Effect Of Nonmetallic Inclusions Research Articles

Effects of Typical Inclusions on the As‐Cast Microstructure and Recrystallization of Low‐Density Steel

Herein, the effect of nonmetallic inclusions (NMIs) on the microstructure and dynamic recrystallization (DRX) of Fe–23Mn–6Al–0.7C low‐density steel is studied. The specimens are separately added sulfur (S) and nitrogen (N) to change the characteristics of NMIs. As a result, the addition of S significantly increases the number of MnS inclusions and AlN–MnS complex inclusions in low‐density steel. The addition of N results in a significant increase in the size of NMIs. In the results, NMIs act as the heterogeneous nucleation sites for austenite and refine the as‐cast grains in low‐density steel. In addition, the treated specimens are subjected to a thermal compression simulation experiment. During the thermal compression process, discontinuous DRX is considered to be the main recrystallization method in the experimental low‐density steels. Meanwhile, the typical NMIs significantly accelerate the DRX within grains in low‐density steel through the mechanism of particle‐stimulated nucleation and continuous DRX.

Effect of non-metallic inclusions and chemical composition of 20GL steel on impact strength of freight car castings

Effect of non-metallic inclusions and chemical composition of 20GL steel on impact strength of freight car castings

A new multiaxial fatigue endurance model for high strength steels taking into account the presence of small defects

In the present work, a new multiaxial fatigue model is proposed for metallic material with small defects. This model correlates the uniaxial fatigue limit obtained from the area parameter of a high strength steel containing small defect with values associated with the amplitude of the principal stresses, whose calculation for non-proportional loadings is not trivial. The performance of the model was evaluated with experimental data from AISI 4140 steel, under various loading conditions, in which smooth cylindrical bars were considered, regarding: (i) the effect of non-metallic inclusions in the material, and (ii) superficial micro hole with a straight bottom machined in the material (550 μm in diameter and depth). The proposed model has provided accurate fatigue strength estimates with average error not exceeding 16 %.

Effect of Non-Metallic Inclusions on the Hot Ductility of High-Mn Steels

Effect of Non-Metallic Inclusions on the Hot Ductility of High-Mn Steels

Effect of Non-Metallic Inclusions on the Fatigue Strength Coefficient of High-Purity Constructional Steel Heated in Industrial Conditions

Steel fatigue strength testing is a process that requires large amounts of time, resources and appropriate equipment. The industry seeks to replace cumbersome destructive testing with non-destructive testing. Coefficients were developed that allow the comparison of the parameters of material properties. One such factor is the fatigue strength coefficient, which allows the estimate of fatigue strength using the known hardness of a given material. The fatigue strength factor should be developed for conditions that are as close to the industrial conditions as possible. It should take into account not only the expected properties of the material and the technological process but also its imperfections, e.g., the share of non-metallic inclusions and the steel microstructure. This paper presents the results of research on the influence of non-metallic inclusions on the fatigue strength coefficient of structural steel subjected to rotary bending. The tests were carried out in seven heats obtained in a 140-ton electric furnace under industrial conditions. The steel was desulfurized and refined with argon. The paper presents the bending fatigue strength of hardened and tempered steel at temperatures from 200 °C to 600 °C as a function of the relative volume of inclusions. The non-metallic inclusions occurring in steel were determined qualitatively and quantitatively. The derived fatigue strength coefficient, k, for different tempering temperatures makes it possible to estimate the fatigue strength of the analyzed steel as a function of its hardness for various microstructures represented by the respective tempering temperatures.

The effect of non-metallic inclusions in refining microstructure and improving cryogenic toughness of novel high-Mn steel weld metals for LNG tanks

The effect of non-metallic inclusions in refining microstructure and improving cryogenic toughness of novel high-Mn steel weld metals for LNG tanks

Effects of Non-Metallic Inclusions and Mean Stress on Axial and Torsion Very High Cycle Fatigue of SWOSC-V Spring Steel

Inclusion-initiated fracture in high-strength spring steel is studied for axial and torsion very high cycle fatigue (VHCF) loading at load ratios of R = −1, 0.1 and 0.35. Ultrasonic S-N tests are performed with SWOSC-V steel featuring intentionally increased numbers and sizes of non-metallic inclusions. The fatigue limit for axial and torsion loading is considered the threshold for mode I cracks starting at internal inclusions. The influence of inclusion size and Vickers hardness on cyclic strength is well predicted with Murakami and Endo’s area parameter model. In the presence of similarly sized inclusions, stress biaxiality is considered by a ratio of torsion to axial fatigue strength of 0.86. Load ratio sensitivity is accounted for by the factor ((1 − R)/2)α, with α being 0.41 for axial and 0.55 for torsion loading. VHCF properties under torsion loading cannot appropriately be deduced from axial data. In contrast to axial loading, the defect sensitivity for torsion loading increases significantly with superimposed static mean load, and no inclusion-initiated fracture is found at R = −1. Size effects and the stress gradient effective under torsion loading are considered to explain smaller crack initiating inclusions found in torsion ultrasonic fatigue tests.

Premature failure of an automobile brake disc: Effect of nonmetallic inclusions

A metallurgical failure analysis was conducted on a grey cast-iron (GCI) automotive brake disc to unravel the root cause of its premature failure. The brake rotor had been in service for about one year and three months and covered a total mileage of 17 173 km before the failure was reported. However, this investigation aims at identifying the causes of the failure and proffer solutions to forestall similar future occurrences. Chemical composition analysis on the disc suggested that its elemental composition is within the required standard for such a component. The disc swan-neck thickness, hardness and microstructure analysis conformed adequately with the material specifications. SEM-EDS study of the fracture surface showed the presence of admixture oxides of Al, Mg, Si, Na, Ca, Ti and Mn, suggesting nonmetallic (slag and sand) inclusions. A fractographic study of the broken surface indicated that the failure was caused by these oxide inclusions embedded in the swan neck region of the rotor during the casting process. Microcracks were observed to have been initiated within the inclusion particles and propagated through the graphite-pearlite interface, eventually leading to the disc failure. Recommendations are also provided to guide the operation of metal-casters to prevent the recurrence of nonmetallic inclusions, which can significantly diminish the service life of cast products.

Adapted multiaxial fatigue models based on the critical plane approach to consider the presence of small defects in steel

Non-metallic inclusions can often be seen in the fatigue crack initiation site in high-strength steels. These inclusions are known to be detrimental to the fatigue strength, as they behave as stress concentration elements. The same is valid for small defects such as notches, holes and scratches. The goal of this research is to investigate not only the effect of non-metallic inclusions but also of small artificial defects on the fatigue strength of the AISI 4140 steel under multiaxial loading conditions. In order to do so, two critical plane based multiaxial fatigue models are coupled with the √area parameter. This is an empirical parameter, which is used to estimate the uniaxial fatigue strength of metals containing small defects or inclusions. One of the major merits of √area parameter is the fact that the material fatigue limits (under push-pull or torsion) can be estimated by considering only the material hardness and the geometry (area) of the small defect, i.e no costly and lengthy fatigue tests are required. To validate the analysis, experiments under pure and combined push-pull and torsional loading in and out-of-phase have been conducted in smooth and also in specimens containing an artificially produced micro hole. Comparison between the estimates provided by the coupled critical plane-√area parameter multiaxial criterion and data provided very good results, with errors around 20%.

The Effects of Non-Metallic Inclusions on Charpy V-Notch Toughness

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On the effect of non-metallic inclusions in production of small diameter wires

Invistigations are directed to detection of the metallurgical reasons of the breakage of alloy steels during production of the small diameter wire. Several batches of the coiled bar(s) of low carbon silicon-manganese steels of the Sv-08G2S and G3Si1 were taken as materials for invistigation. The main influence on the metal breakage during drawing is exerted by its structure and mechanical characteristics, it is known. The initial structure of the coiled bar(s) before drawing to small diameters from the differents smelting within one sort was not differ and represented globular pearlite for Sv-08G2S steel, ferrite and pearlite for G3Si1 steel. The influence of equipment and drawing technology on the wire breakage is minimal, as the processing is performed with the same conditnions. Special attention in the invistigations was paid to the contamination of steel with nonmetallic inclusions during the drawing. Analysis is showed in the wire of low carbon silicon-manganese steels the presence of the point oxides, non-deformable silicates and sulfides, and fragile inclusions, which are located along the rolling direction. The feature of the wire, which has observed the breakage during the production, is the presence of the large quantity of the line inclusions (3...5 points), which are located in some cases over the entire surface of the polished section of the Sv-08G2S steel. The structure of all investigated steels does not differ, the mechanical characteristics of the wire with breakage corresponded to the required standard values. It is shown that contamination of the original wire rod with (more than 2 points) of nonmetallic inclusions are significantly increases the chance of difficulties arising during production of the wire with a diameter of 1,2...0,8 mm and can lead to breaks. The high purity of steel in terms of nonmetallic inclusions guarantees the absence of breakage due to this defect during the production of wire, which contributes to increase of the performance and decrease in the cost of finished products.

Effect of nonmetallic inclusions on localized corrosion of spring steel

Certain inclusions in high-strength 60Si2Mn-Cr spring steel result in poor resistance to localized corrosion. In this work, to study the effect of inclusions on the localized corrosion behavior of spring steel, accelerated corrosion tests were performed by immersing spring steel in 3wt% FeCl3 solution for different times. The results show that severe corrosion occurred in areas of clustered CaS inclusions. Sulfide inclusions containing Ca and Mg induced the strongest localized corrosion susceptibility. For the case of (Ca,Mn,Mg)S inclusions, the ability to induce localized corrosion susceptibility is ranked as follows: MgS > CaS > MnS. Moreover, CaS, (Ca,Mn)S, and (Ca,Mn,Mg)S inclusions were mainly responsible for inducing environmental embrittlement.

Effect of ceramic particles on the dynamic strength, deformation and toughness behavior of 42CrMo4

In this study, the effect of non-metallic inclusions on the material behavior of 42CrMo4 was investigated. By adding aluminum oxide particles to steel powder, different inclusion contents were simulated. The mechanical and fracture toughness properties were measured under dynamic loading. The damage was examined using the acoustic emissions. With an increasing inclusion content, a decreasing strength, deformability and fracture toughness were observed. The distribution of the inclusions along the surfaces of the prior steel particles lead to small distances between inclusions and favors the initiation of cracks at low stress. The early appearance of material damage was proven by acoustic emissions.

Effect of Non-metallic Inclusions on Subsurface Stress and Fatigue Life of High-speed Railway Bearings

The contact simulation model of high-speed railway train axle box bearing is simplified into a two-dimensional plane with an elastic semi-infinite body subjected to semi-elliptical cylindrical compressive stress in one direction. The ANSYS software was used to solve the effects of single inclusion size, the depth of the contact surface and the elastic modulus on dynamic shear stress and Von Mises stress of high-iron bearing subsurface, and compared with the calculation results of bearing material uniformity assumption. Using the modified Basquin equation, the relevant assumptions are made. The maximum Von Mises stress is used as the key stress for fatigue life calculation. The bearing fatigue life calculation method is established to study the influence of the inclusion size, the depth of the contact surface and the elastic modulus on the bearing fatigue life.

Study of Effect of Non-Metallic Inclusions on Structural State and Properties of Low-Carbon Microalloyed Structural Steels

The effect of silicate glassy inclusions, formed in the final stages of ladle treatment and during continuous casting, on the structural state of cast billets and the properties of rolled products made from them is conducted for low-carbon microalloyed structural steels. Nine melts of steels including three different types of chemical composition are studied. Liquid metal samples of four steel melts of the first type are taken from a casting ladle, tundish, and a continuous casting machine crystallizer. Samples from two or three melts of steels of two other types are taken from various sections along the cross-section of continuously cast billets (CCB). Light and scanning electron microscopy, and local X-ray spectral analysis are used to study characteristics of the metal macro- and microstructure, and presence of non-metallic inclusions (precipitates) within selected samples. Impact strength and hydrogen cracking (HC) resistance of rolled products made from CCB are studied. It is shown on the basis of the results obtained that formation of finely dispersed silicate glassy inclusions leads to a significant improvement in cast metal macro- and microstructure, and also the properties of rolled products made from it, primarily impact strength and HC resistance. The mechanisms, conditions, and production parameters of steel processing that control formation of inclusions based on the SiO2–Al2O3–MnO system are studied.

Effect of non-metallic inclusions (NMI) on crack formation in forged steel

Effect of non-metallic inclusions on crack formation in forged steel components is presented in this work. Ultrasonic phased array system was used to locate and identify the defects in the forged steel samples. X-Ray Computed Tomography (XCT), Scanning Electron Microscopy (SEM), optical metallographic and image analysis, Optical Emission Spectrometry (OES) techniques were used for defect analysis and material characterization. Few subsurface cracks were found in the rejected sample of quench tempered steel acquired after the forging process. Defects were clustered near the core of the specimen. Ultrasonic phased array transducer system and XCT confirmed the presence of approximately 100 µm wide and 10 mm long cracks. Optical and SEM images suggested that the cracks were discontinuous and revealed a predominant presence of MnS and Al2O3 inclusions along with traces of SiO2 and SiC inclusions. Further, alumina inclusions were found to be clustered near the core of specimen, which is the crack zone. Cracks could have been initiated due to quench stress and augmented by the clustered alumina inclusions and propagated through the grain boundaries. Strain analysis using EBSD was performed in a sample near the crack to study the distortion of crystal lattice around the alumina inclusions. Considerable strain distribution could be observed in the matrix containing alumina inclusion, but strain seems to be relieved near the crack. It was presumed that alumina inclusions in the matrix acted as a stress concentration factor and led to the crack initiation mechanism.

An experimental investigation on machinability factors of EN alloy steels – A comparative study

In current years, enormous researches have accomplished about an effect of Non-metallic inclusions, in the direction of maximizing productivity and to reduce the effect at the environment. Nowadays many steel manufacturers, not able to produce completely pure steel. Inclusions are compound material embedded inside the steel during the manufacturing process, which primarily affects the homogeneity of steel. A literature review was performed to obtain the effects of inclusions in alloy steels on their machinability and compares the performances of EN alloy steels for different machinability aspects through the whole of machining under the dry circumstance. Cutting speed, feed, and depth of cut were the dominant governing parameters. The present works compares the machining of three different alloy steels and the behavior of numerous non-metallic inclusions in them. The effects of chemical composition and inclusions on machinability factors including resultant cutting force, chip morphology, and its microstructures are discussed. EN 1A Pb&Te alloy steel experiences the lower cutting force thus provides better machinability.

Effect of non-metallic inclusions on fatigue life of high-speed railway bearings

In the process of smelting and manufacturing of high-speed bearing steel, non-metallic inclusions are always inevitable, which destroy the continuity of the metal matrix and decrease the fatigue life of high-speed railway bearings seriously. Under the condition of obtaining the position and the number of the maximum contact load of the high-speed railway bearings, according to the Hertz contact theory, the maximum contact stress σmax between the roller and the raceway of the high-speed railway bearings and the half-width b of the contact surface is calculated, and then the stress distribution equation of the contact surface is obtained. According to the basic theory of fatigue life, the local stress-strain method was used to analyse the influence of the distance, depth and quantity between the inclusions contained in the raceway of the outer ring on the contact surface stress and the fatigue life of the high-speed railway bearings. Quantitative relationship between the influence of non-metallic inclusions and the contact fatigue life of high-speed railway bearings was determined, which provided scientific bases in the smelting process of high-speed railway bearing steel.

A model approach for considering nonmetallic inclusions in the calculation of the local tooth root load-carrying capacity of high-strength gears made of high-quality steels

Demands for higher performance have caused a need for improved component characteristics, e.g. through surface strengthening of gears and increased cleanliness of gear steels. Unfortunately, a resultant drawback is that cracks in such high-strength gears are more often initiated in the material matrix at nonmetallic inclusions and not at the surface. In standardized calculation methods, the degree of cleanliness of steels is not yet directly correlated to the tooth root load-carrying capacity. This paper considers the effects of nonmetallic inclusions in the steel matrix on the tooth root strength based on the theoretical approach of Murakami.

Defects as a root cause of fatigue failure of metallic components. II: Non-metallic inclusions

Abstract This second part of the review on defects as root cause of fatigue failure comprises the origin, the nature and the effects of non-metallic inclusions. Topics addressed are the different kinds of inclusions formed during the manufacturing process, various types of mis-match causing local stresses and, as a consequence, fatigue crack initiation, and effects of characteristics such as size, morphology, localization, spatial distribution and orientation of the defects on the fatigue behavior. Methods for inclusion counting and sizing are discussed along with statistical aspects necessary to be considered when evaluating structural components.