Influence Of Non-metallic Inclusions Research Articles

Nonmetallic Inclusions in 08Kh18N10T Steel as the Cause of Initiation of Defects in Heat-Exchange Tubes of Steam Generators of Nuclear Power Plants

We present the results of investigation of the microstructure of 08Kh18N10T steel in heat-exchange tubes after their long-term operation in steam generators of WWER-1000 power-generating units. We study the influence of nonmetallic inclusions on the degradation of the metal of heat-exchange tubes at the nuclear power plants. It is shown that nonmetallic inclusions located on the metal surface serve as a possible cause of the violation of passivation of the metal and the initiation of corrosion defects. Under the influence of operating factors, alternating stresses are formed in the metal, which leads to microfracture on the inclusion–metal interface and to the development of corrosion fatigue.

Influence of Nonmetallic Inclusions and Corrosion Products on the Wear Resistance of Railroad Wheels

Wear particles are formed at the contact surface of railroad wheels close to nonmetallic inclusions and corrosion products, which are associated with structural changes near the contact surface and reaction of the steel with the atmosphere. Such formation of wear particles is analyzed in the present work. The key factors responsible for the formation of the wear particles are identified, and their mutual influence is studied. That permits prediction of the wear at the wheels’ contact surface in different operating position. The wear of the contact surface is shown to be localized at the recess. The wear resistance of the contact surface may be increased by local laser treatment.

Influence of Nonmetallic Inclusions on the Failure of Cast Stainless Steels

The structure of high-strength 09Kh16N4BL and 14Kh17N2L stainless steels produced by casting on fusible models is studied. The influence of the steel composition on the content of nonmetallic inclusions in the cast steel is of considerable interest. The morphology of the nonmetallic inclusions is studied, and they are identified. Fractographic analysis shows that the nonmetallic inclusions affect the failure of the stainless steels. Two methods are used for quantitative assessment of that influence. Besides the classical methods, multifractal parameterization of the structure is employed to study the structure of the stainless steels. On that basis, correlations are established between the main multifractal parameters and the mechanical properties of the steel.

Влияние неметаллических включений на сопротивляемость металла сварных швов хрупким разрушениям

Влияние неметаллических включений на сопротивляемость металла сварных швов хрупким разрушениям

Influence of non-metallic inclusions and products of corrosion on the wear of railway wheels tread

Formulation of the problem . It is of interest to investigate the effect of nonmetallic inclusions and corrosion products of wheel steel on the formation of wear particles on the tread of railway wheels. It is also necessary to identify the specifics of the interaction of wheel steel with the surrounding atmosphere during the operation of railway wheels. The purpose of the article is to study the mechanisms of formation of wear particles on the surface of rolling of railway wheels during operation. Methodology . The effect of inclusions and corrosion products on the mechanism of wear of railway wheels made of R7 steel, which worked for about 5 years under the passenger train, was studied. The wheels were removed from service due to the extreme wear of the rims. We studied the macrostructure and microstructure of wheel steel along the width of the rims. The research was carried out by several methods: metallographic (Neophot−21), electron microscopy (JSM−35). Findings . The features of the formation of wear particles near nonmetallic inclusions and corrosion products related to structural changes near the rolling surface of railway wheels as well as to the interaction of steel with the surrounding atmosphere during operation were investigated. The influence of various factors on the role of nonmetallic inclusions and corrosion products in the formation of wear particles is shown, which makes it possible to predict the nature of wear of the rolling surface of railway wheels under various operating conditions. Originality . The main sources and the mutual influence of various factors on the formation of wear particles near nonmetallic inclusions and corrosion products have been established, which makes it possible to predict the nature of wear of the rolling surface of railway wheels under various operating conditions. Practical value . The use of the obtained results will allow to develop methods and regimes of smelting of wheel steel, allowing to influence the size, composition, structure and distribution of non-metallic inclusions, as well as to develop anticorrosion measures in order to improve the reliability and durability of railway wheels.

Влияние неметаллических включений на сопротивление стали разрушению при многократном динамическом сжатии

Влияние неметаллических включений на сопротивление стали разрушению при многократном динамическом сжатии

Influence of nonmetallic inclusions in rail steel on the high-temperature plasticity

The influence of nonmetallic inclusions in Э76Ф rail steel on the high-temperature plasticity is considered. In terms of the shear strain, a plasticity maximum is observed in all three zones of the continuouscast billet: the crust, the columnar-crystal zone, and the central zone of the billet. The high-temperature torsion of samples heated to 950–1250°C with 10-min holding is studied for continuous-cast billet of electrosmelted rail steel. Oxides and silicates are present in the crust; oxides and oxysilicates are found in the columnar-crystal zone; and sulfides, oxides, silicates, and alumosilicates are found in the central zone of the billet. The concentration of inclusions that impair the plasticity is greatest in the central zone of the billet.

Influence of non-metallic inclusions on fatigue life in the very high cycle fatigue regime

The present paper deals with the influence of non-metallic inclusions on fatigue life in the high cycle fatigue and the very high cycle fatigue regime. For that purpose, several castings of steel 42CrMo4 (AISI 4140, DIN EN 1.7225) were produced by using recently developed novel metal-melt filters. The specimens were tested in hot-isostatically pressed and heat treated condition. After fatigue failure every fracture surface was intensively investigated by scanning electron microscopy in order to define the type, the size, the chemical composition, the morphology and the location of the crack initiating discontinuity. Subsequently, Murakami’s √area model was used for the evaluation of the influence of non-metallic inclusions on the fatigue life. In the present investigation four common types of chemical compositions of crack initiating discontinuities were identified. Furthermore, four different internal failure types and their influence on the fatigue life in cast steel were investigated and described. Thus, the present contribution proposes a basic correlation determined from fatigue lives in case of various internal crack initiation types. The key parameters for fatigue life prediction in case of internal fatigue failure in the very high cycle fatigue regime are (i) the size of the crack initiating discontinuity, (ii) the inclusion depth and (iii) the crack initiating failure type.

Influence of nonmetallic inclusions on endurance of percussive machines

Based on the results of the industrial testing of downhole hammers with underreamers and on the analysis of the influence exerted by nonmetallic inclusions in steel on the steel fatigue endurance under the impact load, it has been shown that the stringer-type nonmetallics greatly aggravate the steel endurance both under compression and bending, although have no effect on the steel hardness and strength indexes.

The interaction between non-metallic inclusions and surface roughness in fatigue failure and their influence on fatigue strength

In this study, the influence of non-metallic inclusions on the fatigue behavior of 30MnVS6 steel containing different inclusion sizes and surface roughness has been investigated. Scanning electron microscope (SEM) was used to examine fatigue fracture origins. It was concluded that the non-metallic inclusions were dominant fatigue crack initiation sites in both smooth and rough specimens. This was justified by the calculation of stress intensity factor generated by both surface roughness and non-metallic inclusions, based on Murakami’s model. In addition, it was found that for a given stress, the critical inclusion size could be increased by eliminating the surface roughness.

Boundaries for increasing the fatigue limit of the bearing steel SAE 52100 by thermomechanical treatments

High end applications often require high strength materials especially regarding the fatigue limit. It is still an open question what the highest fatigue limits are and how to increase them further in high strength steels. A thermomechanical treatment (TMT) in the temperature range of maximal dynamic strain ageing is an auspicious way to increase the fatigue limit of bearing steel SAE52100. Successful attempts have been published for various materials states. The present investigation deals with the influence of non-metallic inclusions on the fatigue limit and the possibility to increase the fatigue limit by TMT. The fatigue limit of high strength steels increases by reducing the size of the non-metallic inclusions during steelmaking. We found that TMT increases the fatigue limit of a high strength materials state only in cases in which the non-metallic inclusions are the starting points of the fatigue cracks. In the case of high cleanliness of the steel the origin of the fatigue cracks may be at any position in the matrix. If there are no critical non-metallic inclusions a TMT did not increase the fatigue limit further. The reasons for this behaviour will be explained and the border of the fatigue limit of high strength steels will be discussed.

Analysis of Non-Metallic Inclusions in Steel by SEM/EDS Experiences with the Technique as Applied to the Plain Carbon Steel Cf53 (1.1213)

One of the applications of the steel Cf53 are components for constant velocity joints (CVJ) in the driveline of cars and trucks. These components participate in the transmission of torque from the engine to the wheels and are subjected to high dynamic loads. In order to further improve these components, GKN Driveline is studying the influence of non-metallic inclusions on their endurance performance.

Influence of non-metallic inclusions on the fatigue properties of heavily cold drawn steel wires

The influence of non-metallic inclusions on the fatigue properties of heavily cold drawn steel wires is studied. Through a fractography study it is possible to link the inclusion properties, such as chemical composition, geometry, size and location, to the fatigue properties.Comparing the Stress Intensity Factors (SIF) of non-metallic inclusions to the threshold value for long crack growth shows that the defect size that should be used to calculate the SIF is larger than the inclusion size itself. This is validated using Scanning Electron Microscopy (SEM) in combination with a Focused Ion Beam (FIB). This SEM/FIB study shows that the region around non-metallic inclusions is characterized by alterations in the microstructure that should be taken into account. It is calculated that the SIF increases with 16.5±3.6% compared to Murakami’s way of calculating SIF of non-metallic inclusions.

Development of Powder Metallurgy High Speed Steel

High speed steels (HSS) have been widely used worldwide. This paper introduced some research results of high speed steels via Powder Metallurgy process. High speed steels AHPT15 (W12Cr4V5Co5 ) were investigated via gas atomization, hot isostatic pressing, hot working and heat treatment processes. Microstructure of the steels, precipitation of carbides and the influence of nonmetallic inclusions on mechanical properties of the steels were investigated. PM HSS showed fine and uniform microstructure and exhibited excellent toughness and wear resistance, with bend strength up to 3500 MPa and hardness up to 68.0 HRC.

Hydrogen-induced cracking and healing behaviour of X70 steel

In this paper, the electrochemical hydrogen charging for X70 pipeline steel in H 2SO 4 solution was carried out and the influence of non-metallic inclusions and microstructure on the hydrogen-induced cracking (HIC) and healing behavior of X70 pipeline steel was investigated by SEM and TEM technique. Based on the results of hydrogen permeation tests, the diffusivity of hydrogen at room temperature and the density of hydrogen trapping sites in X70 steel were estimated. Heat treatment was used to heal the hydrogen-induced cracks in X70. It was found that non-metallic inclusions, such as nitrides and oxides, played different roles on HIC of X70 steel. Oxides are more sensitive than nitrides to HIC in X70 steel. Cracks initiated and grew preferentially along the grain boundary of polygonal ferrite instead of the acicular ferrite when the sample was charged of enough hydrogen. It also demonstrated that proper heat treatment can heal such cracks. The healing process was divided into two steps: firstly, many cracks dissociated into several detached segments; secondly, theses segments regressed into spherical voids. The mechanism of crack healing was also discussed.

THE EFFECT OF NON-METALLIC INCLUSIONS ON THE CRAK PROPAGATION IMPACT ENERGY OF TOUGHENED 35B2+Cr STEEL

35B2+Cr steel was designed as a material for screws. The investigations were carried out on toughened samples, taken from three ingots of 35B2+Cr steel (delivered from three various steel suppliers), and of different content of non-metallic inclusions. In each case, the fraction of non-metallic inclusions was in agreement with the corresponding standard. This study presents the results of the research focused on the influence of non-metallic inclusions on the impact energy of crack development in 35B2+Cr steel. The role of non-metallic inclusions was considered both in relation to their total fraction and in relation to the fraction of oxides, sulfides, nitrides and exogenous inclusions separately. Assuming linear dependence between notch-root radius and the impact energy of crack nucleation, basing on the impact toughness tests, the impact energy of the crack development was evaluated. It was proved, that in spite of the level of fraction of non-metallic inclusions compatible with the corresponding standards, they directly or indirectly influence the impact energy of 35B2+Cr steel. This influence depends on the character of the inclusions.

Influence of nonmetallic inclusions on the fatigue strength of metals

A model of growth of short fatigue cracks in the vicinity of nonmetallic inclusions in crystalline metallic materials is proposed. We establish the influence of inclusions on the fatigue strength of materials of this type. A conclusion is made that the inclusions whose typical size is smaller than the grain size exert practically no influence on the fatigue strength of the material.

鏡面磨き時のピンホール発生に及ぼす非金属介在物および炭化物の影響

鏡面磨き時のピンホール発生に及ぼす非金属介在物および炭化物の影響

Mechanism of Hydrogen Delamination of Pipe Steels of Oil and Gas Pipelines

We propose a mechanism of hydrogen delamination of pipe steels of oil and gas pipelines and study the influence of nonmetallic inclusions and hydrogen on the initiation of microcracks playing the role of nuclei of delamination of pipe steels.

Influence of non-metallic inclusions on the austenite-to-ferrite phase transformation

During continuous casting of low-alloy steels non-metallic inclusions (e.g. aluminium nitride (AlN)) may precipitate and grow inside the austenite phase at temperatures above 1200 K. At lower temperatures austenite (γ) will partly transform to the ferrite (α) phase, which significantly influences the properties of the cast product. The kinetics of the γ/α phase transformation depends on the mobility of the interface as well as on the diffusion coefficients of interstitial as well as substitutional components. The driving force for the γ/α phase transformation can be separated in a chemical and a mechanical term. The actual chemical compositions in the γ- and in the α-phase very near to the interface determine the chemical contribution to the actual driving force. The mechanical driving force of the γ/α phase transformation is directly related to the strain energy and plastic work generated by the transforming spherical shell. Therefore, AlN-inclusions, producing large strains and stresses in their surroundings, may affect the γ/α phase transformation. Finite element (FE) calculations show that AlN-inclusions are able to trigger the γ/α phase transformation. This leads to the formation of ferrite at a higher temperature compared to a steel grade without AlN-precipitates. Finally, the kinetics of the γ/α phase transformation is determined numerically by a finite difference method.