Structure Of Cast Iron Research Articles

Secondary transformations in the structure of grey cast iron

A nanostructural mechanism of secondary transformations in the structure of gray cast iron is proposed. First, structureforming nanocrystals of austenite, ferrite, cementite and graphite are formed from elementary nanocrystals of iron and graphite, free atoms of iron and carbon. The crystallization centers of microcrystals of phases are formed from them. From these centers, structure‑forming nanocrystals of phases, free iron and carbon atoms, microcrystals of austenite, ferrite, cementite and graphite of binary gray cast irons are formed.

Structural-phase state and properties of heat and wear resistant cast irons of Cr–Mn–Ni–Ti system additionally alloyed with Al and Nb

The paper presents the data on phase composition and structure forming for the alloys, on distribution of elements among the alloy structural components, on variation of wear resistance, scale resistance, growing stability and mechanical properties of cast iron of Cr–Mn–Ni–Ti–Al–Nb system depending on different aluminium and niobium content and thermal ac-cumulating capacity of a casting mould. Complex carbides (Nb, Ti)C are forming in white cast iron during niobium alloying. Quantitative metallographic analysis of (Nb, Ti)C carbides and (Cr, Fe, Mn)7C3 complex carbides was carried out on the samples with examined composition. Aluminium provides favourable influence on forming of the thin protective spinel-type films with minimal amount of defects; diffusion through such oxide film is very difficult. Joint alloying by aluminium and niobium leads to simultaneous increase of heat resistance and wear resistance. Wear resistance increased as a result of enlargement of the part of primary carbides (Nb, Ti)C with high hardness in the structure of cast iron. Composition of oxide films includes aluminium, which strengthens their protective properties and rises of the alloy scale resistance. It is found for the first time that niobium doping leads to secondary solidification during cooling in the casting mold. Dispersion particles of М7С3 carbides are forming in solid state, thereby no structure degradation occurs during testing at increased temperatures, and growing stability rises. On the basis of the complex of the conducted researches the rational composition of heat and wear resistant cast iron is offered at the following ratio of components, wt. %: 2.1–2.2 C; 4.5–5.0 Mn; 18.0–19.0 Cr; 1.0–1.2 Ni; 0.4–0.6 Ti, 2.0 Nb; 2.0 Al. Wear resistance increased 1.2 times compared to cast irons before the introduction of aluminum and niobium, and scale resistance – 2.4–4.5 times depending on the type of casting mold, the index of growth resistance is equal to zero for cast irons cast in dry SLM

ОЦІНКА НАПРУЖЕНОГО СТАНУ РОБОЧОГО ШАРУ ВАЛКІВ КОЕРЦИТИМЕТРИЧНИМ ЕКСПРЕС-МЕТОДОМ

The purpose of the work is the problem of researching the influence of chemical composition and structure on the indicators of operational stability of centrifugal two-layer rolling rolls made of high chromium cast iron by the coercimetric express method. In order to ensure the achievement of this goal, the following tasks were set and solved: conducting an analysis of the causes of the destruction of the surface layer of rolls; building a mathematical model for studying the influence of the chemical composition and structure of cast iron on the level of hardness and coercive force; using the coercimetric method to analyze the quality of rolled rolls. Conclusions. Forecasting the behavior of the rolls during operation is inextricably linked to the analysis of the main factors on which the level of properties and operational stability of the working layer depend. The properties of high-chromium alloys are closely related to the type of phases formed and their ratio. The amount of residual austenite and martensite in the structure of the alloy has the greatest influence on the properties of the alloy (in the studied interval of changes in the proportion of phases). The operational layer of two-layer high-chromium rolls is characterized by a high level of residual stresses. Exceeding the permissible level of stresses or their unfavorable distribution can cause premature destruction during the operation of the roll. With the help of the coercimetric express method, it is possible to solve a fairly wide range of tasks of quality control of rolls, related to the determination of the level and distribution of residual stresses in the working layer of the rolls. This is because the intensity of the process of formation of thermal cracks under conditions of thermo-cyclic loading largely depends on the level of residual compressive stresses. Too high a level of stresses or their unfavorable distribution can cause premature destruction of the working layer of the roll, because the typical type of destruction due to an unbalanced distribution of stresses is cracking. A local increase in the level of coercive force can be the basis of the prediction of crack formation.

Study on friction and wear behavior of gray cast iron with different carbon content at different temperatures

In this paper, we study the friction and wear properties of gray cast iron with different carbon contents at various ambient temperatures. We also examine the failure forms of gray cast iron friction and wear. The research concludes that under low-temperature wear conditions, the graphite in the gray cast iron structure can enter into the interface between the friction pair, have a lubricating effect on the wear surface, and reduce the friction coefficient and wear loss of the gray cast iron material. As the graphite content in the gray cast iron structure increases, its lubrication and protection effects enhance. Consequently, the primary cause of wear failure in gray cast iron is fatigue peeling induced by plastic deformation. Under high-temperature wear conditions, an oxide layer gradually forms on the wear surface. As the experimental temperature increases, the thickness of the oxide layer on the wear surface also increases. When the oxide layer formed on the wear surface reaches a certain level of thickness, the internal expansion stress of the oxide layer increases considerably, causing the oxide layer to peel off and increase the roughness of the wear surface, friction coefficient, and wear loss. Additionally, an increase in the graphite content in the gray cast iron structure makes the surface more prone to oxidation. This leads to increased friction coefficient and wear loss, with the wear failure of gray cast iron primarily caused by the peeling of the oxidation layer.

Evaluation of Microstructure and Abrasive Wear-Resistance of Medium Alloy SiMo Ductile Cast Iron.

Medium-alloy ductile iron with a SiMo ferritic matrix has very good heat resistance. The addition of chromium and aluminum also increases this resistance. This article presents the impact of chromium and aluminum on the structure of SiMo cast iron, especially their impact on the deformation of the spherical graphite precipitates and the formation of M6C and M3C2 carbide phases. These carbides are formed in a ferritic matrix or at the grain boundaries, resulting in increased hardness and a drastic reduction in impact strength. The article presents the influence of heat treatment on the material's microstructure and resistance to abrasive wear. Chromium and aluminum additions can also indirectly reduce the abrasive wear resistance of SiMo cast iron. The presented research shows the possibility of doubling the abrasive wear resistance of SiMo cast iron.

Correction to: Effect of Aluminum, Copper and Manganese on the Structure and Properties of Cast Irons

Correction to: Effect of Aluminum, Copper and Manganese on the Structure and Properties of Cast Irons

The combined effect of boron additives and cooling conditions during solidification on the structure and properties of complex-alloyed white cast irons of the Cr – Mn – Ni – Ti system

The combined effect of boron additives and cooling conditions during solidification on the structure and properties of complex-alloyed white cast irons of the Cr – Mn – Ni – Ti system

Experimental and numerical investigation of porous heat exchangers with Kelvin cell structured foam at high temperatures: Coupled conduction-convection and radiation heat transfer

Heat recovery is crucial in the energy sector, especially for industries operating at high temperatures. One way to achieve high-efficiency heat recovery is to use porous materials in heat exchangers. In this work, the performance of a high temperature heat exchanger was investigated. For this purpose, a tube containing a porous cast iron structure was externally heated by radiation inside a tubular furnace and air at ambient temperature was blown into the tube. Experiments were conducted at different temperatures of up to ▪ and different airflow velocities in a specialized bench, considering the combined effects of conduction, convection, and radiation. Temperature profiles in three sections of the porous structure were measured by using sheathed thermocouples brazed to the porous structure. Power and exergy flow rate extracted from the porous structure to the air flow were calculated and analyzed to quantify recovered heat. In addition, a numerical modeling performed at the pore level using Fluent showed an average relative error of 15% compared to experimental results, indicating acceptable agreement with observed trends. This numerical model will serve as a valuable reference tool for future parametric analyses of porous structures in heat exchanger configurations.

Development of a Method for Increasing the Fire Resistance of Cast-iron Structures of Cultural Heritage Sites under Reconstruction

Development of a Method for Increasing the Fire Resistance of Cast-iron Structures of Cultural Heritage Sites under Reconstruction

ПРОГНОЗИРОВАНИЕ ОТКАЗОВ ДЕТАЛЕЙ МЕТАЛЛУРГИЧЕСКОГО ОБОРУДОВАНИЯ ПО КРИТЕРИЯМ ПРОЧНОСТИ, ИЗГОТОВЛЕННЫХ ИЗ СЕРОГО ЧУГУНА, НА ОСНОВЕ МИКРОСТРУКТУРНОГО МОДЕЛИРОВАНИЯ НАПРЯЖЕННОГО СОСТОЯНИЯ

The article proposes a methodology for estimating the gamma-percent life of metallurgical equipment parts made of grey cast iron on the basis of micro structural modelling of its stress state, which is formulated using known relationships for estimating the average life of mechanical equipment parts by the criterion of kinetic strength, the linearisation method of random arguments allowing to estimate the variance of the function under study and tools of micro structural modelling of the stress state of the material. It allows at the stages of design and operation to take into account the all-round influence of loading conditions of the investigated technical object, its operating temperature, physical and mechanical characteristics of structural components of grey cast iron on gamma-percent resource. Its main distinctive features are mathematical dependences allowing estimating the value of dispersion of parameters necessary for calculation of resource characteristics, as well as the possibility of taking into account the anisotropy of the real structure of grey cast iron. In addition, the procedure of verification of the proposed methodology by comparing theoretically obtained values of gamma-percent resource with the value established in the normative and technical documentation is carried out. The spacer plate of SMD-110 jaw crusher, made of grey cast iron of GI-20 grade, is considered as an object of research physical and mechanical characteristics of its structural components, such as modulus of elasticity and Vickers micro hardness were experimentally evaluated using the method of instrumental indentation. The prediction error does not exceed 18%, which in turn confirms a sufficient level of reliability of the theoretical solutions proposed in this article, which can be used in the design of metallurgical equipment parts made of grey cast iron, as well as in the formation of the periodicity structure of its repairs.

ПРОГНОЗИРОВАНИЕ ОТКАЗОВ ДЕТАЛЕЙ МЕТАЛЛУРГИЧЕСКОГО ОБОРУДОВАНИЯ ПО КРИТЕРИЯМ ПРОЧНОСТИ, ИЗГОТОВЛЕННЫХ ИЗ СЕРОГО ЧУГУНА, НА ОСНОВЕ МИКРОСТРУКТУРНОГО МОДЕЛИРОВАНИЯ НАПРЯЖЕННОГО СОСТОЯНИЯ

The article proposes a methodology for estimating the gamma-percent life of metallurgical equipment parts made of grey cast iron on the basis of micro structural modelling of its stress state, which is formulated using known relationships for estimating the average life of mechanical equipment parts by the criterion of kinetic strength, the linearisation method of random arguments allowing to estimate the variance of the function under study and tools of micro structural modelling of the stress state of the material. It allows at the stages of design and operation to take into account the all-round influence of loading conditions of the investigated technical object, its operating temperature, physical and mechanical characteristics of structural components of grey cast iron on gamma-percent resource. Its main distinctive features are mathematical dependences allowing estimating the value of dispersion of parameters necessary for calculation of resource characteristics, as well as the possibility of taking into account the anisotropy of the real structure of grey cast iron. In addition, the procedure of verification of the proposed methodology by comparing theoretically obtained values of gamma-percent resource with the value established in the normative and technical documentation is carried out. The spacer plate of SMD-110 jaw crusher, made of grey cast iron of GI-20 grade, is considered as an object of research physical and mechanical characteristics of its structural components, such as modulus of elasticity and Vickers micro hardness were experimentally evaluated using the method of instrumental indentation. The prediction error does not exceed 18%, which in turn confirms a sufficient level of reliability of the theoretical solutions proposed in this article, which can be used in the design of metallurgical equipment parts made of grey cast iron, as well as in the formation of the periodicity structure of its repairs.

MULTIFRACTAL ANALYSIS OF THE INFLUENCE OF CHROMIUM-NICKEL CAST IRON STRUCTURE ON ITS QUALITY CRITERIA

The influence of the structure of cast irons on their hardness was studied using multifractal analysis. The spectrum of statistical dimensions of the cast iron microstructure was calculated using the Renyi formula. The hardness of chromium-nickel cast iron was determined at three points of the sample. It was found that the pairwise correlation coefficients for predicting hardness by traditional structure characteristics (length, diameter, area) were R2= 0.73...0.87. When assessing hardness indicators by multifractal characteristics, the correlation coefficients are 0.78...0.88 for the pearlite structure with flake graphite and 0.81...0.93 for the pearlite structure with spherical graphite. The sensitivity coefficients of the hardness indicators of СПХН-43 rolls to the information and correlation dimensions of carbides, as well as to the fractal and statistical D-100 dimensions of flake graphite were determined. The sensitivity of hardness indicators to the fractal and statistical D100 dimensions of carbides and to the fractal and correlation dimensions of flake graphite was determined for СПХНФ-47 rolls. Based on the results obtained, an approach to assessing the hardness of СПХН-43 and СПХНФ-47 rolls was developed, which includes: 1). Determination of the statistical dimension spectrum of the cast iron structure elements. 2). Determination of the sensitivity coefficients of hardness indicators to the spectrum of dimensions of structural elements. 3). Creation of a mathematical model for predicting the hardness of rolls. The considered approach can be interpreted as an alternative method for assessing the quality criteria of cast irons based on the analysis of their structure.

Effect of Aluminum, Copper and Manganese on the Structure and Properties of Cast Irons

Effect of Aluminum, Copper and Manganese on the Structure and Properties of Cast Irons

Термодинамічні закономірності структуроутворення високоміцного чавуну при модифікуванні та різних умовах кристалізації розплаву

The article presents the results of the analysis of thermodynamic regularities of structure formation of high-strength cast iron during modification and under different conditions of melt crystallization. The concept of the formation of graphite nuclei in high-strength cast iron is proposed. It has been established that during the modification of molten iron, as a result of a significant redistribution of all elements dissolved in it, impurities (sulfur, phosphorus, etc.) are removed, which makes it possible to obtain the structure of cast iron with nodular graphite with the use of modifiers. During the crystallization of cast iron with the release of austenite, direct microliquation of silicon with a distribution coefficient less than one is characteristic, manganese is more evenly distributed in the metal, and carbide stabilizing elements are treated in the liquid phase. A thermodynamic calculation of the thermal effects of the reactions of the release of graphite from carbon dissolved in iron, the transition of silicon and manganese from a liquid state to a solid state in the process of forming high-strength cast iron is presented. The physical and latent heat of crystallization of high-strength cast iron was determined by the enthalpy method. Thermodynamic calculations were performed and the thermal effects of reactions (9) in the melt of high-strength cast iron were determined, depending on their concentrations and the temperature of the melt. Using the results of thermodynamic calculations makes it possible to study the crystallization process by changing the number and composition of phases that are formed under the influence of heat release of phase transformations. It was found that the introduction of Si into pre-eutectic alloys (from 1 to 5% at.) leads to a slight decrease in the latent heat ΔН of crystallization of primary graphite (up to 3% for each atomic percentage of Si). As a result of the change in the temperature interval, its release causes a decrease in the total physical heat of crystallization Qf. It is shown that the thermodynamic analysis of the processes that occur during the crystallization of cast iron based on the data on the change in enthalpy for the system Fe-C-Xi (Xi = Si, Mn) indicates that with an increase in carbon, the change in enthalpy in the crystallization interval changes approx lyzno by 16 kJ/mol. The physical heat of crystallization has a significant effect on the change in the value of the total heat of crystallization of cast iron Qkr Fe-C-Xi (Xi = Si, Mn) in comparison with the Fe-C alloy. The latent heat of crystallization during solidification of high-strength cast iron is between 245 and 275 kJ/kg.

Structure and wear characteristics of cast iron after laser surface modification

The paper presents the results of studies of macro- and microstructure of alloyed chromium-vanadium cast iron after laser treatment (LT) in air using a continuous laser source with a variation in its power from 60 to 100 W and scanning speed of the laser beam varying from 5 to 17 mm/s. Metallography and durometry methods were used to determine composition and structure of the laser exposure zones (LEZ). It is shown that LT with a slight melting of the surface leads to a significant increase in microhardness in LEZ. In this case, martensite is the main structure in the near-surface layer of LEZ in the melting zone, and ledeburite structure prevails in the quenching zone. For the studied LT modes, LEZ depth is 220 – 310 μm. At the same time, microhardness is more than 2.5 – 4.2 times higher than microhardness of the base metal and reaches 820 HV0.1, that is a significant factor in increasing the wear resistance of the material. On the contrary, no significant structural changes were found in the case of LT without melting the surface. In order to identify the role of LT in wear of cast iron, sliding friction tests were carried out according to the “disk – finger” scheme at a pressure in the contact zone of 12.5 MPa and indenter rotation speed of 580 rpm. According to the test data, a significant decrease in linear wear and the wear intensity after the surface melting was found. The wear intensity is reduced by more than 100 times, and linear wear – by more than 50 times. The characteristics of LEZ surface cause a decrease in the friction coefficient by 30 % relative to the untreated surface.

Study of the influence of the structure of rolled iron on its hardness

Problem. The influence of the structure of cast irons on their hardness was studied using multifractal analysis. The spectrum of statistical dimensions of the cast iron microstructure was calculated using the Renyi formula. Materials and methods. The hardness of chromium-nickel cast iron was determined at three points of the sample. Results of experiments. It was found that the pairwise correlation coefficients for predicting hardness by traditional structure characteristics (length, diameter, area) were R2 = 0.73...0.87. When assessing hardness indicators by multifractal characteristics, the correlation coefficients are 0.78...0.88 for the pearlite structure with flake graphite and 0.81...0.93 for the pearlite structure with spherical graphite. The sensitivity coefficients of the hardness indicators of СПХН-43 rolls to the information and correlation dimensions of carbides, as well as to the fractal and statistical D-100 dimensions of flake graphite were determined. The sensitivity of hardness indicators to the fractal and statistical D100 dimensions of carbides and to the fractal and correlation dimensions of flake graphite was determined for СПХНФ-47 rolls. Conclusions. Based on the results obtained, an approach to assessing the hardness of СПХН-43 and СПХНФ-47 rolls was developed, which includes: 1). Determination of the statistical dimension spectrum of the cast iron structure elements. 2). Determination of the sensitivity coefficients of hardness indicators to the spectrum of dimensions of structural elements. 3). Creation of a mathematical model for predicting the hardness of rolls. The considered approach can be interpreted as an alternative method for assessing the quality criteria of cast irons based on the analysis of their structure.

Possibility of obtaining rolled sheet from white iron with increased plasticity

Рroblem In the work, a study of the technology of manufacturing sheet metal up to 2 mm thick from white ledeburite cast iron alloyed with vanadium was carried out. Сast-iron purveyances forged preliminary. After forging purveyances were rolled with the different wringing out. At rolling a total degree of deformation was 70%. The additional annealing helped to bring down hardness of sheet and moulding of pipes became possible. White cast-iron has high plasticity because there are phase transformations in a vanadium eutecticum cementite. Goal. The goal of work is a study of sheet rolling of white cast-iron’s bars to use for the armour and weld-fabricated pipes. Methodology. Experimental cast iron contains 2.7 - 2.85% C and up to 2% V. 30 kg of castings were melted. The total degree of deformation was 70%. After forging, rolling was carried out on a two-roll laboratory mill on rolls with a smooth barrel. Results. The technological scheme for the production of white cast iron forgings is applied, which includes preliminary annealing, forging with a degree of deformation from 10 to 15%, intermediate annealing and final forging with a total ε=70%. Оriginality The use of carbide transformation in vanadium-doped cementite made it possible to carry out combined pressure treatment and obtain sheets up to 2 mm thick from iron castings Preliminary hot forging greatly stimulates and accelerates the process of cementite disintegration into austenite and vanadium carbides during high-temperature exposure. Rolling of forging blanks was carried out and the influence of thermal and deformation parameters on the structure of cast iron was investigated. Рractical value. Application of final heat treatment after deformation of cast iron provides a level of mechanical properties that corresponds to the properties of high-strength armor steels, and the hardness indicators even exceed them. Thinner sheets of such cast iron can be used to create compositions of multilayer armor with increased ballistic resistance from several materials with different properties.

Effect of Carbon and Cooling Rate on the Structure of Hypereutectic High Chromium Cast Iron in the Cast State and after Heat Treatment

The article presents experimental data on the changes in the structural parameters and properties of castings from high-chromium cast iron G-X300CrMo27-1 depending on the carbon content, which ranged from 2.8 to 4.5 wt. %. Castings were obtained under cooling conditions with two cooling rates—0.083–0.117 °C/s and 4.67–5 °C/s. Changes in the structure and properties of these castings after destabilizing annealing and subcritical heat treatment were assessed. Changes in carbon concentration and cooling rate in the crystallization interval have a significant effect on the sizes of primary carbides (Cr, Fe)7C3, and on the fraction of eutectic carbides. The microprobe analysis results indicating the effects of cooling rate on the composition of phases in cast iron castings with carbon contents of 4.2 wt. % are presented. The offset value of the crystallization onset temperature and eutectic point with an increase in the cast iron melt cooling rate from 0.083 to 0.83 °C/s is shown. The changes found in the properties of castings with increases in carbon concentration and cooling rate cannot be unambiguously explained by the transformation of the structure of primary and eutectic carbides and changes in the elemental composition of phases. The composition and condition of the matrix has a significant effect on the hardness, bending strength and abrasion resistance of castings. It is suggested that internal stresses arising in primary and eutectic carbides affect the properties of castings in the cast and heat-treated state.

Comparison of Wear Resistance of Overlay Welded Layers and Thermal Sprayed Coatings in Real Conditions.

Tribological tests in real conditions enable obtaining full data on the life of interacting machine parts. This article presents the results of operational tests on the elements of the support ring guidance system in a vertical ball-race mill. The guide and active armour operate under abrasive wear conditions with moderate-impact loads. The wear resistance of elements with overlay welding layers deposited with flux cored wire with a structure of high-alloy chrome cast iron and with a coating flame-sprayed with nickel-based powder was compared. The wear intensity of the overlay weld deposits was much lower than that of the sprayed coatings. The scope of this study also included the analysis of the chemical and phase composition, macro- and microscopic metallographic examinations, and the measurement of the hardness of the deposited layers and coatings.

Backscattering of Ultrasonic Waves as the Basis of the Method of Control of Structure and Physicо-Mechanical Properties of Cast Irons

Increasing the reliability of control of cast iron structure and its physical and mechanical characteristics is an important scientific and technical task of the machine-building industry. The paper studies the possibilities of controlling the structure of cast irons using structural noise created by ultrasonic scattering on graphite inclusions of different shapes. The subject of the present studies was such characteristics of structural noise as amplitude-temporal A(t) and as root mean square value of the amplitude of the ultrasonic waves backscattering field AN, compared with the data on ultrasonic velocity and strength or tensile strength of cast iron samples. As a result of the studies, a significant difference between the amplitude parameters of the AN structural noise obtained for samples with different shapes of graphite inclusions at 5 MHz was revealed for the first time. So, for example, for samples of gray cast iron (Russian: СЧ10, СЧ15, СЧ20, СЧ25), having predominantly plate-like form of graphite inclusions, the value of AN on 14–15 dB exceeds that measured in high-strength specimens of the cast iron with the prevailing form of spherical graphite inclusions ВЧ50 (Russian), etc. At the same time growth of longitudinal ultrasonic velocity amounted to 20–25 %. The method of rejection of gray cast iron from high-strength cast iron according to the data of amplitude parameters of structural noise AN at unilateral and local sounding of the object without using an additional reference signal reflected from its oppositional wall is suggested.