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.     

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.     

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 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.     

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.     

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.     

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.     

Fatigue crack growth rates and fracture toughness in electroslag refined En 52 steel

En 52 steel has been electroslag refined and the resultant effects of refining on its mechanical properties have been assessed. It was found that refining caused a decrease in fatigue crack growth rates and increases in fatigue strength, fracture toughness, Charpy fracture energy and tensile ductility. Fatigue crack growth rates in region I and in region III were found to be considerably lower in the electroslag refined steel: they were unaffected in region II. The fracture toughness values for the electroslag refined steel are nearly twice those estimated for the unrefined steel. Measurements on heat-treated samples have shown that the electroslag refined steel has a better response to heat-treatment. The improvement in the mechanical properties is explained in terms of the removal of nonmetallic inclusions and a reduction in the sulphur content of the steel.     

Fracture mechanics and scale effects in the fatigue of railway axles

Fatigue of railway axles is one of the basic problems of fatigue. However, in spite of the criticality of this component, modern approaches have not been used for addressing a critical revision of traditional design. The scope of this paper is to study the scale effects in fatigue limit and in crack growth rate for a high strength steel used for high speed railway axles.Fatigue limit tests on micro-notched specimens led to the determination of fatigue thresholds for small cracks of the examined steel. This allowed us to successfully analyse the `scale effect' and the fatigue strength of full-scale axles in terms of threshold stress for short cracks emanating from small non-metallic inclusions.A series of crack propagation tests on small scale specimens lead to the definition of an EPFM crack propagation model which has been successfully compared with propagation data on full-scale components. These results support the application of the crack propagation model for the determination of axle inspection intervals.     

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.     

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).     

Fatigue strength and life of compressor blades for marine gas turbine engines

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 on the influence of manufacturing residual stresses and surface defects in the form of simulators of dents, corrosion pits, and nonmetallic inclusions on the fatigue strength of steels and a titanium alloy. The characteristics of the material crack growth resistance have been studied taking into account the effect of the medium (sea water), stress ratio in a cycle, and programmed mode of loading. The authors also consider fatigue strength of newly-manufactured blades and those in operation, as well as specific features of fatigue crack propagation in blades. They have substantiated a method for predicting the life of blades with cracks. Institute for Problems of Strength, National Academy of Sciences of Ukraine, Kiev, Ukraine. Translated from Problemy Prochnosti, No. 1, pp. 28–40, January–February, 1999.     

中碳合金钢双相组织疲劳裂纹扩展的研究

研究了４２ＣｒＭｏ钢亚温淬火及二次淬火两种双相组织的疲劳裂纹扩展行为。结果表明，亚温淬火双相组织可显著提高裂纹萌发生抗力，降低扩展速率；较高的疲劳性能与裂纹尖端闭合应力，断口表面粗糙度以及裂纹扩展路径弯折程度有关。断裂力学分析表明，粗糙度诱发裂纹闭合效应及裂纹路径变折效应是提高裂纹扩展抗力的主要因素，同时得到上述两种效应对裂纹扩展速率影响的表达式。     

单轴拉伸下AerMet100钢中稀土夹杂物开裂过程的原位观察

扫描电镜观察了AerMet100钢中稀土夹杂物的形貌、尺寸;原位观察了单轴拉伸条件下稀土夹杂物的微观力学行为。结果表明:稀土夹杂物呈球状或椭球状,拉伸过程中稀土夹杂物内部最先萌生裂纹。建立了裂纹萌生的应力判据。裂纹在夹杂物内部扩展,不易向基体延伸。数值模拟单轴拉伸试验和理论计算结果与原位观察基本一致。     

Effect of electroslag refining on the fracture toughness and fatigue crack propagation rates in heat treated AISI 4340 steel

The AISI 4340 steel has been electroslag refined and the improvement in mechanical properties has been assessed. Electroslag refining (ESR) has improved tensile ductility, plane strain fracture toughness, Charpy fracture energy, and has decreased fatigue crack growth rates. The K_IC values for the ESR steel are nearly twice those estimated in the unrefined steel and higher than those obtained in the vacuum arc remelted steel. Fatigue crack growth rates in region I and in region III are found to be decreased considerably in the ESR steel, while they are unaffected in region II. Measurements on heat treated samples have shown that the ESR steel has a better response to heat treatment. Both the suggested heat treatments namely austenitizing at 1140–1470 K as well as the conventional heat treatment of austenitizing at 1140 K have been followed. The improvement in the mechanical properties of ESR steel has been explained on the basis of removal of nonmetallic inclusions and reduction in sulfur content in the steel.     

Effect of electron-beam melting upon the properties of grade ShKh15 ball-bearing steel

Summary Electron-beam melting reduces the gas content, harmful impurities and nonmetallic inclusions in ShKh15 steel, thus leading to a considerable improvement in its physical, mechanical, and electrochemical properties. Most marked is the improvement in the resistance of the steel to cyclic loads: its fatigue limit is increased by 33% to a level higher than that recorded for any steel of this class in the USSR and abroad. Compared with electro-slag and vacuum-arcmelted steels, the electron-beam-melted grade has higher fatigue strength, higher UTS under conditions leading to hydrogen embrittlement, and higher resistance to corrosion.     

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.     

INFLUENCE OF RETAINED AUSTENITE ON FATIGUE CRACK PROPAGATION IN HP 9-4-20 HIGH STRENGTH ALLOY STEEL

Abstract— Industrial multi-pass TIG weldments of HP 9-4-20 high strength alloy steel have been found to contain significant volume fractions (around 10%) of retained austenite which are not readily transformed after stress relieving and subsequent refrigeration procedures. To determine whether the presence of such retained austenite in tempered martensitic structures could be detrimental to fatigue resistance in HP 9-4-20 steel, fatigue crack propagation behavior was examined over six orders of magnitude in growth rate, in commercially heat-treated material (containing less than 3% austenite) and in intercritically heat-treated and tempered material (containing approx. 14% austenite) in an environment of moist, ambient temperature air. Whereas crack propagation rates were unchanged at growth rates exceeding 10⁻⁶ mm/cycle, structures containing 14% austenite showed somewhat superior resistance to near-threshold crack propagation at growth rates less than 10 ⁻⁶ mm/cycle, the threshold for crack growth (Δ K ₀) being over 20% higher than in commercially heat-treated material. The presence of retained austenite further appeared to inhibit the occurrence of intergranular fracture at near-threshold levels. It was concluded that significant proportions of retained austenite are not detrimental to fatigue crack propagation resistance in HP 9-4-20 steel, and may indeed have some beneficial effect at very low, near-threshold growth rates by increasing resistance to environmentally-assisted cracking.     

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.