Hypoeutectic White Cast Iron Research Articles

Effect of FeTi-FeB inoculation on the shape of carbide reinforcements in hypoeutectic high chromium white cast iron

Abstract FeTi-FeB was added to molten high chromium white cast iron in amounts of 0.5–2.5 wt% at 50 °C above the melting temperature. The samples were produced in four groups. The first group samples were investigated as cast, the second group homogenized at 1000 °C for 1 h, and the other two groups were also homogenized at 1000 °C but for 3 and 6 h, respectively. To study the effect of FeB and FeTi on the microstructure, the samples were characterized by optical microscopy, scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction and hardness tests. Wear tests were performed using a pin-on disc. A homogeneously dispersed carbide microstructure was produced by the homogenization heat treatment method. The addition of FeTi-FeB inoculants to high Cr white cast iron played an important role in the distribution of hard carbides. The chemical rate and the carbide volume varied on account of the added hard inoculant particles. TiB2, Cr3C2, M7C3, M23C6, and γ-FeCr phases formed on the surfaces. The hardness and wear resistance were improved considerably due to FeTi-B inoculation.

Evaluation of Hardness, Sliding Wear and Strength of a Hypoeutectic White Iron with 25%Cr after Heat Treatments

Hypoeutectic white cast irons with a high chrome content are commonly used in the industrial mining sector where there is a demand for both high resistance to adhesive wear and an acceptable toughness for the absorption of impacts and falls of diverse materials. Through the application of a design of experiment (DoE) technique, factors related to thermal treatment are analyzed with respect to resistance to sliding wear, maximum rupture stress and toughness. The results show that, in order to increase resistance to adhesive wear, it is convenient to use destabilization temperatures of 1050 °C and tempering of two hours at 400 °C. This foments a very hard martensite and a high proportion of highly alloyed retained austenite, which, with low tempering, achieves a precipitation of carbides from this austenite with hardly any loss of hardness of the martensite. In order to increase the energy which this material is capable of absorbing until breakage, furnace cooling set at 150 °C followed by tempering at 550 °C would be favorable. Slower cooling implies a greater quantity of conditioned retained austenite, so that, following this, it may be transformed into lower bainite with a high density of finely dispersed precipitated carbides. Furthermore, this tempering also allows the transformation of martensite into ferrite with finely dispersed carbides.

Verification of the Choice of Cast Iron for Locomotive Parts Operating Under Wear Conditions

The microstructure, the phase composition, the microhardness and the wear resistance of hypoeutectic white cast irons with different contents of chromium are studied. It is shown that the wear resistance of the iron depends substantially on the type of the carbide phase and on the morphology of the ledeburitic eutectic, which is determined in its turn by the content of chromium.

Erosion-corrosion assessment in strong acidic conditions for a white cast iron and UNS S31600 stainless steel

In mining industry, various parts of pumps such as liners and impellers are deteriorated severely due to erosion-corrosion mechanisms reducing the productivity of mining process and the transportation of extracted ores. It has been found that some mines consist of chlorides, very low pH and abrasive erodent particles which enhance the materials degradation. Two groups of alloys that are attractive for those aggressive slurries are white cast irons and stainless steels. In the present study, the erosion-corrosion performance of a hypoeutectic white cast iron with austenitic matrix (37 WCI) and UNS S31600 stainless steel was investigated. The testing apparatus used submerged jet technique and the angle of impingement was the normal incidence. The tests in solid/liquid impingement were conducted in aqueous solution with 3.5% NaCl with silica angular sand at pH 0. The results revealed that 37WCI was superior to UNS S31600, whilst the proportional damage of pure erosion, pure corrosion and their synergistic effects were investigated thoroughly. Detailed analysis was obtained by implementing cathodic protection (CP), potentiodynamic techniques, surface topography and microscopy. The erosion-corrosion phenomena were also analysed in different regions of the tested surface in order to understand how they affect the materials' performance in different hydrodynamic zones. It was found that corrosion was a crucial factor for the alloys’ performance, rather than their wear resistance. In addition, both alloys experienced higher corrosion rates in regions where the mechanical damage was enhanced.

Bifilm Defects in Ti-Inoculated Chromium White Cast Iron.

In recent years, white chromium cast iron has gained a well-settled position among wear-resistant materials. In recent times, chromium cast iron samples containing titanium have attracted attention. In cast iron samples, titanium combines with carbon and forms TiC particles, which may be form a crystallization underlay for eutectic M7C3 carbides and austenite. Accordingly, the inoculation process occurring in the crystallizing alloy should result in the proper, regular distribution of fine eutectic chromium carbides in the austenitic matrix. The presented research was conducted on 20% Cr hypoeutectic white cast iron with the addition of 0.5, 1, and 2% of Ti. Ti inoculation and the presence of TiC allowed for superior wear properties to be obtained. However, the conducted study revealed a significant decrease in the impact strength of examined alloys, especially for the cast iron samples with a high amount of Ti, in which the TiC compounds agglomerated. Titanium compounds accumulate in clusters and their distribution is irregular. Most of the TiC compounds were transported by the crystallization front into the center of the castings, where micropores were formed, meaning they were no longer effective crystallization underlays. In the authors’ opinion, the agglomerate formation is strictly connected with the appearance of bifilm defects in the casting microstructure. The conducted research shows how an incorrect volume of an additive may have negative influences on the properties of the casting. This is a vital issue not only from a technological point of view, but also for economic reasons.

Influence of Thermal Processing Factors, Linked to the Destabilisation of Austenite, on the Microstructural Variation of a White Cast Iron Containing 25% Cr and 0.6% Mo

Hypoeutectic white cast irons containing 25% Cr are used in ore-processing industries due to their high resistance to erosive wear. Applying a Design of Experiments (DoE), the aim of this study is to analyse the influence of thermal processing factors on the microstructural variation of a white cast iron containing 25% Cr and 0.6% Mo. The carbides present in the as-cast state are of the M7C3, M2C, and M3C types. M2C carbides precipitate on the eutectic M7C3 carbides favoured by heterogeneous nucleation conditions. Two kinetics compete during the destabilisation of austenite. One dissolves those eutectic carbides precipitated as a result of non-equilibrium solidification (M7C3 and M2C), while the other enables the precipitation of secondary M7C3 and M23C6 carbides. The M7C3 carbides begin to precipitate first. Low destabilisation temperatures and short dwell times are insufficient to dissolve the precipitated eutectic carbides from non-equilibrium conditions, thus favouring the presence of M2C carbides, which are associated with Mo. The factor that has the greatest influence on hardness is the tempering temperature. The optimal tempering temperature is found to be 500 °C. Short tempering times maintain the distortion of the ferrite unit cell. The precipitation of Cr carbides during tempering requires a temperature of 500 °C and the prior dissolution of the carbon precipitated during the initial stages of said tempering. With short tempering times, the Cr atoms still remain dissolved in the ferrite, distorting its unit cell and increasing the hardness of the matrix constituent of the alloy.

Optimization of Thermal Processes Applied to Hypoeutectic White Cast Iron containing 25% Cr Aimed at Increasing Erosive Wear Resistance

Hypoeutectic white cast irons containing 25% Cr are used in very demanding environments that require high resistance to erosive wear, for instance, the crushing and processing of minerals or the manufacture of cement. This high percentage in Cr, in turn, favors corrosion resistance. The application of a Design of Experiments (DoE) allows the analysis of the effects of modifying certain factors related to the heat treatments applied to these alloys. Among these factors, the influence of prior softening treatment to facilitate the machining of these cast irons and the influence of the factors related to the destabilization of austenite, during both quenching and tempering, were analyzed. The precipitated phases were identified by X-ray diffraction (XRD), while the Rietveld structural refinement method was used to determine their percentages by weight. Erosive wear resistance was calculated using the ASTM G76 standard test method. It is concluded that the thermal softening treatment, consisting of 2 h at 1000 °C and 24 h at 700 °C, does not result in additional softening of the material compared to its as-cast state. Furthermore, it is observed that not only eutectic carbides influence wear resistance, but that the influence of the matrix constituent is also significant. It is also verified that the tempering treatment plays a decisive role in wear resistance. Temperatures of 500 °C and tempering times of 6 h increase the wear resistance and hardness of the aforementioned matrix constituent. Tempering temperatures of 200 °C lead to an increase in retained austenite content and the presence of M3C carbides versus mixed M7C3 and M23C6 carbides. The quench cooling medium is not found to have a significant influence on the hardness or wear resistance.

Influence of Thermal Parameters Related to Destabilization Treatments on Erosive Wear Resistance and Microstructural Variation of White Cast Iron Containing 18% Cr. Application of Design of Experiments and Rietveld Structural Analysis.

High-Cr hypo-eutectic white cast irons are used in very demanding environments that require high resistance to erosive wear. The influence on the microstructural variation and erosive wear resistance of several fundamental factors related to the thermal treatments of these cast irons was analysed by means of a fractional Design of Experiments (DoE). These factors included the ones related to the destabilization of austenite. The precipitated phases were identified by X-ray diffraction (XRD), while the Rietveld structural refinement method was used to determine their percentages by weight. Erosion wear resistance was calculated using the test defined by ASTM G76. It was concluded that the quench cooling medium does not significantly influence either erosive wear resistance or the proportion of martensite or retained austenite. The destabilization temperature is a key factor with respect to the percentage of retained austenite. In order to increase the amount of martensite and decrease the amount of retained austenite, temperatures not exceeding 1000 °C are required. An increase of 100 °C in the destabilization temperature can lead to a 25% increase in retained austenite. Moreover, tempering temperatures of around 500 °C favour an additional increase in the percentage of martensite. Erosive wear commences on the matrix constituent without initially affecting the eutectic carbides. Once the deterioration of the matrix constituent surrounding these carbides occurs, they are released. High tempering times provide an increase in resistance to erosive wear due to a second destabilization of austenite during the said tempering.

Erosive Wear Resistance Regarding Different Destabilization Heat Treatments of Austenite in High Chromium White Cast Iron, Alloyed with Mo

With the aim of improving erosive wear resistance in hypoeutectic white cast irons with 18% Cr and 2% Mo, several samples of this grade were subjected to different heat treatments at 1000 °C to destabilize the austenite. The dwell times at this temperature varied from 4 to 24 h and the samples were cooled in air or oil. The existing phases were identified and quantified by applying the Rietveld structural refinement method. The results were correlated with the hardness of the material and with the microhardness of the matrix constituent. The greatest resistance to erosive wear was achieved in those samples that had a higher percentage of secondary carbides. The longer the dwell time at the destabilization temperature of austenite, the greater the amount of precipitated secondary carbides. However, the percentage of dissolved eutectic carbides is also higher. These eutectic carbides were formed as a result of non-equilibrium solidification. Low cooling rates (in still air) can offset this solution of eutectic carbides via the additional precipitation of secondary carbides in the 600–400 °C temperature range. A sharp decrease is observed in the percentage of retained austenite in those treatments with dwell times at 1000 °C equal to or greater than 12 h, reaching minimum values of around 2% volume. The percentage of retained austenite was always lower after oil quenching and the hardness of oil quenched samples was observed to be greater than those quenched in air. In these samples, the maximum hardness value obtained was 993 HV after a 12 h dwell, which result from the optimum balance between the percentages of retained austenite and of precipitated carbides.

Effect of Rare Earth on M7C3 Eutectic Carbide in 13% Chromium Alloy Cast Iron

The crystallization process of hypoeutectic white cast iron consists of the first secreted austenite branch after the reaction of the austenite -carbide crystal is formed, and the phase crystal fills in the middle of the austenite branches. If the austenite branches are small and smooth, the crystals carbide are fine. The cast iron with 13% chromium which has 3 - 3.2% carbon, have the carbide crystalline as M7C3. The elements in rare earth have a strong affinity for oxygen and sulfur to produce rare earth oxides. These rare earth oxides can create heterogeneous germ center for austenite phases and smooth down these phases. The effect of rare earth on the M7C3 and crystals of 13% chrome white iron has been elucidated. Along with the increase of rare earth content, the microstructure of M7C3 with fine finely graded, more uniformly distributed, dispersed throughout the sample surface. When the carbide is fine and dispersion, will contribute to improving the properties of cast iron especially the impact strength as well as the abrasion resistance of the alloy. The research results show that in the presence of rare earth, rare earth elements created with oxygen and form La2O3 and Ce2O3 as the nucleation for the solidification process and create the small fineness of phases. The orientation of the crystal structure of these oxides is similar to the crystal structure orientation of Fe-γ phase. Finding and proving the oxides of rare earth has crystal structure with phase γ which will be small smooth exogenous minds that the microstructure has a smooth, small size.

Análisis microestructural de revestimientos de fundiciones blancas hipoeutécticas con adiciones de Si y V

Las aleaciones utilizadas para el revestimiento de superficies sometidas a baja o moderada abrasión son altamente complejas. Con la finalidad de buscar una alternativa más simple, en el presente trabajo se estudian tres revestimientos, aplicados utilizando electrodos con diferentes composiciones basadas en fundiciones hipoeutéticas Fe-Si-V-C con 3,2 % de C, V entre 0,47 y 1,57 %, y Si entre 2,30 y 3,82 %. Los revestimientos resultantes fueron estudiados utilizando técnicas de microscopía óptica (MO), microscopía electrónica de barrido (MEB), difracción de rayos X (DRX) y dureza. Los resultados mostraron que para contenidos de Si y V bajos, se obtuvo la dureza más elevada (64 HRC), derivada de una microestructura donde predominan la martensita y la austenita. Al aumentar las cantidades de estos elementos en la aleación, se obtuvo mayoritariamente perlita, con zonas eutécticas y carburos de V distribuidos en ellas, originando una disminución de la dureza hasta 57 HRC. Por lo tanto, utilizando contenidos de Si y V bajos (cercanos a 2,30 % de Si y 0,47 % de V), los electrodos basados en el sistema aleante Fe-Si-V-C pueden ser una alternativa para revestir superficies sometidas a desgaste abrasivo bajo o moderado.

Aplicación del ajuste de Rietveld para correlacionar la evolución microestructural de fundiciones blancas con 18 y 25% en Cromo, templadas en aceite y sucesivos revenidos, con el comportamiento frente al desgaste abrasivo y esfuerzos de flexión

Mediante la aplicación del método de afinamiento estructural de Rietveld se identificaron y cuantificaron las fases presentes en fundiciones blancas hipoeutécticas con 18 y 25% en Cromo, templadas en aceite y tras sucesivos revenidos a 500 ºC. Se correlacionaron los resultados con su comportamiento frente al desgaste abrasivo y bajo esfuerzos de flexión. En ambos casos el porcentaje de austenita retenida tras el temple resultó mínima. Durante los sucesivos revenidos, se constató en la calidad con 18% en Cromo una redisolución parcial de los carburos M7C3 junto a una transformación entre carburos mixtos secundarios M7C3 y M2C. La Martensita tras temple resultó un factor clave frente a la resistencia al desgaste abrasivo, resultando los revenidos tras el temple en aceite desfavorables para esta propiedad. La calidad con 25% en Cromo fue la que presentó un mayor contenido en martensita tras el temple, y por tanto la que mejor comportamiento presentó frente a este tipo de desgaste. Esta misma calidad, tras el doble revenido, fue la que mayor resistencia y capacidad de deformación alcanzó bajo esfuerzos a flexión. La fractura resultó frágil y mayoritariamente transgranular. Sin embargo, pudo observarse la presencia de zonas con fractura dúctil asociadas a martensita doblemente revenida.

The Wear Evaluation of Blasting Machine’s Blades

The contribution deals with the evaluation of wear blades continuous blasting machine. The current state of wear of blades and a description of the blasting process is analyzed. In the experimental part of this work the quality of the blades is evaluated by measuring the hardness of materials, chemical analysis of the samples and their structural analysis. Abrasive wear was evaluated in loose fill abrasive and in the environment with firmly bonded abrasives. The results of the measurements showed that the material of the blades is hypoeutectic white cast iron with different carbon and alloying, especially Chromium.

The influence of pre-heat treatment on white cast irons plasticity

Purpose. The development of heat treatment modes of white cast irons for structure changes in their eutectic constituent, namely in disturbing the monolithic structure of ledeburite colonies cementite structure and eutectic net continuity. Also the mentioned heat treatment modes are targeted to the eutectic net shift for the most suitable position from the point of plastic deforming. Methodology. The hypoeutectic white cast irons with 2.92…3.35 % carbon content and additionally alloyed by 3.18 % vanadium have been used as the research materials. The mentioned alloys have been pre-heat treated and hot twist tested. Findings. The research results showed that the carbide net breaking by plastic deforming leads to cast irons mechanical properties increasing but has difficulties in implementation due to the white cast irons low plasticity. The influence of different pre-heat treatment modes on structure and plasticity of white hypoeutectic cast irons have been investigated. They include the isotherm soaking under the different temperatures as well as multiply soakings and thermo-cycling. The influence of eutectic level, as well as pre heat treatment modes on different composition white cast irons hot plasticity have been investigated. Originality. It was determined that the heat treatment, which leads to double α→γ recrystallization under 860 – 950 °С and reperlitization under 720-680 °С results in significant increase of plasticity, as well as in un-alloyed and alloyed by vanadium white cast irons. It takes place due to carbide matrix phase separation in ledeburite colonies by new phase boundaries forming especially due to carbide transformations under vanadium alloying. Practical value. The implementation of pre-heat treatment with phase recrystallization resulted in hypoeutectic white cast irons plasticity increasing. The obtained level of cast iron plasticity corresponds to the one of carbide class steels, which ensures the successful deformation by forging and rolling.

Effects of a Destabilization Heat Treatment on the Microstructure and Abrasive Wear Behavior of High-Chromium White Cast Iron Investigated Using Different Characterization Techniques

The hypoeutectic white cast iron was subjected to various destabilization heat treatment temperatures of 1173 K, 1273 K, and 1373 K (900 °C, 1000 °C, and 1100 °C) for 2 hours. The as-cast and destabilized specimens were characterized by optical metallography, classical direct comparison, and the Rietveld method. The volume fractions of carbides were measured by optical metallography. Moreover, the volume fractions of retained austenite and martensite were measured by the classical direct comparison method. Despite the limitations of optical metallography and the classical direct comparison method, the Rietveld method was successively and accurately applied to determine the volume fractions of all phases. In addition, the Rietveld analysis yielded certain results, such as the crystallographic properties of the phases that can be used to explain the relationship between the microstructural parameters and the wear behavior. Abrasive wear tests with different sliding speeds were carried out on the as-cast and destabilized alloys to identify the effect of microstructural parameters on the wear behavior. The results indicated that the morphologies of secondary carbides, the crystallographic properties of the phases, and the proper combination of the amount of martensite, retained austenite, and carbides were the principle parameters that affect the hardness and wear behavior of the alloy.

Characterization of corrosion products on archaeological iron coins

Purpose – The purpose of this paper is to investigate the microstructures, slag inclusions, morphology and composition of ancient Chinese iron coins exhumed from Emei Mountain and Baoji after 818‐966 years of being imbedded underground.Design/methodology/approach – Metallography, scanning electron microscopy, energy dispersive spectrometry, X‐ray photoelectron spectrometry and Fourier transform infrared spectroscopy were employed.Findings – The results showed that archaeological coins exhibited characteristics of a typical hypoeutectic white cast iron, with slag inclusions of FeS strips and phosphate. Porous or hexagonal platey corrosion products were discovered on the archaeological iron coin, which were mainly identified as Fe2O3, FeOOH, Fex(OH)1−xCO3 and Fex(OH)1−xSO4. The possible corrosion mechanisms for the iron coins were discussed based on the corrosion products.Originality/value – This study revealed the characterization of corrosion products on archaeological iron coins and may provide guidance ...

Quantification of the microstructures of hypoeutectic white cast iron using mathematical morphology and an artificial neural network

This paper describes an automatic system for segmentation and quantification of the microstructures of white cast iron. Mathematical morphology algorithms are used to segment the microstructures in the input images, which are later identified and quantified by an artificial neuronal network (ANN). A new computational system was developed because ordinary software could not segment the microstructures of this cast iron correctly, which is composed of cementite, pearlite and ledeburite. For validation purpose, 30 samples were analysed. The microstructures of the material in analysis were adequately segmented and quantified, which did not happen when we used ordinary commercial software. Therefore, the proposed system offers researchers, engineers, specialists and others, a valuable and competent tool for automatic and efficient microstructural analysis from images.

Effects of retained austenite on abrasion wear resistance and hardness of hypoeutectic high Cr white cast iron

A hypoeutectic white cast iron of 2.3%C—26%Cr—l%Ni—0.5%Mo was heat-treated with three different methods in order to obtain the specimens with different levels of retained austenite(Vr) in the matrix. Then, the effect of the Vr value on the abrasion wear resistance, and the macro- and micro-hardness of the iron was investigated to derive a mutual relationship among them. While the Vr value is 70.2% in the as-cast specimen, those of the heat-treated specimens range from 0.3 to 65.4%, depending upon the types of heat-treatment. In the scratching abrasion wear test, a linear relationship between wear loss and wearing time was obtained after the primary stage of unsteady wear in all the specimens. Therefore, the rate of wear(Rw: mg/s), equivalent to the slope at the portion of straight line, was adopted as an index of wear resistance. The Rw values range from 2.77×10−2 to 4.12×l0−2, the lowest Rw being obtained in the as-cast specimen with the highest Vr value and the highest Rw in the homogenized specimen with the lowest Vr value. The Rw value decreases with an increase in the Vr value probably due to a transformation of austenite into martensite during abrasion wear test. While the range of micro-hardness is from HV 358 to HV 756, the macro-hardness ranges from HV 529 to HV 785 due to the involvement of eutectic M7C3 carbides in measurements. The highest hardness value is obtained in the specimen heat-treated by fan-air hardening with austenitizing condition of 1323K for 7.2ks. On the other hand, the lowest hardness is obtained in the as-cast specimen due to the presence of large amount of austenite and of less martensite, and the absence of secondary carbides. Mutual relationships among Rw, Vr and hardness show a good correspondence.

Erosive wear and impact damage of high-chromium white cast irons

High-chromium white cast irons are used extensively in environments where small particle impact causes considerable damage. In this study, three white cast irons with a variation in carbide volume fraction were eroded by spherical and angular particles. The white cast irons eroded at a higher rate when the erodent was WC–Co spheres than when the erodent was alumina particles. When eroded by spherical WC–Co particles, the eutectic white cast iron eroded at a higher rate than the hypoeutectic white cast iron. The results of the erosion experiments were interpreted in terms of a mechanism of platelet formation involving strain localization. The greater strain hardening rate of the hypoeutectic white cast iron can account for the better erosion resistance compared to the eutectic white cast iron, based on the strain localization mechanism. The larger size and greater density of the WC–Co spheres can account for the higher erosion rates of the white cast irons when eroded with WC–Co spheres compared to the erosion rate with alumina particles.

Competitive growth of eutectics in chromium-tungsten white cast irons

Unidirectional solidification was carried out to investigate solidification sequences of the eutectics in hypoeutectic chromium-tungsten white cast irons containing 8–17 mass% Cr, 2.7–3.2 mass% C and 5 mass% W at the growth rate of 0.003 to 0.4 mm/s. At lower growth rates, γ+M7C3 eutectic crystallized before g+M3C eutectic. At higher growth rates, γ+M7C3 eutectic crystallized preferentially and no γ+M7C3 eutectic crystallized. The interface temperatures of primary austenite and both eutectics were measured as a function of growth rate and the criterion phase selection was successfully applied to explain the experimental results.