Investigation of nonmetallic inclusions in continuously cast carbon steel by dissolution of the ferritic matrix

One of the main steel plant's problems has been the occurrence of inclusions throughout the process of steel making. In this sense, it is very important to detect nonmetallic inclusions in the steel, to determine their origin and to control the formation of such inclusions, in order to generate a final product of high quality. The aim of this work is to present a characterization method for nonmetallic inclusions which uses the expedient of dissolving the ferritic matrix in hydrochloric acid (HCl). Scanning electron microscopy connected to an energy-dispersive spectrometer (EDS) system is used to obtain the morphology, size and chemical composition of such inclusions. This analysis allows a better understanding about the nature of the inclusions, their incidence and distribution along the process of steel manufacturing, providing subsidies to formulate corrective actions that minimize the occurrence of nonmetallic inclusions.     

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.     

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.     

Breakout of a slab as the result of changes in the thermophysical properties of continuously cast steel

The so‐called secondary cooling zone is an important part of the continuous casting machine. In this zone, a breakout may occur because of an increase of the local and temperature heterogeneity of steel, resulting from an increase of the stress caused by bending of the slab and by high local concentration of nonmetallic slag inclusions. Changes of the chemical composition of steel during continuous casting are particularly dangerous. In the event that two melts are cast one after another, that is, if the melt of steel with chemical composition A ends and is immediately followed by the steel B, it may automatically stop the continuous casting machine, and an atypical breakout may take place. It has happened during continuous casting of the slab, 250 × 1530 mm in the area of straightening, 20 min after flying change of tundish. In the present paper, by employing the dimensional analysis, eight dimensionless numbers are derived. If the values of these dimensionless numbers for two followed steels significantly differ, the atypical breakout may take place.     

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.     

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.     

Improving the physicomechanical properties of heat treated 09G2S steels

Tests on type 09G2S steels in the heat treated condition showed that experimental melts treated with rare earth metals during smelting are much stronger and tougher at subzero temperatures (without being less ductile) than ordinary steels of this kind. The addition of rare earth metals (cerium) produces a substantial change in the nature of nonmetallic inclusions (collectors) and eliminates the segregation of sulfur which has a beneficial effect on the plasticity and certain other properties of steel. One of the possible ways of improving type 09G2S steels is by modifying their composition with trace additions of cerium and boron.     

Computer calculations of phase diagrams

The thermodynamic route of establishing phase diagrams is a relatively recent activity, considering that till about the fifties most phase diagrams were determined by the measurement of certain physical property or quantitative microscopy using light optics or x-ray diffraction. The thermodynamic formalism used by Kaufman and Bernstein is explained and illustrated with examples of the development of hypothetical binary phase diagrams. The calculation of ternary phase diagrams can begin with the binary phase diagram data as a first approximation. However, to calculate a reasonably accurate ternary phase diagram a certain amount of ternary solution data is necessary. Various empirical equations have been proposed in the literature to express ternary thermodynamic data. Calculation of simple ternary isothermal sections is illustrated with the examples of Mo-V-W and Cd-Sn-Pb systems. The numerical techniques which involve the differentiation of thermodynamic parameters with respect to composition get more involved with the number of components becoming 3 or more. A simpler approach has been applied recently to find the minimum position on the Gibbs free energy surface.     

H13钢热挤压模开裂分析

通过宏观检验、化学成分分析、硬度测试和金相检验等方法对H13钢热挤压模开裂的原因进行了分析。结果表明:原材料中非金属夹杂物超标及大块共晶碳化物的存在是模具早期失效的主要因素,同时,少量微裂纹的存在也加速了模具的早期开裂。     

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.     

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 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.     

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].     

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.     

Optimization of the Two- and Three-Dimensional Characterization of Rare Earth-Traced Deoxidation Products

Tracing by means of the light rare earths (REs), particularly La and Ce, is a state-of-the-art method used to track deoxidation products during the steelmaking process. Traced heterogeneous multiphase inclusions are analyzed using scanning electron microscopy with energy-dispersive spectroscopy (SEM/EDS) to perform a 2D characterization. The sequential chemical extraction technique is implemented for a 3D investigation to determine traced particles’ actual sizes and shapes. The automated SEM/EDS measurement must be optimized since RE oxides appear brighter in the backscattered electron images due to their high atomic numbers. Therefore, two grayscales are implemented for the detection of RE-containing multiphase inclusions. Within this technique, individual RE-traced heterogeneous nonmetallic inclusions (NMIs) are counted as separate particles. Thus, the measured NMIs must be recombined, which is achieved using a self-developed MATLAB tool. The extracted particles are also analyzed by automated and manual SEM/EDS measurements to determine the 3D morphologies and sizes of traced NMIs.     

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 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.     

工业锅炉烟管扳边时开裂原因分析

彩用化学分析和金相检验等方法对工业锅炉烟管扳边开裂原因进行了分析。结果表明，钢管中存在折叠及较严重非金属夹杂物是导致开裂的主要原因。     

镜面塑料模具失效表面的缺陷分析

针对1.2083镜面塑料模具在抛光过程中出现的表面疤状凸起缺陷进行了系统分析.综合运用光学显微镜、场发射扫描显微镜等分析技术对表面缺陷的形貌、组织、微区成分及其与非金属夹杂之间的联系进行研究,同时分别对失效模具产品和金相试样的表面粗糙度进行了对比测量.结果表明,由于该模具钢材内部多种非金属夹杂物的存在以及局部成分不均等因素,导致模具在抛光过程中基体的连续性遭到破坏,从而引起产品表面出现肉眼可见的疤状凸起缺陷,导致模具失效.     

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.