Size Of Non-metallic Inclusions Research Articles

Effect of Boron on the Microstructure and Mechanical Properties of Low-Carbon Tube Steel

Effects of boron in low-carbon tube steel grade 17G1SU on nonmetallic inclusions, structure and mechanical properties were investigated. Experimental samples of rolled metal containing boron 0.006 and 0.011% are characterized by predominantly small, nonmetallic inclusions not more than 5 μm, which are represented by complex alumomagnesium spinels in the shell of manganese and calcium sulfides, and small silicate inclusions. Nonmetallic inclusions of comparative pipe steel sample, containing no boron characterized by the presence of larger inclusions presented complex oxysulfide and sulfide films. The main structural component of the comparative and experimental samples is ferrite. The introduction of boron is contributed by a decrease in the average size of ferritic grains from 8.7 μm (0% B) to 6.2 (0.006% B). Increasing the boron content to 0.011% leads to slight increase (up to 6.8 microns) of the size. The mechanical properties of 10 μm rolled metal pipe steel ensured the production of rolled products of strength class X80 without additional (thermal) treatment, as a result of the reduction in the size and shape of nonmetallic inclusions, and formation of dispersed structure.

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.

Study on nonmetallic inclusions in clean Cu-P-RE weathering steels

The compositions, morphologies and sizes of nonmetallic inclusions in rare earth (RE) weathering steels with different oxygen and sulfur contents were analyzed by using electron probe micro-analyzer (EPMA), quantitative image analyzer and scanning electron microscope (SEM-EDS). The formation of inclusions was studied by the thermodynamics theory. The RE solid-soluble content in steel was analyzed by non-aqua electroanalysis and inductively coupled plasma (ICP). To RE weathering steels with different contents of oxygen and sulfur, the optimal RE content was obtained from the perspective of RE modifying inclusions. The results showed the cleanliness of steel was an important factor which influenced the modifying effect of RE on the inclusions. RE changed the character and shape of inclusions in the clean Cu-P weathering steels. The elongated MnS inclusions and brittle oxide inclusions were modified as the small globular RE oxysulfide and RE compound inclusions in the RE weathering steels. The RE inclusions distributed uniformly in matrix and the sizes of more than 90% of the inclusions were less than 2 μm. It was obtained the optimum content of RE was 0.0065 wt% ∼ 0.016 wt% to the Cu-P-RE weathering steels with 0.002 wt% oxygen and 0.004 wt% sulfur, and the optimum content of RE was 0.0092 wt% ∼ 0.023 wt% to the RE weathering steels ( O: ∼ 0.007 wt%, S: ∼ 0.008 wt%). The RE content was the most favorable to modify the harmful inclusions and improve the properties of Cu-P weathering steels.

Effect of Structure on Ductile–Brittle Transition in Steels with BCC-Lattice

The effect of structural characteristics (ferrite, ferrite + pearlite, sorbite) including morphology, size and distribution of nonmetallic inclusions of different morphology, sizes and distribution, on ductile–brittle transition in structural steels is considered. It is shown that an elementary ductile microcrack is initiated by particles of critical size. For steels with ferrite-pearlite and sorbite microstructure, the particle size (carbide, nitride and nonmetallic inclusions) is almost the same. The ductile–brittle transition is caused by competition of the size of the brittle and ductile (pits) microcracks. As a result, the critical brittleness temperature T c in simplified form looks like $$ {T}_c={T}_c^0+B{\Lambda}_d^{1/2}/{\Lambda}_b, $$ where elementary microcracks Λ b and Λ d correspond to the size of a brittle crack of transcrystalline cleavage (Λ b ) and the size of ductile crack (Λ d ), Т c 0 reflects the contribution of different strengthening mechanisms to metal yield strength: dislocation, solid solution, grain size, precipitation hardening, and others, and B is a coefficient taking into account the stress-strain state in the fracture zone. As part of this model of failure, it becomes clear why for hardened steel the grain size does not change up to the recrystallization temperature, and yield strength and the value of T c have a complex dependence on the tempering temperature. Since the steel has particles of different sizes, they initiate the occurrence of pits of different sizes. The larger the particle, the sooner a micropore originates around it and pit growth is faster. A wide range of pit sizes arises that causes a wide range of T c values. A close connection is demonstrated for the width of the ΔT c ductile–brittle transition temperature range with a change in the distance between particles, including between pearlite colonies. This relationship can be positive and negative, which is confirmed by experiment.

Effect of observation position of SUJ2 bar specimens on inclusions distribution

The size and distribution of non-metallic inclusions are strongly related to rolling contact fatigue (RCF) life. SUJ2 steel is manufactured as a round bar, and is cooled from the surface during casting. This indicates that the inclusions may be distributed non-uniformly in the center direction. The objective of this study is a clarification of the difference of the inclusion distribution in the SUJ2 round bar. It was found that the distribution of inclusions in SUJ2 was distributed uniformly in a transverse direction.

Quality of weld seams produced with flux based on silicomanganese slag

The use of metallurgical wastes in welding fluxes is considered. A new welding flux based on slag from silicomanganese production is proposed, along with the corresponding manufacturing technology. The quality of the weld seams is studied by metallographic analysis. The grain size and content of nonmetallic inclusions are determined. An Olympus GX-51 optical microscope is used for metallographic analysis (magnification ×100–1000). The influence of the fractional composition on the performance of the fluxes is studied. The optimal fraction is chosen, ensuring low content of nonmetallic inclusions (in particular, nondeforming silicates and oxides) in the weld seam. If 30–40% of the small fraction of welding flux is employed, the content of nonmetallic oxide inclusions in the weld seam is reduced. Metallographic analysis shows that introducing the small fraction has no effect on the structural components of the weld seam. The seam is characterized by ferrite–pearlite structure. The ferrite is present in the form of grains extended in the direction of heat transfer. The optimal content of the <0.45 mm fraction in the welding flux is 30–40%. To improve flux performance, the small fraction may be mixed with liquid glass. The use of ceramic flux produced from the dust of silicomanganese slag (<0.45 mm fraction) bound by liquid glass reduces the content of nonmetallic inclusions in the weld seam. However, increase in the content of liquid glass from 15 to 40% has little effect on the content of nonmetallic oxide inclusions in the weld seam or on the microstructure. The microstructure in the weld seam consists of pearlite and ferrite. The optimal flux consists of the small fraction with 15–20% liquid glass.

On the Capability of Nonmetallic Inclusions to Act as Nuclei for Acicular Ferrite in Different Steel Grades

Acicular ferrite nucleates intragranularly on nonmetallic inclusions, forming a microstructure with excellent fracture toughness. The formation of acicular ferrite is strongly affected by the size, content, and composition of nonmetallic inclusions, but also by the composition of the steel matrix. The potential of inclusions in medium carbon HSLA (high-strength low-alloyed) steels has been the main focus in the literature so far. The current study evaluates the acicular ferrite capability of various inclusions types in four different steel grades with carbon contents varying between 0.04 and 0.65 wt pct. The investigated steels are produced by melting experiments on a laboratory scale and subsequent heat treatment in a High-Temperature Laser Scanning Confocal Microscope. Inclusions are exclusively formed by deoxidation and desulfurization reactions. No synthetic particles are added to the melt. The inclusion landscape is analyzed by Scanning Electron Microscopy. Final ductility of the samples is evaluated based on performed tensile tests. Inclusion types in every steel grade are assessed regarding their nucleation potential always considering the interaction with the steel composition, especially focusing on the role of manganese. The effects of (Ti,Al)Ox-, MnS-, and MgO-containing inclusions are discussed in detail.

Investigation of changing failure mechanisms in the VHCF regime caused by different strengths of a martensitic steel

The present study gives an overview of recent investigations dealing with the fatigue behaviour of the tempered martensitic steel 50CrMo4 (Fe-0.5wt%C-1wt%Cr) in the HCF and VHCF regime by taking into account a variation in material strength, by modifying the heat treatment parameters. The parameters for the tempering treatment were adapted to receive two material conditions with 37HRC and 57HRC, respectively. Subsequently, fatigue specimens were machined from the heat-treated bars for fatigue tests in an ultrasonic (f=20000Hz) and a resonance (f=95Hz) fatigue testing machine under fully reversed loading (R=-1) at laboratory air atmosphere. It was found that the dominant fatigue and fracture mechanisms change with increasing material strength. For 37HRC moderate-strength specimens crack initiation was shown to occur on the specimen surface within Cr depleted bands (segregation bands) as the dominant fatigue damage mechanism. Contrary to that, only internal crack initiation at non-metallic inclusions was observed for the high strength 57HRC condition. Furthermore, the completely different crack initiation mechanisms of the two heat treatment conditions were assessed by applying the Murakami approach relating the fatigue limit with the size of non-metallic inclusions.

Acicular Ferrite Formation and Its Influencing Factors-A Review

Acicular ferrite is a microstructure nucleating intergranularly on non-metallic inclusions and forming an arrangement of fine, interlocking grains. This structure is known to improve steel properties, especially steel toughness, essentially. The formation of acicular ferrite is mainly affected by steel composition, cooling rate, inclusion landscape and austenite grain size. In recent decades, extensive research has been conducted to investigate these factors. The present paper provides an overview of the impact of published results and the state of knowledge regarding acicular ferrite formation. Special attention is paid to the effect of carbon, manganese and titanium addition to steel, as well as the optimum size, number and composition of non-metallic inclusions. In addition, the reactions during the nucleation and growth of acicular ferrite needles are briefly addressed. Further, characteristics of acicular ferrite and bainite are summarized, which should help to distinguish these similar structures.

Modification of cellulose and rutile welding electrode coating by infiltrated TiO2 nanoparticles

In this paper, a novel method of infiltration of TiO2 nanoparticles into the coating of the cellulose and rutile shielded metal arc welding electrode is shown. Tensile properties and strength of weld metals were correlated to the chemical composition of the weld metals, ferrite type, and non-metallic inclusion type, size and composition. As infiltration time is increased in the cellulose electrodes, the non-metallic inclusion count increases and their size decreases. They act as inoculants and lead to the replacement of Widmanstaetten with the finegrained acicular ferrite which increases the mechanical properties of the welds. The modification of rutile electrodes with low and medium infiltration time also refines the microstructure and increases the mechanical properties. Specimens welded with rutile electrodes infiltrated at maximum duration exhibited the lowest mechanical properties due to the relatively large non-metallic inclusions that act as void nucleation sites and the appearance of large grain allotriomorphic ferrite in the weld metal.

Evolution of Non-Metallic Inclusions from FeTi70R Alloys during Alloying of Fe-40Ni-20Cr Steels

In this study, the composition, size, and number of large non-metallic inclusions (g20μm) are investigated in a commercial refined FeTi70R alloy, which is used for deoxidation and alloying o ...

Influence of refining slag composition on cleanness and fatigue life of 60Si2MnA spring steel

The influence of basicity and Al2O3 content of LF refining slag on T.[O] (total oxygen) as well as type, number and size of non-metallic inclusions in Al killed 60Si2MnA spring steel was investigated. The results showed that with the increase of slag basicity R(CaO/SiO2) or the decrease of Al2O3 content in slag, the T.[O], number and size of non-metallic inclusions decreased significantly. On the one hand, as the slag basicity increased, inclusions in steel were transformed from Al2O3–SiO2–CaO–MgO quaternary system to Al2O3–SiO2–CaO–MgO–CaS quinary system, which made the formation of voids between inclusions and steel matrix to decrease. Furthermore, thermodynamic calculations showed that CaS could only form in steel (R ≥ 3.4). Al2O3–SiO2–CaO–MgO came close to the compositions of the low melting point area, while Al2O3–SiO2–CaO–MgO–CaS deviated from this. On the other hand, as the Al2O3 content in slag increased, Al2O3–SiO2–CaO–MgO–CaS came close to the compositions of the low melting point area. In conclusion, the cleanness and fatigue life of 60Si2MnA spring steel had been improved by the increase of slag basicity or the decrease of Al2O3 content in slag.

Физическая химия и физика металлургических систем

Yttrium belongs to the same group as lanthanum, and its chemical properties are close to those of the latter. Therefore, yttrium is referred to as a rare earth metal. When added to a heavily deoxidized metal, yttrium refines a primary cast grain, reduces the area of treeing, purifies grain boundaries of non-ferrous inter-metallic compounds, reduces the size of non-metallic inclusions, and enhances heat resistance and high temperature strength of special steels. Optimal yttrium additive in the metal does not exceed 0.3 to 0.5 wt. %. Complex interaction of yttrium with oxygen in the presence of residual concentrations of aluminum, calcium and magnesium in the metal was not studied at all. Thermodynamic modelling of steel deoxidation using yttrium in the presence of low concentrations of aluminum, calcium or magnesium is developed. The surfaces of component solubility in liquid steel are created for Fe–Y–Al–O–C, Fe–Y–Ca–O–C, and Fe–Y–Mg–O–C systems. To make calculations related to oxide systems, all possible phase equilibria are established, coordination of equilibrium constants dependency on temperature is carried out, and energy parameters of the subregular ionic solution theory are specified. The surfaces of component solubility show that deoxidation by yttrium is a complex process due to the presence of calcium and aluminum in steel. Deoxidation products will contain complex phase compositions of oxides based on CaO, Al 2 O 3 , and Y 2 O 3 . In case of steel deoxidation by yttrium and magnesium, the process is performed alternately. Either yttrium or magnesium acts as a deoxidizer.

Regulation of Removal Process of Non-Metallic Inclusions at Secondary Treatment of Melt

Background. When secondary refining with inert gases, blowing intensity of metal is generally maintained at a constant level and limited by the level of metal in the ladle. Recent studies show that the blowing intensity effect to remove impurities of different size, so there is the problem of regulating this process.Objective. The aim of the investigation is to research the process of removing non-metallic inclusions from the metal in the ladle by blowing an inert gas in order to increase the efficiency of removing impurities and preventing the emission of metal from the ladle when blowing.Methods. The regulation of removing non-metallic inclusions from steel by changing the blowing intensity in ladle is described. The structural scheme of regulation circuit to control the process of purging the metal in the ladle is created. An example of regulation of removing non-metallic inclusions from steel in the 160-ton ladle has been given.Results. Changing the blowing intensity, giving it a fluctuating nature, in which the maximum intensity is the minimum size of nonmetallic inclusions to be removed and the minimum - maximum possible size of inclusions and frequency - a free ladle capacity, increased efficiency removal of inclusions has been established.Conclusions. It is shown that the determination of probability size of inclusions and free volume of the ladle to regulate the blowing intensity of metal, improve mixing of metal in the ladle warning metal emissions and ensure complete removal of non-metallic inclusions of various sizes.

Fatigue Strength Prediction of Drilling Materials Based on the Maximum Non-metallic Inclusion Size

In this paper, the statistics of the size distribution of non-metallic inclusions in five drilling materials were performed. Based on the maximum non-metallic inclusion size, the fatigue strength of the drilling material was predicted. The sizes of non-metallic inclusions in drilling materials were observed to follow the inclusion size distribution rule. Then the maximum inclusion size in the fatigue specimens was deduced. According to the prediction equation of the maximum inclusion size and fatigue strength proposed by Murakami, fatigue strength of drilling materials was obtained. Moreover, fatigue strength was also measured through rotating bending tests. The predicted fatigue strength was significantly lower than the measured one. Therefore, according to the comparison results, the coefficients in the prediction equation were revised. The revised equation allowed the satisfactory prediction results of fatigue strength of drilling materials at the fatigue life of 107 rotations and could be used in the fast prediction of fatigue strength of drilling materials.

Contribution of the Chair of Ferrous Metallurgy at the Montanuniversitaet Leoben to Enhance the Sustainability of Steel Production and Application

The research work at the Chair of Ferrous Metallurgy at the Montanuniversitaet Leoben contributes in different aspects to a sustainable steel production and application. New advanced methods for characterization of ferrous raw material and carbon carriers are developed with the aim to enhance the efficiency for the use of raw materials and energy input in the blast furnace as well as in direct and smelting reduction processes. The chair is involved in the development of new breakthrough technologies such as endless strip production and hydrogen smelting reduction, sponsored by the Austrian industries. This venture is a contribution to reduce the fossil fuel energy consumption and an enhancement of steel production with lesser carbon consumption. A valuable contribution to the sustainable use of steel in products is done by the research on the prevention of defect formation in casting processes or the control of the nature, shape, and size of non-metallic inclusions.

The Measurement of Hardness and Elastic Modulus of non-Metallic Inclusions in Steely Welding Joints

Trunk pipelines work under a cyclic dynamical mechanical load because when oil or gas is pumped, the pressure constantly changes - pulsates. Therefore, the fatigue phenomenon is a common reason of accidents. The fatigue phenomenon more often happens in the zone of non-metallic inclusions concentration. To know how the characteristics of non-metallic inclusions influence the probability of an accident the most modern research methods should be used. It is determined with the help of the modern research methods that the accident rate of welded joints of pipelines is mostly influenced by their morphological type, composition and size of nonmetallic inclusions, this effect is more important than the common level of pollution by non-metallic inclusions. The article presents the results of the investigations of welded joints, obtained after the use of different common welding materials. We used the methods, described in the state standards: scanning electronic microscopy, spectral microprobe analysis and nano-indentation. We found out that non-metallic inclusions act like stress concentrators because they shrink, forming a blank space between metal and non-metallic inclusions; it strengthens the differential properties on this boundary. Nonmetallic inclusion is not fixed, it can move. The data that we have received mean that during welded joints’ contamination (with non-metallic inclusions) monitoring process, more attention should be paid to the content of definite inclusions, but not to total contamination.

Fatigue strength scatter characteristics of JIS SUS630 stainless steel with duplex S–N curve

The scatter behavior of fatigue strength for 17-4 PH stainless steel (JIS SUS630, equivalent to ASTM-A563 Grade 630), which exhibited a duplex S–N curve, was investigated. It was found that the fatigue strength scatter of the SUS630 at 106 and 107 cycles, which were corresponding to the fatigue strengths for the surface-induced and the subsurface-inclusion-induced crack nucleation modes, respectively, were significantly small and comparable to each other. The scatter of inclusion size in the present material was small and resulted in the small scatter of fatigue strength comparable to that for the surface-induced crack nucleation mode. The variation in size of non-metallic inclusions is known as one of the main factors for the fatigue strength scatter (Murakami, 2002) [1]. It was also found that the scatter of fatigue strength was in the same order of tensile strength.

Hydrogen effects on fracture of high-strength steels with different micro-alloying

Abstract Constant load tests of high-strength carbon steels with different micro-alloying using strengths in the range of 1000–1400 MPa were performed at ambient temperature under continuous electrochemical hydrogen charging. Hydrogen markedly affects delayed fracture of all the studied steels. Fractography of the studied steels shows that fracture mechanism depends on the chemical composition of the studied steels and hydrogen-induced cracking exhibits intergranular or transgranular character occurring often in the form of hydrogen flakes. The size and chemical composition of non-metallic inclusions are analyzed by scanning electron microscopy and energy-dispersive X-ray spectroscopy. Hydrogen-induced cracking initiates at TiN/TiC particles in steels with Ti alloying. Crack paths are studied with electron backscatter diffraction mapping to analyze crack initiation and growth. The thermal desorption spectroscopy method is used to analyze the distribution of hydrogen in the trapping sites. The mechanisms of hydrogen effects on fracture of high-strength steels are discussed.

Evolution of weld metal microstructure in shielded metal arc welding of X70 HSLA steel with cellulosic electrodes: A case study

The microstructure of weld joint in X70 line pipe steel resulted from shielded metal arc welding with E6010 cellulosic electrodes is characterized using optical and electron microscopy. A range of ferritic morphologies have been identified ranging from polygonal inter- and intra-prior austenite grains allotriomorphic, idiomorphic ferrites to Widmanstätten, acicular and bainitic ferrites. Electron Backscatter Diffraction (EBSD) analysis using Image Quality (IQ) and Inverse Pole Figure (IPF) maps through superimposition of IQ and IPF maps and measurement of percentages of high and low angle grain boundaries was identified to assist in differentiation of acicular ferrite from Widmanstätten and bainitic ferrite morphologies. In addition two types of pearlitic structures were identified. There was no martensite detected in this weld structure. The morphology, size and chemistry of non-metallic inclusions are also discussed briefly.