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.     

The particle size effect on abrasive wear of high-chromium white cast iron mill balls

Granite grinding tests, under dry and wet conditions, were performed to assess the influence of abrasive particle size to the wear behavior of martensitic high-chromium white cast iron mill balls. The tests were performed, at first, using raw granite particle sizes between 0.074 and 19.1 mm, and then with coarse and fine granite fractions obtained after screening the raw granite in a 3.36 mm sieve. It is demonstrated that the relative particle/ball size relationship is the determining parameter to ball wear. The highest ball wear rates were observed for fine granite grinding under dry (120 mg/cycle) and wet (129 mg/cycle) conditions. The lowest wear rate (ca. 50 mg/cycle) was observed for coarse granite grinding (dry and wet). These different results were attributed to the different size relationships between grinding body diameter and granite particles size. For wet-grinding of raw granite, the mineral components may influence significantly the wear behavior. Feldspar can act as a bonding agent, gluing fine quartz particles to the coarse granite and to the balls surface and turning the dependence of the relationship between the relative sizes of ball and granite particle less important to the wear process. This explains why wet-grinding of raw granite results in a ball wear two times greater (106 mg/cycle) than dry-grinding (51 mg/cycle).     

白口铸铁电火花表面强化研究

白口铸铁常被用于要求耐磨的工作表面,改善白口铸铁表面的耐磨性具有现实应用价值.利用金相分析、X射线衍射分析及显微硬度和耐磨性测试等手段,对白口铸铁表面进行电火花强化所得强化层的性能进行了研究,结果表明对白口铸铁进行电火花强化可以赋予其表层更高的硬度和更好的耐磨性.     

离心铸造合金白口铸铁轧辊的研究

应用离心铸造方法,研制CrMoWVNb白口铸铁轧辊。分析合金元素在轧辊中的作用及裂纹产生原因,提出了消 除裂纹措施并应用于高速线材轧机预精轧机架,使用寿命达到高镍铬无限冷硬铸铁轧辊的4～5倍。     

Particle size effect on abrasion resistance of mottled cast iron with different retained austenite contents

Effects of particle abrasive sizes on wear resistance of mottled cast iron with different retained austenite contents were studied. Abrasive wear tests using a pin test on alumina paper were carried out, using abrasive sizes between 16 μm and 192 μm. Retained austenite content of the matrix was determined by X-ray diffraction. The wear surface of samples and the alumina paper were examined by scanning electron microscopy for identifying the wear micromechanism. The results show that at lower abrasive sizes the mass loss was similar for the iron with different austenite contents. However, at higher abrasive sizes the samples with higher retained austenite content presented higher abrasion resistance. For lower abrasive sizes tested, samples with higher and lower retained austenite content both presented microcutting. On the other hand, the main wear micromechanism for the samples with higher retained austenite content and higher abrasive sizes was microploughing. The samples with lower retained austenite content presented microcutting and wedge formation at higher abrasive sizes. Higher abrasive size induced more microcutting in samples with lower retained austenite. The iron with lower retained austenite content presented wider grooves for the different abrasive sizes measured. SEM on the abrasive paper used on samples with higher retained austenite showed continuous and discontinuous microchips and the samples with lower retained austenite showed discontinuous microchips at 66 and 141 μm. This research demonstrates the relation between abrasive size, wear resistance, groove width and wear micromechanism for mottled cast iron with different retained austenite contents.     

The influence of surface oxidation on the wear resistance of cast iron

This paper reports a study of the influence of surface oxidation on the wear resistance of ductile iron, grey iron and vermicular iron during dry sliding friction. The mechanisms of wear are also reported. This study shows that the effect of surface oxidation (formed under normal atmospheric conditions) on the wear rate depends on the complex functions of graphite morphology and matrix structure. Generally the presence of surface oxidation decreases the wear rate of grey iron but increases the wear rate of ductile iron and vermicular iron when the cast iron has high hardness. This trend is reversed for low hardness cast iron.     

Sliding wear of graphite crystallized chromium white cast iron

The effects of sliding velocity, heat-treatment and graphite shape on sliding wear of graphite crystallized chromium white cast iron were studied. Two types of graphite crystallized chromium white cast irons having flaky or spheroidal and another type of 2.6C–15Cr white cast iron were prepared for this study. The effect of sliding velocity on wear resistance was studied by the Okoshi type and pin-on-disk type wear tests on materials which have experienced “as cast” and “heat-treated” conditions. The Okoshi type wear test results are divided into two relationships depending on sliding velocity or distance. Two regimes, initial wear and steady-state wear, existed for wear loss and sliding distance. A characteristic form of wear curve with a peak and a minimum was obtained when correlating wear loss and sliding velocity. The wear resistance of graphite crystallized chromium white cast irons were superior to that of 2.6C–15Cr white cast iron. In the results of pin-on-disk tests, there was no clear difference in the reported wear loss and friction coefficient among the alloys. However, an opposite tendency has appeared in the wear loss and friction coefficient: the wear loss value reached a peak in the wear curve at 0.52 m/s, while the friction coefficient reached a minimum at 0.52 m/s.     

Abrasive wear of WC-FeAl composites

The abrasive wear behavior of tungsten-carbide iron-aluminide composite materials was investigated using a pin-on-drum wear-testing machine. Samples were prepared by uniaxially hot pressing blended powders. The wear rates of specimens containing 40 vol.% matrix of atomic composition, Fe₆₀Al₄₀, were measured and results compared with those of conventional WC-10 vol.% Co hardmetal. They were found to be comparable to those of WC-10% Co hardmetal, when abraded by 120 μm SiC papers under identical conditions. The wear resistance of WC-Fe₆₀Al₄₀ composites increased with reduction in WC-grain size and associated with increase in composite hardness. Scanning electron microscopy revealed that the wear surfaces of WC-40% Fe₆₀Al₄₀ composites and WC-Co hardmetal were similar in appearance. The higher hardness and work hardening ability of Fe₆₀Al₄₀ binder, as compared to Co metal, are believed to be responsible for the excellent abrasive wear resistance of WC composites containing iron aluminide binder.     

Mechanism of ploughing wear of martensite nodular cast iron

The mechanism of ploughing wear of martensite nodular cast iron has been investigated by means of elastic contact theory, stress interferometry, and scanning electron microscopy. Stress distributions in the contact area are plotted through numerical quadrature. The results show that the formation of cracks is between 0.2a and 0.5a (a is the radius of the contact curve). The driving force to produce crack extension along the Y axis is τ_yzmax and the extension direction is 45° to the horizontal. The driving force to produce crack extension along the X axis is either τ_x or τ_xzmax and the direction of crack extension is 37° to the horizontal.     

Effect of phosphide and matrix microstructures on the dry sliding wear of grey cast iron

The effect of a continuous phosphide network in matrices of pearlite, ferrite, martensite, and tempered martensite has been investigated on the dry wear of a grey iron, sliding at a speed of 1.5 m s⁻¹ with stresses of 0.5 and 2.0 MPa against cast iron. A running-in period was observed with a 0.2% P iron, whereas no running-in was observed with the 1.0% P irons. The presence of a continuous phosphide network reduced the wear rate of the pearlite iron by a factor of 0.25. In the weaker matrices (pearlite, ferrite, and tempered martensite) the phosphide network stiffened the matrix, fractured, and formed a particulate composite of phosphide in the deformed surface which resisted deformation. The wear rates and wear mechanisms of the irons are presented and discussed.     

Sliding wear response of a grey cast iron: Effects of some experimental parameters

This investigation pertains to the influence of some test parameters like applied load, sliding speed and test environment on the sliding wear behaviour of a grey cast iron. Properties studied were wear rate, frictional heating and friction coefficient in dry and oil lubricated conditions. The wear response of the samples has been discussed in terms of specific characteristics like load bearing, lubricating and cracking tendency of different microconstituents of the cast iron. Examination of wear surfaces, subsurface regions and debris particles has also been carried out to understand the operating wear mechanisms and further substantiate the observed response of the samples.     

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.     

Dry sliding wear response of zinc-based alloy over a range of test speeds and loads: a comparative study with cast iron

This study pertains to the observations made during the sliding wear response of a zinc-based alloy in different test conditions. The effects of sliding speed and load on the wear behaviour of the alloy have been studied. The properties evaluated were wear rate, frictional heating and coefficient of friction. The wear performance of the zinc-based alloy has been compared with that of a conventional cast iron in identical test conditions. The wear rate of the samples increased with applied load and sliding speed while the seizure resistance (load) deteriorated with speed. The zinc-based alloy exhibited less wear rate and reduced frictional heating than that of the cast iron while friction coefficient followed a reverse trend. Observed wear response of the samples has been discussed in terms of specific features like lubricating, load carrying, microcracking and thermal stability of various microconstituents of the samples, and substantiated further through the features of wear surfaces, subsurface regions and debris.     

Abrasive wear behaviour of laser sintered iron–SiC composites

Direct metal laser sintering (DMLS) is one of the popular rapid prototyping technologies for producing metal prototypes and tooling of complex geometry in a short time. However, processing of metal matrix composites (MMCs) by laser sintering is still in infant stage. Thermal cracks and de-bonding of reinforcements are reported while processing MMCs by laser sintering process. There are reports on use of metallic-coated ceramic reinforcements to overcome these problems. The present investigation is aimed at using nickel-coated SiC in developing iron composites by DMLS technique and to characterize its abrasive wear behaviour.Microstructure, microhardness, and abrasive wear tests have been carried out on both DMLS iron and its composites sintered at a laser scan speed of 100 mm/s. Abrasion wear tests have been carried out using a pin-on-disc type machine. SiC abrasive papers of grit size 60, 80, and 150 having an average particle size of 268, 192, and 93 μm, respectively, have been used. Load was varied between 5 and 25 N in steps of 5, while the sliding distance and sliding velocity of 540 m and 2.5 m/s, respectively was adopted for all the tests. Optical, scanning electron micrograph and surface roughness observation of worn surfaces have been undertaken.An increase in microhardness and a decrease in density of the laser sintered iron–SiC composites was observed with increase in SiC content. The abrasive wear resistance of composites increases with increased content of SiC in iron matrix. For a given grit size of SiC abrasive paper, at all the loads studied, iron–SiC composites exhibit excellent abrasive wear resistance. Increase in abrasive wear was observed with the increase in abrasive particle size.     

Single asperity abrasion of coated nodular cast iron

In the sliding contact between a rigid indenter and a softer deforming surface, a wear scar is formed in the softer surface. This wear scar consists of a groove flanked by two shoulders, where part of the material from the groove is transferred to these shoulders and the rest is actually removed from the surface as wear debris. The proportion of actually removed material is characterised by the degree of wear parameter ξ. This paper focusses on the experimental determination of the degree of wear for nodular cast iron with a range of hard surface layers. This is done using a pin-on-disk set-up that is located in the chamber of a scanning electron microscope. From these experimental results, an empirical model that describes the volumetric abrasive wear of coated nodular cast iron in single indenter scratching is developed.     

Abrasive wear resistance of textured steel rings

The fundamental aim of the present research is to study the effect of dimple shape and area density on abrasive wear in lubricated sliding. The other aims are to recommend a method of obtaining the local linear wear of a textured ring on the basis of profilometric measurement and to analyse the changes in the surface topography of this ring with selection of parameters that could monitor the “zero-wear” process.The experiments were conducted on a block-on ring tester. The stationary block made from cast iron of 50 HRC hardness was ground. The rotated ground ring was made from 42CrMO4 steel of 32 HRC hardness. The rings were modified by a burnishing technique in order to obtain surfaces with oil pockets. Oil pockets of spherical and of drop shape were tested. The pit-area ratios were in the range: 7.5–20%. The tested assembly was lubricated by oil L-AN 46. Because of the great hardness of the co-acting parts the wear resistance test was carried out under artificially increased dustiness conditions. The dust consists mainly of SiO₂ and Al₂O₃ particles. Measurement of local microscopic ring wear was made using a three-dimensional scanning instrument. The tendencies of ring surface topography changes during wear were analysed. Various methods of obtaining the local wear value during a low wear process were proposed and compared. We found that a spherical shape of dimples was superior to a drop shape with regard to wear resistance of steel rings.     

Influence of load and speed on wear characteristics of grey cast iron in dry sliding — selection for minimum wear

The wear of grey cast iron in dry sliding conditions has been studied with the aims of (1) finding the influence of working conditions on the wear rate, and (2) determining the region of speed and load where low wear is accomplished. Grey cast iron with flake and nodular graphite was submitted to investigation using a pin-on-disc machine. The results indicate that the flake graphite cast iron is more suitable for applications at speeds greater than 4 m s⁻¹ and lower loads, while nodular cast iron has greater wear resistance at lower speeds in the range of loads investigated - from 50 N cm⁻² to 200 N cm⁻²     

Abrasive wear of metals

Abrasive wear resistance, abrasive wear mode and abrasive wear rate are discussed with experimental results, and abrasive wear theories are introduced and explained from the viewpoints of effective work for plastic deformation and fracture.     

浅析高铬白口铸铁磨球的铸态组织设计

在传统工艺的实际生产条件下，高铬白口铸铁磨球易形成较大的内应力，这是导致此类磨球生产和服役条件失效的主要原因。分析热加工全过程可知磨球铸态组织设计的重要性在于期望目标下的铸态组织完全可能仅需采用亚温处理工艺就可达到组织和性能要求，从而不仅从根本上解决了内应力这一中心问题，而且可降低能耗、成本，改善作业环境和缩短生产周期。     

Tempering temperature effects on abrasive wear of mottled cast iron

The effects of different tempering temperatures (300–600 °C) on abrasive wear resistance of mottled cast iron were studied. Abrasive wear tests were carried out using the rubber-wheel test on quartz sand and the pin test on Al₂O₃ abrasive cloths. The retained austenite content of the matrix was determined by X-ray diffraction. The wear surface of the specimens was examined by scanning electron microscopy for identifying the wear micromechanism. Bulk hardness and matrix hardness before and after the tests were measured. The results showed that in the two-body (pin-on-disc test) system, the main wear mechanism was microcutting and high matrix hardening was presented. The wear rates presented higher correlation with the retained austenite than with the bulk and matrix hardness. In the three-body system (sand–rubber wheel), the wear surfaces presented indentations due to abrasive rolling. The wear rates had better correlation with both the bulk and matrix hardness (before and after the wear test) than with the retained austenite content. There are two groups of results, high and low wear rates corresponding to each tribosystem, two-body abrasive wear and three-body abrasive wear, respectively.