High Chromium White Iron Research Articles

Effects of Impact Energy, Impact Frequency, and Test Time on Impact Wear Characteristics of Zirconia-Toughened Alumina Particles-Iron (ZTAp-Fe) Composites Using Response Surface Methodology

The study aimed to investigate the effects of wear parameters including impact energy, impact frequency, test time, and their interactions on the impact wear characteristics of high chromium white iron (HCWI) and zirconia toughened alumina (ZTA) reinforced HCWI composites fabricated by squeeze casting method using response surface methodology (RSM). The Box-Behnken Design (BBD) method was employed, and a linear model was developed to describe the relationship between wear loss and wear parameters, and to predict the wear behavior of the tested materials. The parameters of energy, frequency, and test time were found to be statistically significant, and positively influencing the wear behavior. Specifically, test time emerged as the most influential factor, followed by energy and frequency. The wear characteristics of HCWI are primarily characterized by shallower plowing and furrows, partial plastic deformation, surface spalling, and inserted abrasives. In contrast, the predominant wear mechanisms for ZTA/HCWI composites include slight breaking of ZTA particles, plowing, and cutting of the metal matrix; breaking and falling of ZTA particles; broken abrasive particles encrusted into the matrix; and the formation of spalling pits.

Scouring erosion resistance of metallic materials with composite microstructures

Slurry erosion can cause severe damage and often constitutes a significant portion of the total production cost in many industries such as oil sands and mining. The most commonly used materials for such applications are metallic materials having a composite microstructure consisting of hard reinforcement phases in a more ductile metal matrix. Typical examples are high chromium white irons and tungsten carbide welding overlays. The main purpose of this work is to evaluate the scouring erosion resistance of such materials for applications in handling fine sand slurries and to introduce a wear model to help understand the correlation between erosion resistance and the characteristics of microstructures.Five high chromium white cast irons and four spray and fusion coatings composed of cast tungsten carbide particles and Ni–Cr–B–Si–Fe matrix have been studied using a Coriolis scouring erosion tester in a fine sand slurry. The relationship between the erosion resistance and different microstructure parameters was explored. For the chromium white cast irons, the erosion resistance increased with increase in carbide volume fraction but the spray and fusion coatings showed the opposite trend, i.e., their erosion resistance decreased with increase in the carbide volume fraction. No clear correlation was found between erosion resistance and free path for the spray and fusion coatings while for the chromium white cast irons, the erosion resistance was found to increase rather than decrease with increase in free path.To help explain the experimental results, a wear model has been proposed for the wear resistance of composite microstructures composed of a reinforcement phase (RP) and a metal matrix. In the model, the wear surface of the material is distinguished by four different features/regions, each having unique wear resistance. The rule of mixtures (ROM) for wear resistance is applied to formulate the wear resistance of the material with the above four wear surface features. It is shown that the results can be reasonably well explained based on the proposed model by using the total edge length, L, of the RP particles exposed on a unit area of the wear surface.

Effect of MXene Ti3C2Tx in situ formed TiCx on oxidation behavior of high chromium white iron

In order to improve the oxidation resistance of high chromium white iron (HCWI), effect of 0.5–1 μm spherical and 5–10 μm lamellar TiCx sourced from Ti3C2Tx on oxidation behavior of high chromium white iron (Ti3C2Tx/HCWI) in air at 600 °C for 96 h was investigated. Oxidized surface displayed that the holes and peeling off caused by oxidation were found at different regions as a result of oxidative difference of double-dimensional-shaped TiCx in Ti3C2Tx/HCWI. Ti3C2Tx/HCWI exhibited improved oxidation resistance, thermodynamics and kinetics of oxidation were discussed.

Assessment on oxidation behaviors of high chromium white iron matrix composite in high temperature air environment

Oxidation behaviors of in situ formed TiCx/high chromium white iron (TiCx/HCWI) composite containing trace alloying elements with super hardness were investigated in air at 650 °C and 700 °C for 96 h, respectively. Rich types of oxides appeared on the oxidized surfaces of the TiCx/HCWI composite both at 650 °C and 700 °C. While, MoO3 appeared on the surface only at 650 °C, FeV2O4 turned up only at 700 °C. The various oxides were enriched in diverse regions inside and outside the oxide layer at 700 °C due to the discrepancy of oxidation thermodynamics and oxidation partial pressure. Oxidation thermodynamics, kinetics, and oxidation mechanisms of the TiCx/HCWI composite were discussed. The present work provides enlightenment for the application of the super hard TiCx/HCWI.

Effect of boron addition on the microstructure and wear resistance of laser beam directed energy deposited high chromium white irons

There is a demand for alloys produced by laser beam directed laser deposition (DED-LB) with better wear resistance than the traditionally manufactured alloys. In DED-LB of high chromium white iron (HCWI), the refined carbides at the micron scale can lead to inferior wear performance than the cast alloy of the same composition. In this study, various concentrations of FeB powder were mixed with HCWI powder and produced by DED-LB. The microstructural evolution and its relationship with the wear resistance in high stress abrasion wear test were studied. The B addition is a C equivalent element in HCWI, which can change the composition from hypoeutectic to hypereutectic. In the hypereutectic alloys, B promotes hard phases in the form of M7(C,B)3 and M3(C,B) (M mainly represents Cr and Fe). With the B additions, the volume loss in high stress wear testing is reduced due to the increase in the fraction of the hard phases and their coarsening. With the predominantly austenitic matrix, the alloy with 1.09 wt % B consisting of near 60 vol% hard phases showed a superior wear performance than the heat-treated cast alloy. This was attributed to the microstructure in the contact. The high fraction of refined hard phases and the relatively ductile austenitic matrix (compared with the martensitic matrix) work synergistically, showing a worn surface of plastic deformation without brittle spalling and pitting.

Effect of 211 MAX phase Ti2AlC in situ formed TiCx on properties of high chromium white iron

High chromium white iron (HCWI) matrix composites reinforced with in situ formed TiCx decomposed from 211 MAX phase Ti2AlC (Ti2AlC/HCWI) have been successfully prepared. The influence of Ti2AlC contents on properties of high chromium white iron has been studied. The Ti2AlC/HCWI composites were testified to have a conspicuous promotion in mechanical properties compared with HCWI. The maximal Young’s modulus and electron work function (EWF) were achieved in 20 wt% Ti2AlC/HCWI, while the maximal hardness was acquired in 15 wt% Ti2AlC/HCWI. Strengthening mechanisms about refining the grain, second-phase strengthening and solid-solution strengthening were discussed.

Effect of Ti and TiC additions on the microstructure and wear resistance of high chromium white irons produced by laser directed energy deposition

Laser directed energy deposition (L-DED) is an additive technology that offers a rapid solution for repairing mining components made of High Chromium White Iron (HCWI) on site. However, the refined carbide morphology from the rapid cooling in L-DED is detrimental to the wear resistance of the repairs. In this study, two types of powder (Ti powder and TiC powder) were added to improve the wear resistance of L-DED HCWI. The Ti powder addition promoted the formation of in-situ TiC while the TiC powder addition resulted in coarse ex-situ TiC and fine in-situ TiC in the as-deposited microstructure. The addition of both powders destabilised the austenitic matrix (γ-Fe). The wear resistance was investigated by a high stress abrasion test using silica sand (softer than M7C3) and a pin-on-disk wear test using a ruby pin (significantly harder than M7C3). The best wear results were achieved with 6.55 wt% Ti powder addition. This destabilised γ-Fe in the as-deposited microstructure which underwent strain-induced martensite formation during the high stress abrasion wear testing, improving the wear resistance of the alloy. The addition of TiC powder improved the wear resistance in the high stress abrasion test due to the increase in the fraction of carbide. In the pin-on-disk wear test, the alloys with TiC powder addition performed better than the cast sample because a greater amount of γ-Fe matrix in the microstructure provided a better combination of hardness and ductility.

Laser processing of high chromium white iron

Mechanical properties, such as wear-resistance and hardness, of laser welded and cladded high chromium white iron were investigated. The study involves the laser welding, cladding, and laser surface melt treatment by 3-kW Nd:YAG continuous wave high power laser. The laser welding of 2-mm thick high chromium white iron samples was laser welded in two combinations: iron-to-iron and iron-to-steel. Strong metallurgical bonding was witnessed between not only the iron samples but also iron and steel samples by laser welding. Three types of powder materials were used to laser clad the samples: metal-ceramic (compositionally close to INCO-702), stellite-21, and stellite-1 in order to estimate mechanical property changes and process ability of high chromium white iron. Even though the microstructure of metal-ceramic coating shows worse than stellite powder coatings it has more hardness and wear resistant property which were comparable to base iron. Hardness of metal-ceramic coating was slightly lower than base iron, yet the wear resistance was increased twofold.

Effects of Primarily Solidified Dendrite and Thermal Treatments on the M23C6 Precipitation Behavior of High-Chromium White Iron

The precipitation behavior of M23C6 carbide during thermal treatment of high-Cr white iron with various fractions of primarily solidified dendrite was studied and reviewed. M23C6 precipitation in the primarily solidified dendrite occurred preferentially during conventional heat treatment, whereas it occurred scarcely in the eutectic austenite. The reaction between M7C3 and austenite caused the dissolution of M7C3 into austenite, followed by precipitation of M23C6 along the periphery of eutectic M7C3. Relatively low-temperature thermal treatment (modified heat treatment) led to precipitation of M23C6 particles in the eutectic austenite, which is presumed to be caused by solubility difference depending on temperature.

Microstructural modification of a static and dynamically solidified high chromium white cast iron alloyed with vanadium

The objective of this study is to analyze the effect of dynamic solidification and vanadium additions in a range from zero to 6.42 ​wt% to a high chromium white iron with the purpose of refining the microstructure and to improve hardness. The alloys were characterized by optical and electron microscopy, EDS and X-ray diffraction and complemented with phase quantification undertaken by image analysis and XRD data. Bulk hardness was measured for different casting thicknesses in both as-cast and after a destabilization heat treatment at 900 ​°C for 45 ​min. The results show that V addition produces a refining effect on the M7C3 carbide as well as the VC carbide formation which can nucleate as primary carbide for V contents higher than 4.75 ​wt%. Dynamic solidification of the experimental irons produced a notable decrease in the size of the carbide phase and increased its volume fraction. This solidification technique also produced a transformation of the iron matrix of the base alloy from predominantly austenitic to a fully pearlitic matrix, while for the 6.42 ​wt% V alloyed iron a notably smaller, slightly elongated and isolated VC carbides embedded in a highly martensitic matrix were observed. This microstructural modification resulted in the maximum harness values obtained in the as-cast conditions. After the destabilization heat treatment, a softening of the microstructure of the V alloyed irons was observed due to the C depletion of the matrix inhibiting the martensitic transformation; conversely, the base alloy experienced a considerably increase in hardness as a result of the high amount of precipitated carbides embedded in a highly martensitic matrix. The results of the present study show that, V alloying and the dynamic solidification technique can be used as effective ways to refine the carbide phase obtaining high hardness levels in the as-cast condition, avoiding this way heat treatments.

High Chromium White Irons for Mining, Grinding and Materials Handling

High Chromium White Irons for Mining, Grinding and Materials Handling

Effect of heat treatment on microstructure and erosion resistance of white cast irons for slurry pumping applications

A series of commercial and non-conventional heat treatments was performed to modify the initial as-cast microstructure of two high-chromium (14 wt% and 18 wt% Cr) white cast irons and a low chromium nickel-bearing grade (Ni-Hard 2) for slurry pumping applications.The effect of each heat treatment on the microstructure of the alloys was carefully investigated by optical and scanning electron microscope and X-ray diffraction analysis.Samples were tested for impact erosion resistance in flowing slurry by using a modified-Coriolis apparatus and their weight losses were related to microstructure and hardness. The analysis showed that the erosion resistance of these alloys is related to the carbides volume fraction and hardness, in combination with the matrix microstructure. In case of high-chromium white irons, the destabilization heat treatment (950°C-2h) produced a hard martensitic matrix with secondary carbides that gave superior erosion resistance compared to all other conditions. Excellent performances were obtained also for Ni-Hard 2 in as-cast condition, indicating that this alloy could be an economic alternative to high chromium irons in applications where good erosion resistance is required.

In situ formed TiCx in high chromium white iron composites: Formation mechanism and influencing factors

Influencing factors on the preparation of high chromium white iron composites reinforced with in situ formed TiCx have been investigated. Various Ti3AlC2 precursor powders with sizes from 6.5 to 75 μm were used to examine their influence on the dimension of in situ formed TiCx. Different heating rates and dwelling times were also adopted to study their effects on the microstructure of the composites. The initial Ti3AlC2 precursor size has a minor influence on the grain size of in situ TiCx. However, the heating rate and the dwelling time have an impact on the distribution of TiCx in the matrix. The microstructure and phase composition of the prepared materials were characterized by scanning electron microscopy, transmission electron microscopy and X-ray diffraction. The nucleation and growth mechanism of TiCx in the composites has been discussed.

Microstructural characterization and abrasive wear resistance of a high chromium white iron composite reinforced with in situ formed TiCx

Abstract A high chromium white iron (HCWI) composite reinforced with in situ formed 17.2 wt.% TiCx has been prepared. The in situ formed TiCx grains resulting from the decomposition of Ti3AlC2 are round and small. The presence of small TiCx grains effectively inhibited the rapid growth of M7C3 (M: Fe, Cr and other strong carbide formers) carbides, refining the microstructure of composite. High resolution TEM micrographs show that interfaces of TiCx/M7C3 and TiCx/matrix are clean, suggesting the formation of strong bonding interfaces in the composite. The wear behavior of the composite and the unreinforced HCWI material as a function of the normal load in the range of 78–123 N was investigated using dry sliding pin-on-disc wear testing against a YG8 disk under ambient conditions. The wear resistance of HCWI and TiCx/HCWI decreased with increasing load. However, the wear resistance of the TiCx/HCWI composite was over six times that of the unreinforced HCWI material even at the highest load of 123 N. The improved wear resistance of the composite should be ascribed to contributions from both the presence of smaller TiCx grains reinforcing the matrix and the refinement of the M7C3 structure. Scanning electron microscopy was used to characterize the microstructures of materials before and after wear testing.

Analysis of Film Formation in High Chromium White Iron Hardfacing Alloys in Alkaline Solution using EIS and SIMS

A popular hardfacing alloy consisting of high chromium white iron (HCWI) was deposited on low carbon steel using shielded metal arc welding. The wear-resistant alloys are not only used in applications requiring wear resistance but also used in applications involving fluids of a range of pH values. It is well known that chromium containing alloys have good corrosion resistance due to the presence of passive film. In this study for understanding the film formation on carbides and eutectic austenite matrix, HCWI alloy were exposed to potentials (0.157 V vs. SCE and 0.758 V vs. SCE) derived from potentiodynamic studies in highly alkaline solution of pH 14, simulating Bayer refining process in alumina industry. Electrochemical impedance spectroscopy (EIS) technique was used to analyse the impedance of films. The thickness and the composition of film properties at various potentials were investigated by time-of-flight secondary ion mass spectrometry (ToF-SIMS). At potential 0.157 V versus SCE, chromium carbide had a thick layer of oxide film consisting of mainly FeO with minor amounts of CrO. The eutectic austenite matrix consisted of a much denser and slightly thinner film of FeO. It is proposed in this study that for the formation of an oxide film on carbides, the carbides would have to dissociate on the surface. This dissociation of carbides may likely render the hardfacing alloy less effective in wear-resistant applications. The results were explained through superimposing the Pourbaix diagram of chromium carbides and iron (Fe).

Effects of in situ formed TiCx on the microstructure, mechanical properties and abrasive wear behavior of a high chromium white iron

High chromium white iron (HCWI) composites reinforced with in situ formed TiCx have been prepared by powder metallurgy. Processing conditions for the preparation of dense composites have been investigated. The influence of TiCx content on the mechanical properties and wear resistance of composites has been studied. Compared to the unreinforced HCWI material, the TiCx/HCWI composites demonstrated a remarkable improvement in mechanical properties and abrasive wear resistance. A strength of 310 MPa and a fracture toughness of 10.19 MPa m1/2, nearly eight times those of unreinforced HCWI, and a wear resistance of 315.1 cm−3, seven times that of unreinforced HCWI, were achieved in the 17.2 wt%TiCx/HCWI composite. Strengthening and wear mechanisms have been discussed.

Effect of impact energy on wear behavior of high chromium white iron produced by liquid die forging

Impact abrasive wear behavior of high chromium white iron (HCWI) produced by liquid die forging process were investigated. the wear tests were performed with the MLD-10 abrasive wear testing machine, using SiO2 abrasive and with four impact energies of 1.5 J, 2.5 J, 3.5 J and 4.5 J for 120 min. The results indicated that the cumulative volume loss of HCWI sample increases with the growth of impact energy, and exhibits best wear resistance under low impact condition. For given impact energy, the volume loss increases with the increasing of wear time, which shown an approximately liner tendency. The macro-morphologies, SEM images of worn surface and cross-sectional images of wear samples were observed by optical microscope and SEM, and the wear mechanism and characteristics were analyzed. Results shown that the wear characteristics is mainly based on the shallow ploughing and accompanied by plastic deformation under lower impact energy, while the fatigue peeling and embedded abrasive become the most significant characteristics when the impact energy is higher.

Fabrication of High Chromium White Iron Surface Layers on Ductile Cast Iron Substrate by Laser Surface Alloying

High chromium white iron surface layers (HWSLs) have been produced on a ductile cast iron EN-GJS-700-2 substrate by diode laser surface alloying with a direct injection of a pure chromium powder into the molten pool. The main objective of this study was to investigate the effect of laser alloying parameters on the microstructural evolution in the HWSLs. The composition of the uniformly alloyed HWSLs contained up to 14.4 wt.% Cr. Both hypoeutectic and eutectic high chromium white iron microstructures were obtained. The type and morphology of eutectic carbides are affected by both the chromium concentration in the molten pool and the solidification conditions. With increasing chromium content, the fraction of eutectic regions in the hypoeutectic HWSLs increases and the eutectic carbides become progressively smaller. The rodtype morphology of the M7C3 eutectic carbides was dominant in the eutectic HWSLs. An average hardness of the HWSLs was influenced by the size of carbide precipitations, and was 675 HV and 650 HV for hypoeutectic and eutectic compositions, respectively.

Effect of in situ formed TiCx grains on the microstructural modification of high chromium white iron

High chromium white irons have excellent abrasion resistance due to the presence of hard eutectic M7C3 (M = Fe, Cr) carbides in a ferrous matrix. However, the appearance of large and coarse M7C3 carbides is detrimental to the performance of high chromium white irons. To modify the microstructure, in situ decomposition of Ti3AlC2 to TiCx which is expected to inhibit the growth of M7C3 in a high chromium white iron has been adopted in the present study. The in situ formed TiCx effectively refined the M7C3 carbide structure. The influences of Ti3AlC2 content, sintering temperature and heating rate on the microstructural evolution of high chromium white iron were investigated. Influencing factors on the size and dispersion of the TiCx grains in the ferrous matrix have been analyzed. A modified microstructure with a fine eutectic M7C3 structure and a homogenous distribution of small round TiCx can be achieved by optimization of temperature and dwell time. X-ray diffraction, differential scanning calorimetry and scanning electron microscopy were used to investigate phase composition, phase transition and microstructure of materials.

Effects of tungsten on the microstructure and on the abrasive wear behavior of a high-chromium white iron

In the present study, systematic additions of tungsten (up to 10.3wt%) and their effects on the microstructure, hardness, microhardness, and abrasive wear of 17%-Cr white iron was analyzed. Six high-chromium iron alloys with different tungsten additions were melted in an open induction furnace and cast into sand molds to obtain 50-mm×25-mm cross-sectional bars. The alloys were characterized by optical and electronic microscopy, energy dispersive spectroscopy, and X-ray diffraction. The bulk hardness and microhardness of the different phases of the microstructure (matrix and carbides) were measured in the as-cast conditions and after a destabilization heat treatment at 950°C for 45min. Abrasive wear resistance tests were undertaken for the different irons according to the ASTM G65 standard in both as-cast and heat-treated conditions. The results show that, when tungsten is added up to 4wt%, it partitions either to the matrix or to the M7C3 carbide, causing a moderate strengthening in both phases and contributing to an increase in the overall hardness of the alloys. When tungsten additions are higher than 4%, the presence of harder M2C and M6C carbides is prevalent in the microstructure and the bulk hardness of the alloys increased. The wear behavior was found to be consistent with the hardness values; an increase in the wear resistance occurred as the tungsten additions were increased. However, such an increase in the wear resistance is not considerable (just 13% higher for 10.3% tungsten addition to the iron). Tungsten was found not to have an important effect on the secondary carbide precipitation during heat treatment, and the wear behavior had the same trend as that in the as-cast alloys. The results are discussed in terms of the partition of tungsten to the carbide and matrix and on its tendency to form harder M6C-type carbides.