scholarly journals Effect of Bubbles on Crystallization Behavior of CaO–SiO2 Based Slags

Metals ◽  
2019 ◽  
Vol 9 (2) ◽  
pp. 193 ◽  
Author(s):  
Shaopeng Gu ◽  
Guanghua Wen ◽  
Zequan Ding ◽  
Junli Guo ◽  
Ping Tang ◽  
...  
Keyword(s):  
Molten Slag ◽  
Casting Process ◽  
Steel Shell ◽  
Slag Film ◽  
Peritectic Steel ◽  
Activation Energy Of Crystallization ◽  
Mold Fluxes ◽  
Temperature Transformation ◽  
Longitudinal Cracks ◽  
Cct Diagrams

Surface longitudinal cracks are a serious problem and particularly prevalent in the casting of peritectic steel (carbon content between 0.10%C and 0.18%C, non-alloyed). It is usually alleviated by controlling the horizontal heat transfer from the steel shell to the mold through increasing the crystallization performance of slags. In the actual continuous casting process, a large number of bubbles are formed in the molten slags, and the crystallization properties of the mold fluxes are affected by bubbles. Therefore, an investigation of the influence of bubbles on the crystallization performance of mold fluxes was carried out by applying the hot thermocouple technique and it is hoped that surface longitudinal cracks can be solved in this way in the peritectic steel casting process. The continuous cooling transformation (CCT) diagrams and time–temperature transformation (TTT) diagrams were constructed for an analysis of the crystallization kinetics. The results showed that the crystallization ability of mold fluxes was enhanced by adding bubbles through shortening the incubation time of crystallization, increasing the critical cooling rate, and decreasing the activation energy of crystallization. As a result, the crystalline fraction, slag film thickness, and surface roughness of the slag films were improved, but the crystalline phase was not affected by bubbles. With an increase of the bubble content remaining in the molten slag, the growth mechanism of the cuspidine crystal phase changed from a low dimension to a high dimension, and the content of the molten slag’s structure unit (Q1) needed for cuspidine in the molten slag was markedly increased.

scholarly journals Calculation and Analysis of the Structure and Viscosity of B2O3-Regulated CaO-Al2O3-Based Mold Fluxes

2020 ◽  
Vol 2020 ◽  
pp. 1-10
Author(s):  
Lifeng Chen ◽  
Kun Liu ◽  
Peng Han ◽  
Bin Yang ◽  
Lianghua Feng
Keyword(s):  
Molten Slag ◽  
Chemical Properties ◽  
Casting Process ◽  
Degree Of Polymerization ◽  
Particle Migration ◽  
Mold Slag ◽  
Migration Resistance ◽  
O2 Concentration ◽  
Mold Fluxes ◽  
Physical And Chemical

The high content of aluminum in the steel reacts with the CaO-Si2O-based mold fluxes, resulting in deterioration of the mold slag physical and chemical properties, which cannot be applied to the continuous casting molten slag casting process of high-Mn high-Al steel Herein, the thermodynamic and structural properties of low-reactivity CaO-Al2O3-based mold fluxes were investigated. The thermodynamic properties were studied based on the first principles of quantum mechanics. The results show that the formation of stable structures of B-O and O-B-O in the mold fluxes was beneficial to reduce the probability of structural interconnection, degree of polymerization, and viscosity of the molten slag. The increase in the ratio of CaO/Al2O3 = 0.88–2 led to an increase in the O2− concentration. O2− entered the [AlO4] structure to form a stable structure of [AlO6] and [AlO5], wherein [AlO6] was more stable than [AlO5], reducing the degree of polymerization of the network structure. When cosolvent content B2O3 = 2%–10%, a simple layered structure of [BO3] was formed, and the particle migration resistance, break temperature, and viscous activation energy of the mold fluxes were reduced, while the corrected optical basicity of mold fluxes was gradually increased.

Surface Defect Formation in Steel Continuous Casting

2018 ◽  
Vol 941 ◽  
pp. 112-117 ◽  
Author(s):  
Matthew L.S. Zappulla ◽  
Brian G. Thomas
Keyword(s):  
Continuous Casting ◽  
Thermal Model ◽  
Defect Formation ◽  
Casting Process ◽  
Element Model ◽  
Steel Shell ◽  
Formation Mechanisms ◽  
Δ Ferrite ◽  
And Behavior ◽  
Longitudinal Cracks

Serious defects in the continuous casting of steel, including surface cracks and depressions, are often related to thermal mechanical behavior during solidification in the mold. A finite-element model has been developed to simulate the temperature, shape, and stress of the steel shell, as it moves down the mold in a state of generalized plane strain at the casting speed. The thermal model simulates transient heat transfer in the solidifying steel and between the shell and mold wall. The thermal model is coupled with a stress model that features temperature-, composition-, and phase dependent elastic-visco-plastic constitutive behavior of the steel, accounting for liquid, δ-ferrite, and γ-austenite behavior. Depressions are predicted to form when the shell is subjected to either excessive compression or tension, but the shapes, severity, and appearance differ with conditions. Cracks appearing without depressions are suggested to form in the lower ductility trough when the shell is colder but more brittle. The local thickness of the shell and austenite layer appears to have major effects as well. The model reveals new insights into the formation mechanisms and behavior of surface depressions and longitudinal cracks in the continuous casting process.

scholarly journals Study of the Effect of Carbon on the Contraction of Hypo-Peritectic Steels during Initial Solidification by Surface Roughness

Metals ◽  
2018 ◽  
Vol 8 (12) ◽  
pp. 982 ◽  
Author(s):  
Dazhi Pu ◽  
Guanghua Wen ◽  
Dachao Fu ◽  
Ping Tang ◽  
Junli Guo
Keyword(s):  
Surface Roughness ◽  
Cooling Rate ◽  
Solidification Process ◽  
Casting Process ◽  
Continuous Casting Process ◽  
Peritectic Steel ◽  
Laser Confocal Microscope ◽  
Initial Solidification

In the continuous casting process, the shrinkage of the peritectic phase transition during the initial solidification process has an important influence on the surface quality of peritectic steel. The initial solidification process of 0.10C%, 0.14C%, and 0.16C% peritectic steels was observed in situ by a high temperature laser confocal microscope, and the contraction degree during initial solidification was characterized by surface roughness. The results showed that under the cooling rate of 20 °C/s, the surface roughness value Ra(δ/γ) of 0.10C% peritectic steel was 32 μm, the Ra(δ/γ) value of 0.14C% peritectic steel was 25 μm, and the Ra(δ/γ) value of 0.16C% peritectic steel was 17 μm. With increasing carbon content, the contraction degree of the δ→γ transformation decreased, and the value of the surface roughness Ra(δ/γ) declined. Therefore, surface roughness can characterize the contraction degree of the δ→γ transformation in the initial solidification process of peritectic steel under the condition of a large cooling rate.

scholarly journals Analysis of Non-Symmetrical Heat Removal during Cast-ing of Steel Billets and Slabs

2021 ◽  
Author(s):  
Adán Ramirez-Lopez ◽  
Omar Davila-Maldonado ◽  
Alfronso Nájera-Bastida ◽  
Rodolfo Morales ◽  
Jafeth Rodríguez-Ávila ◽  
...  
Keyword(s):  
Liquid Steel ◽  
Cooling System ◽  
Liquid Core ◽  
Heat Removal ◽  
Casting Process ◽  
Steel Shell ◽  
Steel Ladle ◽  
Ingot Casting ◽  
Friction Forces ◽  
Steel Section

Steel is one of the essential materials in the world's civilization. It is essential to produce many products such as pipelines, mechanical elements in machines, vehicles, profiles, and beam sections for buildings in many industries. Until the '50s of the 20th century, steel products required a complex process known as ingot casting; for years, steelmakers focused on developing and simplifying this process. The result was the con-tinuous casting process (CCP); it is the most productive method to produce steel. The CCP allows producing significant volumes of steel sections without interruption and is more productive than the formal ingot casting process. The CCP begins by transferring the liquid steel from the steel-ladle to a tundish. This tundish or vessel distributes the liquid steel, by flowing through its volume, to one or more strands having wa-ter-cooled copper molds. The mold is the primary cooling system, PCS, solidifying a steel shell to withstand a liquid core and its friction forces with the mold wall. Further down the mold, the rolls drive the steel section in the SCS. Here the steel section is cooled, solidifying the remaining liquid core, by sprays placed in every cooling segment all around the billet and along the curved section of the machine. Finally, the steel strand goes towards a horizontal-straight free-spray zone, losing heat by radiation mechanism, where the billet cools down further to total solidification. A moving torch cutting-scissor splits the billet to the desired length at the end of this heat-radiant zone.

Research of Transverse Corner Crack and Optimization of Concasting Process for Bloom of Peritectic Steel Q235D

2011 ◽  
Vol 284-286 ◽  
pp. 1115-1119
Author(s):  
Cheng Gong Yao ◽  
Shou Qian Yuan ◽  
Lie Chen ◽  
Zhi Jun Wang ◽  
Hai Long Wang ◽  
...  
Keyword(s):  
Crack Formation ◽  
Cooling Water ◽  
Casting Process ◽  
Electromagnetic Stirring ◽  
Continuous Casting Process ◽  
Steel Composition ◽  
Corner Crack ◽  
Peritectic Steel ◽  
Casting Production

Q235D is one kind of peritectic steel, so the casting production inevitably encounter the universality defects of peritectic steel casting. The bloom(250mm×280mm) of Q235D is produced by 60t consteel EBT—LF(VD)—CC process at Xining Special Steel. The main problem in the production is the transverse corner crack, finally lead to occur the cracks and “triangular gaps” at surface of round bar（Φ130mm）after rolled. In order to eliminate the defects caused by transverse corner crack of bloom, the morphology and microstructure and principle of crack formation is researched. The results showed that the crack is caused by stress along the intergranular, and no obvious segregation and particles founded around the defects. The following parameters on the continuous casting process are optimized: steel composition, superheat, the choice of a various slag, the cooling water of different section, casting speed and the electromagnetic stirring parameters. Finally the cracking defects of the bloom is eliminated, and the quality of the bar is optimized.

Evolution of Temperature and Solid Slag Film During Solidification of Mold Fluxes

2017 ◽  
Vol 48 (2) ◽  
pp. 1292-1307 ◽  
Author(s):  
Changlin Yang ◽  
Guanghua Wen ◽  
Qihao Sun ◽  
Ping Tang
Keyword(s):  
Slag Film ◽  
Mold Fluxes ◽  
Solid Slag

Comparison of Measured Phase Volumes with Calculated ones Created by TTT-CCT Diagram Transformation

2007 ◽  
Vol 537-538 ◽  
pp. 497-504
Author(s):  
Zoltán Dudás
Keyword(s):  
Phase Transformation ◽  
Experimental Work ◽  
Experimental Results ◽  
Mechanical Processing ◽  
Continuous Cooling Transformation ◽  
Temperature Transformation ◽  
Continuous Cooling Transformation Diagrams ◽  
Transformation Diagrams ◽  
Cct Diagrams ◽  
Measured Phase

Knowledge of the TTT (Time-Temperature-Transformation) or CCT (Continuous- Cooling-Transformation) diagrams of steels is an important factor in the thermo-mechanical processing of steels. Much experimental work has been undertaken to determine such diagrams. Significant works have been written which can calculate TTT and CCT diagrams for steels. The aim of the present work is to show the developed model that can provide accurate enough TTT and CCT diagrams for steel 42 CrMo4 (where the austenitisation temperature was 1050°C). The calculated results are compared by the experimental results. The developed TTT phase transformation diagrams based on FEM-based phase elements and the star-like cooling simulation make it possible to create virtual CCT diagram data.

scholarly journals Effects of Li2O on Structure and Viscosity of CaO-Al2O3-Based Mold Fluxes

2021 ◽  
Vol 2021 ◽  
pp. 1-8
Author(s):  
Lifeng Chen ◽  
Kun Liu ◽  
Peng Han ◽  
Bin Yang ◽  
Lianghua Feng
Keyword(s):  
Molecular Dynamics ◽  
Mold Flux ◽  
Molten Slag ◽  
Complex Structure ◽  
Degree Of Polymerization ◽  
Dynamics Simulation ◽  
Systematic Analysis ◽  
Structure Characteristics ◽  
Mold Fluxes ◽  
Stable Structures

Since CaO-Al2O3-based mold fluxes are one of the most important mold flux systems in metallurgic processes, it is important to explore their structure characteristics and viscosity. Molecular dynamics simulation is performed to study the effect of w(CaO)/w(Al2O3) ratio on both the structural and viscosity properties of CaO-Al2O3-based mold fluxes. A systematic analysis of the structure and thermodynamics on CaO-Al2O3-based mold fluxes is carried out, and it is well known that the viscosity of mold fluxes is related to the structure. The results show that the formation of stable structures of Si-O in the mold fluxes was beneficial to reduce the probability of structural interconnection, degree of polymerization, and viscosity of the molten slag. In the cationic structure, the contents of Ca-O-Al and Ca-O-Si are more stable, the interconnection of the Ca-O-Al and Ca-O-Si network weakens, and the viscosity decreases. The tetrahedra [AlO4] and [SiO4] have similar structures, but they exhibit different thermodynamic and physical properties. Viscosity test shows that CaO/Al2O3 = 0.88–2 continuously increased, when the cosolvent content Li2O = 1%–4%, CaO-Al2O3-based mold flux viscosity decreased, the degree of network structure polymerization decreased, and the complex structure depolymerized. Increasing the water content in the cosolvent is beneficial to reduce the viscosity of the crystallizer.

scholarly journals Crystallization characteristics of B2O3 and TiO2-bearing glassy fluoride-free mold fluxes

2020 ◽  
Vol 56 (2) ◽  
pp. 279-287
Author(s):  
Z. Wang ◽  
Q.-F. Shu ◽  
K.-C. Chou
Keyword(s):  
Sem Analysis ◽  
X Ray Diffraction ◽  
Slag Film ◽  
X Ray ◽  
Glass Forming ◽  
Mold Fluxes ◽  
Transfer Behavior ◽  
Ability Index ◽  
Crystallization Tendency ◽  
Copper Mould

To explore the effects of TiO2 and/or B2O3 on crystallization of the glassy fluoride-free slag film near the copper mould, the crystallization characteristics of glassy fluoride-free mold fluxes with fluoride being substituted by TiO2 and/or B2O3 were investigated using X- ray diffraction (XRD), scanning electron microscope (SEM) and differential thermal analysis (DTA) techniques. The glass forming ability index (Kgl) of the glassy fluoride-free mold fluxes was studied using Hruby?s method. The XRD and SEM analysis show that Ca2Al2SiO7, CaTiO3 and CaSiO3 are the dominant crystals of this fluoride-free mold fluxes system. With the content of TiO2 increasing from 0 to 7%, the crystallization of Ca2Al2SiO7 and CaSiO3 are inhibited and the formation of CaTiO3 is also weak, so crystallization tendency of the glassy fluoride-free mold fluxes weakens. But as TiO2 content reaches 10%, the crystallization tendency strengthens because of the strong crystallization of CaTiO3. An increase of B2O3 inhibits the crystallization of calcium silicate, so it weakens the crystallization tendency of the glassy fluoride-free mold fluxes. The crystallization processes of the studied fluoride-free mold fluxes correspond to the surface crystallization mechanism. This research provides important reference for further investigation on the heat transfer behavior of the TiO2 and B2O3-bearing slag between copper mould and slab to evaluate the feasibility of B2O3 and TiO2- bearing fluoride-free mold fluxes.

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