Variations of nitrogen with silicon content of electrical steels

The nitrogen content of commercial heats of electrical steels has been observed to increase with decreasing silicon content prior to teeming despite a constant nitrogen content prior to addition of alloying silicon to molten steel. This behavior can be qualitatively described by a nitrogen transfer model which predicts: the rate of absorption of nitrogen by the metal is greater at lower silicon contents; a final nitrogen level increasing with decreasing silicon; the thermodynamic activity of nitrogen is approximately constant regardless of silicon content at teem time; the nitrogen level increases with longer holding times; and ladle practice will affect nitrogen levels.     

Modification of oxide inclusions in calcium-treated Al-killed high sulphur steels

A study has been carried out to understand the modification of alumina inclusions in Al-killed high sulphur steel with calcium treatment. For calcium treatment to be effective, a general practice is to desulphurise the steel to prevent the formation of solid CaS inclusions that are harmful to steel quality and final properties. To avoid this additional desulphurising step, the authors developed a new approach of calcium treatment of steel at an industrial scale. This approach involves treating the liquid steel with calcium treatment at low aluminium levels which enables formation of liquid calcium aluminate inclusions (C12A7) in the melt and then adding remaining amount of required aluminium. Based on this principle, Al-S diagram has been developed and calcium treatment has been modified accordingly. The inclusion transformation and morphology were studied using scanning electron microscope /energy dispersive spectroscopy analysis and. activity of CaS was calculated.     

Precipitation behaviour and control of TiN inclusions in rail steels

This paper studied the precipitation behaviour and the control of TiN inclusions in rail steels by thermodynamic calculation and industrial experiments. The results showed that TiN inclusions could not precipitate in molten steel at present condition owing to low [Ti] and [N] content in rail steels; but when solid fraction exceeded 0.87 in mushy zone during solidification process, TiN inclusions could precipitate because of the separation–crystallisation of [Ti] and [N], and even long strip inclusions were formed around grain boundaries. Two types of TiN inclusions, including long strip type with size ranging 20–30?μm and block type with size below 10?μm, could be found in rail steels. The formation of TiN inclusions could be affected by the content of [Ti] and [N], the superheat of liquid steel, secondary cooling intensity and the intensity of strand electromagnetic stirring. The metallurgical process III was conducive to the control of TiN inclusions precipitated and grown up. The results of thermodynamic analysis were consistent with those of the metallurgical process tests.     

Ce-La合金化处理对取向硅钢夹杂物特征的影响

 为了研究稀土处理对取向硅钢中夹杂物特征的影响,借助FE-SEM/EDS和图像分析软件分析了稀土处理前后热轧取向硅钢夹杂物的成分、形貌、尺寸和数量并解明了影响机理。研究结果表明,未添加稀土的试验钢中,典型的夹杂物为形貌不规则的MnS-AlN复合夹杂物以及片状或条状的AlN夹杂物;添加稀土后,夹杂物则以球状或椭球状的CeS-LaS、CeS-LaS-AlN、Ce₂O₂S-La₂O₂S复合夹杂物和AlN夹杂物为主。稀土处理有效改善了夹杂物形貌,特别是大尺寸氮硫化物的形貌特征,未检测到MnS类夹杂物。尽管加入较多的稀土后夹杂物数量增加,大于5 μm夹杂物的平均尺寸增大量明显(增大0.89 μm),但整体夹杂物的平均尺寸仅增大了0.40 μm。由于稀土的脱硫作用,且稀土硫化物与AlN晶格常数差异大,钢中氮硫化物的数量密度和面积分数降低。稀土降低了AlN在钢中的平衡溶度积,使AlN夹杂物提前析出,导致AlN夹杂物数量增多,且先析出的AlN出现一定程度的长大。稀土对MnS在凝固前沿的析出有抑制作用,有利于热轧和常化过程析出更多用作抑制剂的MnS和AlN。在充分脱氧的取向硅钢中适当降低钢中酸溶铝含量,调整稀土在钢中的用量,在不增加钢中大尺寸夹杂物含量的前提下,发挥MnS、AlN抑制剂作用和Ce-La合金化作用。此外,通过稀土处理控制钢中夹杂物形貌特征,将有望达到改善钢的热轧组织和轧制加工性能的目的。     

Evolution of oxide inclusions in W800 non- oriented electrical steel

Inclusion is one of the major factors affecting magnetic properties of non- oriented electrical steel. Steel and slag samples were sampled in the production route of W800 non- oriented electrical steel. The composition of slags and the content of TO were measured by XRF and oxygen and nitrogen analyzer. The morphology, amount and composition of oxide inclusions were analyzed by an automated scanning electron microscope ASPEX. Before adding aluminum, the oxide inclusions are mainly spherical silicon oxide and a few SiO2- MnO wrapped by SiO2. Due to the high affinity with oxygen of aluminum, the oxide inclusions changed to alumina and MgO??Al2O3 spinel after adding aluminum. Only two types of morphologies of Al2O3 can be observed by polishing and acid etching. Sphere shape, cluster and polyhedron shape of Al2O3 can be observed after electrolysis of nonaqueous solution. Therefore, electrolysis of nonaqueous solution is more effective and accurate in revealing the morphologies of oxides. The average content of MgO in inclusions increases to 8. 1 mass% during soft blowing, due to the erosion of refractories.The inclusions grows larger and are removed effectively by argon blowing. Nearly no CaO exists in oxides because of low basicity and mass ratio of CaO to Al2O3. With the addition of Al, the inclusions are SiO2, liquid SiO2- Al2O3 and Al2O3, which are in agreement with the observed results.     

Nonmetallic inclusions in important steels

The contamination of 30Cr2Ni4MoV rotor steel with exogenous nonmetallic inclusions is studied. Technological measures intended to decrease the level of contamination of the steel with nonmetallic inclusions and to enhance its quality are recommended.     

Nature and diagnostics of nonmetallic inclusions in steels

The chemicomineralogical nature of nonmetallic inclusions (NIs) in a number of steel grades prepared by traditional melting, elecroslag refining, and casting has been studied. Suboxides and phases having variable nonstoichiometric compositions are found to comprise nonmetallic inclusions. Their role in the formation of the properties of steel is demonstrated.     

轴承钢中夹杂物分析

对轴承钢热轧板中的夹杂物以及浇铸过程结晶器浸入式水口上的结瘤物进行了电镜检测.发现轧板试样中夹杂物类型主要是TiN、MgO·Al₂O₃和MnS以及少量的CaS,尺寸大多在20μm以内,除此之外,还观察到一些大尺寸MgO·Al₂O₃和Al₂O₃夹杂物及其伴生的裂纹.通过对水口结瘤物的检验分析,发现结瘤物主要以MgO·Al₂O₃尖晶石类夹杂物为主,还有少量的MgO-Al₂O₃-CaO系夹杂物,此外还含有部分凝钢.结瘤物成分与钢水中氧化物夹杂一致,因此推测水口结瘤产生原因为钢液中的固态氧化物夹杂在浇注过程中在水口上的聚集沉淀,轧板中大尺寸夹杂可能是由水口结瘤物剥落造成.     

Physico-chemical aspects of the behaviour of inclusions in steels

Adequate physical and mechanical properties, for numerous steel grades, can be obtained only with a precise control of the composition, morphology and plasticity of oxide and sulphide inclusions that remain in the product. In liquid metal, the composition of complex inclusions can be monitored by appropriate deoxidation practice, calcium treatment and/or slag-metal reaction. Further transformation may occur during solidification or heat treatments prior to hot-rolling: reaction between oxides and sulphides, as well as crystallization of oxides. An analysis of these factors, and of tools (thermodynamic models and laboratory experiments) which have been developed to comprehend and control them is presented.     

脱氧工艺对车轮钢氧化物夹杂控制的影响

从脱氧材料的选择、加入时间和加入方式以及脱氧产物排除方法试验了不同脱氧工艺对车轮钢中氧化物夹杂控制的影响,试验结果表明:采用出钢预脱氧+LF一次性加Al+钙处理工艺,能有效降低钢中B类夹杂,可完全满足车轮钢对B类夹杂物的技术条件要求。     

Behavior of alumina-magnesia complex inclusions and magnesia inclusions on the surface of molten low-carbon steels

It is well known that alumina inclusions on the surface of molten Al-killed steel quickly attract each other to form clusters. On the other hand, alumina-magnesia complex inclusions on the surface of molten low-carbon steel with a high oxygen content have a much weaker tendency to form clusters. In the present work, the reason for the different behaviors of the two types of inclusions was analyzed in detail. A confocal scanning laser microscope was used to carry out the experiment of in-situ observation of the two types of inclusion on the molten pool. The first type of inclusion was 93 mass pct alumina-7 mass pct magnesian, obtained in a Mg-added Al-killed steel. The second type of inclusion was nearly pure magnesia, obtained in a Mg-killed steel. The attractive force between a pair of inclusions, for both cases, was found to be approximately 1O⁻¹⁷ to 10⁻¹⁶ N and one-tenth of that between a pair of alumina inclusions. The various effects of contact angle, surface tension, and oxygen content of the steel melt on the attractive force are discussed in detail from the viewpoint of the capillary force.     

The re-solution of inclusions in remelted stainless steels

As a follow-up to work done on the remelting of three grades of 300 series stainless steels on a small scale electroslag remelting unit, adjunct studies were made on the kinetics of inclusion re-solution during the “electrode stage” of remelting. The objective of this study was to attempt to quantify the metallographic observations of many investigators that vary-ing degrees of inclusion re-solution do take place during the consumable remelting of numer-ous grades of metals and alloys. In specific, the rate(s)of re-solution of the large stringer inclusions found in the 300 series air melt stock was investigated. A known and controlled temperature gradient was imposed on long cylindrical specimens for varying times and, by a metallographic inclusion sizing and counting technique described in this paper, a series of isochronal and isothermal data was generated. Plots of rates of re-solutionvs time indi-cated a zero-order reaction mechanism and the activation energy calculated from the mea-sured reaction rate constants was found to be 36,000 J/mole. C. F. CHAN, J. W. GUERARD, and D. MILLER were all Seniors in the Metallurgical Engineering Department, at Queen’s University, Kingston, Ontario, when this work was done.     

帘线钢中氧化物夹杂控制技术在生产中的应用

在帘线钢冶炼过程中,通过采用炉后弱脱氧、防止钢液污染,以及控制精炼顶渣碱度指数和Al₂O₃含量指数等措施,使钢中夹杂物向低熔点区域转变,促进钢中夹杂物上浮、排出钢液,同时也使钢中残留氧化物夹杂具有良好的变形性能.实践表明,通过采用上述工艺措施,帘线钢中夹杂物成分、尺寸和变形性得到了有效控制.     

无取向电工钢WG350生产过程中夹杂物的行为与控制

为了更好地控制WG350无取向电工钢中的夹杂物,采用扫描电子显微镜、Aspex系统分析了精炼、连铸过程和成品板中夹杂物的类型、数量及尺寸的演变规律.结果 表明,氩站开始出现大尺寸含P复合夹杂物,该类型夹杂物大部分在RH脱碳后会上浮去除.RH加铝脱氧时生成的Al2O.以团簇状和块状为主,前者尺寸范围为0.5～5μm且大部...