Erosive wear behaviour of weld hardfacing high chromium cast irons: effect of erodent particles

Five commercial hardfacing high chromium cast iron alloys were deposited by flux cored arc-welding method. The solid particle erosion studies were carried out using air blast type erosion test rig with 125–150 μm cement clinker, 125–150 μm blast furnace sinter, 100–150 μm silica sand and 125–150 μm alumina particles at a velocity of 50 m s⁻¹ and at impingement angles of 15–90°. The observed erosion rates were rationalised in terms of relative hardness of erodent particles and ability of erodent particle to cause gross fracture of the carbides. The dependence of erosion rate on impingement angle was found to be quite weak for hardfacing high chromium cast iron alloys. However, significant differences were observed in the ranking of the alloys when eroded with different erodent particles. The presence of large volume fraction of carbides proved to be beneficial to the erosion resistance when the erodent particle were softer than the carbides. With silica sand particles at normal impact and with alumina particles large volume fraction of carbides proved detrimental to the erosion resistance. The operating erosion mechanisms involved small-scale chipping, edge effect, indentation and fracture and fatigue.     

Abrasive wear resistance of spheroidal vanadium carbide cast irons

The effect of the chemical composition and heat treatment on the microstructure and abrasive wear resistance of V-Mn, V-Ni-Cr, and V-Mo spheroidal vanadium carbide cast irons (18–23 vol %) has been studied. The wear resistance has been determined under conditions of wear by abrasives with various hardnesses, i.e., corundum and quartz and compared to that of high-chromium cast iron with 13% Cr. It has been found that the advisability of using high-vanadium cast irons is governed by the hardness of the abrasive. When a hard abrasive, i.e., corundum was used, V-Mo cast iron with the maximum concentration of spheroidal VC carbides, which were uniformly distributed in the martensitic matrix, had the highest wear resistance. When a soft abrasive, i.e., quartz, was applied, high-chromium cast iron with a hardness of 68 HRC, which contained the largest amount of M₇C₃ carbides, was more wear-resistant. In the course of isothermal exposure at 300–1000°C, V-Ni-Cr and V-Mo cast irons with an austenitic structure had high resistance to phase and structural transformations. However, the properties and microstructure of V-Mo cast irons with a martensitic matrix depended strongly on the temperature of exposure during heat treatment.     

Solidification and abrasion wear of white cast irons alloyed with 20% carbide forming elements

Three different white cast irons with compositions of Fe–3%C–10%Cr–5%Mo–5%W (alloy no. 1), Fe–3%C–10%V–5%Mo–5%W (alloy no. 2) and Fe–3.5%C–17%Cr–3%V (alloy no. 3) were prepared in order to study their solidification and abrasion wear behaviors. Melts were super-heated to 1873 K in a high frequency induction furnace, and poured at 1823 K into Y-block pepset molds. The solidification sequence of these alloys was investigated. The solidification structures of the specimens were found to consist of austenite dendrite (γ); (γ+M₇C₃) eutectic and (γ+M₆C) eutectic in the alloy no. 1; proeutectic MC; austenite dendrite (γ); (γ+MC) eutectic and (γ+M₂C) eutectic in the alloy no. 2, and proeutectic M₇C₃ and (γ+M₇C₃) eutectic in the alloy no. 3, respectively.

A scratching type abrasion test was carried out in the states of as-cast (AS), homogenized (AH), air-hardened (AHF) and tempered (AHFT) using the abrasive paper with 120 mesh SiC and 10 N application load. In all the specimens, the abrasion wear loss was found to decrease in the order of AH, AS, AHFT and AHF states. Abrasion wear loss was lowest in the specimen no. 2 and highest in the specimen no. 1 except for the as-cast and homogenized states in which the specimen no. 3 showed the highest abrasion wear loss. The lowest abrasion wear loss of the specimen no. 2 could be attributed to the fact that it contained proeutectic MC carbide, eutectic MC and M₂C carbides having extremely high hardness. The matrix of each specimen was fully pearlitic in the as-cast state but it was transformed by heat-treatments to martensite, tempered martensite and austenite. From these results, it becomes clear that MC carbide is a significant phase to improve the abrasion wear resistance of white cast iron.     

Effect of oxidation on erosive wear behaviour of boiler steels

High efficiency of thermal processes in energy applications is available at high temperatures. The ashes and other components in fluidized-bed boilers act as an erodent particles provoking the competition and interaction between the oxidation and erosion processes. The aim of the study was to investigate the effect of oxidation on the erosive behaviour of boiler steels. Tests were performed using specially developed device allowing testing in either oxidizing or protected atmosphere in a cyclic mode. Several parameters are proposed and the assessment is done on their applicability to describe the erosion–oxidation phenomena under different impact angles. It is shown that under specific conditions oxide scales provide improved wear resistance for some steels, particularly austenitic ones, that enables reduced material losses.     

Comments on “The unlubricated wear of cast irons”

A numerical solution is developed for the equations governing the laminar hydrodynamic flow in a sector-shaped thrust bearing with its axis parallel to but offset from the rotational axis. The lubricant viscosity is assumed to be a function of the temperature distribution in the fluid film. The rotating plate is assumed to be an isothermal component and the heat conduction equation in the stationary component is solved simultaneously with the governing equations of the fluid film. Thermal effects are shown to be pronounced especially at large values of offset from the rotational axis.     

The wear behaviour of high-chromium white cast irons as a function of silicon and Mischmetal content

The sliding wear behaviour of high-chromium white cast iron (16.8% Cr) has been examined as a function of silicon and Mischmetal alloy additions (1, 2, 3 and 5% Si and 0.1 and 0.3% Mischmetal). Such additions are known to modify the structure, but there is considerable controversy as to the exact effect. Silicon was found to refine the dendritic structure and increased the eutectic carbide volume fraction. However, for contents above 3%, transformation of the austenitic matrix to pearlite occurred in preference to martensite. Mischmetal additions reduced the austenite dendrite arm spacing, but did not have a significant effect on the carbide structure. The wear behaviour was investigated for each alloy in the as-cast (austenitic matrix) and hardened (martensitic) conditions using a block on ring configuration in pure sliding in the load range 42–238 N for a distance of 70 km against a hardened M2 steel counterface. For low loads (42 and 91 N), all the alloys showed a similar wear rate (3×10⁻⁴ to 4×10⁻⁴ mm³/m), associated with the formation of a thin (3 μm) oxide film of Fe₂O₃, the formation of very fine debris and a small depth of deformation below the worn surface (7 μm). For higher loads, wear was a strong function of microstructure, and was associated with a thicker film of the oxides Fe₂O₃ and Fe₃O₄ and greater depths of deformation. The iron with 2% silicon exhibited the best performance with a wear rate of 7×10⁻⁴ mm³/m and this was attributed to its finer structure and the formation of a thicker oxide film. In contrast, the iron with 5% silicon exhibited the worst performance, with a wear rate of 14×10⁻⁴ mm³/m, attributed to the pearlitic matrix. A linear relationship was observed between the depth of carbide fracture and the wear rate. The relationship between microstructure and wear mechanism is discussed.     

Effect of carbide fraction and matrix microstructure on the wear of cast iron balls tested in a laboratory ball mill

The effect of carbide volume fraction from 13 to 41% on the wear resistance of high chromium cast irons was evaluated by means of ball mill testing. Martensitic, pearlitic and austenitic matrices were evaluated.

The 50-mm diameter balls were tested simultaneously in a 40 cm diameter ball mill. Hematite, phosphate rock and quartz sand were wet ground. The tests were conducted for 200 h.

Quartz sand caused the highest wear rates, ranging from 6.5 to 8.6 μm/h for the martensitic balls, while the wear rates observed for the phosphate rock ranged from 1.4 to 2.9 μm/h.

Increasing the carbide volume fraction resulted in decreased wear rates for the softer abrasives. The almost complete protection of the matrix by carbides in eutectic microstructures caused the eutectic alloy to present the best performance against hematite or phosphate rock. The opposite effect was observed for the quartz sand. The quartz abrasive rapidly wears out the matrix, continuously exposing and breaking carbide branches. A martensitic steel presented the best performance against the quartz abrasive.

With phosphate rock, the wear rate of 30% carbide cast irons increased from 1.46 to 2.84 and to 6.39 μm/h as the matrix changed, respectively, from martensitic to austenitic and to pearlitic. Wear profiles of worn balls showed that non-martensitic balls presented deep subsurface carbide cracking, due to matrix deformation. Similar behavior was observed in the tests with the other abrasives.

In pin-on-disc tests, austenitic samples performed better than the martensitic ones. This result shows that pin tests in the presence of retained austenite can be misleading.     

Influence of alumina dispersoid and test parameters on erosive wear behaviour of a cast zinc–aluminium alloy

Observations made pertaining to the erosive wear characteristics of a cast zinc-based alloy and its composite containing 10 wt.% (corresponding to 11.2 vol.%) alumina particles have been presented in this study. Matrix alloy has also been tested under identical test conditions in order to examine the role played by second phase alumina particles on the erosive wear resistance of the matrix alloy. Eroded surfaces and subsurface regions of the specimens were also characterized to understand the operating wear mechanisms.The composite exhibited higher erosive wear resistance (inverse of erosive wear rate) than the unreinforced matrix alloy in general. Further, the wear rate increased with increasing impingement velocity as also evident from higher surface damage. Increasing angle of impingement at lower impinging velocity led to reduced erosive wear rate. On the contrary, the erosive wear rate increased initially with impingement angle, attained the peak and then decreased at still higher angles at the higher impingement velocity. The eroded surfaces showed more abrasion grooves at lower impingement angle and greater tendency of crater formation at higher angles of attack. In case of the composite, protrusion and fracture of the dispersoid phase was also noted. The composite also revealed less severe surface and subsurface damage than the matrix alloy.     

Effect of structural features on erosion resistance of cast irons

Erosion resistance of four types of cast iron of different microstructures and graphite morphologies (viz., grey cast iron, compacted graphite iron, spheroidal graphite iron and austempered ductile iron) was evaluated in three different erosive media. Results indicate that austempered ductile iron has the highest erosion resistance in all three media, followed by spheroidal graphite iron, compacted graphite iron and grey cast iron, in that order. Graphite morphology has a significant effect on the erosion resistance of these irons in quartz-water and iron oxide-oil slurry. However, the matrix microstructure determines the erosion resistance of these irons in quartz-oil slurry. The parameter H/E (which is the ratio of the Brinell hardness number to Young's modulus of the material) has been found to be a good indicator of erosive wear in quartz-oil slurry.     

Oxidation and wear behaviour of carbide cutting tools

The oxidation and wear behaviour of carbide cutting tools was studied by service simulation tests and the machining of cast iron was examined in an oxidising environment and the presence of a direct electric current. The oxides were investigated by chemical analysis, X-ray diffraction and optical microscopy. The rate of oxidation increases with increase in current flow and the composition of the oxide depends upon the magnitude of the current. The oxide structure is affected by the amount of current.     

Transition wear behaviour of an abrasion-resistant cast iron

The transition wear behaviour of an abrasion-resistant cast iron was examined using a laboratory test apparatus which models sliding abrasive wear. Low carbon and high carbon 15Cr-3Mo cast iron in the as-cast and hardened condition were used. Loads from 7 to 156 N were applied via a diamond indenter which was used to cut the grooves in the specimen surfaces. The volume of the grooves and the wear coefficients were calculated. A transition in wear was observed when the critical plastic deformation was exceeded. The transition is explained by the onset of unstable cracking in the process of particle separation; this is revealed by scanning electron microscopy.     

Investigating the effects of microstructure on the wear mechanisms in lamellar cast irons via microscratch tests

This work investigates the effects of microstructure on the wear mechanisms in lamellar cast irons using a microscratch test. Various applied loads and indenter geometries were utilised. The results indicate that the surface damage depends on the indenter geometry, the penetration depth, the orientation and the depth of the graphite flakes. Increasing the applied load and the attack angle increases the friction coefficient, the tangential force and its fluctuation. Beyond a certain load, the friction coefficient remains nearly constant. The proposed schemes explain the role played by both the matrix and graphite in the wear process.     

Effect of microstructure on erosive wear behavior of SiC ceramics

Grit blasting wear tests (gas-blast method) have been performed on three SiC structural ceramics by silicon carbide particles using different impingement angles and blasting velocities at room temperature. The three SiC ceramics were sintered with different technologies of pressureless sintering, hot pressing and hot isostatic pressing respectively. The damage to the surfaces that has been observed to occur in the wear of test ceramics is described in detail. The major part of the paper concentrates on the different surface microstructure of test ceramics and the effect of the microstructure on wear.     

High stress abrasive wear behaviour of aluminium hard particle composites: Effect of experimental parameters, particle size and volume fraction

High stress abrasive wear behaviour of aluminium alloy (ADC-12)–SiC particle reinforced composites has been studied as a function of applied load, reinforcement size and volume fraction, and has been compared with that of the matrix alloy. Two different size ranges (25–50 and 50–80 μm) of SiC particles have been used for synthesizing ADC-12–SiC composite. The volume fraction of SiC particles has been varied in the ranges from 5 to 15 wt%. It has been noted that the abrasive wear rate of the alloy reduced considerably due to addition of SiC particle and the wear rate of composite decreases linearly with increase in SiC content. It has also been noted that the wear resistance of composite varies inversely with square of the reinforcement size. The wear rate of the alloy and composite has been found to be a linear function of applied load but invariant to the abrasive size; at critical abrasive size, transition in wear behaviour is noted. This has been explained through analytically derived equations and wear–surface examination.     

Erosive and erosive-corrosive wear behaviour of cast nitrogenated stainless steels

Corrosive-erosive and erosive wear in cast low nickel nitrogenated austenitic stainless steels is higher than that in a standard CF8 grade steel. Niobium addition (I wt.%) to such (FeCrNiMnN) stainless steels, however, improves their resistance to both corrosive-erosive and erosive wear.     

Comparison of the sliding wear process of various cast irons in the laser-surface-melted and as-cast forms

The sliding wear characteristics of cast irons having a range of compositions and initial graphite forms have been determined in both as-cast and laser-surface-melted conditions using a pin-on-ring test configuration. Observed differences in equilibrium wear behaviour between the as-cast alloys were principally in the mild-to-severe transition load and the nature of the severe wear process. Such effects are interpreted in terms of the mean interparticle spacing of graphite in the microstructure which determines the relative propensity for subsurface crack propagation during wear. The ledeburitic structures produced by laser surface melting of the cast iron substrates acted to stabilize a regime of mild equilibrium wear with substantially lower wear rates than for the mild oxidative wear of the as-cast microstructures. Metallographic observations of the laser-melted layer have identified a wear process consisting of fine polishing abrasion.     

FEM analysis of erosive wear

Surface damage caused by the impact of dispersed particles in gas or liquid flow is called “erosion”. Much attention has been paid to this phenomenon as one of the most serious problems to be solved, particularly concerning pipe-bends or valves in pneumatic conveying systems. But the phenomena of erosive wear are so complicated and vary depending on the factors of not only the kinds of material, hardness, shapes, sizes and mechanical properties of the particles, but also of blasting angles and velocity.

For the purpose of this study, mild steel was prepared and erosion wear tests were carried out. Steel grits were impacted against target materials at different incident angles. The results showed that the wear losses varied markedly as a function of the impact angles, and that the maximum wear occurred at specific angles. Maximum wear occurred at 20–30° for mild steel, and 60° for ductile iron. This impact angle dependence of wear was simulated by Tabor’s theory and FEM which could analyze the plastic deformation of alloy surface as a result of a single particle impact. In the case of both mild steel and ductile cast iron, it was found that the impact angles play a very important and valid role in the corrosion process.     

Effect of bulk heat treatment and plasma surface hardening on the microstructure and erosion wear resistance of complex-alloyed cast irons with spheroidal vanadium carbides

The results of an investigation of the effect of bulk quenching from temperature in the range of 760–1050°C, cryogenic treatment (–196°C) and surface plasma hardening on the abrasive-erosion wear of frugally alloyed V–Cr–Mn–Ni cast irons with spheroidal vanadium carbides have been presented in this article. It has been found that cast irons containing 5.0–7.5% V, 4.5–9.0% Cr, and 5.5–5.7% (total) of Mn and Ni after heat treatment have a 2–3-fold advantage in wear resistance compared to the prototype high-vanadium cast iron (11.9% V, 12.9% Mn). The maximum wear resistance of cast irons studied is achieved by quenching at 760°C followed by plasma surface hardening, as well as quenching at 840°C, followed by cryogenic treatment. These treatments result in the formation of an optimum microstructure that consists of spheroidal vanadium carbides, eutectic carbides M₇C₃, and a martensite-austenite matrix reinforced by secondary carbides. The increase in quenching temperature leads to an increase in the amount of residual austenite and decrease in the erosive wear resistance of cast irons.     

Solid particle erosion behaviour of hardfacing deposits on cast iron—Influence of deposit microstructure and erodent particles

Solid particle erosion (SPE) behaviour of different hardfacing electrodes deposited on gray cast iron (ASTM 2500) was studied using quartz sand and iron ore as erodent particles. Erosion test was carried out as per ASTM G76 test method. Considerable differences in erosion rates were found among different hardfacing electrodes at normal impact. Both volume fraction of carbides and type of carbides played an important role in the erosion behaviour of the deposits when quartz sand was used as erodent particles. On the other hand, only volume fraction of carbides irrespective of carbide type mainly controlled the erosion rate of the same deposits when iron ore was used as erodent particles. Such difference is attributed due to difference in metal removal mechanisms by the two erodent particles used. Hard quartz sand particles were capable of causing damage to most of the carbides while relatively softer iron ore particles were unable to fracture any carbides present in the microstructures. Furthermore, relatively brittle matrix led to high erosion rate which is significant in case of quartz sand as erodent, but not in case of iron ore particles. Like abrasion resistance, hardness is not a true index of erosion resistance of hardfacing deposits.     

Reduction of wear via hardfacing of chisel ploughshare

The objective of this study was to increase the wear resistance by covering the chisel ploughshare produced from low-alloy steel with three different hard facing electrodes. Comparative wear tests on a regular share and three kinds of hardfacing with electrodes were conducted in the field and laboratory. These three different hardfacing electrodes, which are designated EH-600, EH-350 and EH-14Mn, were used for hardfacing. The wear rate in the laboratory and in field tests was found to be significantly different statistically. When the cost is taken into consideration; EH-600 and EH-350 have been found to be the best hardfacing electrodes.