Design of TRIP Steel With High Welding and Galvanizing Performance in Light of Thermodynamics and Kinetics

A new type of transformation induced plasticity （TRIP） steel with not only high strength and high ductility but also superior welding and galvanizing properties was designed and developed recently. Low carbon and low silicon content were preliminarily selected with the aim of meeting the requirements of superior quality in both welding and galvanizing. Phosphorus was chosen as one of the alloying elements, because it could reduce carbon activity in cementite and increase the stability of austenite. In addition, the possibility of phosphorus segregating at grain boundary was also discussed by thermodynamics as well as kinetics. Phase diagram was estimated at high temperature and the composition of the steel was then selected in the hyperperitectic range to avoid problems, which might occur in sheet steel continuous casting. Phase diagram in the inter.critical temperature was estimated for the steel to obtain the starting temperature of fast cooling. For understanding the minimum rate of fast cooling, pearlite growth kinetics was calculated with self-developed diffusion coefficients of elements in grain boundary. Overaging temperature was determined through the calculation of To temperature by both equilibrium and para-equilibrium assumptions, which was different from the current determination, which is only based on an equilibrium estimation.

Design of a low-alloy high-strength and high-toughness martensitic steel

To develop a high strength low alloy （HSLA） steel with high strength and high toughness, a series of martensitic steels were studied through alloying with various elements and thermodynamic simulation. The microstructure and mechanical properties of the designed steel were investigated by optical microscopy, scanning electron microscopy, tensile testing and Charpy impact test. The results show that cementite exists between 500℃ and 700℃, M7C3 exits below 720℃, and they are much lower than the austenitizing temperature of the designed steel. Furthermore, the Ti（C,N） precipitate exists until 1280℃, which refines the microstructure and increases the strength and toughness. The optimal alloying components are 0.19% C, 1.19% Si, 2.83% Mn, 1.24% Ni, and 0.049% Ti; the tensile strength and the V notch impact toughness of the designed steel are more than 1500 MPa and 100 J, respectively.

Thermodynamic study on welding wire design of high nitrogen austenitic stainless steel

Based on thermodynamic calculations, the effect of pressure and alloying elements on the nitrogen content, solidification mode, and welding characteristics were investigated in this study. By increasing the partial pressure of N_2, the nitrogen content in the weld pool increased dramatically, and the γ zone was enlarged. The nitrogen content increased as alloying elements such as Cr and Mn were added to the molten steel. The δ zone with high temperature treatment was compressed by adding Ni. These alloying elements play important roles in the formation of the single γ region at the temperature of 298 K. With proper Mn addition, the phase area of γ was extended and became more stable, and the "ferrite trap" was also avoided. Two kinds of welding wires with different nitrogen contents were developed and corresponding MIG welding experiments were performed. As the nitrogen content in wire was higher than that in the base metal, severe blowhole defects and mixture microstructure of δ and γ developed.

Computer Aided Composition Design of Prehardened-Mould Steel for Plastic

The improvement of machining behavior of prehardened-mould steel for plastic is realized by using computer-aided composition design in this work. The results showed that the matrix composition of large sectional prehardened mould steel for plastic markedly influences the precipitation of non-metallic inclusion and the control of composition aided by Thermo-Calc software package minimizes the amount of detrimental oxide inclusion. In addition the modification of calcium is optimized in the light of composition design.

A new methodology for energy-based seismic design of steel moment frames

A procedure is proposed whereby input and hysteretic energy spectra developed for single-degree-of-freedom （SDOF） systems are applied to multi-degree-of-freedom （MDOF） steel moment resisting frames. The proposed procedure is verified using four frames, viz., frame with three-, five-, seven- and nine-stories, each of which is subjected to the fault- normal and fault-parallel components of three actual earthquakes. A very good estimate for the three- and five-story frames, and a reasonably acceptable estimate for the seven-, and nine-story frames, have been obtained. A method for distributing the hysteretic energy over the frame height is also proposed. This distribution scheme allows for the determination of the energy demand component of a proposed energy-based seismic design （EBSD） procedure for each story. To address the capacity component of EBSD, a story-wise optimization design procedure is developed by utilizing the energy dissipating capacity from plastic hinge formation/rotation for these moment frames. The proposed EBSD procedure is demonstrated in the design of a three-story one-bay steel moment frame.

Advances in machine learning-and artificial intelligence-assisted material design of steels

With the rapid development of artificial intelligence technology and increasing material data,machine learning-and artificial intelligence-assisted design of high-performance steel materials is becoming a mainstream paradigm in materials science.Machine learning methods,based on an interdisciplinary discipline between computer science,statistics and material science,are good at discovering correlations between numerous data points.Compared with the traditional physical modeling method in material science,the main advantage of machine learning is that it overcomes the complex physical mechanisms of the material itself and provides a new perspective for the research and development of novel materials.This review starts with data preprocessing and the introduction of different machine learning models,including algorithm selection and model evaluation.Then,some successful cases of applying machine learning methods in the field of steel research are reviewed based on the main theme of optimizing composition,structure,processing,and performance.The application of machine learning methods to the performance-oriented inverse design of material composition and detection of steel defects is also reviewed.Finally,the applicability and limitations of machine learning in the material field are summarized,and future directions and prospects are discussed.

INVESTIGATION OF FRACTURE DESIGN FOR MEDIUM CARBON STEEL UNDER EXTRA-LOW CYCLIC FATIGUE IN AXIAL LOADING

The extra-low cyclic fracture problem of medium carbon steel under axial fatigue loading was investigated. Several problems, such as the relations of the cycle times to the depth and tip radius of the notch, loading frequency, loading range and the parameters of fracture design for medium carbon steel on condition of extra-low axial fatigue loading were discussed based on the experiments. Experimental results indicated that the tension-pressure fatigue loading mode was suitable for extra-low cyclic fatigue fracture design of medium carbon steel and it resulted in low energy consumption, fracture surface with high quality, low cycle times, and high efficiency. The appropriate parameters were as follows： loading frequency 3-5 Hz, notch tip radius r = （0.2-0.3） mm, opening angle α = 60°, and notch depth t = （0.14-0.17）D.

Computer-Aided Design of Some Advanced Steels and Cemented Carbides

Thermodynamic and kinetic study on TRIP （transformation induced plasticity） steels, cemented carbides and mold steel for plastics were carried out in order to design modern advanced materials. With the sublattice model, equilibrium compositions of ferrite and austenite phases in TRIP steels, as well as volume fraction of austenite at inter-critical temperatures for different time were calculated. Concentration profiles of carbon, manganese, aluminum and silicon in the steels were also estimated in the lattice fixed frame of reference. The effect of Si and Mn on TRIP was discussed according to thermodynamic and kinetic analyses. In order to understand and produce the graded nanophase structure of cemented carbides, miscellaneous phases in the M-Co-C （M= Ti, Ta, Nh） systems and Co-V-C system were modeled. Solution parameters and thermodynamic： properties were listed in detail. The improvement of machining behavior of prehardened mould steel for plastics was obtained by computer-aided composition design. The results showed that the matrix composition of large-section prehardened mould steel for plastic markedly influences the precipitation of non-metallic inclusion and the composition control by the aid of Thermo-Calc software package minimizes the amount of detrimental oxide inclusion. In addition, the modification of calcium was optimized in composition design.

Peak displacement patterns for the performance-based seismic design of steel eccentrically braced frames

Performance-based seismic design(PBSD) aims to assess structures at different damage states. Since damage can be directly associated to displacements, seismic design with consideration of displacement seems to be logical. In this study, simple formulae to estimate the peak floor displacement patterns of eccentrically braced frames(EBFs) at different performance levels subjected to earthquake ground motions are proposed. These formulae are applicable in a PBSD and especially in direct displacement-based design(DDBD). Parametric study is conducted on a group of 30 EBFs under a set of 15 far field and near field accelerograms which they scaled to different amplitudes to adapt various performance levels. The results of thousands of nonlinear dynamic analyses of EBFs have been post-processed by nonlinear regression analysis in order to recognize the major parameters that influence the peak displacement pattern of these frames. Results show that suggested displacement patterns have relatively good agreement with those acquired by an exact nonlinear dynamic analysis.

Design and Preparation of Steel Slag SMA

On the basis of the characteristics of high rigidity and excellent friction resistance,a new kind of steel slag SMA (stone matrix asphalt) concrete was designed and prepared.The main processes include aggregate gradation,performance analysis of steel slag before and after aging,preparation methods and properties test of steel slag SMA.The experimental results indicate that the index of steel slag's activation is less than 1 percent,the dynamic stability is 5699 times/mm,and both the residual stability and ratio of frozen splitting strength are more than 80 percent;the friction factor and structure depth are 67.1% and 0.7mm respectively.These results show the steel slag SMA is superior to the common asphalt concrete and SMA that uses common aggregate.

Computer-aided designing and manufacturing of advanced steels

Suitable optimization and simulation were performed using a powerful software package with a mature database as well as modem measurement facilities, which led to the successful designing and manufacturing of advanced steels. In the course of designing, the composition of a large section of prehardened mold steel for plastics was estimated so as to lower the quantities of oxide inclusions to change the type of carbides and to raise the machinability. The composition and process were adjusted to obtain satisfactory surface quality for the prevailing galvanization in transformation-induced plasticity （TRIP） steel. The refuting process of low-carbon steel was simulated in the light of both Thermo-Calc and Factsage. Thermodynamic and kinetic analyses were always conducted during the test and the procedure.

Application of Empirical Electron Theory of Solids and Molecules to Composition Design of Multi-Component Medium-Low-Alloy Steels

For austenitic octahedral segregation structure units, their pure mathematics statistic distribu!ive probability is calculated by the empirical electron theory （EET） of solids and molecules and K-B formula. The practical distributive probability can be obtained only if the statistic distribution of austenitic octahedral segregation structure units and the interaction of the alloying elements in steel are considered. Based on 8 groups of experimental data of original steels, three empirical formulas revealing relationships between material macromechanics factor （Sm） and tensile strength （ab）, or impact energy （AK）, or hardness （HRC） of multi-component medium-low-alloy steels were established, respectively. Through the three empirical formulas, new supersaturated carburizing steel has been successfully designed and developed. The other 2 groups of the original experimental steels are used as the standard steel for testing the percentage error of the new steel. The results show that the calculated values are well consistent with those of measured ones and the new supersaturated carburized steel can meet the requirements of the die assembly of cold-drawn seamless stainless steel tube of Taiyuan Iron ＆ Steel （Group） Company LTD.

Floating-roof steel tanks under harmonic settlement: FE parametric study and design criterion

Large vertical steel tanks for fluid storage are usually constructed on soft foundations, so it is not surprising that the tank wall will settle unevenly with the settlement of the foundation, thus inducing deformations and stresses in the tank. This work investigates the linear static behavior of floating-roof tanks under harmonic settlement through finite element (FE) analyses. The influences of the radius-to-thickness ratio, the height-to-radius ratio and the wind girder stiffness on the structural behavior are first analyzed. Comparisons between the circumferential stresses in the wind girder and the vertical stresses in the tank bottom are then made. The displacement and the stress along the tank height are also discussed, and the concept of tank division along its height is presented. Finally, a design approximation for the radial displacement at the tank top is developed based on FE results, and a settlement criterion based on the top radial displacement is proposed which can be used in practical design.

Design methods of headed studs for composite decks of through steel bridges in high-speed railway

Aimed at two typical composite floor systems of through steel bridges in high speed railway,design methods of headed studs were put forward for different composite members through comparing and analyzing the structure,mechanical characteristics and transmission routes of deck loads.The simplified calculation models were brought out for the stud design of the longitudinal girders and transverse girders in the composite floor system of Nanjing Dashengguan Yangtze River Bridge (NDB).Studs were designed and arranged by taking the middle panel of 336 m main span for example.The results show that under deck loads,the longitudinal girders in the composite floor system of through steel bridges are in tension-bending state,longitudinal shear force on the interface is caused by both longitudinal force of "The first mechanical system" and vertical bending of "The second mechanical system",and studs can be arranged with equal space in terms of the shear force in range of 0.2d (where d is the panel length) on the top ends.Transverse girders in steel longitudinal and transverse girders-concrete slab composite deck are in compound-bending state,and out-of-plane bending has to be taken into account in the stud design.In orthotropic integral steel deck-concrete slab composite deck,out-of-plane bending of transverse girders is very small so that it can be neglected,and studs on the orthotropic integral steel deck can be arranged according to the structural requirements.The above design methods and simplified calculation models have been applied in the stud design of NDB.

Study in the design and manufacture process of the elastic cable anchor box in steel box girder of Taizhou Bridge

Taizhou Yangtze River Highway Bridge is a large span suspension bridge with three pylons. The elastic cables are installed to connect the steel tower and the steel box girder. The constraints can increase the safety coefficient of the middle saddle, and improve the stress conditions of the middle pylon and decrease the deflection in the middle of the main girder, as well as the longitudinal displacement of the main girder caused by live loads. The anchorage boxes of the elastic cable are installed in the wind fairing outside the vertical web plate of the box girder. Two anchor boxes form a pair and are arranged parallelly. Eight anchor boxes are installed in the bridge. In this paper, the design scheme and the technical difficulties in manufacturing are briefly discussed with the precision control techniques.

GMA material design and construction quality control for asphalt pavement of steel box girder: Case study of the Hong Kong–Zhuhai–Macao Bridge

To improve the quality of the Hong Kong–Zhuhai–Macao Bridge paving project,a new paving layer material,Guss-mastic asphalt(GMA),was proposed in this paper by combining the advantages of two types of cast asphalt mixtures:mastic asphalt(MA)and Guss asphalt(GA).Based on the characteristics of GMA,to simulate its actual production process,this study developed a small-simulated cooker mixing equipment.Moreover,the flow degree,60C dynamic stability,and impact toughness were proposed to be used to evaluate the construction and ease,high temperature stability,and fatigue resistance of GMA cast asphalt mixtures,respectively.Moreover,the quality control standards for GMA paving materials by indoor tests,field trial mix GMA material performance tests,and accelerated loading tests were finalized.The study showed that the developed simulated cooker yielded consistent mixing results in the same working environment as the engineering cooker device.Increasing the coarse aggregate incorporation rate,coarsening the mastic epure(ME)gradation composition,and using a smaller oil to stone ratio can reduce the flowability of the GMA materials to varying degrees.The four-point bending fatigue life and impact toughness of the different GMA materials are correlated well.A mobility of<20 s,60C dynamic stability of 400–800 times/mm,15C impact toughness of400 N⋅mm,and cooker car mixing temperature control standard of 210C–230C form an appropriate control index system for the design and production of GMA cast asphalt mixtures.Simultaneously,accelerated loading tests verified the accuracy and reliability of the quality control index system that has been used in the GMA paving project of the Hong Kong–Zhuhai–Macao Bridge deck and has achieved good application results.

COMPOSITION DESIGN FOR A BEARING STEEL WITH LIMITED HARDENABILITY

The composition of a bearing steel was designed for limited hardenability by use of Grossmann's method. A medium frequency induction Process was applied to heat bearings to ensure penetrant heating and suitable solving of carbon and other elements in the matrix. The hardened depth measured from the end quenching test samples and actual bearings matches well with the designed one.

Integrity Design Strategy in Steel Structure Bridge Design

Nowadays,the scope of bridge construction projects in China is becoming wider,which promotes China's economic development to a large extent and also improves China's transportation system.Meanwhile,people also put forward new requirements for the quality of steel structure bridges.However,in actual design,due to the influence of many fectors,some problems are inevitable,which will affect the integrity of the design.Therefore,the designer needs to fully grasp the possible design problems,and then take efiective measures to improve the integrity of the design scheme,so as to ensure the quality of the steel structure bridge and improves the safety of the steel structure bridge from the fundamentals.This paper mainly focuses on steel structure bridges,analyzed the current status of steel structure bridge types and their selection,and proposes the integrity design strategy of steel structure bridges.

Simulation and Reasonable Design of Bridge Steel Fenders to Reduce Ship Impacts

Steel fenders are increasingly used for ship-impact resistance structures in the design of navigable bridges. As an important approach to investigating this anti-impact structure effectiveness to reduce influences of vessel impact, simulation analyses are still not perfect yet. So this paper is intended to discuss several issues related to ship collision simulations, including steel constitutive relationship, connections between steel box and pile cap, contacts definition and friction consideration, and the determination of impact waterlines and angles. Consequently based on two examples of ship-steel fender-bridge structure systems, some conclusions about effectiveness and design of fenders to reduce ship impact are drawn.

Optimization of design parameters for controlled rocking steel braced dual-frames

A controlled rocking concentrically steel braced frame(CR-CSBF)is introduced as an alternative to conventional methods to prevent major structural damage during large earthquakes.It is equipped with elastic post-tensioned(PT)cables and replaceable devices or fuses to provide overturning resistance and dissipate energy,respectively.Although CR-CSBFs are not officially legalized in globally valid codes for new buildings,it is expected to be presented in them in the near future.The main goal of this study is to determine the optimal design parameters consist of the yield strength and modulus of elasticity of the fuse,the initial force of the PT cable,and the gravity load on the rocking column,considering different heights of the frame,spanning ratios and ground motion types for dual-configuration CR-CSBF.Nonlinear time-history analyses are performed in OpenSees.This study aims to define the optimal input variables as effective design parameters of CR-CSBFs by comparing four seismic responses consisting of story drift,roof displacement,roof acceleration and base shear,and also using the Euclidean metric optimization method.Despite the previous research,this study is innovative and first of its kind.The results demonstrate that the optimal design parameters are variable for various conditions.