high-Cr White Cast Iron Research Articles

Achieving the Superior Abrasive Wear Resistance in ZTAP/Fe Composites from the Theoretical Calculations Guided Designing of Metallurgical Interface Transition Layer

Using the first-principles calculations and phonon QHA method, the thermodynamic stability, mechanical and thermophysical properties of binary Ni-Ti phases are obtained. The most thermodynamically feasible binary Ni3Ti phase with a superior elasticity and mechanical tensile strength is designed as the interfacial transition layer between ZTA ceramic particles and iron matrix. A high-Cr white cast iron matrix composite reinforced with ZTA particles is fabricated via infiltration casting process. The microstructures and three-body abrasive wear resistance of the composite are investigated. The obtained ZTAP/Fe composite has a compact metallic Ni3Ti metallurgical transition layer with a small amount of AlNi2Ti and TiO phases in the interfacial region, leading to a strongly adhesion between iron matrix and ZTA ceramic particles due to the presence of covalent Ti-O, Fe-O and Zr-O bonds. The composite exhibits the relative wear resistance 12.9 times higher than that of reference Cr15 specimen. The wear mechanism of the ZTAP/Fe composite is mainly attributed to the removal of iron matrix under the SiO2 abrasives, as revealed from the secondary electron images and laser scanning confocal topography.

Effects of Silicon in High-Cr White Cast Irons

Effects of Silicon in High-Cr White Cast Irons

Effect of Mn and Al additions on the microstructure and hardness of a high Cr white cast iron for severe wear applications

Effect of Mn and Al additions on the microstructure and hardness of a high Cr white cast iron for severe wear applications

Effects of solidification conditions on the microstructural morphologies and strengths of hypereutectic high-chromium white cast iron castings

Although studies on hypereutectic high-Cr white cast iron (HCWCI) castings have been conducted to improve the toughnesses and quantify the microstructures of these castings, to date, only few studies have been reported on the quantitative influences of solidification conditions on the microstructures and mechanical properties of these castings. Accordingly, herein, the effects of solidification conditions on microstructural morphologies and strengths of hypereutectic HCWCI castings were investigated. Microstructural observation implied positive correlations between the minimum Feret diameter of primary M7C3 and length of M7C3 calculated from a three-dimensional geometric relationship under the approximation of the cylindrical shape of M7C3 and between experimental minimum Feret diameters of primary and eutectic M7C3. Additionally, the experimental minimum Feret diameter of primary M7C3 divided by the cube root of the volume fraction of M7C3 corresponded to the solidification velocity and temperature gradient obtained via solidification simulation. These results indicate that the parameters demonstrating three-dimensional morphologies of primary and eutectic M7C3 can be obtained by solidification simulation. Then, the strengths of the HCWCI castings were evaluated from the rule of mixtures considering the Stroh and Kelly–Tyson equations, where the volume fraction of M7C3 was acquired via thermodynamic calculations according to the chemical compositions of the castings and the strength of the matrix was substituted by the standard strengths of carbon steels under the same C equivalents as that of the matrix. The calculated strength exhibited almost the same magnitude and tendency as those of the experimental strength. The abovementioned findings reveal that not only the microstructural morphologies but also the strengths of the HCWCI castings can be estimated via computer-aided engineering. The results of this study can be utilized to predict the distributions of microstructural morphologies and strengths of the HCWCI castings.

Effect of Chromium on Microstructure and Corrosion Behavior of High-Cr White Cast Irons Used in Coal-Fired Power Plant Desulfurization Facilities

Effect of Chromium on Microstructure and Corrosion Behavior of High-Cr White Cast Irons Used in Coal-Fired Power Plant Desulfurization Facilities

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.

Effects of chromium carbide volume fraction on high-stress abrasion performance of NbC-bearing high chromium white cast irons

The addition of NbC to high chromium white cast irons (WCIs) has potential to improve component wear lives in mining and ore beneficiation environments, due to the combined presence of Cr-rich and niobium carbides. While the effect of chromium carbide volume fraction (Cr-CVF) on abrasion performance of plain-Cr WCIs is well understood, its effect on NbC-bearing WCIs is unknown. This work studies the effect of Cr-CVF on high-stress abrasion of this newer class of dual-reinforced high-Cr WCIs, using the ball mill abrasion test with quartzite and basalt. The alloys cover a wide range of Cr-CVF, from M7C3-free NbC-reinforced steel to hyper-eutectic WCI. Bulk hardness increased linearly with Cr-CVF, at a rate of 3.9 HV per 1% Cr-CVF. In basalt, abrasion resistance increased linearly with Cr-CVF, at an average life improvement rate of 24% per 1% Cr-CVF. This confirms that performance is maximized by increasing Cr-CVF even in the presence of substantial volumes of cubic carbides. In quartzite the trend is again linear up to 30 vol% M7C3 (3.7% life increase per 1% Cr-CVF), but the hyper-eutectic alloy shows poorer resistance than slightly hypo-eutectic alloy. SEM studies of the worn surfaces demonstrate that micro-fracture of the hard carbides was the controlling damage mechanism. Primary M7C3 was observed to suffer fragmentation in high-stress abrasion in quartzite, confirming the expectation from the quantitative trend.

Friction welding of high Cr white cast iron to AISI 1030 steel with Ni interlayer

Abstract In this study, the effect of friction time on microstructure and weldability of AISI 1030 steel with nickel interlayer and high chromium white cast iron welded by the friction welding method were investigated experimentally. The weld joints were produced with 2000 rpm rotational speed, under 80 MPa friction pressure, 150 MPa forging pressure, for 8 s forging time and 8, 10 and 12 s friction times. After the friction welding process, the microstructures of the weld interfaces were analyzed by optical microscopy, scanning electron microscopy, energy dispersive spectrometry, elemental mapping and X-ray diffraction analysis. The results were lateron compared theoretically and experimentally. The increasing friction time led to high frictional heat input. The results indicated that friction time plays a vital role on the microstructure and weldability.

Effects of niobium macro-additions to high chromium white cast iron on microstructure, hardness and abrasive wear behaviour

Abrasive wear is a principal cost in mining and mineral processing operations. High chromium white cast iron (WCI) further reinforced with niobium carbide (NbC) shows promise to increase component wear lives. This work investigates the effect of niobium macro-additions on microstructure, hardness and high-stress abrasive wear behaviour of Nb-containing high-Cr WCIs. Eight alloys with Nb between 0 and 10.7 wt% were produced by sand casting. Increasing niobium carbide volume fraction (Nb-CVF) increased hardness from 724 to 812 HV (7.3 HV per 1% Nb-CVF). Abrasive wear resistance, assessed using the ball mill abrasion test in basalt (less competent) and quartzite (competent rock), showed clear beneficial effect of NbC macro-addition up to 11.4 and 7 vol% in basalt and quartzite, respectively. These correspond to life improvements of 37% and 7% per 1% Nb-CVF in the optimum range of Nb macro-addition, in basalt and quartzite respectively. Micro-mechanistic observations of worn surfaces showed that NbC particles not only protrude from the matrix but do so more than Cr-rich M7C3 carbides. In deep wear grooves created by quartzite, M7C3 particles were cut flush with the matrix, whereas NbC protruded, visibly impeding the progress of the abrasion event.

Effects of matrix chromium-to-carbon ratio on high-stress abrasive wear behavior of high chromium white cast irons dual-reinforced by niobium carbides

Wear behavior of white cast irons (WCIs) is largely attributable to the particulate-reinforced composite phenomenon, in which both reinforcing particles and matrix play important roles. In high-Cr WCIs, matrix properties are influenced by chromium-to-carbon (Cr:C) ratio. Without a strong matrix, the carbides would not have sufficient support during the abrasion interactions. The effects of Cr:C ratio on the wear properties of plain-Cr WCIs have been only partially studied; but its effect on Nb-containing WCIs has never been explored. This work studies the influence of Cr:C ratio on high-stress abrasion performance of WCIs further reinforced by niobium carbides (NbC). The alloys covered wide range of Cr:C ratios, resulting in considerable variation in hardness — low hardness for both very-low and very-high Cr:C. Abrasion resistance was assessed by the ball mill abrasion test in quartzite and basalt, showing an optimum matrix Cr:C around 14.6 and 18, respectively. The very-high Cr:C alloy exhibited poorest resistance in both abrasives, and the very-low Cr:C alloy was second-poorest. SEM of worn surfaces revealed the effects of Cr:C ratio on the type and level of damages to microstructure, manifested by various morphologies and depths of indentations and grooves on the matrix, and various types and severities of damages to Cr-rich carbides, including micro-cutting and micro-fracture. NbC particles appeared to be protective across the full range of Cr:C ratios.

Electrochemical Corrosion Behaviour of Different Grades of WC-Co, High-Cr White Cast Irons and Hadfield Steel in 1 M Sulphuric Acid.

Electrochemical polarisation tests were carried out on three grades of WC-Co cemented carbides to investigate the corrosive behaviour of the hardmetals and rank them as viable protective liners for chutes and skips in the mining industry. The cobalt binder content and WC particle size varied. The binder content ranged from 6–12 wt%, and the grain size of the WC particles ranged from 0.4–2.3 µm. The performance of the WC-Co hardmetal was compared to three different grades of high chromium white cast irons and Hadfield steel. The cast irons varied in both their chromium content and the morphology of the Cr-rich primary carbides. Potentiodynamic polarisation and linear polarization resistance scans were used to determine the corrosion current density and other electrochemical parameters. The microstructural characteristics of the samples were analysed using Scanning Electron Microscope(SEM) with Energy Dispersive Spectroscopy (EDS), and optical microscopy. The potentiodynamic scans revealed that, although the WC-Co alloys were found to have generally improved corrosion resistance, it was the high-Cr white cast iron (22 wt% Cr) that recorded the lowest corrosion current density and therefore displayed the best resistance against corrosive attack in 1 M H2SO4. The Hadfield steel exhibited the poorest resistance to corrosion and therefore, suffered the most degradation to its exposed surface.

Soft annealing technology applied to high chromium white cast iron

High Cr white cast iron is an alloy widely used in the field of manufacturing parts working in conditions of high wear resistance. However, the machining process for this alloy is often difficult due to its high hardness. Therefore, the objective of this study is to find out the appropriate parameters of heat treatment process to be able for softening of high Cr white cast iron with a lower hardness, ensuring the cutting process. In this study, the samples were austenitized partially and soft annealed in a resistance furnace. Optical microscope, X-ray diffractometer and field emission scanning electron microscope were used to observe and evaluate the microstructure of samples before and after heat treatment. The Rockwell hardness tester (RHT) is also used to evaluate hardness variation of samples. Research results have shown that the change of primary carbide grain size and formation of secondary carbides during heat treatment can reduce the hardness of white cast iron to the suitable range for machining.

Investigation and Prediction of Abrasive Wear Rate of Heat-Treated HCCIs with Different Cr/C Ratios Using Artificial Neural Networks

In this study, artificial neural networks (ANNs) technique was used in the prediction of abrasive wear rate of high-Cr white cast irons (HCCIs) after subcritical heat treatment at different temperatures. High Cr WCI alloys with different compositions were tested at sliding speed of 1.04 m s−1 under the normal load of 30 N and different sliding distances of 500, 1000 and 1500 m. The abrasive wear rates obtained from wear tests were used in the formation of the data sets of the ANN. A multilayer perceptron model has been constructed with back-propagation algorithm using the input parameters of load, tempering temperature, and Cr/C ratio. The output parameter of the model is abrasive wear rate. Experimental results showed that abrasive wear rate of high-Cr WCI was significantly increased with the increasing of Cr/C ratio. High-Cr WCI alloys with higher volume fraction of carbides and structures with martensitic matrix at lower Cr/C ratio exhibited lower abrasive weight losses. The increasing of both sliding distance and load increases the abrasive weight losses. The HCCI-2 alloy exhibited the lower abrasive weight losses as compared with the other alloys in both as-cast and heat-treated conditions. In addition, the abrasive weight losses for all investigated alloys with different Cr/C ratios after destabilization heat treatment are lower than alloys in the as-cast state. This is may be due to the presences of stronger martensitic matrix structure rather than austenitic or pearlitic matrix structures. Correlation coefficients between the experimental data and outputs from the ANN established the feasibility of ANNs to effectively model and predict the wear rate of high Cr WCI. From the sensitivity analysis, it is concluded that the tempering temperature had the most influence on the wear rate, while the applied load and Cr/C ratio had a small influence on the wear rate of high-Cr WCI.

Effects of different tool material grades and lubri-cooling techniques in milling of high-Cr white cast iron

Mechanical components applied in ore crushing, the drilling of oil wells, and soil plowing need to be manufactured from materials with high resistance to abrasive wear, erosion, and corrosion. Typical materials applied under these severe conditions are cold work tool steels, high-speed steels and high-Cr white cast iron (HCWCI), which present a challenge in machining. In milling, the cutting fluid can easily access the cutting region due to interrupted cutting. In this context, coated cemented carbides associated with lubri-cooling techniques may be an alternative to improve the process feasibility. The aim of this study was to evaluate the effects of different coated cemented carbide grades and lubri-cooling techniques on the tool life and surface residual stress of the milled surface of HCWCI. Therefore, two coated cemented carbide grades associated with two lubri-cooling techniques (flood emulsion and liquid nitrogen—LN2) were applied in milling tests. The results demonstrated the feasibility of using the coated cemented carbide as a tool material in the milling of HCWCI (cutting time longer than 15 min). Furthermore, LN2 increased, by at least a factor of 2, the tool life when compared with flood emulsion. Regarding the milled surface, values above 500 MPa were obtained for the compressive residual stresses with the use of the worn cutting edges and the application of LN2.

Preparation and Microstructural Characterization of a High-Cr White Cast Iron Reinforced with WC Particles.

High-chromium white cast iron (WCI) specimens locally reinforced with WC–metal matrix composites were produced via an ex situ technique: powder mixtures of WC and Fe cold-pressed in a pre-form were inserted in the mold cavity before pouring the base metal. The microstructure of the resulting reinforcement is a matrix of martensite (α’) and austenite (γ) with WC particles evenly distributed and (Fe,W,Cr)6C carbides that are formed from the reaction between the molten metal and the inserted pre-form. The (Fe,W,Cr)6C precipitation leads to the hypoeutectic solidification of the matrix and the final microstructure consists of martensite, formed from primary austenite during cooling and eutectic constituent with (Fe,Cr)7C3 and (Fe,W,Cr)6C carbides. The presence of a reaction zone with 200 µm of thickness, between the base metal and the composite should guarantee a strong bonding between these two zones.

Microstructure, abrasive wear and corrosion characterisation of laser metal deposited Fe-30Cr-6Mo-10Ni-2.2C alloy

Advances in Laser Metal Deposition (LMD) provide technical opportunities such as the geometric restoration of worn components and custom surface coatings to enhance wear and corrosion resistance. Commercial applications include high Cr white cast iron (HCWCI) alloys for mining applications. In this study, a Fe-2.2C-30Cr-10Ni-6Mo alloy was deposited on mild steel substrates to characterise the effect of the LMD process, and a subsequent 1030 °C/4 h s heat treatment, on the microstructure, corrosion behaviour, and abrasive wear behaviour. The LMD microstructure consisted of fine eutectic Cr enriched M7C3 and Mo enriched M2C carbides in a γ-Fe matrix. This led to good abrasive wear and corrosion properties. The post heat treatment had an adverse effect on both the abrasion and corrosion resistance of this alloy, primarily due to the transformation of M7C3 to softer M23C6 carbides, and Cr depletion in the matrix.

Effect of TiBAl inoculation on abrasive wear resistance of high Cr white cast iron

AbstractHigh chromium white cast iron (HCrWCI) is generally used in applications requiring superior wear resistance. The alloys were inoculated with 1–3 wt.-% TiBAl to rearrange the crystallography of the carbides. The alloys were subject toheat treatment at 1000 °C for 1 and 2 h. The microstructuresof the alloys was examined by SEM. Chemical composition was determined by EDS. For wear tests, alloys were tested using 10, 20 and 30 N loads under pin-on-disc wear conditions. Worn surfaces of the alloys were analyzed by SEM. The worst wear resistance was obtained in the alloy inoculated with 3 wt.-%. TiBAl.

Low Stress Abrasion-Corrosion of High-Cr White Cast Iron: Combined Effects of Particle Angularity and Chloride Ions

Tribo-electrochemical behavior of a high chromium white cast iron (high-Cr WCI) used in, e.g., slurry pumps in mining and mineral processing applications, was investigated using a combination of electrochemical techniques, including zero resistance amperometry as well as potentiostatic and potentiodynamic polarisation. The effects of third body particles angularity on the localised tribocorrosion response of the cast alloy was studied during and post abrasion-corrosion by round ceramic beads and semi-angular silica sand particles. Advanced characterization methods such as electron backscatter diffraction and focused-ion beam cross-sectioning of affected areas were also employed to understand the wear and corrosion interactive actions. It was found that in chloride-free solutions, the behavior of high-Cr WCI resembled that of the austenitic 316 SS studied before. In contrast, in chloride-containing electrolytes, the semi-angular silica sand particles increased interfacial (carbide/matrix) localised corrosion susceptibility during and post-abrasion as indicated by the stark increase in anodic current and the morphology of the attack. Semi-angular silica sand abrasives had a greater adverse impact on post-abrasion interfacial corrosion vulnerability, compared to round ceramic beads. The complex behavior observed indicates that any material developed for tribocorrosive conditions must account for the particles angularity and their subsequent effects on localised corrosion.

Wear and Corrosion Behavior of High-Cr White Cast Iron Alloys in Different Corrosive Media

This study aims to investigate the effect of Cr/C ratio on wear and corrosion behavior of a group of high-Cr white cast iron (HCCI) alloys. Three different alloys of HCCI with different chemical compositions were tested against 3.5 % NaCl, 0.5 M H2SO4, and 0.5 M NaOH solutions as corrosive media. Electrochemical polarization technique has been used to determine the corrosion current density. The microstructure characteristics of HCCI alloys were analyzed by using optical microscope, SEM, EDS, and XRD. XRD analysis reveals that the microstructure of the HCCI alloys is composed of a network of chromium-rich carbides (M7C3) in an austenitic matrix. The abrasive wear resistance of HCCI alloys was found to be rely on their chemical composition and microstructure. The corrosion resistance of the HCCI alloys strongly depends on the Cr/C ratio and the ratio of chromium content in the M7C3 carbide to that in the matrix (CrM7C3/Matrix). The experimental results of this study showed that the alloy HCCI-2 with the lower Cr/C ratio exhibited the lowest abrasive wear loss while the alloy HCCI-1 with higher Cr/C ratio exhibited the highest abrasive wear loss. On the other hand, the HCCI-1 alloy was the most corrosion resistant and revealed the lowest current density. In addition, the corrosion current density of all specimens is elevated in 0.5 M H2SO4 solution in comparison with 3.5 wt% NaCl and 0.5 M NaOH solutions.

Beneficial Effects of the Core–Shell Structure of Primary Carbides in High-Cr (45 wt%) White Cast Irons on Their Mechanical Behavior and Wear Resistance

High-chromium cast irons (HCCIs) are widely used in many industrial processes involving wear and corrosion, such as oil sands mining and slurry handling in the oil sands industry. In very harsh mining environment and severe working conditions, conventional HCCIs, however, often exhibit a short service life. Great efforts have been made to improve the performance of HCCIs. One of the trials is to extend the chromium content to a higher level, e.g., 45 wt%, and widen the carbon content to a range of 1–6 wt%. In this study, we investigated the wear behavior of 45-series (Fe–45 wt%Cr with 1–6 wt%C) and observed that 45-4 HCCI (Fe–45 wt%Cr–4 wt%C) had the highest hardness and exhibited remarkably high resistance to abrasion and erosion. Microstructure analysis showed that the primary carbides in 45-4 had a core–shell structure. The outer shell was M23C6, while the inner core was harder M7C3, confirmed by the EBSD technique. The ferrous matrix was eutectic colony with martensite and fine M23C6 carbides. Micro-mechanical probing in combination with finite element analysis demonstrated that the core–shell structure helped reduce the interfacial stress, thus enhancing the hardness and overall wear resistance of the material.