Investigation of the chemical composition of nonmetallic inclusions utilizing ternary phase diagrams

Nonmetallic inclusions are normally present in steel products, as they originate from reactions that occur during the steelmaking process. Inclusions, which consist of stable nonmetallic phases depending on their chemical composition, can strongly affect the final quality of the metallurgical product. In this sense, the influence of inclusions in the steel is determined by their chemical composition. The aim of this work is to present the evolution of the chemical composition of nonmetallic inclusions utilizing ternary phase diagrams by means of the analysis of steel samples collected during the steel (aluminum-killed steel, SAE 1015) manufacturing process. A computational program was developed to furnish the positions of the inclusions on appropriate ternary phase diagrams by using as input data the chemical composition of the inclusions, determined with a scanning electron microscope (SEM) connected to an energy-dispersive spectrometer (EDS).     

热轧带肋钢筋断裂分析

为进一步提高产品质量,针对螺纹钢出现的裂纹和断裂事故进行了系统的生产工序分析.采用光谱分析仪分析了断裂钢筋的化学组成,利用光学显微镜、电子能谱仪分析断裂钢筋组织结构和断裂钢筋中非金属夹杂物的类型、数量、大小、组成及分布,并讨论了目前生产工艺中非金属夹杂物的来源.研究表明,钢筋中非金属夹杂物的产生是钢筋裂纹和断裂的根源,夹杂物主要是由炼钢脱氧和耐火材料腐蚀的铝硅酸盐组成.     

Corrosion Fracture of Platelike Heat Exchangers

In heat-transfer plates, independently of the type of steel, corrosion pits appear mainly at the tops of corrugations (at the sites of minimum gaps between the adjacent plates). The role of sites of their initiation is played by nonmetallic inclusions of complex oxides (Al, Si, Ti, and Mg) and oxysulfides (Ti and Ca). It is experimentally established that the deformation of heat-transfer plates has almost no influence on the corrosion losses in the course of the tests carried out in chloride-containing media. The process of stable depassivation and development of pitting runs near nonmetallic inclusions of a certain type. In chloride-containing solutions without oxidizers, the pits are initiated near oxides and oxysulfide nonmetallic inclusions, whereas in chloride-containing solutions with oxidizers, they are initiated near oxysulfide and nitride inclusions.__________Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 41, No. 1, pp. 104–108, January–February, 2005.     

Effect of nonmetallic inclusions on properties of cast steel

The result's of a study of the effect of nonmetallic inclusions on physicochemical and electrochemical properties of steel 45L are reported. A new (linear) method of determining the content of nonmetallic inclusions in steel, which makes it possible to determine also the shape of inclusions, was used.     

Influence of refining time on nonmetallic inclusions in a low-carbon, silicon-killed steel

Nonmetallic inclusions are harmful to the mechanical properties of every kind of steel produced worldwide. The greater the size of the inclusion present in the structure of a determined kind of steel, the greater its negative effect on the quality of the steel. Therefore, the objective of this work was to investigate the size, the quantity, the shape and the chemical composition of nonmetallic inclusions formed throughout the refining process of silicon-killed, low-carbon steel, as a function of the treatment time in a ladle furnace, trying to ensure the flotation of inclusions bigger than 25 μm. This investigation was carried out using a scanning electron microscope (SEM), with an analysis system using energy dispersive spectometry (EDS). Based on this work, it was possible to know more precisely the nature of the inclusions, the necessary time to ensure flotation of large inclusions, the efficiency of the slag to capture the inclusions, and the inclusion level of the steel throughout its refining process to try to obtain a higher quality steel product.     

Effect of nonmetallic inclusions on crack propagation in steel 45L

The effect of nonmetallic inclusions on the character of crack propagation in deformed steel 45L specimens was investigated. The optimum shape of nonmetallic inclusions ensuring a high resistance to crack propagation, i.e., a high resistance of steel to brittle fracture at subzero temperatures, was established.     

Variations in steel cleanness during transient continuous casting practices

Abstract

During sequenced continuous casting, concerns have been expressed about the density of nonmetallic inclusions present in steel slab produced during the transition period as successive ladles are teemed. Consequently, for critical applications such as thin wall tinplate products, with can wall thicknesses of ～0.26 mm, only steel cast during 'steady state' conditions is selected. In contrast, slab cast over defined lengths before and after a ladle change is downgraded to less demanding applications, irrespective of cleanness. To evaluate this practice, steel inclusion levels have been assessed during ladle change operations, when the steel reservoir in the tundish fell to below 20 t. This plant based study confirmed that, during the transition period, marked variations occur in the size and morphology of the nonmetallic inclusions, as well as in the oxygen content of the steel slab.     

钢中非金属夹杂物的鉴定

根据钢中非金属夹杂物的来源和分类,综述了鉴定钢中非金属夹杂物的方法和定量评级标准,并且给出了典型夹杂物的扫描电镜照片,分析了不同类型夹杂物的形成机理及其在光学显微镜下的基本特征.     

Effect of Nonmetallic Inclusions on the Mechanical Properties of Hydrogenated Steels

We have studied intermediate-alloy Ni-Cu-Mo-V steel of open-hearth and converter (more pure as to nonmetallic inclusions) melting. In the case of middle hydrogen concentrations (up to 5 cm³ per 100 g), the strength characteristics, plasticity, and fracture energy of transverse and vertical specimens of converter steel decrease less than those for open-hearth steel. For higher hydrogen concentrations, the characteristics of steel become very low and almost identical for both materials. Under loading, cracks are initiated on nonmetallic inclusions; in hydrogenated steel, they propagate along the shortest path from one inclusion to another, without involving significant volumes of the specimen in plastic deformation. We have established that nonmetallic inclusions accelerate crack initiation under conditions of corrosion in pipe steels in the course of operation of pipelines.__________Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 40, No. 6, pp. 115–119, November–December, 2004.     

The effect of sulfur on the fracture of CrNiMoS steel at low temperatures

Sulfur, whose solubility in ferrite at room and subzero temperatures is low, is present in steel in the form of nonmetallic inclusions (sulfides and oxysulfides), the type and nature of which are determined by the final deoxidizing treatment. The nature and quantity of nonmetallic inclusions have a marked effect on such mechanical properties of steel as, , anda _i [1–3].     

氧化物冶金技术及其应用

氧化物冶金是利用钢中细小非金属夹杂物诱导晶内铁素体形核细化晶粒的新技术,应用氧化物冶金技术已成功开发出了高强度高韧性的非调质钢和低碳钢.讨论了氧化物冶金型钢的显微组织特征,分析了氧化物冶金型钢中非金属夹杂物的性质和晶内铁素体的形核机理,简述了氧化物冶金技术的应用.     

Melting and crystallization of nonmetallic inclusions and steel matrix in the course of laser treatment

We have studied the mechanism of melting and crystallization of nonmetallic inclusions in contact with steel matrix in the course of laser action. On the example of 08kp, 08Yu, and 60G steels, we have shown that laser action represents a method for local change in the structure of inclusions in surface fused layers as well as in the properties of surface of nonmetallic inclusions.     

Einflüsse unterschiedlicher Reinheitsgrade auf die Dauerschwingfestigkeit des Federstahles 55 Cr 3

Influence of Different Degrees of Purity on the Fatigue Strength of Spring Steel 55 Cr 3 One of the most important factors for construction and development of high strength springs is the material selection. In this connection the opinion is often represented in bibliography that material defects are the main reason for fractures. Besides surface defects (surface decarburization or rolling defects) essentially nonmetallic inclusions are described as causes of fractures. Therefore high degrees of purity are demanded especially for severe strained springs, which only can be obtained by very expensive special melting processes. By testing specimens of spring steel 55 Cr 3 with different degrees of purity in the present work the quantitative influence of nonmetallic inclusions on the fatigue life was to be examined. About 400 repeated torsion tests with annealed as well as annealed and shotpeened specimens were carried out accompanied by investigations to determine inclusions causing fracture and their size.     

New Type of Corrosion-Active Nonmetallic Inclusions and their Influence on the Corrosion of 38KHN3МFА Steel

Materials Science - We study the influence of corrosion-active nonmetallic inclusions on the corrosion of 38KhN3MFA steel. A new type of fluorine-containing inclusions of this kind with a size...     

A 3D numerical and experimental investigation of microstructural alterations around non-metallic inclusions in bearing steel

Non-metallic inclusions such as sulfides and oxides are byproducts of steel manufacturing process. When a component is subjected to repetitive loading, fatigue cracks can emanate from these inclusions due to stress concentrations that happen because of mismatch in elastic–plastic properties of inclusions and matrix. In certain applications such as gears and bearings, crack initiation from inclusions is accompanied with microstructural alteration. This paper employs a numerical as well an experimental approach to investigate these microstructural changes which are so-called “butterfly wings”. A 3D finite element model was developed to obtain the stress distribution in a domain subjected to Hertzian loading with an embedded non-metallic inclusion. A formerly introduced 2D model based on continuum damage mechanics (CDM) was developed to simulate the butterfly wing formation in 3D. Wingspan-to-inclusion ratios were observed at different cross sections following an analytical serial sectioning procedure. A closed form solution was suggested for the wingspan-to-observed-inclusion-diameter ratio and the results were corroborated with the data available in the open literature. On the experimental front, nonmetallic inclusions inside a sample made of bearing steel was detected using ultrasonic inspection method. Rolling contact fatigue (RCF) tests were run on the specimen and post-failure serial sectioning was conducted to understand the 3D shape of butterflies formed around an inclusion detected by ultrasound. Comparison of experimental and numerical serial sectioning of the wings showed a close correlation in the butterfly wings geometry.     

汽车发动机曲轴断裂失效分析

采用断口分析、显微组织检验、低倍组织检验、能谱分析和化学成份分析等方法对某汽车发动机曲轴断裂进行了失效分析,判断断裂失效的主要原因是非金属夹杂和次表面的原始微裂纹,建议改进热处理工艺,保证组织的均匀性,选用非金属夹杂物含量小的钢材。     

Effect of Hydrogen on Structural Strength of High-Nitrogen Chromium–Manganese Steels

To increase the crack resistance of tire materials in hydrogen media, one adds admixtures of lanthanum (up to 0.05 vol. %) and cerium (up to 0.1 vol. %) to nitrogen-containing 18Mn-4Cr and 18Mn-18Cr steels in the process of experimental melting to refine, modify, and alloy these steels. These admixtures have a positive effect on the amount, form, and uniformity of the distribution of nonmetallic inclusions, qualitatively improve the state of the metal, and change its dislocation structure. The application of calcium (up to 0.05 vol. %) for deoxidation of steel leads to a considerable change in the form and composition of nonmetallic inclusions revealed in the investigation of the fracture surface of specimens. Experimental steels with a high content of chromium, copper, and other alloying elements demonstrate an increase in a resistance to corrosion-mechanical fracture and in long-term strength in a hydrogen medium.     

Effect of elongated nonmetallic platelet inclusions on the ductile-failure resistance of structural steel

The geometric characteristics of elongated platelet sulfide nonmetallic inclusions are determined for hot-rolled strip steel ON6 with various sulfur contents, and their effect on the reduction in ductility and plasticity in the direction across the roll is investigated. A distinct relation is observed between the resilience (plasticity) and the number of pore traces in the fracture, which are initiated by elongated platelet inclusions. An attempt is made to derive an analytic expression for the influence exerted by elongated platelet oriented inclusions on the limiting plasticity based on the Braun-Embury model.Translated from Problemy Prochnosti, No. 9, pp. 63–69, September, 1990.     

Cluster adsorption on oxide inclusions in liquid steel

We refine the determination of forms of the existence of disperse oxide inclusions in liquid steel by taking into account the phenomenon of cluster adsorption near interfaces in structurally microinhomogeneous liquids. We show that every nonmetallic inclusion in steel is surrounded by a shell consisting of many layers of adsorbed metal clusters with thicknesses of a few tens of micrometers. From new positions, we quantitatively evaluate certain specific features of the behavior of oxide inclusions in liquid steel, namely, the effect on its viscosity, the buoyancy of inclusions, and their ability to float up depending on their nature (MgO, ZrO₂, Al₂O₃, and SiO₃) and size. Odessa State Polytechnic University, Odessa. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 35, No. 5, pp. 53–58, September–October, 1999.     

Contact endurance of electroslag-refined steels

The article describes the results of contact fatigue tests on specimens of Cr15 ball-bearing steel subjected to various electroslag-refining treatments. It was shown that a reduced content of nonmetallic inclusions, changes in the nature of these inclusions, and increased density by electroslag-refining lead to an increase in the contact endurance of the steel studied.Translated from Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 5, No. 5, pp. 581–583, September–October, 1969.