Structural effects near nonmetallic inclusions in laser treatment of steels

We investigated the behavior of nonmetallic inclusions in laser treatment of steels. We established the structural and phase transformations near inclusions, on the inclusion-matrix interfaces, and in inclusions, and the change in the character of microfractures in the vicinity of inclusions under deformation from laser irradiation. Ukrainian Metallurgical Academy, Dnepropetrovsk. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 35, No. 6, pp. 57–66, November–December, 1999.     

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.     

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.     

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.     

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.     

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.     

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.     

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.     

Physical Simulation of Nonmetallic Particle Movement in Al Melt under Electromagnetic Field

Physical simulation is used to study the movement of nonmetallic particles in AI melt in electromagnetic field. It is found that the terminal velocity of particles in different Reynolds number range has different functions. By confirming drag force coefficient of nonmetallic particles with Reynolds number in the range of 0.2～10 and 10～25 respectively, two functions of terminal veIocity for spherical nonmetallic particles have been got accordingly, which provide a theoretical basis for separating nonmetallic inclusions from AI melt in electromagnetic field.     

Failure analysis of a high-speed pinion shaft

The failure of a high-speed pinion shaft from a marine diesel engine was investigated. The shaft, which had been in service for more than 30 years, failed shortly after a service operation in which the bearings were replaced. Examination of the shaft revealed cyclic fatigue as the failure mechanism, with a substantial distribution of nonmetallic inclusions near the fracture initiation site. Fracture mechanics analysis indicated that the inclusions would be unlikely to have served as failure initiation sites if only stresses acting on the shaft were induced by normal service loads. Further examination of the bearing elements revealed an abnormal wear pattern, consistent with the application of elevated bending loads to the shaft after bearing replacement. The root cause of failure was determined to be an increase in service stresses after bearing replacement along with the presence of significant nonmetallic inclusions in the pinion shaft.     

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.     

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.     

Surface quality control of nonmetallic workpieces in diamond abrasive finishing

The paper presents a procedure for measuring laser radiation reflection and scattering coefficients of polished nonmetallic workpieces. A relation between the scattered light intensity and the polished surface roughness is studied. It is demonstrated that colorimetric characteristics of nonmetallic materials can be determined from the light scattering and reflection coefficients.     

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.     

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。     

Failure analysis of a wire rope

Wire ropes, pulleys, counterweights, and connecting systems are used for auto tensioning of contact wires of electric railways. A wire rope in one such auto tensioning system suffered premature failure. Failure investigation revealed fatigue cracks initiating at nonmetallic inclusions near the surface of individual wire strands in the rope. The inclusions were identified as Al-Ca-Ti silicates in a large number of stringers, and some oxide and nitride inclusions were also found. The wire used in the rope did not conform to the composition specified for AISI 316 grade steel, nor did it satisfy the minimum tensile strength requirements. Failure of the wire rope was found to be due to fatigue; however, the ultimate fracture of the rope was the result of overload that occurred after fatigue failure had reduced the number of wire strands supporting the load.     

Transformations of Nonmetallic Inclusions in Steels Subjected to High-Temperature Heating

Materials Science - We study the mechanism of dissolution of nonmetallic inclusions under the conditions of high-temperature heating. It is shown that the dispersion of inclusions is associated...     

Fatigue strength of gas turbine compressor blades

An experimental procedure has been developed for the investigation of fatigue and crack growth resistance of materials and real compressor blades. Methods for the determination of stress intensity factors in specimens and in blades with cracks have been justified. Investigations have been performed into the influence of manufacturing residual stresses and surface defects in the form of simulators of dents, corrosion pits, and nonmetallic inclusions on fatigue strength of steels and a titanium alloy. The characteristics of the material crack growth resistance have been studied considering the effect of the medium (sea water) and stress ratio in a cycle, as well as fatigue strength of newly-manufactured blades and those after being in operation. Specific features of fatigue crack propagation in blades have been considered and a method for predicting the life of blades with cracks has been justified.