between the equivalent measured values of the steel deformation resistance in hot strip rolling.Based on the characteristics of the steel components the composition calculation formula CEQ is created by the trial and error method,so as to achieve the consistency between the CEQ and the equivalent deformation resistance by cluster analysis,that is the composition calculation formula CEQ can be used to characterize the equivalent deformation resistance of the steel in hot rolling.In the actual production process,through the composition formula CEQ,the classification of the steel is made,by which the steel rolling force learning calculation is classified and the rolling force setup deviation is reduced,the rolling stability is improved.

Characterization of the globular oxide inclusion ratings in steel using laser-induced breakdown spectroscopy

Grade assessment of steel is generally performed via the metallographic method, which is time-consuming and is not able to provide the elemental distribution information. In this paper, we present a method to measure the globular oxide inclusion ratings in steel using laser-induced breakdown spectroscopy (LIBS). The measurement is performed in two basic steps: steel samples are polished using metallographic sand paper and the Al2O3 inclusion number and size distribution in a marked area are observed using scanning electron microscope/energy dispersive X-ray spectroscopy (SEM/EDS) for further LIBS scanning analysis. The threshold intensity that distinguishes soluble aluminum and insoluble aluminum inclusions is determined using LIBS combined with the SEM/EDS statistical data. Carbon steel (the sample number is S9256) and bearing steel (the sample number is GCr15) are analyzed in scanning mode, and the number of Al2O3 inclusions in different size ranges is obtained from the statistical information derived from the Al2O3 size calibration curve. According to heavy and thin series for globular oxide inclusions grade assessment, the method we propose is comparable to the traditional metallographic method in terms of accuracy; however, the process is simplified and the measurement speed is significantly improved.

Effect of Nb on Mechanical Properties of HAZ for High-Nb X80 Pipeline Steels

The mechanical properties of heat affected zone （HAZ） of two commercial high-Nb X80 grade pipeline steels with different alloy elements were investigated using thermal simulation performed on a Gleeble-3500 thermal simulator. The results showed that the high-Nb steels have excellent weldability. Ernbrittlement regions appear in coarse grain heat affected zone （CGHAZ） and intercritically heat affected zone （ICHAZ） ~ Softening region appears in fine-grain heat affected zone （FGHAZ）, and the strength here was even lower than 555 MPa as required in the standard. Meanwhile, with the increase of heat input, the strength and the toughness of HAZ of steel with high Nb, C and lower alloy decrease notably. Therefore, take into account the welding procedure during manufacture of weld pipe, suitable amount of alloy elements, such as Cr, Ni, Cu, Mo and so on, is necessary for high Nb X80 heavy- thick steel plate.

Effect of Heat Treatment on Microstructure,Mechanical Properties and Fracture Behaviour of Ship and Dual Phase Steels

Grade A （GA） and high strength steel DH36 ship steels possessing different chemical compositions were used, and strength properties of GA steel and DH36 steel were compared. Additionally, 4 types of dual phase （DP） steels with different martensite volume fractions （MVFs） were produced from GA steel by means of heat treatment and they were compared with other steels through conducting mierostructure, microhardness, tensile and impact tests. The fracture surfaces of specimens （DH36, GA and DP steels） exposed to tensile and Charpy impact tests were investigated by scanning electron microscope. Furthermore, it was found that the specimens quenched from 800 and 900℃ had better strength than DH36 steel. The tensile test results indicated that the tensile strength of DP steel water quenched from 900℃ was 3 times that of GA steel and twice that of DH36 steel.

CO_2 Corrosion and Grooving Corrosion Behavior of the ERW Joint of the Q125 Grade Tube Steel

In order to investigate the CO2 corrosion behavior and the grooving corrosion susceptibility of electric resistance welded tubes of the Q125 grade, the high temperature and high pressure autoclave was employed to conduct CO2 corrosion experiments for the welded joint. The mechanisms of grooving corrosion and the factors influencing grooving corrosion susceptibility were identified by electrochemical measurement, microstructure observation, residual stress examination, micro-region composition and orientation analysis. The CO2 corrosion results show that the corrosion resistance of the base material is the best, followed by heataffected zone and the welded seam is the worst. The grooving corrosion occurred in the welded seam, and the grooving corrosion susceptibility of welded seam is relativity high. The dominated reason for the grooving corrosion of the electric resistance welded joint is the notable inclusions consisting of MnS as the main content in the welded seam. The proportion of high-angle grain boundaries in the welding zone is higher than that of base metal and the heat affected zone, which plays an important role in the corrosion behavior of the welded seam.

Effect of Finish Rolling Temperature on Microstructure and Mechanical Properties of High Grade Pipeline Steel

The correlation among finish rolling temperature (FRT),microstructure and mechanical property of the high grade pipeline steel was investigated in this study.The microstructure of the steels with different finish rolling temperatures was observed with scanning electronic microscope (SEM) and transmission electronic microscope (TEM).The martensite/austenite (M/A) islands distribution was fixed by colour metallography,and the mechanical properties of the steels were tested with quasi-static tensile testing machine.The result shows that the fraction of M/A island increased with the finish rolling temperature decreasing,and when the finish rolling temperature is 800℃,the mechanical properties are the best.

Effect of Layers Position on Fracture Toughness of Functionally Graded Steels in Crack Divider Configuration

In the present study, fracture toughness of functionally graded steels in crack divider configuration has been modeled. By utilizing plain carbon and austenitic stainless steels slices with various thicknesses and arrangements as electroslag remelting electrodes, functionally graded steels were produced. The fracture toughness of the functionally graded steels in crack divider configuration has been found to depend on the composites＇ type together with the volume fraction and the position of the containing phases. According to the area under stress-strain curve of each layer in the functionally graded steels, a mathematical model has been presented for predicting fracture toughness of composites by using the rule of mixtures. The fracture toughness of each layer has been modified according to the position of that layer where for the edge layers, net plane stress condition was supposed and for the central layers, net plane strain condition was presumed. There is a good agreement between experimental results and those acquired from the analytical model.

A New Analytical Expression for the Relationship Between the Charpy Impact Energy and Notch Tip Position for Functionally Graded Steels

The effect of the distance between the notch tip and the position of the middle phase in the FGSs on the Charpy impact energy is investigated in the present paper. The results show that when the notch apex is close to the middle layer, the Charpy impact energy reaches its maximum value. This is due to the increment of the absorbed energy by plastic deformation ahead of the notch tip. On the other hand, when the notch tip is far from the middle layer, the Charpy impact energy strongly decreases. Another fundamental motivation of the present work is that for crack arrester configuration, no accurate mathematical or analytical modelling is available up to now. By considering the relationship between the Charpy impact energy and the plastic volume size, a new theoretical model has been developed to link the Charpy impact energy with the distance from the notch apex to the middle phase. This model is a simplified one and the effect of different shapes of the layers and the effect of microstructureon the mechanical properties and plastic region size will be considered in further investigation. The results of the new developed closed form expression show a sound agreement with some recent experimental results taken from the literature.

Effect of cerium addition on microstructure and mechanical properties of as-cast high grade knives steel

The carbides and mechanical properties of as-cast high grade knives steel with and without cerium(Ce)addition were studied.The as-cast microstructure of the steel,the size of carbide precipitation,carbide morphology,and mechanical properties were systematically studied through optical microscopy,scanning electron microscopy,and X-ray diffraction.Besides,through the Equilib module of the FactSage thermodynamics software,the changes in the precipitation type of the inclusions with Ce during the solidification of the steel were calculated.The results indicate that the rare earth Ce is added into the steel to refine the as-cast microstructure of the steel.The types of inclusions in the steel are changed by the addition of Ce.The precipitated carbide morphology changes from a complex rod shape to a relatively single lamellar shape.The rare earth inclusions formed in steel by a moderate addition of Ce can be severed as the core of heterogeneous nucleation of carbides,which reduce the size of carbide precipitation,promote the uniform distribution of carbide in the as-cast steel,and improve the mechanical properties of the as-cast high grade knives steel.

Impact Energy of Functionally Graded Steels with Crack Divider Configuration

Functionally graded steels were produced via electroslag remelting process using the primary electrodes of plain carbon and austenitic stainless steels. Charpy impact energy of as-prepared specimens was measured in the form of crack divider. The obtained results show that the impact energy of the specimens depends on the type and the volume fraction of the present phases. Based on the rule of mixtures, a mathematical model, which correlates the impact energy of functionally graded steels to the impact energy of the individual layers through Vickers microhardness of the layers, was presented. A good compatibility between the experimental results and those obtained from the model was observed.

Low‑Carbon‑Emission Hot Stamping:A Review from the Perspectives of Steel Grade,Heating Process,and Part Design

Hot stamping steels have become a crucial strategy for achieving lightweighting and enhancing crash safety in the automo-tive industry over the past two decades.However,the carbon emissions of the materials and their related stamping processes have been frequently overlooked.It is essential to consider these emissions during the design stage.Emerging materials and technologies in hot stamping pose challenges to the automotive industry's future development in carbon emission reduc-tion.This review discusses the promising materials for future application and their special features,as well as the emerging manufacturing and part design processes that have extended the limit of application for new materials.Advanced heating processes and corresponding equipment have been proven to improve heating efficiency and control temperature uniformity.The material utilization and the overall performance of the components are improved by tailored blanks and an integrated part design approach.To achieve low-carbon-emission(LCE)hot stamping,it is necessary to systematically consider the steel grade,heating process,and part design,rather than solely focusing on reducing carbon emissions during the manufacturing process stage.This review aims to present the latest progress in steel grade,heating process,and part design of hot stamping in the automotive industry,providing solutions for LCE from a holistic perspective.

Functionally Graded Stainless Steel Fabricated by Direct Laser Deposition: Anisotropy of Mechanical Properties and Hardness

Direct laser metal deposition is a kind of advanced rapid manufacturing technology, which can produce near net shape parts by depositing metal powders layer by layer. This study demonstrates fabrication, the anisotropy of mechanical properties and hardness of a graded steel. The characteristics of constituent phases, microstructure, mechanical anisotropy, and microhardness were investigated using electron backscatter diffraction, optical microscopy, tensile test machine, and microhardness tester. It was found that the graded steel is dense and free of cracks. The crystal structures of the as-built samples evolved in three grades from fcc structures to fcc ＋ bcc structures and then to bcc ＋ fcc structures. Samples in x and z directions showed obvious mechanical anisotropy. The samples machined in x direction showed higher strength and lower elongation than those machined in z direction due to the presence of lack-of-fusion pores and the higher metallurgical bonding between layers in the x direction. The microhardness of the as-built samples increased along the cross section from the substrate （159.7 HV） to the top surface （545.4 HV）.

Local Strain Energy Density Applied to Bainitic Functionally Graded Steels Plates Under Mixed-Mode(Ⅰ+Ⅱ) Loading

In this paper, the averaged value of the strain energy density （SED） over a control volume is used to predict the critical load of V-notched specimens made of functionally graded steels （FGSs） under mixed-mode loading. The studied FGSs contain ferritic and austenite phases in addition to bainitic layer produced by electroslag remelting. The mechanism- based strain gradient plasticity theory is used to determine the flow stress （yield stress or ultimate stress） of each layer. The Young＇s modulus and the Poisson＇s ratio have been assumed to be constant, while other mechanical properties vary exponentially along the specimen width. The control volume is centered in relation to the maximum principal stress present on the notch edge and assumes a crescent shape. The points belonging to the volume perimeter are obtained numerically. In the present contribution, the effects of notch radius and notch depth on the SED and the critical load are studied. The notch radius varies from 0.2 to 2.0 mm, and the notch depth varies from 5 to 7 ram. By using the SED approach and finite element simulations, the critical load is determined, and the obtained results show a sound agreement with the experimental results.