Showing papers in "Isij International in 2018"

Overview of Dynamic Strain Aging and Associated Phenomena in Fe–Mn–C Austenitic Steels

Abstract: This paper presents an overview of the recent works on dynamic strain aging (DSA) of Fe–Mn–C austenitic steels including Hadfield and twinning-induced plasticity (TWIP) steels. First, a model of the DSA mechanism and its controlling factors are briefly explained in terms of Mn–C coupling and dislocation separation. Then, we introduce the effects of DSA on mechanical properties such as work hardening capability, uniform elongation, post-uniform elongation, and fatigue strength. Specifically, we note (1) the pinning effect on extended dislocation for the work hardening, (2) the Poretvin–Le Chatelier banding effect on damage evolution for the tensile elongation, and (3) the crack tip hardening/softening effect on crack resistance for the fatigue strength. We believe that this overview will help in designing advanced highstrength steels with superior ductility and fatigue resistance.

A Review of the Chemistry, Structure and Formation Conditions of Silico-Ferrite of Calcium and Aluminum (‘SFCA’) Phases

Abstract: This paper critically reviews published research on silico-ferrite of calcium and aluminum (‘SFCA’) phases, the major bonding phases found in modern iron ore sinters. In particular, we focus on describing the different ‘SFCA’ phases formed in iron ore sinter and examining their phase chemistry, crystal structures, characteristic textures and microstructures, and formation conditions. Information for the two main bonding phases SFCA and SFCA-I are reviewed and, based on a critical analysis of the data, we suggest future research directions required to generate the information necessary to fully describe the properties of both phases.

Effect of Argon Injection in Meniscus Flow and Turbulence Intensity Distribution in Continuous Slab Casting Mold Under the Influence of Double Ruler Magnetic Field

Abstract: In most of the modern integrated steel plants, argon gas is usually employed in the continuous casting process to prevent nozzle clogging, encourage mixing, and encouraging floatation of non-metallic inclusion particles from the molten steel by altering the flow field. The injected argon gas into the molten steel enters into the continuous casting mold through the SEN. Thereafter, the argon gas disintegrates into swarm of bubbles with different diameters due to intense shear forces exerted by molten steel. In general, bubbles with larger in diameter have the tendency to escape from the liquid steel surface through the mold flux powder layer, whereas, smaller diameter bubbles track the primary stream of molten steel flowing deep into the mold cavity.1) In contrast, these small bubbles and non-metallic inclusions sticking to the surface of these bubbles can be entrapped by solidified shell. This, eventually results in defects in the final cast product, namely, “pencil pipe” blisters, slivers, etc.2) The complexity and instability imparted by the injected argon gas on the transient flow pattern may be further circumvented by the application of electromagnetic forces during continuous casting. One of such celebrated practice is the Electromagnetic brake (EMBr), where a static magnetic field on the mold region of a steel continuous caster is applied to control meniscus flow and turbulence intensity distribution. The influence of superimposed magnetic field Effect of Argon Injection in Meniscus Flow and Turbulence

Physical and Mathematical Modeling of Multiphase Flows in a Converter

Abstract: Currently, Basic Oxygen Furnace (BOF) steelmaking is the predominant steelmaking process around the world.1) The BOF steelmaking process can rapidly refine hot metal and ambient scrap into qualified steel of desired carbon content and temperature with the aid of oxygen-blowing top lance and nonreactive gas-blowing bottom plugs. Figure 1 illustrates the composition of a converter and the blowing information.2) The vessel is lined with basic refractories made from magnesite, dolomite, etc. that provide a relatively inert ambient to the corrosive basic slag prepared by lime dissolution. During the blowing process, highly pure oxygen with high pressure and velocity is injected into the molten bath through nozzles in the form of a gas jet for decarburization, which leads to sophisticated transport phenomena in the bath.2) Besides, the bottom-blowing is also of significant importance, which is aimed to obtain a homogenized melt, to decrease the Fe content in slag and to minimize refractory erosion. Fluid flows in the converter bath work together to affect the viability, effectiveness, and efficiency of converter.3) Due to the fairly sophisticated transport phenomena and the difficulty in direct observation, physical water modeling, coupled with mathematical modeling, offers important tools Physical and Mathematical Modeling of Multiphase Flows in a Converter

Influence of soft reduction on the fluid flow, porosity and center segregation in CC high carbon- and stainless steel blooms

Abstract: Mechanical soft reduction, MSR, is today an established technique for reducing center segregation and center porosity in the continuous casting of blooms. The bloom cross section is reduced by pinc ...

Recovery of Phosphorus from Modified Steelmaking Slag with High P2O5 Content via Leaching and Precipitation

Abstract: The P contained in steelmaking slag is regarded as a potential phosphate source, especially with regard to slag with high P2O5 content, which is generated from the utilization of high P iron ores. If P can be efficiently extracted from slag, the obtained P can be used as a phosphate fertilizer. Moreover, the remaining slag can be recycled inside the steelmaking process. Compared with other phases, the P-condensed C2S–C3P solid solution in slag is more easily dissolved in water; therefore, selective leaching was applied to recover P from slag with high P2O5 content. In this study, the effect of K2O modification on P dissolution in the citric acid solution was investigated, and subsequently, a process for extracting phosphate product from the leachate, via precipitation, was explored. It was determined that K2O modification promoted dissolution of the solid solution, resulting in a higher dissolution ratio of P. By modification, the majority of the solid solution was dissolved at pH 6, and other phases remained in residue, indicating that a better selective leaching of P occurred. As the pH decreased, the dissolution ratios of both P and Fe increased. Following leaching at pH 5, a residue with a higher Fe2O3 content and lower P2O5 content was obtained. When the pH of the leachate increased, the dissolved P in the aqueous solution was precipitated. Through separation and calcination, a phosphate product with a P2O5 content of 30% was obtained, which has the potential to be used as a phosphate fertilizer.

Bubble Behavior and Size Distributions in Stopper-Rod Nozzle and Mold during Continuous Casting of Steel Slabs

Abstract: Argon gas injection is widely used to prevent nozzle clogging during continuous casting of steel. Argon gas is well known to improve clogging resistance via several mechanisms1) which include preventing deoxidation products/inclusions from contacting the nozzle wall,2–4) flushing the inclusions off of the nozzle,4,5) promoting the flotation of inclusions,6) reducing negative pressure and air aspiration through the nozzle walls,4,7,8) and preventing chemical reactions between the steel and the nozzle refractory.6) However, unoptimized argon gas injection may be detrimental to final steel product quality. The annular or slug flows produced by abnormal high gas flow rate compared to the molten steel flow rate in a nozzle can produce asymmetric jet flow in the mold,9,10) shallower jet angle,11) and higher turbulence energy,11) resulting in severe surface velocity and level fluctuations,12) and finally causing surface defects in the final steel products.9–12) In addition, abnormal big bubbles easily float upwards to the surface near Bubble Behavior and Size Distributions in Stopper-Rod Nozzle and Mold during Continuous Casting of Steel Slabs

Evolution Mechanism of Inclusions in Al-killed, Ti-bearing 11Cr Stainless Steel with Ca Treatment

Abstract: Titanium-bearing stainless steel, due to their good formability, excellent corrosion resistance in high temperatures and cost-effectiveness, has been widely used in various applications including culinary, automobile and calorifier. Titanium suppresses chromium carbide precipitation at grain boundary through the formation of more stable titanium carbide, which substantially improves the resistance to intergranular corrosion.1,2) What is more, the heterogeneous nucleation of delta ferrite on the TiN formed during primary solidification of stainless steel promotes the generation of the equiaxed fine-grain structure.3,4) However, the generation of oxide inclusions is inevitable due to de-oxidation by Al before Ti alloy addition and the interactions between reactive elements in the steel melt and its environment (slag, refractory, or atmosphere). These inclusions generally cause the clogging of submerged entry nozzle (SEN) and deteriorate the quality of final steel products, such as skin laminations or line defects on the rolled strip.5–8) Therefore, it is necessary to investigate the formation mechanism of oxide inclusion to control the inclusion population. Aluminum is usually added to be the final deoxidizer Evolution Mechanism of Inclusions in Al-killed, Ti-bearing 11Cr Stainless Steel with Ca Treatment

Dissolution Mechanism of Carbon Brick into Molten Iron

Abstract: In recent years, many studies have been carried out to extend the campaign life of blast furnace (BF).1,2) The hearth sidewall which is considered as the key area of BF has attracted more and more concerns.3,4) The direct contact between carbon refractory and carbon-unsaturated molten iron is regarded as the main reason for the hearth sidewall erosion. The erosion is inevitable due to the carbon is easily dissolved into molten iron.5–7) Therefore, the dissolution of carbon refractory into molten iron is an important reaction for the ironmaking process. Many papers have been reported to describe the dissolution of carbon into molten iron. The dissolution rate of carbon into molten iron was investigated by Dahlke.8) The effects of carbon structure and extent of porosity on the dissolution were studied in some literature.9–11) Cham et al.12) calculated the activation energy for the dissolution of carbon from graphite. Shigeno et al.13) supposed that the dissolution rate of carbon from coke is lower than that of pure graphite. Mourao et al.14) asserted that a viscous layer formed by ash in carbon source was found around the interface. Orsten et al.15) observed that a gas film around the interface formed by volatile matter from carbon source will hinder the dissolution process. Kayama et al.16) assumed a high rate of dissolution can be obtained when the coke with low porosity. Wright and Badlock17) investigated the increase of sulfur content in molten iron decreases the graphite dissolution Dissolution Mechanism of Carbon Brick into Molten Iron

Distribution and Morphology of MnS Inclusions in Resulfurized Non-Quenched and Tempered Steel with Zr Addition

Abstract: Non-metallic inclusions in steels are generally harmful to their material performance, so extensive researches have been conducted to reduce their presence in steels.1–4) However, the utilization of inclusions for control of microstructures and enhancement of mechanical properties is becoming of considerable interest.5–8) Manganese sulfide inclusions are typical inclusions detected in non-quenched and tempered (NQT) steels. Medium content of sulfur is usually added into steels for their beneficial effects on improving machinability,9,10) retarding grain growth11,12) and inducing intragranular ferrite.11,13,14) However, the large-sized elongated MnS inclusions, which exist in longitudinal section after deformation, are severely detrimental to the transverse mechanical properties of steels.15,16) Therefore, numerous studies focusing on the control of the morphology, size and distribution of MnS inclusions have been conducted over the years.17–20) MnS inclusions have been classified into three types according to their morphologies in ingots, i.e., (1) randomly dispersed globular sulfides (type I), (2) rod-like or dendritic Distribution and Morphology of MnS Inclusions in Resulfurized Non-Quenched and Tempered Steel with Zr Addition

Effect of TiO2 and MnO on Viscosity of Blast Furnace Slag and Thermodynamic Analysis

Abstract: The effect of TiO and MnO on the viscous behavior and structure of CaO–SiO–MgO–AlO–TiO–MnO slags were studied using rotating cylinder method and FTIR spectroscopic analysis. Furthermore, the heat capacity and enthalpy change of the slag were calculated to clarify the influence of TiO and MnO on the heat quantity of the slag at elevated temperatures, and then the equilibrium temperatures and corresponding viscosities of the slag under various fixed heat quantities were also analyzed. The higher TiO and MnO contents resulted in lower viscosity. The FTIR results revealed that TiO and MnO depolymerized the slag by modifying the silicate network structure and breaking the linkage between the silicate and aluminate structure, while have little effect on aluminate structure of the slag. In the temperature range of interest, the enthalpy change of the slag increased with increasing TiO content, but remained basically unchanged with MnO additions. The fluctuations of the slag heat quantity had a significant influence on the slag temperature and viscosity. With the increase of TiO content, the equilibrium temperature of the slag at fixed heat quantity decreased and the corresponding viscosity increased. However, as the MnO content increased, the equilibrium temperature of the slag at fixed heat quantity was almost constant and the corresponding viscosity decreased.

Iron Powders from Steel Industry by-products

Abstract: Global iron and steel making industries generate immense number of by-products, among which few are already being utilized for the generation of high value products, while few are still struggling to gather a good market space. Waste utilization is the major concern for every industrial maker. In this context, iron powder which holds immense market in applications like powder metallurgy (PM) parts, welding electrodes, advanced oxidative agents for water treatment, food fortifying agents, metal injection moulding, catalysts, fuels etc., can now be a novel outcome from steel industry by-products. Iron powder can be manufactured by various techniques like reduction, atomization, electrolysis, etc., resulting in fine particles of various morphologies ranging from spherical to irregular shapes and low to high purity. The application of these iron powders is depended on the process, quality and purity of the desired product.

Effects of CaCO 3 as Additive on Coal-based Reduction of High-phosphorus Oolitic Hematite Ore

Abstract: Nowadays, because of the limited reserves and quick depletion of hematite-rich iron ores, many iron and steel companies are attempting to exploit refractory and low-grade iron ores as alternative resources for ironmaking.1) Oolitic hematite ores are widely distributed in USA, France, Germany, Russia and China.2) In China, the total proven reserves of such resources are over 4.0 billion tons and are therefore receiving considerable attention.3) The oolitic hematite ore, which has a special concentric and layered oolitic texture as well as high phosphorus content (0.4 mass%–1.8 mass%), is regarded as one of the most refractory iron ore resources.3–5) Besides, phosphorus is mainly in the form of apatite, where the particle size of the crystal is very fine and not easy to separate. Therefore, the high-phosphorus oolitic hematite is difficult to utilize as a raw material in ironmaking.6–8) Recently several phosphorus removal processes for high phosphorus oolitic hematite have been investigated, including physical separation, flotation, acid leaching and bio-leaching etc. For example, dephosphorization of oolitic hematite by gravity separation (e.g. hydrocyclone, shaking table), magnetic separation was reported.9–11) Among them, an iron concentrate with 61.18 mass% Fe grade was obtained, but the phosphorus content of the concentrate was as high as 0.51 mass%.10) Meanwhile for physical Effects of CaCO3 as Additive on Coal-based Reduction of High-phosphorus Oolitic Hematite Ore

Hydrogen Embrittlement Behavior of Ultra-high Strength Dual Phase Steel Sheet under Sustained Tensile-loading Test

Abstract: The hydrogen embrittlement behavior of an ultra-high strength (1180 MPa grade) dual phase steel sheet composed of ferrite and tempered martensite, as compared with that of a single phase steel sheet composed of tempered martensite, has been investigated by a sustained tensile-loading test. No fracture of the dual phase steel occurs under the low hydrogen-charging current density of 5 A/m except under high applied stress substantially larger than the yield stress. With the high current density of 50 A/m, the time to fracture of the dual phase steel varies widely, but is almost the same as that of the single phase steel. The critical applied stress for fracture of the dual phase steel is higher than that of the single phase steel. Under the high applied stress, however, the time to fracture of the dual phase steel is shorter than that of the single phase steel, and a unique intergranular-like morphology is observed at the crack initiation area on the fracture surface. Upon plastic deformation before the sustained tensile-loading test under the high applied stress, the time to fracture of the dual phase steel increases and the initiation area on the fracture surface exhibits typical quasi-cleavage features. The results of the present study indicate that the hydrogen embrittlement of the dual phase steel displays some anomalous behavior.

Effect of strain rate on the hydrogen embrittlement property of ultra high-strength low alloy TRIP-aided steel

Abstract: High-strength steels of tensile strength of 780 and 980 MPa grade have been positively applied for automotive frame parts to attain the improvement of the impact safety and the reduction of car weight. Moreover, in present, ultra high-strength steels have gotten attention because the ultra high-strength steels possessing the tensile strength of more than 1 470 MPa grade using a hot stamping technique1) have been applied for the automotive structural parts. A lot of studies about hydrogen embrittlement was strongly conducted since the occurrence of the hydrogen embrittlement of automotive ultra high-strength steel sheets with tensile strength of more than 980 MPa grade is serious problem in the same way as conventional structural steels.2,3) Transformation induced plasticity (TRIP)4)-aided bainitic ferrite (TBF)5–8) steels with bainitic ferrite matrix are expected to be used for the next generation automotive frame parts due to an excellent formability, an impact property and a fatigue property. Moreover, it has been reported that TBF steels exhibited excellent hydrogen embrittlement resistance in comparison with conventional bainitic and Effect of Strain Rate on the Hydrogen Embrittlement Property of Ultra High-strength Low Alloy TRIP-aided Steel

Optimum conditions for phosphorus recovery from steelmaking slag with high P2O5 content by selective leaching

Abstract: Utilization of high-P iron ores is gaining considerable attention because of large reserves and the depletion of high-grade iron ores. The use of low-grade iron ores results in an increase in the P content in hot metal. Therefore, P is removed from iron ores prior to its use in smelting.1) A variety of dephosphorization processes for high-P iron ores have been developed such as acid leaching, carbothermic reduction, and physical beneficiation.2–4) Due to the large amount of iron ores, an enormous processing capacity is required and the treatment cost is also huge, which restricts the industrialization of these methods. P existing in high-P iron ores is considered a potential source of phosphorus. We should therefore pay attention to the comprehensive utilization of high-P iron ores. Through efficient dephosphorization using multi-phase slag, high levels of P in hot metal can be removed, leading to its concentration in slag.5) P is mainly found in the 2CaO∙SiO23CaO∙P2O5 (C2S–C3P) solid solution in steelmaking slag, which has a high P2O5 content and high distribution ratio between C2S–C3P solid solution and other phases.6) If the P-concentrated solid solution can be extracted from the slag, the obtained phosphate will be suitable for producing phosOptimum Conditions for Phosphorus Recovery from Steelmaking Slag with High P2O5 Content by Selective Leaching

Effect of Super-gravity Field on Grain Refinement and Tensile Properties of Cu–Sn Alloys

Abstract: It is well known that the mechanical properties of castings can be improved by grain refinement. Common methods to refine the grain structure are adding grain refiner into the melt and low temperature casting in the casting process.1) With the development of external physical field technology, many articles have been published concerning the magnetic, electric current and ultrasonic fields on the grain refinement.2–7) However, super-gravity is often overlooked in regards to the effects of external physical fields on the solidification structure. In recent years, super-gravity technology exhibited great advantages on the metal purification and the recovery of valuable metals.8–13) In the field of casting, metallurgists were mainly focused on the mold filling behavior by centrifugal method previously.14–17) However, studies specialized to grain refinement of castings in super-gravity field are seldom reported as a whole and the refining mechanism is far from clear. Previously, four mechanisms were contributed to the structure refinement of as-cast alloys under super-gravity (centrifugal force) field: the change of nucleation energy mechanism by Chen et al.,18) the dendrite fragments mechanism by Zhao et al.,19) the coexist of free-chill crystals and Effect of Super-gravity Field on Grain Refinement and Tensile Properties of Cu–Sn Alloys

A Reaction between High Mn–High Al Steel and CaO–SiO2-Type Molten Mold Flux: Reaction Mechanism Change by High Al Content ([pct Al]0 = 5.2) in the Steel and Accumulation of Reaction Product at the Reaction Interface

Abstract: A series of laboratory-scale experiments were carried out in order to elucidate the reaction mechanism between high Mn-high Al steel and CaO–SiO2-type molten mold flux at 1 450°C, which represents the reaction taking place during continuous casting of the steel. Compared to the previous study [Kim et al., Metall. Mater. Trans. 44B (2013) 299–308], high Al content in the liquid steel ([pct Al]0 = 5.2) and high MgO content in the liquid flux ((pct MgO)0 = 5 to 15) were employed, in order to confirm change of rate-controlling step from mass transport of Al in liquid steel to more complicated steps including mass transport in liquid flux. It was found that Al2O3 was rapidly accumulated near the interface of the flux, and SiO2 and Na2O were reduced simultaneously, regardless of (pct MgO)0. At the early stage of the reaction (1 min), MgAl2O4 particles were observed in the flux near the interface, then the particles were spreading out into the bulk flux as the reaction time passed. Other solid phases (CaAl4O7, Al2O3) were also observed due to local depletion of MgO in the flux. The MgAl2O4 formation mechanism and its effect on mass transfer in the molten flux were discussed. A series of simple kinetic analyses showed that the mass transport of Al in liquid steel is no more controlling the reaction rate. It was concluded that there were possibilities of mass transport in the flux phase contributing reaction rate controlling step.

Dissolution Behavior of Mg from MgO–C Refractory in Al-killed Molten Steel

Abstract: MgO·Al2O3 spinel inclusions (henceforth referred to as spinel inclusions for simplicity), which have the property of high melting temperature and poor deformability, are harmful to both the surface quality and fatigue resistance of steel.1,2) Moreover, the spinel inclusions are easy to sinter with the Al2O3–C nozzle materials at high temperature and subsequently cause clogging, which leads to problems in continuous casting operations.3,4) Therefore, spinel inclusions have harmful effects on both the steel product and production operations. A significant number of laboratory and field experiments have been performed on this subject.5–25) MgO–C refractory is one of the most widely employed refractories in steel refining, owing to its high resistance to erosion and thermal shock. However, when in contact with steel melt, MgO–C refractory is considered as a source of Mg to form spinel inclusions. Brabie et al.26) investigated the mechanism of the reaction between MgO–C refractory containing 20 mass% of carbon and Al-killed molten steel. They observed that Mg dissolved into the steel melt from the MgO–C refractory and spinel inclusions were formed. For the supply mechanism of Mg from the MgO–C refractory, they identified the generation of Mg vapor by the reaction between carbon and MgO in the refractory. J. Shan et al.27) Dissolution Behavior of Mg from MgO–C Refractory in Al-killed Molten Steel

Oxidation of Ti Added ULC Steel by CO Gas Simulating Interfacial Reaction between the Steel and SEN during Continuous Casting

Abstract: Submerged Entry Nozzle (SEN) clogging is one of the major problems lowering quality of steel products and productivity during the continuous casting process. Nozzle clogging occurs often during casting of Al-killed Low Carbon (LC) steel and Ultra Low Carbon (ULC) steel.1) The clogging mechanism in Al-killed ULC steel was well established that the clogging is developed by two steps: network alumina formation and buildup of alumina inclusions suspending in liquid steel.1–3) The network alumina is formed on inner surface of a nozzle due to a reaction between dissolved Al in liquid steel and CO gas generated from the nozzle.1,2,4) Once the network alumina is formed, other alumina inclusions suspending in the liquid steel as a product of deoxidation move to the inner wall due to eddies induced by steel flow. The roughness of inner wall of the nozzle provides a favorable condition for the alumina inclusions to attach to the already formed network alumina layer.1) As this alumina adheres repeatedly, inner passage of the nozzle becomes narrower. Finally, it causes the nozzle Oxidation of Ti Added ULC Steel by CO Gas Simulating Interfacial Reaction between the Steel and SEN during Continuous Casting

A Review of Fluorine-free Mold Flux Development

Abstract: In the mid-19 century, Sellers and Bessemer et al. first proposed the concept of continuous casting for molten steel, which was originally used for the casting of low melting point metals such as Lead. Until 1943, the first continuous casting machine for casting steel was invented. By the 1950s, the continuous casting technology was formally applied to the industrial process of steel production. Subsequently, the continuous casting technology has been rapid developed and wide applied, as it owns the advantages of short production process, high metal recovery rate and low A Review of Fluorine-free Mold Flux Development

Effect of CaO/Al2O3 Ratio of Ladle Slag on Formation Behavior of Inclusions in Mn and V Alloyed Steel

Abstract: The Mn and V alloyed steel, which has a ferrite-pearlite composite microstructure, have been widely used as automotive parts such as crankshafts, push rods, rotating bearings, etc. due to its excellent machinability and high-strength. However, the product performance can be significantly affected by the steel cleanliness. Gojić et al.1) reported the resistance to hydrogen embrittlement could be improved by lowering the non-metallic inclusions. In addition, the MgAl2O4 spinel inclusion, which generally formed during the ladle refining process, potentially causes nozzle clogging as well as surface defects in products.2–14) Hence, it is crucial to predict and control the inclusion composition during the ladle refining process. Thermodynamics of the formation behavior and modification of spinel inclusion in molten steel have been extensively investigated since the 1980’s.2–15) Specifically, Park et al.8–13) reported the formation mechanism of spinel inclusion and suggested versatile countermeasures during stainless steel refining and casting processes. Todoroki and Mizno reported that silica in the slag enhanced the formation of spinel inclusions and suppressed extensive reduction of CaO in the slag.7) In fact, most of studies were carried out with respect to molten stainless steels. However, studies on the inclusion formation behavior of specialty steels such as Mn and V alloyed steels are insufficient. Effect of CaO/Al2O3 Ratio of Ladle Slag on Formation Behavior of Inclusions in Mn and V Alloyed Steel

Effect of Microstructure and Precipitates on Mechanical Properties of Cr–Mo–V Alloy Steel with Different Austenitizing Temperatures

Abstract: In recent years, high-speed railway develops rapidly, especially in Europe, Japan and China. Meanwhile, higher requirements have been suggested on the performance of their parts. The material of train axle requires excellent fatigue strength and impact toughness for the safe application in high-speed railway. 30NiCrMoV12 as-quenched and tempered steel developed by French ALSTOM has been used for train axle of high-speed railway in Chinese cold regions due to its excellent mechanical properties with the tensile strength of 950–1 079 MPa, fatigue strength of more than 495 MPa, longitudinal impact toughness of above 50 J and especially lower ductile-brittle transition temperature (DBTT). The heat treatment process should be optimized to obtain the required mechanical properties through appropriate microstructure and carbide precipitates. Effect of Microstructure and Precipitates on Mechanical Properties of Cr–Mo–V Alloy Steel with Different Austenitizing Temperatures

Carbothermic Reduction of Vanadium-Titanium Magnetite in Molten NaOH

Abstract: Vanadium-titanium-bearing magnetite of Panzhihua, China, is a complex iron ore with the coexistence elements of vanadium and titanium. It accounts for more than 90% of the titanium reserves in China. By the beneficiation process of the ore, titanomagetite concentrates and ilmenite concentrates are produced.1,2) The titanomagnetite concentrates are used as the main materials for the blast furnace process in Panzhihua area now. In this process, most of the iron and partly of the vanadium can be reduced into the hot metal; however, almost all of the titanium remains in the slag, forming the high titanium bearing slag, which contains about 21%–25% of TiO2, and emission in every year is more than 3 million tons.3) This slag is the considerable strategic resources and the precious wealth. There is no appropriate and economic method to deal with such slag so far. Titanium and vanadium are widely used in the aerospace and chemical industrial because of their great use and importance. Many countries regard the deposit of titanium and vanadium as a strategic resource. China is abundant in titanium, account for about 48% of the world. However, the recovery ratio of the titanium is too low in the current smelting process of the vanadium tianomagnetite resource. Carbothermic Reduction of Vanadium-Titanium Magnetite in Molten NaOH

Numerical Study of Inclusion Removal in Steel Continuous Casting Mold Considering Interactions Between Bubbles and Inclusions

Abstract: Bubble coalescence-breakup and bubble-inclusion interaction models were implemented into EulerianLagrangian models of steel liquid flow and discrete particles transport, which was applied to examine the interaction and removal of discrete bubbles and inclusions during continuous casting. Bubble distribution affected by coalescence-breakup and its connection with the inclusion removal rate were analyzed. The inclusion removal rates at different initial bubble diameters and inclusion diameters were predicted. Larger inclusions have a higher removal rate and the predicted removal rates ranging from 14% to 30% agree well with industrial experiment measurements. It is also found that smaller bubbles have a higher capacity to remove inclusions and very small bubbles may cause more production defects when it is attached to inclusions. These results show that the developed model can reasonably predict the behaviors of discrete bubbles and inclusions and their interactions in molten steel. Such a model should be useful for the operation of steel continuous casting.