Size Distribution Of Inclusions Research Articles

A Comprehensive Model for Assessing the Impact of Steel Cleanliness on Bearing Performance

Steel cleanliness as measured by nonmetallic inclusion content in steel plays a major role in affecting bearing durability. A high-fidelity virtual bearing life test model was developed to predict the impact of inclusions on bearing fatigue life. This model analyzes distributions of inclusion size, shape, orientation, and location, and computes stress alterations to bearing material due to inclusions and the resulting life reduction. Comparisons between model predictions and experimental test results were made, confirming the validity of the model. Parametric studies were conducted to explore the effects of inclusion counts, inclusion size distributions, and the effect of overall bearing size on bearing life. A regression equation was proposed based on simulation results, linking the bearing life reduction factor (LRF) to the accumulative inclusion length within the stressed volume under contact load.

Effect of early stages of thermomechanical processing on inclusions in high carbon steel

The effect of heat treatment and thermomechanical processing on size, size distribution, distribution and chemistry of non-metallic inclusions in a continuously cast high carbon steel was investigated using a Gleeble hot compression simulator at temperatures of 1050 and 1150°C and strains of 0·3 and 0·7 at strain rate 1 s−1. The results showed that the total number of inclusions classified into three main types, namely, sulphide, oxide and duplex, was reduced after the deformation at high temperature. Inclusions of different size and chemistry were found being present in different locations of the bloom, which was related with microsegregation in the as cast bloom. This suggested that inclusions were influenced by solidification conditions and subsolidus homogenisation. Furthermore, the observed changes of chemistry of inclusions during heat treatment and thermomechanical processing at high temperature (∼1100°C) are discussed. These changes were substantiated by evidence of devitrification of oxide inclusions including different manganese silicates.

Te Inclusions in CdMnTe Crystal Grown by the Traveling Heater Method and their Effects on the Electrical Properties

The concentration and size distribution of Te inclusions in CdMnTe (CMT) are key factors in nuclear devices performance. High-concentration and large-size Te inclusions degrade the performance drastically, especially for electrical properties. In this paper, the Te inclusions along the axial and radial directions in CMT crystal grown by the Traveling Heater Method (THM) were revealed by Infrared Microscopic System. The size of Te inclusions is 5-17 μm and the concentration is (2.5-4.6) ×105cm-3. The Current-Voltage measurements were performed and the resistivity of the CdMnTe crystal with excess Te was in the range of 108-109Ωcm, and the correlation between the Te inclusions and resistivity was investigated. The large size (>17 μm) and high concentration (4.5 of ×105cm-3) Te inclusion decrease the resistivity of the CMT crystal seriously.

Inclusion Evolution and Estimation during Secondary Refining in Calcium Treated Aluminum Killed Steels

The objective of this study was to investigate the evolution of inclusions during secondary refining in aluminum killed steels. As calcium treatment is also used to modify solid alumina inclusions to liquid or partially liquid calcium aluminates for keeping free from nozzle clogging, a thermodynamic model has been calculated using Factsage to predict the type of calcium aluminates and sulfides present in the steel. The results showed that alumina generated from deoxidation had transformed to MgOAl2O3 spinel with a small amount of CaO by using high basicity and high Al2O3 slag during ladle furnace (LF) refining. Though soft blowing after LF refining is benefit for the removal of inclusions by floatation, vigorous stirring which may make slag layer exposing an “eye” to air reoxidation should be avoided. After calcium treatment, the inclusions were restricted mainly to globular calcium aluminates and the sulfur in the steel was associated with these inclusions as calcium sulfide. The ND (number density) of inclusions seems to appear a similar tendency to the size distribution of smaller inclusions, and the similar change between the AF (area fraction) of inclusions and the total oxygen content of the steel can be also found by careful comparison. Predicted inclusion type in the steel were validated with measurement based on samples collected from industrial heats and a reasonable range of Ca content was also given for the experimental steel.

Effect of surface roughness of MgO substrate on size distribution of inclusions

Experiments were carried out to investigate the effect of surface roughness of MgO substrate on the formation and size distribution of inclusion particles employing new experimental methodology. The reaction of MgO refractory with Al deoxidised liquid Fe can take place, which results in forming both MgO and spinel type of inclusions. The number density of inclusions increases with increasing surface roughness of the substrate, which could be explained by Gibbs–Thompson effect. Activated interfacial reactions between the substrate and liquid Fe are believed to be more dominant than the effect of increased surface roughness of the substrate on the number density of inclusions. It is recommended to use Al2O3 based nozzle than MgO based one of similar surface roughness from a viewpoint of the generation of lower number density of inclusions.

Effects of Lanthanum and Boron on the Microstructure and Magnetic Properties of Non-oriented Electrical Steels

AbstractThe effects of lanthanum and boron on the inclusion size distribution, microstructure, texture and magnetic properties of three non-oriented electrical steels have been studied. After final annealing, lanthanum effectively inhibited the precipitation of MnS precipitates and promoted the growth of grains, an addition of 0.0041 wt.% boron led to the precipitation of Fe2B particles and inhibited grain growth. On the other hand, steel containing 0.0055 wt.% lanthanum had the strongest {100} and {111} fiber texture and the weakest {112}〈110〉 texture among the steels. Compared to steel without lanthanum and boron, steel with 0.0050 wt.% lanthanum and 0.0041 wt.% boron obtained slightly stronger intensities of {100} and {111} fiber texture, and a little weaker intensity of {112}〈110〉 texture. Steel containing 0.0055 wt.% lanthanum achieved the best magnetic properties, whose core loss and magnetic flux density were 4.268 W/kg and 1.768 T, respectively.

Effect of lanthanum content on microstructure and magnetic properties of non-oriented electrical steels

The effect of lanthanum content in the range of 0–0.011 wt.%, on the inclusion size distribution, microstructure, texture and magnetic properties of three non-oriented electrical steels was studied. After final annealing, lanthanum effectively inhibited the precipitation of MnS precipitates in steel, the formations of La2O2S and LaS inclusions not only acted as nuclei of AlN precipitates, but also combined with Al2O3 and formed composite inclusions with larger size. Grain size firstly increased and then decreased with lanthanum content increasing. Steel containing 0.0066 wt.% lanthanum obtained the largest grain size, the strongest {110}<110> texture and the weakest {112}<110> texture among all the tested steels. Magnetic flux density firstly increased and then decreased, core loss firstly dramatically decreased and then slightly decreased with lanthanum content increasing. Among the three tested steels, steel with 0.0066 wt.% lanthanum demonstrated the best comprehensive magnetic properties mainly through the development of favorable texture and appropriate final grain size.

Evolution of Non-Metallic Inclusions in Secondary Steelmaking: Learning from Inclusion Size Distributions

Evolution of Non-Metallic Inclusions in Secondary Steelmaking: Learning from Inclusion Size Distributions

Determination of Size Distribution and Probable Maximum Size of Inclusions in AISI304 Stainless Steel

The probable maximum sizes (PMS) of inclusions in AISI304 stainless steels were predicted by two methods of the statistics of extreme values (SEV) and the particle size distributions (PSD). Firstly, the PMS of inclusions in the molten steel taken from a tundish agreed well with those in the slab sample. The particle size distributions (PSD) of inclusions almost obeyed exponential functions. The results of comparison between the two methods showed that the PMS by the SEV analysis agreed with that by the PSD approximation in the case of the steel with the higher oxygen content. However, in the case of the steel with the lower oxygen content, the PMS by the PSD approximation overestimated the predicted size with the reference to the SEV analysis. In this case, the approximations with elimination of some largest inclusions which were deviated from an exponential distribution were found to be effective to predict the probable largest size in a reference area. This above result suggests that it is necessary to decide if some largest inclusions are employed for adequate predictions. It is considered that necessity of this operation increases with decreasing oxygen content.

Experimental and Numerical Investigations on Non-metallic Inclusions Distribution in Billets Casted at a Multi-strand Continuous Casting Tundish

Modern tundishes plays an important role of refining treatments to improve the quality and purity of casted steel. Purity of steel is defined by the non-metallic inclusions in the steel product, including their size, quantity, distribution, chemical composition and mineralogy. The aim of presented studies was to investigate the number and distribution of non-metallic inclusion in individual billets casted in a six-strand tundish. The industrial measurements, performed during stable production conditions at the continuous steel casting (CSC) plant, were performed for different tundish working space configurations. Analysis of the size and number of non-metallic inclusions has been done on the metallographic samples using light microscope. Experimental studies were supported with numerical simulations using large eddy simulations (LES) method. A modified boundary condition describing inclusion separation at the liquid steel surface was implemented in commercial code AnsysFluent. Experimental results concern size distribution of inclusions in billets for current tundish configuration showed big differences between casted ingots. Numerical results shown the domination in the number of inclusions occurring in the nozzles number 3 and 4 (for basic tundish configuration) and in the nozzles number 2 and 5 (for tundish with turbulence inhibitor). The reason for that is the change in configuration tundish working space, that has an impact on the flow field inside the tundish. Experimental measurements performed for proposed modified tundish configuration (with turbulence inhibitor) shown that those differences are much smaller, which in consequence has an influence in higher quality of continuously casted ingots for individual strand of CSC.

Effect of single pass welding heat input on microstructure and hardness of submerged arc welded high strength low carbon bainitic steel

The bead on plate test method was employed to investigate the effect of single pass welding heat input on microstructure and hardness of submerged arc welded high strength bainitic steel. The weld metal microstructure contains very high volume fraction of acicular ferrite regardless of heat input. By contrast, with the increase in heat input, the main microstructure in coarse grained heat affected zone (HAZ) changes from a mixture of lath martensite and ferrite sideplate to full ferrite sideplate. Microhardness measurement showed that maximum hardness values always present at the coarse grained HAZ under lower heat input condition, which indicates that the minimum heat input of experimental steel should be higher than 0·92 kJ mm−1 to avoid the formation of welding cold crack. The size distributions of complex inclusions in the weld metal are very similar for all heat inputs mainly because the short residence time does not make the inclusion grow rapidly.

The Measurement of Total Inclusion Content in Nickel-Titanium Alloys

Inclusion content is important for the properties of high performance alloys used in fatigue rated devices. A method to analyze the total inclusion content of NiTi alloys was applied to vacuum induction melted vacuum arc remelted hot rolled coil and cold drawn wire. Carbides and oxides populations were analyzed separately. Pursuant to ASTM standards, a definition for stringers was formulated and applied to cold drawn wire. It was shown that changes in melting and hot working result in changes in the amount and size of carbides and oxide inclusions. The inclusion size distributions are highly skewed. It is hypothesized that the statistics of extreme values must be applied to these populations in order to predict a maximum inclusion size.

Three-dimensional observation of carbonaceous chondrites by synchrotron radiation X-ray CT – Quantitative analysis and developments for the future sample return missions

Carbonaceous chondrites were observed by synchrotron radiation X-ray computed tomography (SR-CT) three-dimensionally. We analyzed the chemical composition of the components of the carbonaceous chondrites, such as chondrules, matrix and iron inclusions, from the linear attenuation coefficient (LAC) of X-rays. Histograms of the LAC were used for the analysis of chemical composition of the internal material, and we could find a clear relation of the compositions between the chondrules and matrix. We also analyzed the size distribution of low-Fe inclusions (chondrules) using image processing of CT images. Cumulative size distribution of chondrules shows power-law distribution, and slopes of the distribution changed for different chondrite classes. Results of these analyses show that the chondrule and matrix would have formed from the same precursor, and were incorporated into the parent bodies without large scale mixing in the solar nebula.The method will also provide important information for the analysis of future sample return missions. Our examinations demonstrate great potential of the quantitative determination of chondrite class nondestructively, by SR-CT.

On the Permeability of Fractal Tube Bundles

The permeability of a porous medium is strongly affected by its local geometry and connectivity, the size distribution of the solid inclusions, and the pores available for flow. Since direct measurements of the permeability are time consuming and require experiments that are not always possible, the reliable theoretical assessment of the permeability based on the medium structural characteristics alone is of importance. When the porosity approaches unity, the permeability–porosity relationships represented by the Kozeny–Carman equations and Archie’s law predict that permeability tends to infinity and thus they yield unrealistic results if specific area of the porous media does not tend to zero. The aim of this article is the evaluation of the relationships between porosity and permeability for a set of fractal models with porosity approaching unity and a finite permeability. It is shown that the tube bundles generated by finite iterations of the corresponding geometric fractals can be used to model porous media where the permeability–porosity relationships are derived analytically. Several examples of the tube bundles are constructed, and the relevance of the derived permeability–porosity relationships is discussed in connection with the permeability measurements of highly porous metal foams reported in the literature.

Influence of melt purification on mechanical properties of AZ31 magnesium alloy

This experimental study was conducted to investigate the effect of melt cleanliness with respect to the presence of inclusions on the mechanical properties of AZ31 alloy. The type, morphology and size distribution of inclusions in the alloy were analysed. The tensile properties of the AZ31 alloy with and without melt purification were tested at room temperature. The fracture surface of the AZ31 alloy was observed by SEM to reveal the mechanism of fracture nucleation. By melt purification treatment, most of the inclusions are removed from the AZ31 alloy, and the average size of inclusions in the alloy is decreased from 16·5 to 2·0 μm. In addition, the tensile strength and especially the elongation of the alloy are increased. Tensile fracture analysis showed that the inclusions act as crack initiation sites during fracture. The MgO film, which is the main inclusion in the alloy, contributed to poorer mechanical properties.

Inclusion Population Evolution in Ti-alloyed Al-killed Steel during Secondary Steelmaking Process

This paper presents a new approach towards the evolution of non-metallic inclusion (NMI) populations in Ti-alloyed Al-killed steels, based on an extensive inclusion analysis campaign at Tata Steel Europe, IJmuiden Works. Automated SEM techniques were used to characterize the inclusion populations in 120 steel samples taken from nine heats out of two casting series of this steel grade. As NMI in Ti-alloyed Al-killed steels are overwhelmingly dominated by chemically simple Al2O3, most of the process relevant information lies in the analysis of particle size distribution during the secondary steelmaking process. The population density function (PDF) concept was applied, for the first time, to the characterization of inclusion size distributions sampled from secondary steelmaking practice. Two size distribution forms predominate in the entire dataset: i) Lognormal size distributions associated with active nucleation and growth of alumina (deoxidation and reoxidation), indicating net transfer of matter between NMI and solutes in liquid steel and ii) Power-law size distributions, associated with an inclusion population in chemical equilibrium with the melt and subject to collision/breakup processes controlling the distributions. Based on inclusion PDF observations, it is found that the size distribution of alumina inclusions suspended in steel melt, after equilibration and effective float out of large inclusions, tends to approach a Reference Distribution of power-law type function (f(r) = a ⋅ r –3.5) that appears to be a fundamental feature of the alumina-steel system. This Reference Distribution can guide efforts to improve and engineer inclusion populations for a better controlled steel product.

Endurance limit prediction for sulphur-alloyed spray-formed steels

Crack initiation in fatigue specimens takes place in highly stressed regions either at the surface or in the volume. In the latter case, often inclusions are the responsible origins influencing the fatigue strength by their size and orientation: The endurance limit decreases with increasing inclusion dimensions perpendicular to the loading direction. In this paper a calculation method based on the weakest-link concept is presented which enables the prediction of the fatigue limit as well as the fracture initiation site in specimens which fail predominantly at inclusions. It considers the inclusion size distribution, the hardness and the residual stresses of the specimens.

Magnetodielectric composite with ferrite inclusions as substrates for microstrip patch antennas at microwave frequencies

A study has been conducted to estimate the complex permittivity and permeability along with magnetic characterization of different volume fractions of magnetodielectric composites with cobalt ferrite nano inclusions. Using an in touch superstrate technique dielectric properties are estimated. Cavity perturbation technique is used to study the complex permeability of the samples. 4πMs value and coercivity is measured using vibrating sample magnetometry. Structural and surface morphologies on the composite samples are conducted to determine the size and homogeneous distribution of nano inclusions. The average grain size of cobalt ferrite nanoparticles is found to be ∼10nm. The real part of permittivity and permeability of the samples varies from ∼1–2.905 to ∼1.01–1.05 with increase in inclusion content from 1%VF to 5%VF, respectively. The tanδ of permittivity and imaginary part of permeability is found to be of the order of ∼10−3 and ∼10−1 respectively. Verification of these composites as potential substrates for microstrip patch antenna is carried out by fabricating simple rectangular patch at 9.5GHz using transmission line model. Rectangular patch is designed on 5%VF composite system. The return loss for the composite system was found to be ∼−19.451dB which is comparable with that designed on standard glass epoxy substrate (ɛr=4.5).

The fatigue limit of bearing steels – Part I: A pragmatic approach to predict very high cycle fatigue strength

Bearing steels and other high strength steels exhibit complex fatigue behavior in excess of 10 7 cycles due to their sensitivity to defects like inclusions. Failure occurring in the very high cycle fatigue regime and the lack of an asymptote in the measured S–N data raise the questions as to the existence of fatigue limit and prediction of the fatigue strength of the high strength steel components. A series of two papers are written to discuss on the characteristics of the very high cycle fatigue and their implication for engineering applications. In the present paper (Part I) a deterministic defect model is developed to describe the fatigue crack growth from de-bonded hard inclusions. The model is shown to provide a unified prediction of fatigue behavior in different regimes, i.e. low cycle fatigue regime dictated by the tensile strength, high cycle fatigue regime obeying Basquin’s law and the very high cycle fatigue regime featured by the fish-eye and ODA (optically dark area) surrounding an interior fatigue-initiating inclusion on the fracture surface. The model predictions agree well with experiments. A combination of the deterministic model with a stochastic model that describes the inclusion size distribution allows prediction of fatigue strength and fatigue limit associated with certain reliability of a steel component. It is found that very high cycle fatigue, associated with interior inclusions, is attributed to the very slow crack propagation in vacuum condition, and that an asymptote for fatigue limit observed for mild steels also exists for high strength steels such as bearing steels, but extends beyond the very high cycle fatigue regime normally measured to-date. Monte Carlo simulation shows that such a fatigue limit asymptote becomes clearly visible in excess of 10 12 cycles, which is difficult to measure with today’s testing devices. Furthermore, the effects of steel cleanliness and specimen type and shape are studied by means of Monte Carlo simulations.

Fatigue Strength of Conventionally Cast Tool Steels and its Dependence of Carbide Microstructure

AbstractThe axial fatigue strength at two million cycles was experimentally determined for two conventionally cast tool steels and successfully compared with results from a fatigue limit model. Specimens were tested both in the rolling and transverse direction and showed large differences in fatigue properties due to the segregated carbide microstructure. Rolling direction specimens experienced higher fatigue strength than the transverse direction specimens. This is due to smaller carbides present in the load affected cross section of the rolling direction fatigue test bars compared to the cross section of the transverse direction fatigue test bars. Fractographic analysis of failed specimens showed that large carbides had caused fatigue failure, which was also predicted by the model. Measured size distributions of carbides and inclusions were used as input data in the model. The probability that at least one particle will be present in the material volume having a size larger than the threshold value for crack propagation was calculated.