Continuous Casting of Steel

Top PDF Continuous Casting of Steel:

Factors Affecting Solidification of Steel in the Mould during Continuous Casting of Steel Billets

Factors Affecting Solidification of Steel in the Mould during Continuous Casting of Steel Billets

Abstract— Casting of steel is an operation which is sensitive to a number of factors. It should be performed with great control and steadiness in such a way to produce safe casting operation and sound steel mechanical properties, and ensure a continuous process with limited delays. In this study, effects of factors encountered in the process of continuous casting of steel billets on the thickness of solidified steel layer in the mould area were mathematically modeled in order to identify the most predominant ones. Of these factors modeled are mould thickness, mould material thermal conductivity and molten steel superheat. Simplified calculation were performed in which heat transfer equations governing the process solidification were solved using an explicit method of finite difference technique. The results showed that the most effective factor on solidified steel thickness in the mould is the magnitude of molten steel superheat prior to entering the mould. Thermal conductivity of mould material showed little effect due to the small thickness of mould wall. Changing mould thickness showed some effect of solidification but were not significant . Index Terms — solidification, heat transfer, finite difference, explicit method, superheat .

5 Read more

Macrosegregation Quality Criteria and Mechanical Soft Reduction for Central Quality Problems in Continuous Casting of Steel

Macrosegregation Quality Criteria and Mechanical Soft Reduction for Central Quality Problems in Continuous Casting of Steel

Several improved models of different heat transfer and solidification phenomena have been developed. El- Bealy [9], extended the fluctuation macrosegregation technique to simulate mold heat transfer phenomena in addition to the microstructure evolution [5] [10]. The comparison between these phenomena reveals that the fluctuated macrosegregation technique is more accurate than the use of microstructure evolution technique. Nassar et al. [10], studied the growth irregularities during continuous casting caused by local variations in sur- face temperature due to the solidification behavior of 310S stainless steel. They concluded that large variations in the surface temperature were expected due to the variation in heat extraction. This results in further shrinkag- es and then affects the growth of irregularities of solid shell. Manojlovie [11], proposed a mathematical model of dendritic solidification processes of continuously cast steel slabs. This was to optimize the continuous casting process variables and to improve the quality of slabs. This was by using a finite element method and also, by an analytical method applying isothermal method of Green’s function. The comparison between the model predica- tions of different methods solutions with real temperature measurements displays satisfying results in terms of appropriate determination of solidification process of steel slabs.

22 Read more

Fluid Flow, Heat Transfer, Mixing Time and Inclusion Motion in Molten Steel Continuous Casting Tundish

Fluid Flow, Heat Transfer, Mixing Time and Inclusion Motion in Molten Steel Continuous Casting Tundish

Steady 3-D flow of steel in the continuous casting tundish is simulated with finite-volume based software (fluent), the turbulence model used is the standard k-ε, Inclusion trajectories are calculated by integrating each local velocity, considering its drag and buoyancy forces. A “random walk” model is used to incorporate the effect of turbulent fluctuations on the particle motion. For the mixing time curves and its data, unsteady 3-D flow is used, to explore the fluid flow mechanism [2] [13]. Plant observations and final products mechanical properties tests in GIAD steel factory in Sudan have found that a serious quality problems, mainly brittleness of the final product (building bars), which may be as the results of many factors, including inclusion entrapment, slag entrapment in the steel melt and flow pattern in the tundish. As the results, these problems affect the productivity so as the improvement of the final product quality, which are permanent requirements concerning the continuous casting process, this was the motivation signal to conduct this research.

13 Read more

Electromagnetic techniques for imaging the cross section distribution of molten steel flow in the continuous casting nozzle

Electromagnetic techniques for imaging the cross section distribution of molten steel flow in the continuous casting nozzle

Abstract—Control of molten steel delivery through the pouring nozzle is critical to ensure an optimum laminar flow pattern in continuous casting, which influences the surface quality, clean- liness, and hence the value of the cast product. A nonintrusive and nonhazardous visualization technique, which uses rugged and noninvasive sensors, would be highly desirable in such harsh industrial production environments. This paper presents an electromagnetic approach for tomographically visualizing the molten steel distribution within a submerged entry nozzle (SEN). The tomographic system consists of an eight-coil sensor array, data acquisition unit, associated conditioning circuitry, and a PC computer, which have been purposely designed and constructed for hot trials. The paper starts with an overview of electromagnetic imaging techniques. The construction of the sensor array and associated electronics are then discussed, followed by sensitivity map analysis and a description of the applied image reconstruction algorithm. Image results, as reconstructed from cold sample mea- surements and hot pilot plant trials, are also presented. Despite a low frame acquisition rate (1.35 s per frame), the images generated from the prototype system are capable of providing an adequate representation of the changes of real molten steel flow profiles within the SEN. The paper demonstrates that the application of electromagnetic tomographic technique to this problem shows significant promise for future industrial processes.

9 Read more

Fluid Flow, Inclusion removal and Slag Entrapment in Molten Steel Continuous Casting Mould

Fluid Flow, Inclusion removal and Slag Entrapment in Molten Steel Continuous Casting Mould

Conventional continuous casting is one of the most cost effective production routes for producing semi-finished materials from molten steel. This cost–effectiveness is largely dependent on both quantity and quality of the final products. Therefore, it is important to control the dependent physical phenomena occurring at the same time inside the mould such as heat transfer, solidification and fluid flow to offer a steady and smooth casting process. This then decreases the probability of defects (i.e, transverse and longitudinal cracks,deep wavy marks etc.) and increases the overall production in the form of reducedrequisite for surface treatments and a decreased amount of scrapped materials [28] The first objective of this sub-model within this research was to develop a mathematical model of the flow pattern in the liquid pool which determines how both molten steel and inclusion particles carried in by the nozzle are distributed. To verify acceptable accuracy of the model, its predictions were compared with experiments and models conducted by [2] [3].

13 Read more

Anchor Shaped Design of a Submerged Entry Nozzle for the Continuous Casting of Steel

Anchor Shaped Design of a Submerged Entry Nozzle for the Continuous Casting of Steel

Nowadays, around 95% of the world raw steel is cast by means of the continuous cast- ing process [1]. The quality of the steel slabs is greatly influenced by the fluid flow in the continuous casting mold [2], and the geometry of the Submerged Entry Nozzle (SEN) is the most important parameter [3] [4]. In the continuous casting mold, mold powder is added in order to prevent heat losses, provide good lubrication, and protect the molten steel from air oxidation. However, sometimes the mold powder is entrapped into the molten steel, and this entrapment deteriorates the quality of the solid steel [5].

9 Read more

Dendrite growth direction measurements : understanding the solute advancement in continuous casting of steel

Dendrite growth direction measurements : understanding the solute advancement in continuous casting of steel

the nature of their preferred crystallographic growth direction, dendrites are observed to grow in the form of branched tree-like morphology. In the continuous casting process, liquid steel transforms into solid, due to cooling, in a process wherein a liquid feedstock is continuously fed to an oscillating mold and a semi-solid product is extracted at the outlet. It is a quite complicated process where the phenomena of heat transfer and mass transfer take place simultaneously in presence of the incoming turbulent liquid jet, which after entering the mold creates a high degree of bulk convection. This incoming liquid stream on its way from the submerged entry nozzle (SEN) towards the mold exit takes away the rejected solute (rejected by the growing solid phase) thereby changing the local chemical driving forces and creating a washing effect. The liquid flow sweeps away the solute ahead of the growing interface from the upstream side to the downstream side. Thus it lowers the degree of undercooling on the downstream side (i.e in the direction of the outgoing fluid flow from SEN to the mold exit in the casting direction in Fig. 1) and promoting the driving force for solid growth on the upstream side (i.e towards the incoming fluid flow from SEN in Fig. 1). This has a direct effect on the evolving solidification microstructure. As the amount of solid fraction increases, the magnitude of the convection effect of the bulk flow decreases, thereby decreasing the effectiveness of the washing effect. During the process, if after a certain extent of time there exists a region with excessive solute accumulation, the undercooling will reduce drastically. This excess solute, if not further washed away, will lead to macro-segregation in the cast product. This macro-segregation is the inhomogeneity in the chemical composition when allowed to extend over large distances will lead to undesirable mechanical properties of the end product. Chemically driven precipitation can occur in this region between reactive metallic alloying additions and interstitial solutes. Thus the interface growth direction depends on the solute profile in front of the moving interface - which in turn depends on the casting process parameters. Hence to maintain the quality of the cast steel slab, it would be beneficial for the casting operators to have a good estimate about the interface growth direction and its dependency on the combination of heat transfer, mass transfer, and fluid flow. This will help to dynamically re-adjust the casting process parameters in order to minimize the degree of macro-segregation.

6 Read more

Scrap Analysis For Steel Billet Production In Continuous Casting Process

Scrap Analysis For Steel Billet Production In Continuous Casting Process

The main raw material in Billet Manufacturing process is mild steel scrap which is procured from local and International markets. The scrap is mixed in pre- determined proportions in the scrap yard and fed to the furnaces in charging buckets and melted by Electric Arc using Graphite Electrodes. The molten metal is processed to remove the impurities like sulphur and phosphorous and is subjected to slag off and further refining by adding Ferro alloys and other fluxes to bring it to the required standard specifications. Liquid metal samples are analysed at frequent intervals to ensure quality if the product as per I.S. The molten steel is tapped at the required temperature to the pre-heated ladles. Steel ladles are equipped with latest slide gate opening system. Temperature of the molten metal in the ladle is measured to ensure correct temperature at the continuous casting machine. The liquid metal is then poured from ladle to the tundish and then to the water cooled copper mould on continuous casting machine. There takes place the billet formation by solidification of the molten steel due to water cooling. Billets coming out of the continuous casting machine are cut to the required length by gas cuttingFor structural steel making process the scrap are an important raw material, the coast and quality of final product is mainly depends upon the cost of scrap and scrap quality. The collection of scrap from various sources is an important work during manufacturing of structural steel .The scrap are mainly available locally and foreign countries. The circulating and process scrap is returned to the steel furnace without any deleterious contamination. In particular may be contaminated with non- ferrous metals like tin, copper, nickel etc. Since it is not possible to oxidize these during refining they remain as residuals in steel. The properties of steel are adversely affected by the presence of these residuals. The specifications of steel do to maximum allowable limits. A proper scrap blend is necessary to minimize this problem during steel making. The scrap-based steelmaking process starts by charging the predetermined scrap mix into an electric arc furnace (EAF). Melting a single charge in the furnace is called a heat. When the charge is melted, the uncertainty in the chemical composition of the charge

6 Read more

Thermal Analysis of Tundish in Continuous Casting Machine in Steel Industry

Thermal Analysis of Tundish in Continuous Casting Machine in Steel Industry

production is casted using a continuous casting process where the liquid steel flows from ladle to Tundish next to mold in a continuous casting system. In modern steelmaking and continuous casting plants, Tundish technology from both fundamental and practical point of view is most important. Steel is produced in three basic route like, basic oxygen furnace (BOF), electric arc furnace (EAF) & induction furnace (IF). In BOF hot metal and scrap are blown by oxygen gas with a flux addition such as lime etc. The aim of this project is to minimize the slag layer developing during the casting sequence and to improve the performance of M.B.S. and Tundish also. For that one Tundish model made to experiment and same result check by means of ANSYS analysis and also analytical result of Tundish heat loss verified.

7 Read more

Velocity Monitoring of Molten Steel in a Continuous Casting Mold Using Three Submerged Entry Nozzle Designs

Velocity Monitoring of Molten Steel in a Continuous Casting Mold Using Three Submerged Entry Nozzle Designs

It is widely accepted that the quality of the continuous-cast products is severely af- fected by the fluid flow in the mold and the SEN design, and that sudden transients are responsible of flow instabilities that cause surface turbulence [1]. In accordance to [2], powder entrainment is influenced, among other factors, by rapid mold level fluctua- tions, surface waves, SEN design and shallow SEN immersion. A Computational Fluid Dynamics (CFD) study on mold powder entrapment caused by vortexing flow at the interface between mold powder and molten steel near the SEN is reported in [3]. Mold properties, mainly viscosity, prevent the entrapment phenomenon in ultra-low carbon steels [4]. More specifically, mold powder entrapment is enhanced by Kelvin-Helm- holtz instability (KHI) [5] [6] and Karman vortex streets (KVS) [4] [6]. KHI is present in the powder-molten steel interface, and it is recognized that KHI represents an im- balance of the destabilizing effect of inertia of a light phase (powder) moving in the ho- rizontal direction over the stabilizing effect of buoyancy of a heavy phase (molten steel) [7]. Meanwhile, in the mold KVS are generated behind the SEN in the downward ver- tical direction [6], and they arise when the velocity goes beyond certain excitation value [8].

10 Read more

Mold Thermo Mechanical Rigidity Criterion for Surface Quality of Continuous Casting of Steel

Mold Thermo Mechanical Rigidity Criterion for Surface Quality of Continuous Casting of Steel

The surface temperature profiles shown in Figure 4(b) illustrate the effect of various mold cooling zones on the surface temperature “T”. These profiles demonstrate that T falls by different cooling rates based on the natu- ral of cooling region in the mold zone. Subsequently, in initial BAGF, the slab surface cools gradually into 1320˚C when the molten steel is still in the liquid zone. As solidification starts, the cooling rate reduces slightly until 1300˚C where the latent heat of fusion starts to dis- sipate during solidification process. Based on the magni- tude of coherence temperature, T cools rapidly into 1200˚C. When the air gap begins to form, the solid shell separates from the mold wall in AAGF. This results in a complete changing in the heat transfer mode and the slab surface reheats into 1225˚C. This is followed by a grad- ual reheating of slab surface until 1244˚C at 500 mm beneath the meniscus. T cools again and leaves the mold by different values where T in the case of heat 2 is higher than T in the case of heat 1. This agrees with experimental work and measurements performed by Brimacombe et al. [16] where heat 2 reveals a higher

13 Read more

Research and Application on Numerical Simulation of Heavy Rail Steel in Continuous Casting Process

Research and Application on Numerical Simulation of Heavy Rail Steel in Continuous Casting Process

The CET position in bloom should be controlled to expanding equixed grains in rail producing process. On the one hand, the equixed grains area is bigger, the rail performance is more homogeneous. On the other hand, the biggest shear stress of rail is located under the surface of rail tread from 10mm to 15mm. Serious composition segregations did not be allowed existed at that area. Comparing casting bloom with rolling rail, the same positions were 10 to 15 mm area under rail head tread and 25 to 40mm under bloom surface. Therefore, bloom CET position should not be controlled in these areas by modifying the continuous casting parameters.

8 Read more

The design of a linear quadratic optimal regulator for transient heat flow in continuous casting of steel

The design of a linear quadratic optimal regulator for transient heat flow in continuous casting of steel

Difficulties associated with measurement of the surface temperature of the workpiece during the rolling process made direct measurement of the heat transfer coefficients at these locations almost impossible. Indirect method of measurement which involves use of radiation pyrometers has been adopted generally (Kim and Huh, 2000; Polukhin, 1975). The disadvantage of this technique of temperature measurement was that the other modes of cooling were not monitored. Consequently, the accuracy of the results so obtained depends largely on the effectiveness of the radiation mechanism, and the surface heat flux of the material becomes a direct function of the radiation mechanism. Harding (1976) argued that this is misleading since convection was a more important heat transfer mechanism than was generally thought. Polukhin (1975) and Hills (Obinabo, 1991) also considered a combined effect of convection and radiation mechanisms and related it to the surface heat flux of the workpiece. Meanwhile, in their classical experiments on heat flow in continuous casting of steel ingots, Savage and Pritchard (Hills, 1963) obtained a relationship that expresses the surface flux as a function of time. This was done by measuring the rise in the temperature of the cooling water. The data so generated was used to estimate the total quantity of heat removed from the surface of the cooling steel ingot. The expression obtained from the heat flux was of the form

10 Read more

Inclusions control and refining slag optimization for fork flat steel

Inclusions control and refining slag optimization for fork flat steel

inclusions, and the size difference of the inclusions is huge—the larger is about 50 µm and the smaller is less than 10 µ m. It is not desirable for these composite inclusions which exist in steel to be seen in actual production. They mainly come from the cooling and solidification process of continuous casting, due to the decrease in solubility and element interactions. Oxygen, nitrogen, and other impure elements dissolved in molten steel were precipitated as the compound from the liquid phase or solid solution during the cooling and solidification process, and finally, they remained in the steel to form inclusions [11]. This kind of inclusion is harmful to the welding performance, corrosion resistance, and fatigue resistance of steel. However, by analyzing the solubility product of related compounds, we can find ways to reduce the generation of such inclusions.

12 Read more

Thermal Simulation of Solidification Process in Continuous Casting

Thermal Simulation of Solidification Process in Continuous Casting

Continuous casting technology is immensely influencing the steelmaking practice in the worldwide. Basic components of a continuous casting machine (CCM) are schematically shown in Figure 1. The productivity and quality of a continuous casting product depend mainly on process parameters, i.e. casting speed, casting temperature, steel composition, melt cleanliness, water flow rates in the different cooling zones, etc. In this process, there are moving boundary problems known as Stefan problems involving heat conduction in conjunction with change of phase. Since this class of problems requires solving heat equation in an unknown region which has also to be determined as part of the solution, they are inherently non-linear problems. Owing to nonlinearity of thermal energy balance at the

10 Read more

A Hybrid Modeling for Continuous Casting Scheduling Problem

A Hybrid Modeling for Continuous Casting Scheduling Problem

Most studies dealing with continuous caster scheduling are in the centralized static scheduling domain, which may not respond effectively to the needs of real-world problems because steel production is an extremely complex problem in a dynamic environment [1]. Multi-agent-based scheduling can dynamically and flexibly schedule manufacturing processes by means of cooperation and coordination abilities [19]. Hence, exploiting multi-agent systems can be helpful as such systems follow an intelligent distributed approach, which suits applications that are complex, changeable, and modular [4]. Multi-agent systems are made up of autonomous agents that collaborate dynamically to satisfy both local and global objectives [2]. Such agents yield a flexible and dynamic scheduling process rather than a mathematically optimal schedule [1].

8 Read more

DESIGN OF A FUZZY CONTROLLER FOR THE CONTINUOUS CASTING PROCESS

DESIGN OF A FUZZY CONTROLLER FOR THE CONTINUOUS CASTING PROCESS

In this paper a fuzzy rule base was developed based on the solidification characteristics of steel. A fuzzy controller was then designed to control the major casting parameters that cause cracks and breakouts. For the continuous casting of steel, the developed fuzzy controller is a helpful tool in enhancing product quality, reducing rework and eliminating operational hazards such as breakouts. There are several opportunities to combine fuzzy logic with other soft computing methods, that is, neural networks and genetic algorithms that could result in more robust intelligent control practices.

8 Read more

Critical Review On Pull-In Of Aluminium In Continuous Casting

Critical Review On Pull-In Of Aluminium In Continuous Casting

region, which shows an admirable result with related to the casting of aluminium ingot. Hasan and begum [30] by considering 3D turbulent melt flow and heat transmission in liquid sump, vertical low head direct chill slab casting process was modelled for aluminum alloy AA-6061. Experimental results showed that only 10-15 % of heat from incoming melt was removed at the mould in vertical direct chill casting process, while 85-90 % of heat was taken out through secondary cooling by direct water injecting onto the emerging ingot. Formation of air gap decreases heat transmission rate from ingot to mould which further cause reheating of shell will promote to drag marks, segregation knot, surface cracks and mixed microstructure (fine/course). Maurya and Jha [31] were investigated effect of casting speed and superheat on steel slab in continuous casting by developing three-dimensional mathematical models. The study is based on investigation of solidification and heat transmission of steel within mould and in secondary cooling zone. Porosity method was implemented for the mushy zone to treat as porous medium. They were observed mushy region to find out shell thickness of solidified shell. The study reported that casting speed has a major effect on temperature distribution, while superheat has less effect on metallurgical length of strand and on temperature distribution. Higher casting speed has tendency to breakout of solidified shell and mould due to lack of slag film for lubrication between shell and mould.

10 Read more

Effect of Cooling Rate on Phase Transformation and Microstructure of Nb Ti Microalloyed Steel

Effect of Cooling Rate on Phase Transformation and Microstructure of Nb Ti Microalloyed Steel

The cooling rate is a key factor of controlling the slab surface microstructures during continuous casting of steel. The effect of cooling rate on phase transformation and microstructure of Nb ­ Ti microalloyed steel was investigated by a confocal laser scanning microscopy and a Gleeble-3800 thermal simulation machine. The process of phase transformation can be analyzed through in situ observation. A critical cooling rate of 5 K·s ¹1 was revealed, below which the proeutectoid ferrite along austenite grain boundaries and widmanstatten structures were observed, and carbonitrides precipitated were also observed in the proeutectoid ferrite. With the increase of cooling rate, the quantity of the precipitates decreases while the width of the proeutectoid ferrite becomes smaller. The carbonitrides precipitated along the austenite grain boundary result in the decrease of the carbon concentration near the grain boundary, which is more favorable to form the proeutectoid ferrite as well as to change its width. When the cooling rate was greater than or equal to 5 K·s ¹1 , the precipitates were dispersed uniformly in the grain, and the bainite was observed mainly. [doi:10.2320 / matertrans.M2013395]

6 Read more

A Model Estimating the Slab Corner Transverse Cracking Susceptibility of Microalloyed Steel Based on Microstructure

A Model Estimating the Slab Corner Transverse Cracking Susceptibility of Microalloyed Steel Based on Microstructure

The equivalent size of the prior austenite can be calculated to predict the transverse corner cracking upon the availability of slabs D £ . However, another way was needed for slabs C, F, H and K because they cannot have D£ as the austenite grain boundaries were not obvious in low-carbon microalloyed steel or less film-like pre-eutectoid ferrite. Hashio et al. 24) suggested that the slab corner transverse cracking suscepti- bility can be predicted using the grain size and distribution of ferrite grains indirectly. Relationship between the structures and crack index is listed in Table 6. It is easy to find out that the slab corner transverse cracking susceptibility was low as the ferrite grain was fine and uniform. Though the effect of inheritance between austenite grain size and ferrite grain size is well known, the numerical relationship which is used to predict the slab corner transverse cracking susceptibility should be further studied in future.

5 Read more

Show all 10000 documents...