Development of electrochemical silicon sensors for iron and steel melts

Based on the commonly used oxygen sensors with O^2- ion-conducting ZrO₂ electrolytes and solid metal-metal oxide references, new sensors have been developed for direct measurements of Si content in iron and steel melts. The sensors are designed in such a way that local chemical equilibrium of the reaction ZrO₂ + [Si] + 2[O] = ZrSiO₄ is established at the surface of the ZrO₂ electrolyte tube or inside a cavity adjacent to the ZrO₂ electrolyte sensor tip using a saturating ZrO₂-ZrSiO₄ mixture. Concepts and dimensions of the sensors were optimized in view of a fast EMF response upon immersion and the maintenance of a stable EMF recording over extended periods. Reliable measurements were performed in Fe-Si melts at 0.05 to 5 wt.-% Si.     

Development and application of a new hot-work die steel for hot stamping

A new hot-work die steel for hot stamping was developed, and used the die for mass production. The produced die showed good performance owing to its high heat conductivity and wear-resistant characteristics. Two different benchmarking hot-work die steels were investigated, and then compared in terms of their impact ductility,temper characteristics, heat conductivity, and thermal stability. The result of the high-temperature friction wear test indicated that oxidative wear was the main mode in high temperature. On the basis of the comparison and test results, the alloying composition of the new hot-work die steel was especially designed. The new die steel showed good performance with good wear-resistant quality, as well as temper hardness and heat conductivity of HRC 50 and34.3 W/(m·K), respectively. Furthermore,without surface plasma nitriding, the die made of the new steel had no obvious galling with 6142 strokes. After surface plasma nitriding, the die completed 40000 strokes with good surface. The die life is expected to exceed 200000 strokes.     

Sensors based on new oxide electrolyte and oxygen reference materials for on-line measurements in steel melts

Oxygen sensors are helpful tools to control and monitor continuous operations in steelmaking processes, e.g. in ladle refining and in the tundish of a continuous casting system. Up to the present no suitable oxygen probes for on-line measurements have been developed. In search of new sensors much work has been done to investigate and discuss possible error sources which impede the use of the conventional one-reading probes for continuous measurements. In the present study modified plug-type sensors and new combined tube plug-type sensors with optimized cell design are presented. Furthermore, new solid oxide electrolytes combined with new reference materials are used to reduce the flux of ionic oxygen across the solid electrolyte and thereby minimize polarisation effects over extended periods. It is shown that these oxygen sensors enable reliable long-term measurements over periods of at least 5 h in Al-deoxidized unalloyed and high alloyed steel melts.     

耐海洋环境腐蚀高强度不锈钢的设计与性能

 通过新的成分设计和综合应用超洁净化技术和金属间化合物及碳化物的时效沉淀强化技术,成功设计了一种新型的超高强度不锈钢。该钢的抗拉强度[Rm]可达1 940 MPa,[KIC]大于90 MPa·m1/2,并且具有较高的疲劳性能及高温力学性能,在海洋大气及海水全浸的环境下,该钢的耐腐蚀性能与15-5PH不锈钢相当,且明显优于同强度级别的Aermet100钢。     

Physical refining of steel melts by filtration

The removal of nonmetallic inclusions from steel melts prior to casting has significant merit. Laboratory prepared steel melts containing carefully prepared alumina inclusions have been successfully filtered at 1600 °C. Two distinct types of filters were used: (i) tabular alumina packed bed (0.2 to 0.5 cm nominal diameter) and (ii) extruded monolithic alumina (400 cells per square inch). The kinetics of the filtration process have been modeled, and inclusion removal efficiency of up to 96 pct has been achieved in laboratory melts. The results show that inclusion removal efficiency is a strong function of melt velocity in the range of 0.08 to 0.68 cm per second and is weakly dependent on filter length. The type of filter utilized affects inclusion removal efficiency significantly. The inclusion capture kinetics and the filtration characteristics of the filter media tested are discussed. Formerly with Drexel University, Philadelphia, PA.     

Development of new grade of steel shots for casting cleaning

A technology has been developed for producing a new grade of steel shots used in casting cleaning. The developed technology is based on obtaining molten steel with the specified chemical composition microalloyed with titanium and using a highly efficient method of dispersing molten steel stream by water jet under high pressure followed by spheroidisation of produced particles and their solidification in water bath. The chemical composition and tapping temperature have been adjusted and different parameters of atomization process such as molten stream nozzle internal diameter, impact angle, water nozzle system and water pressure have been optimized to attain steel shots with the desired mechanical properties, microstructure, density and grain size. After drying, the steel shots are screened to different sizes. The desired grain size is then subjected to only one‐step tempering process. This technique reduces the processing steps (by omission of the reheating‐quenching treatment) and consequently gives significant savings in processing cost.     

Ejection of steel and slag droplets from gas stirred steel melts

Abstract

Liquid ejections from gas stirred melts can be classified into small film and jet droplets caused by bubble bursting and larger splashes resulting from gas channels formed at higher exiting gas velocities. In view of the conditions in ladle metallurgy, experimental investigations were carried out at moderate to low gas flowrates in an arc heated, bottom stirred 150 kg steel melting furnace and an 80 L water tank. Droplets were collected at different heights above the melt level, while gas flowrates, viscosities, surface tensions, and slag layer thickness were varied. The number of steel droplets collected decreased greatly with height (in the range 30-110 mm) and with size (in the range 0·1-1·8 mm). Calculations showed that the entrainment of droplets is strongly influenced by the velocity of upward flowing gases. While at low flowrates typical for secondary metallurgy (0·1 m s ^-1), only droplets <50 μm will be entrained, BOF (basic oxygen furnace) typical flowrates (20-50 m s ^-1) will cause particles up to 500 μm to be carried into the dust removal systems. Higher surface tensions resulted in increased droplet ejection, while higher viscosities led to a decreasing quantity of ejected melt. Slag layers led to a decrease in the ejection of steel droplets and to an increase in ejected slag but they did not completely stop steel ejection, because gas bubbles appear to entrain steel drops when they rise through the slag layer. Bubble bursting in a pure slag system caused large but few slag droplets due to the high viscosity of the slag as compared to the steel melt.     

Formation of iron-based melts and scope for improvement in steel properties

The formation of melts is considered at the structural level on the basis of viscosimetry. The equilibrium and stability of melts in the course of melting, alloying, and microalloying are considered. Data regarding the interrelated properties of liquid and solid metals indicate the possibility of significantly improving the mechanical and corrosion properties of steel on the basis of metallurgical measures that affect the melt structure prior to solidification. Industrial tests show the great significance of such measures in producing impurity-free steel.     

漏钢预报新技术研发及应用

介绍了目前国内外现有的几种漏钢预报识别方法,分析其原理及应用情况,提出了中冶连铸的漏钢预报模型及该新技术在数学方法、计算机技术、自动化控制应用方面的特点,并介绍了近期该新技术较好的应用效果。     

Refining of steel melts using alkaline earth metals

In secondary refining of steel melts, the use of alkaline earth metals as a slag phase can be of great significance to remove tramp elements of the main groups IV and V. Fundamental data on corresponding refining equilibria and on the solubilities of the alkaline earth metals Mg, Ca, Sr and Ba in iron and iron alloys have been determined by equilibrating the two metal phases, contained in CaO crucibles, under excess argon pressure at 1600°C. The experimental results indicate that tramp elements such as Sn, N, and P are largely transferred from the iron to the alkaline earth metal phase using Ca, Sr or Ba. Equilibrium alkaline earth metal contents are found to be 0.03 % Ca, 0.004 % Sr and 0.0005 % Ba. Solubilities of Ca, Sr and Ba in iron are increased in the presence of Ni and decreased by additions of Cr. In the potential industrial application, reducing conditions must be provided and excessive vaporization must be avoided by adequate techniques of addition of the alkaline earth metals.     

Development of a new method to produce melts suitable for the production of amorphous Fe−Si−B materials

Research work was performed on the development of a new reduction process for the melting and refining of boron containing alloys used in the production of amorphous material for transformer cores. Based on fundamental thermodynamics principles, a reduction refining process was developed which employs conventional steelmaking vessels for using steel scrap, ferro alloys, and boron ores to produce an Fe−Si−B alloy. The process can eliminate the need for ferro boron alloy, high purity iron, and remelt stock to produce the Fe−Si−B alloy. Process variables were established which show the effects of mixing time, reductant alloy additions, slag chemistry, and temperature on the reduction kinetics. Final melt chemistries have lower levels of sulfur, nitrogen, and other tramp elements than conventional methods for producing the Fe−Si−B melt.     

Mathematical modelling of alloy melting in steel melts

This paper deals with a mathematical model for melting of ferro-manganese particles in liquid iron in a ladle. With the assumption that the resistance of heat transport in the iron shell that initially freezes at the particle surface is zero, the particle melting time can be calculated analytically. To describe the total melting rate of alloy particles added into the ladle, a melting distribution function is introduced. It includes the melting time of the individual particles, the particle size distribution, and the addition function of the particles. The factors influencing the melting behaviour of the addition are investigated. The melting behaviour is greatly affected by the particle size distribution, the temperature of the melt, and the particle-melt slip velocity. The addition time and the addition function have only a small influence on the melting behaviour.     

CSP 流程低碳铝镇静钢铸坯碳覆夹杂物析出行为

在使用 CSP 工艺生产低碳或超低碳钢时,在铸坯中,特别是铸坯宽面的中心经常观察到相当数量的微米级碳覆夹杂物.通过对 CSP 流程不同的钢种铸坯取样,研究了这类夹杂物的结构特点和析出机制.指出碳覆夹杂物呈双层结构,外面包裹一层富碳层、中心为钙铝酸盐或含 CaO 的复合夹杂物.热力学计算结果显示这层富碳物质并非 CaC2.通过对比球墨铸铁中球状石墨的形成条件,指出 CSP 铸坯中存在冷却速度快、S 元素含量低、加钙处理后促球化元素 Ca、Mg 含量相对较高,有大量夹杂物作为形核核心等促进碳覆夹杂物析出的有利条件.C 为易偏析元素,在低碳或超低碳钢铸坯凝固过程中液芯中 C 含量的升高,能够析出球状的碳覆夹杂物.并指出由于碳覆夹杂物的析出,中心钢基体 C 含量降低,碳覆夹杂物析出能够减轻铸坯凝固过程中 C元素的偏析程度.     

Prospects of technologies for the direct alloying of steel from oxide melts

This article examines a promising technology for the direct alloying of steel that reduces the amounts of energy and materials used in the process. The scientific principles behind the direct alloying of steel by oxide-based materials are explained, and a method is devised for calculating the composition of oxide mixtures with a low melting point. Compositions of such mixtures are found for the manganese-and chromium-alloying of steel with the use of common oxide-based raw materials. Recommendations are given for preparing oxide mixtures for direct alloying.     

新式分选机入料对输送效果的影响研究

入料堆积方式和入料量的合理选择对新式分选机的分选和输送阶段均有着重要的意义.本文分析研究了静态入料、动态入料以及不同的入料量对新式分选机输送效果的影响,结果表明:不同的入料堆积方式下,排料时间的差异主要源于物料分散所需时间的不同,分散后的排料段物料输送速度相同,排料时间与入料量不成简单的正比关系.     

基于新型辊式机的细粒转炉钢渣干法磁选试验

 选取低品位、多组分磁性铁矿物转炉初炼钢渣,设计适用于细粒钢渣处理的多级辊式磁选机,开展了不同磨矿粒度下单级磁辊粗选及多级磁辊精选试验,对比了磁辊转频、分选行程对各粒度钢渣精矿品位及回收率的影响。结果表明：精选精矿品位明显高于粗选精矿品位,回收率略低;磁辊转频影响回收率较为明显,分选行程两边取值对磁选指标影响程度明显高于中间取值;磨矿粒度越细,磁选机综合处理效果越好;磨矿粒度小于0.3 mm粒级的占90%,精选精矿品位比原矿品位提高约32个百分点。     

激光陶瓷合金化

通过陶瓷合金化涂料的研制,在激光淬火的工艺条件下获得激光陶瓷合金化层.经过陶瓷合金化的钢铁材料,其耐磨性能比激光淬火高约一倍.陶瓷合金化涂料具有与目前广泛使用的激光淬火吸光涂料同样的粘结性能,吸光性能和施涂工艺性能.激光陶瓷合金化是纳米技术、氮化硅应用技术、稀土应用技术、不同质材料之间的偶联技术,激光加工技术和涂料粘结...     

Analysis of the complex deoxidation of carbon steel melts

The joint complex deoxidation of carbon steel melts is analyzed. A procedure is proposed to calculate the equilibrium oxygen concentration in a melt. Rail steel is used as an example to study the joint complex deoxidation of a melt by aluminum and silicon. Mullite (2Al₂O₃ · 3SiO₂) and kyanite (Al₂O₃ · SiO₂) are considered as the reaction products. Thermodynamic calculations demonstrate that the deoxidizing capacity of aluminum is increased in the presence of silicon in a melt. In this case, a substantial increase in the deoxidizing capacity in the concentration range 0.001–0.1 wt % Al is achieved when kyanite (Al₂O₃ · SiO₂) forms in the reaction products. The results of laboratory and industrial experiments on complex deoxidation are shown to agree well with the calculated data. These results demonstrate that the proposed calculation procedure can be recommended to determine the equilibrium oxygen concentration in a melt in the presence of several deoxidizing elements.     

Kinetics of inclusion precipitation during steel solidification

The precipitation of non-metallic inclusions (complex oxides, sulphides, nitrides …) during steel solidification is analysed using the multiphase equilibrium code CEQCSI and a nucleation and growth model. The CEQCSI code is based in part on the Irsid slag model, and it provides an evaluation of the composition of inclusions formed at equilibrium, as well as guidelines for industrial treatments in order to reach desirable compositions in semi-killed steel grades. The nucleation and growth model can be applied to the formation, during steel solidification, of stoichiometric compounds or liquid oxide inclusions. Two particularities of this kinetic model are that nucleation and growth are treated simultaneously, and they compete in consuming the supersaturation at each moment, and that a mixed controlled growth model transport/interfacial kinetics at the precipitate/liquid steel interface is considered. The predicted size distribution of TiN precipitates formed in two steel grades is in good agreement with the results of laboratory experiments. In the case of liquid oxide precipitation, the first calculations indicate that the composition of inclusions can be significantly different from that of inclusions assumed to precipitate under equilibrium conditions.