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 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 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.     

The influence of nonmetallic inclusions on the mechanical properties of steel: A review

The literature regarding the influence of nonmetallic inclusions on the mechanical properties of steel is reviewed, with critical comments on various studies. A brief discussion of inclusion rating methods and a synopsis of the effects of applied stress on inclusions in an isotropic, elastic matrix are presented. The parameters considered are tensile strength, impact strength, reduction of area, fatigue properties and fracture toughness. It is concluded that in many applications, the type of inclusions are more important than the total content and as matrix strength increases, the notch effect of inclusions becomes more significant. Also, mechanical properties can be influenced by any one or a combination of the following inclusion parameters; shape, size, quantity, interspacing, distribution, orientation, interfacial strength, and physical properties relative to the matrix.     

Influence of nonmetallic inclusions on fatigue crack growth in a structural steel

A study of the fatigue behaviour of a hardened and tempered steel, at two inclusion levels, has been carried out according to the linear elastic fracture mechanics criteria. The influence of inclusions on the fatigue crack growth rate has turned out to be a function of the local stress intensity factor range,K _I, at which fracture propagates. At lowK _I values, to which are related crack growth rates less than 10^–5 mm cycle^–1, the crack growth rate in the steel with higher inclusion content is lower than in the steel with lower inclusion content. AsK _I increases, an inversion in the difference between the two rates occurs. In the dirtier steel, the higherK _I, the higher the growth rate than in the other steel. The difference between the two rates becomes nil just below the fast propagationK _Ic level. By fractographic analysis, it has been possible to find out how inclusions affect fatigue behaviour.     

Nature of splashes of microinhomogeneous strain in steel with nonmetallic inclusions

We study the distribution of microinhomogeneous strain in steel near nonmetallic inclusions of various types, which are not susceptible to the formation of hollows. We establish the features of the influence of temperature, plasticity of inclusions, and intersurface stresses on the distribution of microinhomogeneous strain. We study the nature of splashes of microstrains caused by fracture of inclusions and development of sliding along inclusion-matrix interfaces. Ukrainian Metallurgical Academy, Dnepropetrovsk. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 35, No. 2, pp. 53–59, March–April, 1999.     

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.     

On the cohesive strength of the boundaries between nonmetallic inclusions and steel

We investigated the mechanisms (and conditions) of the formation of plastic cracks (cavities) near non-deformable oxides in steels subjected to various kinds of treatment (plastic deformation, explosive treatment, and laser irradiation) and determined parameters of the formation and evolution of microdefects: critical sizes of inclusions, levels of strain, strain ranges in which fracture processes are controlled by inclusions, and sizes of cavities at various temperatures. We also analyzed the influence of processing conditions (temperature, strain level and rate, loading mode, and the conditions of laser treatment) on the character of interphase cracks on the boundaries of inclusions in steel.Dnepropetrovsk Metallurgical Institute, Dnepropetrovsk. Translated from Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 31, No. 3, pp. 50–57, May – June, 1995.     

Fatigue properties of a cast steel

Fatigue crack initiation and propagation from notches in a cast steel to the specification B.S.1456A has been examined. Fracture mechanics methods are used. It is shown that reproducible data can be obtained on both initiation and propagation and that such data could be used in design. The experiments show that in the region of growth of small cracks from a notch there is a smooth change from the initiation behaviour to the growth characteristics of the longer crack.

---

Résumé On a étudié l'amorçage et la propagation de fissures de fatigue à partir d'entailles dans un acier moulé répondant à la spécification BS. 1456. A. En utilisant les méthodes de la mécanique de rupture, on montre que des données reproductibles peuvent être obtenues en amorçage et en propagation et qu'elles sont utilisables pour la conception. Les essais montrent que dans la région où de petites fissures croissent à partir d'une entaille, il se produit une évolution régulière entre le comportement à l'amorçage et les caractéristiques de propagation d'une fissure.

     

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.