Microstructure Of Cast Iron Research Articles

Effect of TiB2 addition on microstructure and mechanical properties of a hypereutectic high chromium cast iron

Effect of TiB2 addition on microstructure and mechanical properties of a hypereutectic high chromium cast iron

Chilling Effect of Inoculation on the Microstructure and Hardness Property of Hypo-Eutectic Grey Cast Iron

The influence of varied weight percent of inoculant (ferrosilicon) on the microstructure and hardness property of hypo- eutectic grey cast iron was investigated. Four sets of chill wedge samples were produced using two chill wedge wooden patterns (W3 1/2 and W4). The first set, the control samples W3 1/2 and W4 were uninoculated. The second, third and fourth sets were inoculated with 1.0wt.%, 1.5wt.% and 2wt.% ferrosilicon respectively to give inoculated samples W3 1/2 and W4. Wedge test was conducted on the samples at the four different points (1, 2, 3 and 4) in accordance with ASTM A367. From the results, microstructures of the control and the inoculated samples were differently influenced by the varied percentage of the inoculant at the four designated points 1, 2, 3 and 4. The average hardness property of the inoculated samples decreases with increasing ferrosilicon addition. Samples W3 1/2 and W4 with 1.0wt.% ferrosilicon revealed high hardness property at chill zone, and hardness property of W3 1/2 was high relative to sample W4 with the values of 34.9 HRA and 30.6 HRA respectively. Similarly, the control samples showed the highest hardness property at the chill zone. Sample W3 1/2 revealed high hardness value of 33.0 HRA relative to sample W4 of 26.8 HRA at the chill zone. Keywords - inoculant; Microstructure; hypo- eutectic; chill zone; hardness property

Study of the effect of nanomodifiers from silicon production wastes on morphological form of gray cast iron graphites

The influence of modifiers obtained from silicon production waste on the morphological form of graphite in gray cast iron was evaluated. Experimental melts were performed to study the effect of nanomodifiers. Series of ten samples were obtained, in each of which one sample was a control sample without the use of an experimental modifier. The other nine samples of each series were obtained using the studied additives. Cast iron was smelted in an induction furnace of the IST-0.6/0.4 brand, with a capacity of 500 kg. The conducted researches included: determination of the chemical composition of cast iron; determination of the hardness of samples using the Brinell method; tensile testing of samples; study of the macro- and microstructure of gray cast iron. The graphite phase in the modified cast iron was obtained using our proposed modifiers and is represented by vermicular graphite. The mechanisms of graphite formation using the suggested modifiers are considered.

MICROSTRUCTURE AND PROPERTIES OF HIGH CHROMIUM WHITE CAST IRONS ALLOYED WITH BORON

The microstructure and mechanical properties of high chromium white cast iron with composition: 2,6÷3,4% C; 0,9÷1,1% Si; 0,8÷1,1% Mn; 1,0÷1,3% Mo; 12,3÷13,4% Cr, additionally doped with boron in an amount of 0,18% to 1,25% is investigated. The microstructure of six compositions of white cast irons is studied by means of an optical metallographic analysis - one without boron, and the others contain 0,18%; 0,23%; 0,59%; 0,96% and 1,25% boron. A test is performed to determine: hardness by the Rockwell method; microhardness; bending strength and impact toughness. It was found that at a boron content of 0,18%; 0,23% and 0,59%, the structure of white cast irons is subeutectic, with impact toughness in the range of 1,80÷1,52 J/cm2; with a boron content of 0,96%, the structure of white cast iron is close to the eutectic, with impact toughness 0,98 J/cm2 ; at a boron content of 1,25% the structure of white cast iron is supereutectic and the impact toughness decreases to 0,68 J/cm2. With a change in the boron content from 0,8% to 1,25%, the amount of carbide phase in the structure of white cast iron increases, which leads to an increase in hardness from 53 to 59 HRC. The highest bending strength (Rmi=660,85 MPa) was obtained in white cast irons with a boron content of 0,23%.

EFFECT OF CARBON CONTENT ON MICROSTRUCTURE EVOLUTION AND PROPERTIES OF HYPEREUTECTIC HIGH CHROMIUM CAST IRON

This study is to reveal the influence of the amount of carbon content on the microstructure evolution, mechanical properties, and wear properties of Hypereutectic High Chromium Cast Iron (HHCCI). The results indicated that the carbon content plays a key role in the regulation of carbides in the cast iron microstructure. As the amount of carbon content rises, the primary carbides in the cast iron microstructure become apparently coarser, and the volume fraction of carbides gradually increases. The carbide volume fraction reaches 62% when the carbon content is 5[Formula: see text]wt.%. When the value of the carbon content increases, the accumulation and growth of eutectic carbides in the heat-treated cast iron become more and more obvious. After heat treatment, a large number of secondary carbides will be precipitated from the austenite matrix, in the form of fine particles or short rods, with a dispersed distribution. The macroscopic hardness of HHCCI has increased. When the carbon content is 3.5[Formula: see text]wt.%, the macroscopic hardness is 61.2 HRC, and when the carbon content becomes 5[Formula: see text]wt.%, it reaches 64.3 HRC. The wear resistance of HHCCI increases with the value of the carbon content increases. When the carbon content was increased from 3.5[Formula: see text]wt.% to 5.0[Formula: see text]wt.%, the wear resistance of the material increased by 85.7%. The wear of HHCCI is mainly adhesive wear and fatigue wear, and the wear morphology is mainly spalling pits and wear debris.

Investigation of the effect of addition of boron nitride on microstructure and mechanical properties of cast iron brake materials used in railway vehicles

In this study, characterization of cast iron break shoes used in locomotives and the effect of BN addition and BN addition on microstructure and mechanical properties by using powder metallurgy (PM) method by adhering to the chemical composition of cast iron break shoes were investigated. In this context, cast iron sabers were chemically analyzed and all elements were supplied in powder form, and then BN added powder compositions were produced by cold and hot pressing technique. A total of 4 different compositions were created without BN, with 0.25, 0.5 and 1 % BN addition. Cold pressing was made in a steel mold with a diameter of 10 mm under 700 MPa pressure under room conditions. Hot pressing was carried out in a graphite mold with a diameter of 15 mm in an argon atmosphere under a pressure of 45 MPa at a temperature of 900 °C. Then the cold and hot pressed samples were sintered at 1 200 °C for 2 hours in argon atmosphere. Density measurement of the produced compositions, microstructure examination, micro hardness measurement were made. Generally, in density measurements, the densities of the samples subjected to hot pressing were higher than the cold pressing process. The hardness value decreased in parallel with the addition of BN. Keywords: Brake shoe; powder metallurgy; microstructure; mechanical properties

Investigation on the Influence of Tempering on Microstructure and Wear Properties of High Alloy Chromium Cast Iron

AbstractMechanical properties, wear resistance and impact resistance of a high-alloy chromium cast iron used in the fabrication of grinding balls have been studied. A rank of tempering heat treatments under several temperatures 500°C, 525°C, 550°C and 575°C was performed after austenitized at 1050°C. The Scanning Electron Microscope (SEM) and X-ray Diffraction (XRD) techniques have been used to characterize the microstructures and identify the phases. The wear balls tests were conducted in a rotating drum with a velocity 0.5 r/s. The tribological tests were carried out by evaluated a weight loss as function time. The measurement of the rebound resilience was determined by Charpy impact tests. The results of XRD showed the presence of the martensite, carbides type M7C3and M2C for all tempering heat treated. The hardness of the sample increased after the tempering and reach nearly 65 HRC at 1050°C. In another hand, it decreased after the tempering treatment it could be explained by precipitation of the carbides type M2C.

On uniqueness of thermophysical properties and prospects of cast iron with vermicular graphite for internal combustion engines

The article is devoted to the problem of implementation new cast irons into mechanical engineering, namely, cast iron with vermicular graphite (CGI) for the manufacture of parts for engines operating under thermomechanical stress. The article presents the results of the analysis of the CGI modern situation. It is shown that the serial production of engineering products in the world began relatively recently due to the development of reliable technology of cast iron modifying for vermicular graphite (VG) only by the end of the XX century. The use of CGI in mechanical engineering in Russia is extremely limited mainly because of outdated inaccurate and even erroneous information about its properties. The data of own research of microstructure, thermal conductivity and strength of cast iron obtained with the use of modern methods and techniques of control are presented. It is shown that the thermal conductivity of CGI may significantly differ within the grades regulated by the obsolete domestic standard GOST 28394-89 which, inter alia, requires reworking for this reason. All investigated microstructures of CGI have thermal conductivity in the temperature interval from 22 °C to 300 °C varying within no more than 5 %. At high and irregular share of sphere graphite (SG) with temperature growth thermal conductivity can grow a little, with decrease of SG share its growth slows down, and since ~200 ºС it starts to fall. At a high share of VG more than 90 % the thermal conductivity starts to fall from ~100 °С, but by 300 °С the fall is no more than 10 %, which is much less than the fall in the same temperature range of the thermal conductivity of lamellar graphite iron (GI) more than 30 %. The difference in thermal conductivities between the perlitic gray cast iron and CGI with a low and medium share of SG already at temperatures higher than 200 °C becomes commensurate with the error of measurement, and at 300 °C practically disappears. At the same time, in the presence of a high SG share in the structure of CGI its thermal conductivity at 300 °С remains considerably lower than that of the perlitic gray cast iron, the difference being ~30 %.

Effect of austempering temperature on microstructure and mechanical properties of ductile cast iron modified by niobium

Abstract Owing to their exceptional physical, mechanical, and technological properties, ductile cast irons have been increasingly used, especially in automotive industries. Alloying elements and heat treatment routes can increase the strength of ductile irons. In this work, the effects of austempering temperature and time on the microstructure and mechanical properties of a ductile cast iron modified by 0.35% Nb have been studied. Two austempering temperatures of 320 °C and 360 °C for a holding time of 15, 30, 60, and 90 min were applied. The niobium addition was found to be effective in homogenizing the size and distribution of graphite nodules, maintaining the degree of nodularization above 90%, favoring pearlite refining, increasing the volume fraction of pearlite, forming niobium carbides in dispersed blocks in the matrix and graphite nodules, increasing both the yield and tensile strength, and reducing the elongation. Both the niobium addition and austempering temperature improved the yield and tensile strength but decreased the elongation compared to those of the reference ductile iron. The best combination of strength and ductility was observed at an austempering time of 60 min. The effect of austempering temperature on the microstructure and tensile mechanical properties of tested irons was found to be crucial.

Influence of the Melt Treatment Method on the Properties of Cast Iron

The article is devoted to studying the effect of liquid melt treatment with a substance having high affinity with hydrogen – lead-base silumin. Taking into account that gases (hydrogen, nitrogen and oxygen) are present everywhere, including alloys, a series of experiments was carried out on treating melt of blast furnace iron with substances having great affinity with hydrogen. It is established: when treating melt with lead-base silumin in the low-temperature test interval, there is a slight increase in the linear expansion coefficient (LEC) at 100°C, compared with the initial one, to 8.210-6, deg-1. In the temperature range of 100-150°C LEC decreases to a minimum value of 7.210-6, deg-1. In the average temperature range of 150-300°C, a sharp, anomalous increase is noticeable, compared with the initial one up to 15.5210-6, deg-1. When studying the microstructure of cast iron after processing the melt with lead silumin, the formation of ledeburite structure is stated. Samples treated with lead-base silumin were subjected to cementation by feeding water steam at 900°C for 1-5 hours. It should be noted that, in the temperature range of 50-150°C, the values of the linear expansion coefficient lie almost in a straight line in the entire field of study. The coefficient varies from 10.810-6, deg-1 at 50°C to 13.710-6, deg-1 at 450°C. Preliminary heat treatment of cast iron in the carburizer made by the Bondyuzhsky plant with water steam smoothes anomalies of LEC and increases its initial values, and grinds perlite and cementite as well. Subsequent quenching in water with a temperature of 1000°C significantly changes the linear expansion coefficient of cast iron. Hardening of samples after cementation sharply reduces the linear expansion coefficient in the test range of 150-200°C, and in the temperature range of 350-450°C negative values of LEC are observed. Thus, it can be concluded, that treating the melt with lead-base silumin, cementation in the medium of the carburizer made by the Bondyuzhsky plant and subsequent hardening leads to sharp changes of the linear expansion coefficient up to negative values. The identified properties suggest the possibility of using cast iron where it is necessary to constancy of LEC and there are no requirements for the weight of the product.

Analysis of the microstructure of wear resistant chrome cast irons after heat treatment

At the Navoi Mining and Metallurgical Combine, which uses a large number of machine parts for mining operations, the issue of optimizing the compositions of wear-resistant chromium cast irons while maintaining their operational characteristics has arisen. The paper presents the results of studying the phase composition of the cast alloy, as well as the effect of heat treatment of cast iron with a high chromium content on its structure and properties. As heat treatment operations, quenching in various modes and low tempering were used. The study made it possible to systematize the known literature data on the heat treatment parameters of a group of wear-resistant chromium cast irons, as well as to optimize their heat treatment modes for parts operating in mining and processing industry.

Structure forming and managing of properties of phosphorous cast irons for parts of internal combustion engine

Purpose. Improving the mechanical and operational properties of details of internal combustion engines by managing the structure formation of phosphorous cast irons.
 Research methods. Graphitized and bleached phosphorous cast irons with lamellar and globular graphite of laboratory and industrial melts, melted in electric induction furnaces with alloying modification and fractional casting into dry sand molds were investigated. Chemical composition, microstructure, physical and mechanical properties were determined using standard methods. Non-destructive quality control of engine parts, statistical analysis of experimental data and deterministic factor analysis of the influence of structural components on the properties of the cast irons were carried out according to the methods developed with the participation of the authors. Bench and road motor tests of optimal composition cast irons details were carried out in engines according to standard and factory methods in accordance with state standards.
 Obtained results. The general laws and principles of the formation of the microstructure of cast irons with lamellar and nodular graphite are determined depending on the degree of their alloying with phosphorus and the influence of the scale factor. It has been established that phosphide eutectic in an amount of up to 5.8 % is a strengthening structural component and increases strength, hardness, wear resistance, heat resistance, and machin-ability of phosphorous cast irons with blade tools. The negative effect of phosphide eutectic on plastic properties and cyclic fracture toughness is less significant than the effect of increasing amounts of ferrite, its grain size and graphite. Optimal chemical compositions and microstructures of phosphorous cast irons for internal combustion engines details are recommended.
 Scientific novelty. For the first time, a comprehensive system for managing the properties of phosphorous cast irons has been developed, including the analytical determination of the required characteristics of structural components and the technology for their production.
 Practical value. Methods and technologies for melting, alloying, modifying, heat treatment and surface hardening of phosphorous cast irons have been developed. They make it possible to provide the required level of mechanical and operational properties of internal combustion engines details.

Influence of Nickel on the Microstructure and Mechanical Properties of Nodular Cast Iron

This research investigates the nickel content added by 1.1wt%, 2.2wt%, 3.7wt% and 4.5wt% on the microstructure and mechanical properties in the nodular cast iron. The results demonstrate that the microstructure of nickel addition consists of nodule graphite, ferrite and pearlite phase while nickel was added to 4.5 wt% the microstructure becomes ferrite transform to fully pearlite phase. In addition the ductile iron has the highest nodularity (0.79%), followed by 1.1%Ni (0.75%), 2.2%Ni (0.71%), 3.7%Ni (0.69%) and 4.5%Ni (0.58%). The hardness and tensile strength increase when increasing the nickel content. Elongation is enhanced with nickel increasing and reaches a maximum of 12% at 1.1 wt% Ni, then decreases with the further increase of nickel.

Efficient Technologies for Producing Cast Iron Billets and Products with Specified Properties and Microstructure

The article discusses the use of resonant-pulsating refining technology in order to improve the quality of cast iron products. This technology is used in the cast iron production and cast iron mold induction. It is relatively simple and easily fits into existing production. The effectiveness of this technology is at the world’s best indicator level. The chemical composition and smelting modes of cast iron influences significantly on the microstructure of gray cast iron. The determining factors are the content of silicon in cast iron, carbon, manganese, titanium and vanadium. The carbon content affects significantly taking into account its content above 3.8%, since this content increases the content of large, ripe forms of graphite in cast iron. Titanium and vanadium also influence significantly on the microstructure of cast iron. These two elements, even in small amounts, affect the size and shape of graphite greatly. It also affects the amount of ferrite, perlite and cementite in the structure of cast iron. Vanadium also affects greatly the service life of cast iron products.

Microstructure and erosion wear properties of high chromium cast iron added nitrogen by high pressure in alkaline sand slurry

Erosion wear is a common and serious problem in slurry transportation field. In order to improve the erosion wear performance of high chromium cast iron (HCCI), a new type of high chromium cast iron with 0.38% nitrogen (HCCI–N) was fabricated by vacuum induction positive pressure melting furnace under 0.4 MPa nitrogen partial pressure on the basis of the established pseudo-binary phase diagram of (Fe–27Cr-2.2C)–N alloy system. The microstructure and erosion wear behavior of HCCI–N were researched in alkaline sand slurry. Results show that the microstructure of HCCI–N has the characteristics of multi-scale and multi-type carbides, including eutectic M7C3 (~20 μm), secondary M23C6 (~2 μm) and Cr2C (~1 μm), distributed in matrix composed of martensite and austenite. A sandwich structure of M7C3-ferrite-martensite was formed at the interface of eutectic M7C3. The nitrogen element is mainly distributed in matrix. The Cr2C (−1011) is coherent with Martensite (110). The erosion wear is caused by the synergy of corrosion and wear. The pure wear rate (Ve) of HCCI–N accounts for 71%–93% of total erosion wear rate (Vt) under different test conditions, indicating that wear loss mainly results from the mechanical action under alkaline sand slurry. Nevertheless, the synergism rate of corrosion and wear (Vs) is also significant to Vt, which accounts for 7%–29% of Vt for HCCI–N relative to 13%–31% of HCCI. The HCCI–N has more excellent erosion wear resistance compared with that of HCCI under all the test conditions, and the optimal wear resistance of HCCI–N is 1.34 times that of HCCI. The nitrogen and chromium dissolved in matrix improves corrosion resistance, and reduces the synergistic rate of corrosion and wear. Multi-scale carbide strengthens the matrix and resists mechanical wear. The combined action of the two factors makes the HCCI–N have excellent erosion wear resistance.

Corrosion of cast iron sections of gas-collecting bells of EcoSoderberg electrolyser

The article presents results of the research of high-temperature gas corrosion of sections of EcoSoderberg electrolyzers’ gas-collecting bells (GSB) made of high-strength VCh50 cast iron with spherical graphite. The gravimetric method was used to study the specific mass losses of the sections due to corrosion. The microstructure of cast iron, structure, chemical and phase composition of corrosion products were studied using optical, electron microscopy and electron microprobe analysis. It was established that the specific weight loss of the sections during operation reaches 0.36 – 0.46 g/(cm2·month). Corrosion of cast iron sections of EcoSoderberg electrolyzers’ GSB is characterized by high unevenness by area. There are cases of decommissioning sections due to local through “burnouts” with a weight loss of 19 – 24 kg. With relatively uniform corrosion, the maximum allowable weight loss of the sections is 25 – 30 kg. To make predictive estimates based on experimental data, dependence of the sections’ mass loss on the operating time was obtained. It was found that the corrosion products of the sections consist of iron oxides and alloying elements of cast iron. Most samples are characterized by increased content of C, S, F, K, Al, and Na. Corrosion products have a pronounced layered structure and contain a large number of defects in the form of pores and cracks. The layers differ in chemical, phase composition, and macrostructure. All the studied samples are characterized by cyclic alternation of relatively dense layers of iron oxides Fe2O3 and Fe3O4 and more porous layers between them. The layers are characterized by increased content of C and F. Sulfur is evenly distributed over the thickness of corrosion products. The studied samples of corrosion products have high defectiveness, friability, large number of pores, cracks, discontinuities, and low adhesion to the surface of cast iron. This is due to the presence of phases and compounds with different coefficients of thermal expansion. The mechanism of corrosion products layers formation was established and scientifically proved.

Quantitative models for microstructure and thermal conductivity of vermicular graphite cast iron cylinder block based on cooling rate

The relationships of cooling rate with microstructure and thermal conductivity of vermicular graphite cast iron (VGI) cylinder block were studied, which are important for design and optimization of the casting process of VGI cylinder blocks. Cooling rates at different positions in the cylinder block were calculated based on the cooling curves recorded with a solidification simulation software. The metallographic structure and thermal conductivity were observed and measured using optical microscopy (OM), scanning electrical microscopy (SEM) and laser flash diffusivity apparatus, respectively. The effects of the cooling rate on the vermicularity, total and average areas of all graphite particles, and the pearlite fraction in the VGI cylinder block were investigated. It is found that the vermicularity changes in parabola trend with the increase of cooling rate. The total area of graphite particles and the cooling rate at eutectoid stage can be used to predict pearlite fraction well. Moreover, it is found that the thermal conductivity at room temperature is determined by the average area of graphite particles and pearlite fraction when the range of vermicularity is from 80% to 93%. Finally, the quantitative models are established to calculate the vermicularity, pearlite fraction, and thermal conductivity of the VGI cylinder block.

Effect of Tib <sub>2</sub> Addition on Microstructure and Mechanical Properties of a Hypereutectic High Chromium Cast Iron

Hypereutectic high chromium cast iron (HCCI) is featured with high abrasion resistance and hardness, making it one of the most widely used materials in mining, minerals and cementation industries. However, the alloy is also naturally brittle partially due to the coarse needle-shaped primary M7C3 carbides. The present work challenges one of the long-term issues associated with HCCIs to modify the primary carbide through addition of a newly discovered additive, TiB2. Addition of 300 ppm such particles led to significant decrease in the fraction of needle-shaped primary carbides by 35%, and reduction in average size of the carbide by 32% in length for the needle-shaped carbide and by 32% in diameter for the equiaxed carbide. As a result, the transverse rupture strength (TRS) of the alloy after heat treatment was increased by 37% together with no noticeable loss in wear or hardness. Although excess TiB2 addition up to 8000 ppm continued reducing the amount of needle-shaped carbide, the improvement in TRS was annulled by the embrittlement of TiB 2 . Detailed microstructural examination showed that upon addition, TiB 2 decomposed in the melt, leading to the formation of TiN particles with fresh surfaces, which acted as M7C3 carbide refiner through promotion of the heterogenous nucleation of the carbide.

Influence of Niobium Addition on Microstructure and Machinability of High Chromium Cast Iron

High Chromium Cast Iron (HCCI) is mostly utilised in environments under severe abrasion and corrosion wear conditions, and research on this material with added niobium obtained positive results regarding wear resistance. The casting process has surface finish and dimensional accuracy limitations compared to machining processes. There are too few studies about HCCI machinability and no one about HCCI with niobium additions. HCCI machinability studies may allow new applications for this material when excellent surface finish and high dimensional accuracy are required. This study analyses the influence of 0.5% Nb addition on the microstructure and machinability of a HCCI alloy with 25.6% Cr and 3.2% C. The samples were heat treated and subsequently machined in dry cutting conditions. Annealing was used to facilitate the pre-machining of the samples, which were later quenched and tempered. Microstructure and hardness were analysed at each stage of the heat treatment. The material was machined after tempered using polycrystalline cubic boron nitride (pcBN) tools. The alloys solidified in the hypereutectic condition. The addition of niobium reduced the hardness and carbide volumetric fraction, increased the service life of the cutting tools in all tests, provided better surface finishing and modified the wear mechanisms.

Influence of Residual Elements Contained in Steel Scrap for the Production of Nodular Cast Iron

Abstract Nodular cast iron is a fundamental material used in engineering. It has unique properties and is one of the most produced materials in the world nowadays. The production of nodular cast iron involves melting of raw materials such as steel scrap, pig iron, machining returns and alloy irons. With the development of increasingly technological steels through the addition of chemical elements to meet a specific application, there is an increasing difficulty in acquiring steel scrap content low alloy for the production of nodular cast iron. The chemical elements present in the steel scrap favor the appearance of unwanted phases and particles. The present study evaluated the effect of the addition of the elements copper, chromium, molybdenum and nickel in levels between 0.50% w and 1.0% w in the formation of nodular cast iron microstructure. While nickel and copper were evenly distributed in the matrix, chromium and molybdenum formed carbides. In addition, chromium strongly favored the formation of perlite in nodular cast iron and molybdenum, the martensite.