Effect of casting process on the inner-wall band segregation of high-strength antisulfur pipes

Controlling inner-wall band segregation is one of the difficulties in the production of high-strength antisulfur pipes.Comparative tests were carried out on different casting processes(superheat,mold electromagnetic stirring,end electromagnetic stirring,casting speed and soft reduction)for the smelting of high-strength antisulfur pipes.The microstructures of continuous-casting billets and hot-rolled or tempered pipes were analyzed using a metallographic microscope and scanning electron microscope.The mechanism and evolution law regarding the inner-wall band segregation of high-strength antisulfur pipes were studied,and the influence of different casting processes was explored.

AlN Precipitates and Microstructure in Non-oriented Electrical Steels Produced by Twin-roll Casting Process

Aluminum nitride （AIN） precipitates and microstructure of 4 wt.% （Si＋AI） non-oriented electrical steel were investigated. The 2.0 mm thick cast strips with three different silicon/aluminum （Si/AI） ratios were produced by twin-roll casting process, then the strips were reheated, warm rolled, cold rolled and annealed. The microstructure and AIN precipitates were characterized using optical microscopy, scanning electron microscopy and transmission electron microscopy. The results showed that with the increase of Si/AI ratio, on the one hand, the casting microstructure changed from columnar grains to equiaxed grains, and the uniformity of annealed microstructure was improved; On the other hand, the number of AIN precipitates in cast strips reduced meanwhile the distribution became dispersed. By the reheat treatment, the size and distribution of the AIN precipitates can be changed. Moreover, the grain size of the annealed strips is in the range of 20-50 #m, at the same time, many AIN precipitates were located at grain boundaries. Therefore, controlling the Si/AI ratio is a simple method to obtain desired microstructure. Then AIN precipitates in non-oriented electrical steel prepared by twin-roll casting process hinder markedly the recrystallized grains growth, A compatible reheat treatment can be an approach worth exploring to control the behavior of AIN precipitates.

NUMERICAL SIMULATION OF MOLTEN POOL AND CONTROL STRATEGY OF KISS POINT IN A TWIN-ROLL STRIP CASTING PROCESS

Coupled turbulent flow, temperature fields of the twin-roll casting strip process were simulated by three-dimensional finite element method. Based on the heat balance calculation and using inverse methods between the simulations and real experiments, the relational models among casting speed, location, and coefficient of heat transfer between molten metal and rolls in different regions are given. In the simulation, the calculated surface temperatures are in good agreement with the measured values. An on-line model of kiss point is derived by simulations and the geometry of molten pool, corresponding control strategy is also proposed.

Investigation of the solute transportation coupled with heat transfer and fluid flow during twin-roll strip casting process

Mathematical model of solute [C] distribution in twin-roll strip casting process has been setup successfully with Calcosoft for the first time. Simulation result shows that in the center of the molten steel pool between the two rolls there is a vortex flow, which is a solute enriched area. But the highest solute concentration position is at the solidification front of the columnar grain zone near the cooling roll surface. Another solute enriched position is in the back flow above the nip point. Combined with the formation mechanism of microstruoture in final as cast strip, analysis shows that solute enriched area is in the transitional area between columnar and equiaxed grain zone.

Mathematical modeling of fluid flow and level profile during twin-roll strip casting process

In twin-roll strip casting process,transport phenomena of fluid in the molten pool directly affect the process stability and the quality of products.In order to elucidate the fundamental transport phenomena in twin-roll casting,a commercial software called ProCAST was employed to simulate the transient fluid flow and level profile behaviors during the early stage of the process in this study.The coupled set of governing differential equations for mass,momentum and energy balance were solved with the finite element method and the transient free surface problem was treated with a volume of fluids(VOF) approach.The effect of different delivery systems configuration on flow pattern,level profile in the pool was studied and analyzed in this paper. The new wedge metal delivery systems have been optimized for the twin-roll strip caster.It was shown that new type metal delivery systems had a preferable effect on the uniform distribution of fluid and level fluctuation in the pool.The simulation results also provide a valuable basis for the optimization of delivery system and process parameters during the initial pouring stage.

The future of the twin-roll strip casting and rolling process

Twin-roll strip casting and rolling is a typical near-net-shape steel manufacturing process.The twin-roll strip casting and rolling of low-carbon steel strips has made a number of breakthroughs and achieved significant results during the past 20 years.Baosteel has been paying close attention to the development of this technology and set up a research and development project focused on its industrialization in 2001.The Ningbosteel-Baosteel strip casting industrialization demo project(NBS),which was launched in 2016,marks the strip-casting technology(registered as Baostrip) developed by Baosteel as having reached an advanced international level after 15 years of effort.This paper summarizes the results obtained in the industrialized demonstration plant and considers the future development of strip casting and rolling.

Physical and computational study of a novel submerged entry nozzle design for twin-roll casting process

With significant emphasis on reducing the turbulence in the bath and the need for effective distribution of metal along the roller length in twin-roll casting,a novel submerged entry nozzle(SEN)configuration with two“gap regions”was provided.The“gap regions”of the new SEN divide the bath into two parts,the“upper melt bath”(casting region)and the“lower melt bath”(rolling region).The newly designed SEN was tested by using both full-scale water modeling experiments and numerical simulations.Results demonstrated that the turbulence could only be found near the rotating roller surfaces.The“gap regions”can make the near-wall flows more uniform.They can also prevent the instabilities in the“upper melt bath”to be transferred to the“lower melt bath”,thus improving the stability of the process.Moreover,the novel SEN can stabilize the meniscus where the initial solidification occurs.This is achieved by increasing the SEN immersion depth,which in turn,can enlarge the volume of the upper part of the bath.

Data-driven casting defect prediction model for sand casting based on random forest classification algorithm

The complex sand-casting process combined with the interactions between process parameters makes it difficult to control the casting quality,resulting in a high scrap rate.A strategy based on a data-driven model was proposed to reduce casting defects and improve production efficiency,which includes the random forest(RF)classification model,the feature importance analysis,and the process parameters optimization with Monte Carlo simulation.The collected data includes four types of defects and corresponding process parameters were used to construct the RF model.Classification results show a recall rate above 90% for all categories.The Gini Index was used to assess the importance of the process parameters in the formation of various defects in the RF model.Finally,the classification model was applied to different production conditions for quality prediction.In the case of process parameters optimization for gas porosity defects,this model serves as an experimental process in the Monte Carlo method to estimate a better temperature distribution.The prediction model,when applied to the factory,greatly improved the efficiency of defect detection.Results show that the scrap rate decreased from 10.16% to 6.68%.

Review of Design of Process Parameters for Squeeze Casting

Squeeze casting(SC)is an advanced net manufacturing process with many advantages for which the quality and properties of the manufactured parts depend strongly on the process parameters.Unfortunately,a universal efficient method for the determination of optimal process parameters is still unavailable.In view of the shortcomings and development needs of the current research methods for the setting of SC process parameters,by consulting and analyzing the recent research literature on SC process parameters and using the CiteSpace literature analysis software,manual reading and statistical analysis,the current state and characteristics of the research methods used for the determination of SC process parameters are summarized.The literature data show that the number of pub-lications in the literature related to the design of SC process parameters generally trends upward albeit with signifi-cant fluctuations.Analysis of the research focus shows that both“mechanical properties”and“microstructure”are the two main subjects in the studies of SC process parameters.With regard to materials,aluminum alloys have been extensively studied.Five methods have been used to obtain SC process parameters:Physical experiments,numeri-cal simulation,modeling optimization,formula calculation,and the use of empirical values.Physical experiments are the main research methods.The main methods for designing SC process parameters are divided into three categories:Fully experimental methods,optimization methods that involve modeling based on experimental data,and theoreti-cal calculation methods that involve establishing an analytical formula.The research characteristics and shortcomings of each method were analyzed.Numerical simulations and model-based optimization have become the new required methods.Considering the development needs and data-driven trends of the SC process,suggestions for the develop-ment of SC process parameter research have been proposed.

Numerical simulation of the temperature fields of stainless steel with different roller parameters during twin-roll strip casting

The temperature field of stainless steel during twin-roll strip casting was simulated by experiment and a finite element （FE） model. By comparing the measured result with the simulated values, it is found that they fit close to each other, which indicates this FE model is effective. Based on this model, the effects of roll gap （t） and roll radius （R） on solidification were simulated. The simulated results give the relationship between t or R and the position of the freezing point. The larger the t is and the smaller the R is, the closer the position of the freezing point is to the exit.

Water Modeling of Twin-Roll Strip Casting

Twin-roll strip casting is regarded as a prospective technology of near net shape continuous casting. The fluid flow field and level fluctuation in the pool have a strong influence not only on composition and temperature homogeneity of pool, but also on the strip quality. A 1 ： 1 water model of a twin-roll strip caster was set up based on the criteria of Froude number and Reynold number similarity. The level fluctuation was measured. The influence of pool depth, casting speed and feeding system configuration on level fluctuation in the pool was studied. The experimental results provided a basis for the optimization of feeding system and process parameters.

Simulation of Fluid Flow, Heat Transfer and Micro-Segregation in Twin-roll Strip Casting of Stainless Steel

In twin-roll strip casting process, metal flow and temperature distribution in the molten pool directly affect the stability of the process and the quality of products. In this paper, a 3D coupled thermal-flow fenite element modeling （FEM） simulation for twin-roll strip casting of stainless steel was performed. Influences of the pouring temperature and casting speed on the temperature fields were obtained from the numerical simulation. The micro-segregation of the solutes during the strip casting process of stainless steel was also simulated. A developed micro-segregation model was used to calculate the micro-segregation of solutes in twin-roll casting of stainless steel. The relationship between the solidus fraction in solidification and temperature was given, which was used to determine the LIT （liquid impermeable temperature）, ZST （zero strength temperature） and ZDT （zero ductility temperature） in the period of non-equilibrium solidification. The effect of temperature on the micro-segregation was discussed. According to the computational results, the solidification completion temperature in the twin-roll strip casting of stainless steel was then determined, which can provide a basis for controlling the location of solidification completion temperature and analysing the crack of the casting strip.

Application of Fuzzy Logic Controller to Level Control of Twin-Roll Strip Casting

An intelligent fuzzy-PID controller consisting of fuzzy logic controller and PID controller was developed to control the molten steel level of twin-roll strip caster.Additionally,a feedforward differential PID controller was used for stopper position control in order to avoid differential kick.It is proved by simulation that the proposed intelligent controller is able to obtain zero steady state error asymptotically and the control system is robust due to its fuggy behavior of the controller.

Heat Transfer Characteristic of Molten Pool for Twin-Roll Strip Casting

Body-fitted coordinate transformation equation was deduced and used to generate the body-fitted grids of molten pool for twin-roll strip casting.The orthogonality of the grids on the boundary was modified by adjusting source item.The energy equation and the boundary conditions were transformed from physical space to computational space.The velocity field model proposed by Hirohiko Takuda was used to calculate the temperature field of molten steel,and the influence of technical factors was also discussed.

Morphological Variation of Eutectic Carbide in Twin-Roll Casting Strip of W9Cr4Mo2

The netlike eutectic carbide in twin-roll casting strip of W9Cr4V2 was dissolved and broken up gradually with increasing heating temperature during annealing treatment.Almost all eutectic carbides exist in granular form with heating temperature up to 950 ℃.It is considered that the refining of lamellar spacing made it possible for eutectic carbide to be granulated.

Wear analysis of a side dam in twin-roll strip casting

Reducing wear on a side dam can prolong the casting operation life of a twin-roll strip casting process,thus reducing production cost and improving casting stability.To lengthen the service life of the side dam,it is necessary to understand the wear performance of the side dam material.To investigate the wear behavior mechanism of the side dam,in this study,the UMT-2 friction and wear tester was used to determine the relationship between the wear rate of the side-dam material and various parameters.Based on the roughness of the contact area between the side dam and the end of the casting rolls as well as on the amount of deformation of the side dam,which was derived using a thermal-deformation simulation model,the reasons for the uneven wear of the side dam were obtained.

Nonmetallic inclusions in SUS304 strip produced by twin-roll strip casting

The shape, type, content, and dimension of nonmetallic inclusions in SUS304 strip produced by twin-roll strip casting were studied using scanning electron microscopy （SEM）. The results show that the inclusions are mainly spherical Al2O3 and complex oxides composed of MnO, Al2O3 , and SiO2. The percentage of fine oxides smaller than 3 μm reaches up to 51.8%. The theoretical calculations show that fine oxides have precipitated during solidification. Therefore, it is concluded that during twin-roll strip casting, because of high cooling rate, the size of inclusions precipitated during solidification decreases, and the amount increases.

Study of measurement and control of free loop of hot steel strip in twin-roll strip casting

In the twin-roll strip casting process, hot cast strips can be broken or tom if the casting speed does not match the rolling speed. Usually, a certain length of hot steel strip is hung freely between the caster and rolling mill to deal with the effect of this speed difference. In this paper,the freely hanging hot steel strip is referred to as the free loop of hot steel strip. Accurately measuring and controlling the height of this free loop is the key factor in maintaining a stable casting operation. Several methods for measuring the loop height of a steel strip are discussed and a method for accurately measuring and controlling the free loop height of hot steel strip is presented. Based on the results of the casting loop quantity change curve, this control method is confirmed to be effective and able to meet the requirements of continuous casting strip production.

基于AnyCasting的磨辊辊皮铸造模拟与工艺优化

针对磨辊辊皮铸造过程中易出现缩孔等缺陷问题,运用AnyCasting软件对其充型、凝固过程进行模拟。首先,分析铸件金属液的凝固规律,预测缩孔缺陷产生的部位;其次,通过在型腔底部下方增设冷铁,对初始铸造工艺进行优化。结果表明,上移缩孔在冒口中的位置可有效防止在铸件上发生缩孔。按此工艺生产的辊皮铸件无缩孔、组织致密且硬度高。