Content Of Nonmetallic Inclusions Research Articles

Influence of temperatures of melt overheating and pouring on the quality of aluminum alloy lost foam castings

Lost foam casting (LFC) is currently one of the most efficient and promising methods of fabricating high-quality thin-wall castings possessing specified dimensional accuracy, required surface roughness, and other properties. This technology is widely used in the production of aluminum alloy products. To minimize costs in the fabrication of wares and to fabricate high-quality castings, it is reasonable to use an increased amount of secondary materials in the charge, herewith paying attention to the melt overheating temperature and holding time. The results of studying the temperature modes of smelting pouring aluminum alloys in the LFC are presented. The most efficient modes in manufacturing conditions under consideration which provide the best quality characteristics of leak-tight castings by dimensional accuracy and surface roughness were as follows: the melt overheating temperature is 880–890°C and the melt pouring temperature into the casting mold is 820–830°C. The influence of various variants of temperature parameters of smelting and pouring the melt of the AK7 composition during the LFC on the content of nonmetallic inclusions in the cast state is investigated. It is revealed that the minimal γ-Al2O3 content in the final alloy is provided by a melt overheating temperature of up to 880–890 or 940–950°C and a melt pouring temperature into the casting mold of 820–830°C.

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.

The Study of Nonmetallic Inclusions Formation for Kaplan Blades during the Solidification Process

The exploitation durability of Kaplan hydraulic turbines blades is first of all determined by their structure, by the steel elaboration technology, respectively by the content of non-metallic inclusions and later by the physical-chemical parameters of the exploitation environment.This paper presents a study regarding the situations in which the elaboration-casting technology of Kaplan blades using alloyed austenitic stainless steel, X5CrNiMo17-13-3 which has an important role in the quality of castings. Thus, the authors verify the formation of sulfides and of oxi-sufides during the steel elaboration process, treatment during a liquid state and their influence in the castings behavior to wearing. It is a well known fact that the presence of sulfides and oxi-sufides in the cast blades structure accelerates the corrosion process in contact with river waters.

Complex Nonmetallic Inclusions Formed in Billets Heated for Rolling and Characteristics of Structural Steels

Complex bimetallic inclusions formed in billets from steels 09G2S and K52 during heating for rolling are studied by methods of electron microscopy and local x-ray spectrum analysis. To check the established evolution of oxide inclusions based on aluminomagnesium spinel and other oxide compositions, individual inclusions of manganese sulfide and complex oxide-sulfide inclusions, a method developed by the Severstal’Company and the Karpov NIFKhI for determining the content of corrosion-active nonmetallic inclusions (CANI) as a function of the heating mode is applied to the steels studied. It is recommended to increase the temperature and duration of heating of billets for hot rolling in order to lower the content of CANI and to raise the resistance of the steels to local corrosion.

Effect of Secondary Vacuum Treatment on Performance Characteristics of A516 Grade 65 Carbon Steel

The purpose of this research is to analyze the making technology of clean steel used in the oil, gas and petrochemical industry. The steel was obtained into conventional electric arc furnace. To enhance the steel quality a secondary refining treatment was applied. The purity characteristics of the steel A516 Grade 65, before and after the treatment in the vacuum arc degassing equipment are discussed and compared. The deoxidation, desulphurisation in the presence of basic slag and degassing by injecting an inert gas and also by vacuum exposure are effective in reducing non-metallic inclusions and for chemical composition control. Data from 31 melts obtained in two industrial conditions are presented according to steel making parameters. The variation of chemical composition, especially of content of S, P, and the cleanliness of the steel in terms of content of non-metallic inclusions are analyzed.

INFLUENCE OF MELTING CONDITIONS OF ALUMINUM ALLOYS ON THE PROPERTIES AND QUALITY OF CASTINGS OBTAINED BY LOST FOAM CASTING

The development of modern foundry is characterized by a constant increase of requirements to the quality of the casting, the rational use of material resources, the search for new technical and technological solutions to ensure resource conservation along with obtaining the desired properties of castings. At the same time questions to identify and study the impact of the laws of temperature and time parameters of melting and pouring into the mold of aluminum alloys during lost foam casting on integrity, mechanical and quality parameters of thin-walled castings are poorly understood and difficult to implement, especially in view of resource saving measures. This article examines the influence of casting process parameters on strength, integrity and content of nonmetallic inclusions in AK7 alloy castings of the gas analyzer housing cover obtained by lost-foam casting. The dataset obtained on the basis of experimental research was subjected to statistical analysis. Statistical models allowed us to obtain the effect of time of melt holding and the content of recycled materials in the charge on strength and integrity of the specified castings. The effect of the time of AK7 melt holding at 880–890 °С on the content of nonmetallic inclusions in the castings was studied, and it was shown that the holding time variation allows controlling the nonmetallics content. This reduces melt microinhomogeneity and provides more castings with the minimum content of nonmetallic inclusions.

Effect of inclusions on mechanical properties of Nb stabilized austenitic stainless steels (316Nb) with centrifugal and sand casting techniques

In this study, 316Nb stabilized austenitic stainless steel pieces were produced via sand and centrifugal casting method in order to be investigated. Heat treatments were done in two stages, and cooling was made in various quenching mediums. As-cast parts and the parts with only the highest and the lowest tensile strength were investigated. Metallographical analyses were made and the content of non-metallic inclusions was examined. Various types of carbides in microstructures were determined by means of SEM-EDX analysis. The sand casting samples had more non-metallic inclusions than the centrifugal casting ones. After the tensile tests, it was seen that these inclusions had significant effect on the mechanical properties. The tensile strength, the yield strength, the elongation and the hardness values of the centrifugal casting samples were higher than the sand casting ones. Investigating the SEM-EDX analyses, it was determined that the sand cast samples had chromium carbides in small quantities, in addition to niobium carbides. Centrifugal cast parts had niobium carbides.

THE EFFECT OF OVERHEATING TEMPERATURE AND MELT POURING TEMPERATURE ON THE ALUMINUM ALLOY CASTING QUALITY IN LOST FOAM CASTING

Lost foam casting (LFC) is currently one of the most effective and promising methods to produce high-quality thin-walled castings that exhibit a desired dimensional accuracy, the required surface roughness, and other properties. This technology is widely used in the manufacture of aluminum alloys products. In order to ensure cost minimization in the manufacture of products and the production of quality castings, it is advisable to use an increased amount of recycled material in the charge, paying attention to the overheating temperature and the melt holding time. The paper presents research findings on temperature regimes of melting and casting of aluminum alloys during LFC. Under the concerned industrial conditions, the following regimes were most effective to ensure the best quality indicators of leak-tight castings with respect to dimensional accuracy and surface roughness: melt overheating temperature – 880÷890 °С, pouring temperature – 820÷830 °С. The paper studies the effect of different temperature parameter options for melting and casting of the AK7 melt composition during LFC on the content of nonmetallic inclusions in the as-cast state. It was found that the minimum content of γ-Al 2 O 3 in the finished alloy was provided by the melt overheating temperature up to 880÷890 or 940÷950 °С, and the pouring temperature of 820÷830 °С.

电工硅钢连铸过程中非金属夹杂物行为研究

本文以国内某钢厂电工硅钢为研究对象，通过工业试验及取样分析，研究了不同浇铸阶段电工硅钢中间包钢液和连铸坯中w(T.[O])和w([N])的变化以及大颗粒非金属夹杂物的含量、粒度、类型及来源。在本实验条件下得到以下结论：硅钢头坯中w(T.[O])、w([N])明显高于交接坯、正常坯和尾坯，不同浇铸阶段硅钢连铸坯中的w([N])均高于中间包钢液中的w([N])，连铸过程二次氧化严重；连铸坯中的大颗粒夹杂物主要源于渣金混卷和耐火材料的侵蚀，中间包和结晶器内流场的稳定性控制水平有待于提高。 In this paper, the continuous casting process of the non-oriented electrical Si-steel from a domestic steel company was taken as a research subject. Through sampling from tundish and continuous casting slab followed by oxygen and nitrogen analysis and bulk sample electrolysis, the content change of oxygen and nitrogen and the change of content, scale, type and source of large-size non-metallic inclusions was systematically studied. Under the experiment conditions of this paper, the main conclusions are as follows. The content of w(T.[O]) and w([N]) in the head slab and the molten steel of the corresponding tundish was significantly higher than the one in the other casting state. During different casting states, the content of [N] in the slab was lower than the molten steel of the corresponding tundish. The re-oxidation by air in the continuous casting process was serious. The large-size inclusions in the slab were formed by slag entrapment and refractory material erosion. The flow field of tundish and continuous casting mold should be further optimized.

Influence of rare-earth modification on the formation of nonmetallic inclusions in high-carbon steel

The content of nonmetallic inclusions when rail and wheel steel is produced by intensive modern technology and modified by rare-earth metals is analyzed. The composition, morphology, dimensions, and distribution of the inclusions in the steel are determined in the case without oxidation by aluminum or treatment by silicocalcium and also with treatment of aluminum-bearing steel by both rare-earth metals and silicocalcium. Modification with rare-earth metals reduces the content of oxide inclusions in the rail and wheel steel. That improves the plasticity and impact strength of the products.

Improving the production of pipe steel

Melts of pipe steel (strength class K52) obtained at the casting and rolling complex of AO OMK (a branch of AO OMK-Stal’) are analyzed. The initial data correspond to a set of 30 melts. The production system includes batch preparation, steel production in an arc furnace, treatment in a ladle–furnace unit, vacuum treatment (with microalloying and modification), hot rolling, and cutting of the rolled steel into sheet and strip. The basic factors affecting steel quality are identified. The rejection of the steel produced is mainly due to brittle and undeformable nonmetallic silicate inclusions. Changes in the process so as to reduce the content of nonmetallic silicate inclusions are recommended.

New C–Si–Mn–Cr–V–Mo powder wires for roller surfacing

Laboratory data indicate the positive effects of introducing fluorocarbon and nickel in 25Kh5FMS steel powder wire for the surfacing of rollers. In particular, the replacement of amorphous carbon by a material containing fluorocarbon lowers the content of nonmetallic inclusions in the applied layer, while introducing nickel in the powder wire reduces the austenite grain size and ensures the formation of small carbide particles. That increases the thermal stability of the applied layer. Increase in the carbon equivalent of the 25Kh5FMS powder wire boosts the hardness of the applied metal layer.

Advanced reactor vessel steels for reactors with supercritical coolant parameters

A set of studies, tests, and technological works is performed to design promising high-strength vessel steels for reactors with supercritical coolant parameters. Compositions and technological parameters are proposed for the production of reference steel (within the limits of the grade composition of 15Kh2NMFA-A steel) and high-nickel steel. These steels are characterized by high properties, including metallurgical quality and service and technological parameters. Steel of the reference composition has high (higher by 15%) strength properties, improved viscoplastic properties, and ductile–brittle transition temperature tc of at most–125°C. The strength properties of the high-nickel steel are higher than those of the existing steels by 40–50% and higher than those of advanced foreign steels by 15–20% at ductile–brittle transition temperature tc of at most–165°C. Moreover, the designed steels are characterized by a low content of harmful impurity elements and nonmetallic inclusions, a fine-grained structure, and a low susceptibility to thermal embrittlement.

Research of Influence Modification of Natural Concentrate on Quality Metal

Questions of increase of mechanical, technological and service properties of metal at minimum cost to produce it are relevant for the metallurgical enterprises.Modification of complex steel alloys containing reactive elements is one of the effective ways to improve the quality of steel. At the same time the direct costs for the use of modifiers are 0.2-0.3%, which little effect on the cost of production.The paper presents the results of the application of natural concentrates as a modifier steel. The effects on the metal quality changes due to the impact of the modification concentrates demonstrate the effectiveness of their application. As a result of modification decreased the content of nonmetallic inclusions and grain size. Reduction of impurity modified metal of was the cause more high plastic properties, especially, impact strength at ordinary and low temperatures of tests. Based on the experimental data evaluated hardening mechanisms that lead to a significant improvement of physic-mechanical properties of the metal workpiece after administration modifier.

THERMODYNAMIC FORECASTING OF FORMATION NONMETALLIC OXIDIC INCLUSIONS IN SEAM METAL AT ARC WELDING UNDER HIGHSILICEOUS GUMBOILS CONTENT

At arc welding under gumboil are formed nonmetallic inclusions of different morphology, with their variable volume fraction in seam metal. The physical model of formation of nonmetallic oxidic inclusions in seam metal is developed. The thermodynamic model of formation of oxidic nonmetallic inclusions in seam metal at arc welding under gumboil on the basis of the created physical model is offered. The conducted metalgraphic researches on studying of content of nonmetallic inclusions in metal of a seam and their morphology, have shown adequacy to the offered thermodynamic model Purpose. Creation of settlement thermodynamic model of formation of oxidic nonmetallic inclusions in seam metal at arc welding under gumboil of general purpose. Determination of adequacy to the offered model when using gumboils of various slag systems, and at a variable ratio of components as a part of gumboil. Design/methodology/approach formulate the basic principles of application of equilibrium chemical thermodynamics for modeling of process of formation of oxidic nonmetallic inclusions in seam metal; create thermodynamic model of determination of content of oxidic nonmetallic inclusions in seam metal at arc welding under gumboil; conduct pilot studies for an assessment of adequacy to the developed model of formation of oxidic nonmetallic inclusions. Findings. It is offeredthe thermodynamic model of formation of oxidic nonmetallic inclusions in seam metal at arc welding under

IMPACT OF INTERSTITIAL ALUMINIUM CONTENT ON OCCURRENCE OF NON-METALLIC INCLUSIONS IN STEEL

This paper details the study of interstitial aluminium impact on non-metallic inclusion occurrence on the basis of individual samples examination taken during steel production and processing. The aim was to identify and describe the relation between the content of interstitial aluminium in metal volume and the concentration of non-metallic inclusions on AlxOy basis occurring in steel. The identification of the non-metallic inclusions occurring in liquid steel was within this study implemented by the (AES) method based on the atom emission spectrometry evaluating the presence of the respective elements in the metal volume. This method works on a principle of emitted light from the existing source with a high voltage spark. The results of this study indicate a correlation between the interstitial aluminium content and concentrations of non-metallic inclusions on the AlxOy basis.

Operation of imported rail on the East Siberian Railroad

Japanese R65 rail is metallographically analyzed after operation in the East Siberian Railroad. Its chemical composition complies with Technical Specifications TU 0921-239-01124323–2007 for the steel used in the production of 350LDT rail. The macrostructure of the metal is of satisfactory quality. The tensile mechanical properties, hardness, and impact strength at +20°C determined on samples from the nonoperational chamfer of the rail head are consistent with Technical Specifications TU 0921-239-01124323–2007 for the steel used in the production of 350LDT rail. The impact strength at negative temperatures does meet the corresponding requirements. The content of nonmetallic inclusions is low. However, exogenous inclusions are present at unacceptable levels. The microstructure of the Japanese rail sample consists of sorbite and plate pearlite, whose dispersity declines on moving away from the surface. In operation of the rail, thin inclined cracks (depth 1.1 mm) form at the surface of the working chamfer in the rail head; in addition, lateral wear is considerable (up to 15 mm).

Production of continuous-cast pipe blank without large nonmetallic inclusions

The quality of metal in continuous-cast pipe blanks is investigated, for different steel-production technologies. The presence of large nonmetallic inclusions is largely due to disruptions in the continuouscasting technology. Other significant factors are nonoptimal modification of the nonmetallic inclusions and problems in ladle treatment. Measures ensuring acceptable content of nonmetallic inclusions are developed and tested.

New Medium-Carbon Free-Machining Steels Containing Bismuth and Calcium

The paper describes the properties of two new medium-carbon free-machining alloy structural steels. These steels are environmentally friendly since lead in them is replaced with much less harmful elements bismuth and calcium. Bismuth and calcium are rather uniformly distributed in the ingot, though there are two zones of bismuth heterogeneity in the bottom and in the head part of the ingot. Mechanical properties of steels are at the same level as for steels without bismuth and calcium. Non-metallic inclusion content is typical for structural steels melted in open electric arc furnaces with basic lining and is not changed by the presence of bismuth and calcium. Machinability of the steels with bismuth and calcium is at the same or higher level than that of lead-bearing steels. Melting, casting, forging and rolling of steel containing bismuth and calcium is not associated with working area air-pollution with harmful substances in amounts exceeding maximum permissible concentrations. During rolling of the lead-free steels harmful emissions are almost absent, unlike the lead-bearing steels.

Developing a Technological Means of Obtaining Superior Properties and Quality for Quenched and Forged Structural Steels

In order to establish the scientific principles of a technology for the production and ladle treatment of new steels that can be quenched at forming, steels which were made in factory and laboratory heats and had different carbon contents were analyzed to explore the key factors and processes that determine both their total content of nonmetallic inclusions (NIs) and their content of certain types of NIs – particularly the types that are harmful. It was found that the most important factors in producing steel which is clean based on its content of all types of inclusions (which has an NI rating no higher than 1.5 in the government standard GOST 1778) are the slag regime and the ratio of the weights of the lime and aluminum added to the steel-pouring ladle during tapping. The optimum ranges of values for these parameters are determined. The existing requirements on the slag-regime parameters are observed to ensure a low content of harmful corrosion-active nonmetallic inclusions (CANIs) in the steel. However, it is essential to maintain a low (at or below the lower limit of 0.02% specified for the grade of steel) aluminum content for the duration of the ladle treatment. Aluminum content can be increased during the final stages, if necessary. A study was made of the effect of the MgO content of the covering slag on the possibility and rate of formation of CANIs based on alumomagnesian spinel. it was found that the steel’s content of such inclusions rises sharply when the concentration of MgO in the covering slag is greater than 14.1%. An MgO content of up to 8% guarantees that the steel will be clean based on its content of all types of inclusions. The results obtained for the metal of two trial heats confirmed the adequacy of the key parameters that were identified and the ranges of values for those parameters which were determined to be optimum for obtaining a low CANI content and high resistance to local corrosion.