The effect of boron on the abrasive wear behavior of austenitic Fe-based hardfacing alloys

The effect of boron on the abrasive wear behavior of the austenitic Fe–Cr–C–Si–B hardfacing alloys was investigated with varying boron concentration. It was found that the abrasive wear resistance of the hardfacing alloys increased up to 50% compared to that of boron-free alloys with increasing boron concentration. The mechanism of the abrasive wear resistance changed at 0.6 wt.% boron. Below 0.6 wt.% boron concentration, the abrasive wear resistance was improved almost linearly and strain-induced martensitic transformation was considered as the controlling factor for improving the resistance. Above 0.6 wt.% boron, it was observed that the primary borides started to precipitate. Further increase in boron concentration was not able to enhance the resistance due to the negligible change of primary borides’ size and volume fraction. With these results, it was concluded that two different effects of boron on the wear resistance of the austenitic Fe–Cr–C–Si–B hardfacing alloys existed depending on the boron concentration.     

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.     

Abrasive wear resistance of starch consolidated and sintered high speed steel

The abrasive wear resistance of starch consolidated (SC) and super solidus liquid phase sintered (SLPS) M3/2 high speed steel (HSS) samples have been evaluated by a two-body micro-abrasion test (low stress abrasion), using 6 μm diamond abrasive particles, and a three-body abrasion test (high stress abrasion), using significantly larger abrasive particles of blast furnace slag (600 HV) and silicon carbide (2400 HV), respectively. In the tests a commercial powder metallurgical (PM) HSS was used as a reference material.The results show that the microstructure of the SC and SLPS HSS samples is strongly dependent on the sintering temperature used. With increasing temperature the microstructure ranges from a porous (5% porosity) relatively fine grained low temperature sintered microstructure to a fully dense relatively coarse grained high temperature sintered microstructure with eutectic carbides/carbide networks. However, despite the pronounced microstructural differences displayed by the as-sintered HSS microstructures these show a relatively high abrasive wear resistance, comparable with that of a HIPed HSS reference, both under low and high stress abrasion contact conditions. The characteristic features of the low and high temperature sintered microstructures, i.e. the pores and coarse eutectic carbides/carbide networks, only show a limited impact on the wear rate and the wear mode (dominant wear mechanism). The results obtained imply that near net shaped components manufactured by starch consolidation and super solidus liquid phase sintering might be of interest in tribological applications.     

Wear behaviour of Al/(Al2O3p+SiCp) hybrid composites

In this study, dry sliding metal–metal and metal–abrasive wear behaviours of the aluminium matrix hybrid composites produced by pressure infiltration technique were investigated. These composites were reinforced with 37 vol% Al₂O₃ and 25 vol% SiC particles and contained up to 8 wt% Mg in their matrixes. While matrix hardness and compression strength increased, amount of porosity and impact toughness decreased with increasing Mg content of the matrix. Metal–metal and metal–abrasive wear tests revealed that wear resistance of the composites increased with increasing Mg addition. On the other hand, abrasive resistance decreased with increasing test temperature, especially above 200 °C.     

Steels’ wear resistance definition method by their standard mechanical characteristics

The basic regularities of abrasive outwearing for steels of different structural classes are considered. The reliable function bond of steels’ wear resistance with their mechanical characteristics is proved. The correlation of toughness and plasticity with wear resistance is revealed and the new method of steels’ wear resistance definition based on the use of standard mechanical characteristics is offered. The complex criterion for steels’ wear resistance estimation at mechanical outwearing—the product of ultimate strength on relative reduction of area—(σ_b×ψ) characterizes a nature of steels’ outwearing and is reliable enough for determination of wear resistance in conditions of sliding friction, rolling friction on an abrasive and at erosive outwearing. Using offered complex criterion of steels wear resistance, it is possible to determine or estimate the wear resistances of many steels without running their wear tests. The leading role of metal science in the decision of problem of wear resistance increase for equipment working under abrasive wear conditions is marked.     

Slurry abrasion response of surface engineered Ti6Al4VELI

Titanium alloys, by virtue of their outstanding combination of properties, continue to evolve as direct replacements for steels in offshore production systems to meet the challenging offshore application conditions. However, the wider use of titanium and its alloys is frequently retarded by their reputation for poor tribological behaviour. It is because of this simple engineering scenario that comparative tribological behaviour of surface engineered Ti6Al4VELI in abrasive slurry has been evaluated to identify treatments capable of improving its wear behaviour. To best simulate potential application conditions, sliding wear tests were carried out using a block-on-wheel test configuration in abrasive mud slurry. The wear volumes lost from the surface engineered Ti6Al4VELI test blocks ranged from negligibly small for substrates plasma sprayed with either WC–Co, Ni–Cr or Mo, to approximately twice that measured for a steel test block in the cases of untreated, shot peened, electroless Ni plated and anodised Ti6Al4VELI. Hard chrome plated material and thermochemically treated material demonstrated a certain degree of wear, which however, was significantly less than that found for the steel block.     

Effect of Sintering Temperature and Atmosphere on Nonlubricated Sliding Wear of Nano-Yttria-Dispersed and Yttria-Free Duplex and Ferritic Stainless Steel Fabricated by Powder Metallurgy

The nonlubricated sliding wear behavior of nano-yttria-dispersed and yttria-free duplex and ferritic stainless steel against a diamond tip was studied. The stainless steel samples were fabricated by a conventional powder metallurgy route in which nano-yttria-dispersed and yttria-free duplex and ferritic stainless steel powders were cold compacted and then conventionally sintered at either 1000, 1200, or 1400°C in an argon atmosphere. For comparison, another set of samples was sintered at 1000°C in a nitrogen atmosphere. The wear behavior of sintered stainless steel samples against a diamond indenter was investigated using a pin-on-disc apparatus at 10 and 20 N loads and at a constant speed of 0.0041 m/s. It is proposed that yttria-dispersed stainless steels showed higher wear resistance compared to yttria-free stainless steel due to their improved hardness and density. Stainless steel sintered in a nitrogen atmosphere exhibited better wear resistance than those sintered in an argon atmosphere due to the formation of hard and brittle Cr₂N. The wear mechanisms of stainless steels against diamond were found to be mainly abrasive and oxidative. Semiquantitative analysis of the worn surfaces and wear debris confirmed the occurrence of oxidation processes during wear.     

Fretting and fretting corrosion behavior of novel micro alloyed rail steels

The fretting behavior of two novel rail steels of composition Cu–Ni and Cr–Cu–Ni has been studied and compared with that of C–Mn and Cu–Mo rail steels. The rail steels were fretted in dry condition and in 3.5% NaCl solution. All the four rail steels exhibited similar fretting behavior in dry condition. The morphological features of the wear scar surface indicated delamination process as the main wear mechanism. The wear damage in 3.5% NaCl was lower compared to that in dry condition for all the rail steels due to lubricating effect of the solution. Fretting in presence of 3.5% NaCl resulted in lower wear volume for Cu–Ni and Cr–Cu–Ni rail steels. The friction coefficient for Cr–Cu–Ni rail steel was lower than that of C–Mn, Cu–Mo and Cu–Ni rail steels. Scanning electron microscopy (SEM) showed better adherence of tribo-electro-chemical layers formed on Cu–Ni and Cr–Cu–Ni rail steel than the C–Mn and Cu–Mo rail steels. This has been related to the improved fretting corrosion behavior of Cu–Ni and Cr–Cu–Ni rail steels.     

Abrasive wear resistance of some commercial abrasion resistant steels evaluated by laboratory test methods

The aim of the present study is to evaluate the abrasive wear resistance of some potential abrasion resistant steels exposed to different types of abrasive wear contact conditions typical of mining and transportation applications. The steels investigated, include a ferritic stainless steel, a medium alloyed ferritic carbon steel and a medium alloyed martensitic carbon steel.The abrasive wear resistance of the steels was evaluated using two different laboratory test methods, i.e. pin-on-disc testing and paddle wear testing that expose the materials to sliding abrasion and impact abrasion, respectively. All tests were performed under dry conditions in air at room temperature. In order to evaluate the tribological response of the different steels post-test characterization of the worn surfaces were performed using optical surface profilometry, scanning electron microscopy and energy dispersive X-ray spectroscopy. Besides, characterization of the wear induced sub-surface microstructure was performed using optical microscopy.The results show that depending on the abrasive conditions a combination of high hardness and toughness (fracture strain) is of importance in order to obtain a high wear resistance. In the pin-on-disc test (i.e. in sliding abrasion) these properties seem to be controlled by the as-rolled microstructure of the steels although a thin triboinduced sub-surface layer (5–10 μm in thickness) may influence the results. In contrast, in the paddle wear test (i.e. in impact abrasion), resulting in higher forces acting perpendicular to the surface by impacting stones, these properties are definitely controlled by the properties of the active sub-surface layer which also contains small imbedded stone fragments.     

The unlubricated wear of sintered steels

The unlubricated wear of 10.3% porosity sintered medium-carbon and 12.8% porosity sintered low-alloy steels was investigated under different sliding conditions. Their wear characteristics were found to be similar to their non-sintered counterparts. Within this range of sliding conditions, both mild-oxidational and delamination wear took place, with the former dominating the wear processes. The oxide debris produced changed with the applied load: switching from a low-temperature oxide to a high-temperature one at higher loads. The wear rates agreed reasonably well with Archard's law and with data from other sources, suggesting that Archard's law can account for the wear rates produced by both mild-oxidational wear and delamination wear. This agreement also suggests that within the range of porosites investigated an overall framework can be established in the unlubricated wear of both sintered and non-sintered steels.     

Oil-Lubricated Fretting Behaviors of 304 Stainless Steels under Different Fretting Strokes and Normal Loads

The influence of oil lubrication on the fretting wear behaviors of 304 stainless steel flat specimens under different fretting strokes and normal loads has been investigated. The results proved that fretting regimes and fretting wear behaviors of 304 stainless steels were closely related to the fretting conditions. In general, the increase in normal load could increase wear damage during sliding wear. However, according to the results, a significant reduction in wear volume and increase in friction coefficient was observed when the normal load was increased to critical values of 40 and 50 N at a fretting stroke of 50 μm due to the transformation of the fretting regime from a gross slip regime to partial slip regime. Only when the fretting stroke further increased to a higher value of 70 μm at 50 N, fretting could enter the gross slip regime. There was low wear volume and a high friction coefficient when fretting was in the partial slip regime, because oil penetration was poor. The wear mechanisms were fatigue damage and plastic deformation. There was high wear volume and low friction coefficient when fretting was in the gross slip regime, because the oil could penetrate into the contact surfaces. Unlike the wear mechanisms in the partial slip regime, fretting damage of 304 stainless steels was mainly caused by abrasive wear in the gross slip regime.     

Delamination wear of metal injection moulded 316L stainless steel

The wear behavior of metal injection moulded (MIM) stainless steels was studied using a pin-on-disc apparatus under dry sliding conditions. Pin specimens were MIM 316L stainless steel, while disc specimens were wrought 316L stainless steel. At low sliding speeds (0.2–0.6 m/s), the wear rates gradually decreased with increasing sliding speed, but then increased at high sliding speeds (0.6–2 m/s). The adhesive-induced delamination wear dominated at low sliding speeds, while abrasive-induced delamination wear dominated at high sliding speeds. At low sliding speeds, the surface densification occurred on the worn surface of pin specimens, hence no difference was found between the wear resistances of MIM pins containing 2% and 6% porosity. In contrast, the abrasive-induced delamination wear at high sliding speeds was enhanced by porosity; therefore the wear rates of MIM pins containing 6% porosity were higher than those of MIM pins containing 2% porosity.     

Effects of Material Composition and Microstructural Features on Dry Sliding Wear Behaviour of Fe–TiC Composite and a Cobalt-Based Stellite

This investigation deals with the influence of hardfacing En31 steel separately with Fe–TiC composite and commercial cobalt base (stellite 6) material on their sliding wear behaviour at 2.94 m/s speed and varying applied pressures. Wear response of the samples was substantiated through the scanning electron microscopic studies of the wear surfaces, subsurface regions and debris particles. The hardfaced samples revealed superior wear performance than that of the substrate. Further, the steel hardfaced with cobalt-based stellite offered higher wear resistance over the one overlayed with Fe–TiC composite. The applied pressure controlled the wear behaviour (rate) in a complex manner and its influence was dependent on material composition/microconstituents and test conditions. The friction coefficient got reduced with pressure except in the case of the Fe–TiC composite overlay beyond 2 MPa. The hardfaced samples were noted to be better suited for more severe conditions. Microcracking was quite frequently observed on wear surfaces of the hardfaced material especially under mild wear conditions. Sticking of fine debris particles on to the specimen surface was also observed.     

Correlation between abrasive wear resistance and changes in structure and residual stresses of steels

The connection between the structure and abrasive wear resistance of steels was studied. Samples of AISI 1020, 1040 and 1080 steels were tested. The initial hardness of the samples ranged from HV221 – for annealed steel AISI 1020, to HV868 – for water quenched and tempered at 180°C steel AISI 1080. Two‐body abrasive tests on silicon carbide abrasive paper of grit size 1200–240 were carried out on a friction machine under identical conditions for all specimens. X‐ray studies of the specimens were conducted before and after these tests. It was shown that characteristics such as the integral width of diffraction lines could be used as a universal indicator of abrasive wear resistance for steels, independently of their heat treatment. The compressive residual stresses in the surface layers of the steels were observed. The results showed that there is a correlation between abrasive wear resistance and the sign and magnitude of residual stresses in the surface layers of steels, as well as between abrasive wear resistance and the structural changes in these layers. This revised version was published online in July 2006 with corrections to the Cover Date.     

Frictional hardening and softening of steel 52100 during dry sliding

The behavior of frictional hardening and softening of steel 52100 with different microstructures during dry sliding was studied based on dynamic metallographic analysis. It was demonstrated that such frictional behavior significantly affected wear resistance of the steel. The results showed that anti-softening microstructures exhibited a rather better wear resistance; the difference in the wear resistance of various steels with different microstructures was caused by the difference in the energy consumption in surface layers during wear. These results indicate that the original structures and properties of steels should not be taken as the only criterion for judging the wear resistance. It is necessary to consider the influence of dynamic microstructural changes under specific wear conditions in order to evaluate the wear resistance.     

Wear behaviour of forging steels with different microstructure during dry sliding

Sliding wear behaviour of two types medium carbon microalloyed steels containing various microstructures was investigated on a 320 mesh SiC paper at a sliding speed of 0.33 m/s with a load of 6 N and sliding duration of 4 min under dry sliding conditions (the sliding distance, 80 m). The experimental results showed that the different microstructures cause a great influence on the wear resistance performance of the steels. Water quenched samples with martensite structure have the highest hardness and wear resistance performance. That is because, water cooled samples contained higher amount of carbon in the solid solution. On the other hand, air or sand cooling from forging temperature results in a decrement of hardness and wear resistance in steel-1 and steel-2. However, air cooled samples showed slightly higher wear resistance than sand cooled samples due to finer grain sizes and the larger pearlite and/or precipitation contributions.     

GCr15及G20CrNi2Mo轴承钢高温润滑条件下摩擦磨损性能

为了探究轴承钢在高温润滑条件下的摩擦磨损性能,采用扫描电子显微镜(SEM)、X射线衍射仪(XRD)、洛氏硬度计等对GCr15高碳轴承钢和G20CrNi2Mo渗碳轴承钢组织、物相及硬度进行了表征,利用QG-700型气氛高温摩擦磨损试验机研究轴承钢材料不同条件下的高温润滑摩擦磨损性能,并分析其磨损机制.结果表明:2种轴承钢...     

Effects of vanadium and carbon on microstructures and abrasive wear resistance of high speed steel

The effects of vanadium and carbon on microstructures and abrasive wear resistance of high speed steel were studied. The results show that the microstructures are characterized by VC, M₇C₃ and Mo₂C in the martensite and austenite matrix. Typical morphologies of vanadium carbides are found to be spherical, lumpy, strip, and short rod. On the other hand, the vanadium carbides have three kinds of distributions, i.e. grain boundary, chrysanthemum-like, and homogeneous distributions. The abrasive wear resistance of high speed steel depends on the hardness and microstructures. When the hardness is lower than HRC58, the abrasive wear resistance of the high speed steel mainly depends on its hardness. But when the hardness is higher than HRC58, it mainly depends on the amount, morphology and distribution of VC in the matrix. Many spherical or lumpy VC carbides are obtained when vanadium and carbon content is up to 8.15–10.20 and 2.70–3.15%. The excellent abrasive wear resistance would be obtained if such VC carbides disperse uniformly in the hardened matrix of high speed steel after quenched at 1050 °C and tempered at 550 °C.     

Dry sliding wear mechanism for P/M austenitic stainless steels and their composites containing Al2O3 and Y2O3 particles

Austenitic stainless steels are used in applications demanding general corrosion resistance at room or moderate operating temperatures. However, their use is often limited by the relative softness of these materials and their suceptibility to wear and galling. The present investigation deals with the dry sliding wear behaviour of two P/M austenitic stainless steels (AISI 304L and 316L) and their composites containing two different ceramic particles (Al₂O₃ and Y₂O₃) and two different sintering activators (BN and B₂Cr). Unlubricated pin-on-disc wear tests were carried out. Wear mechanisms were analysed by means of scanning electron microscopy and X-ray diffraction. A plastic deformation and particle detachment wear mechanism was revealed. Plasticity during sliding induced an austenite to martensite transformation. The presence of ceramic particles (Al₂O₃ and Y₂O₃) and sintering activators (B₂Cr, BN) improved significantly the wear resistance (especially the combination Al₂O₃ and B₂Cr). Ceramic particles limited plastic deformation while sintering activators decreased final porosity.     

A comparative study of the wear behaviour of sintered and laser surface melted AISI M42 high speed steel diluted with iron

Powders of AISI M42 high-speed steel (HSS) were blended with different proportions of water-atomised iron powders. The powders were subsequently submitted to uniaxial pressing and then divided in three lots. The first was submitted to sintering, the second was submitted to sintering plus laser surface melting (LSM) and the third was submitted to sintering plus LSM plus double tempering at the secondary hardening peak temperature of M42 HSS. The objective of this procedure was to evaluate the processing route that leads to reduced porosity in AISI M42 HSS and to higher abrasive wear resistance. Therefore the samples, with different chemical compositions and microstructures, were submitted to a detailed microstructural characterisation followed by microscale hardness and abrasive wear tests. It was observed that LSM leads to almost complete elimination of residual porosity and to the dissolution of large brittle carbides that are present in the as-sintered samples, leading to a homogeneous and extremely fine microstructure. This microstructure is formed of saturated plate martensite and a small proportion of retained austenite. The double tempering treatment, carried out in the laser surface melted samples samples, leads to the elimination of retained austenite and to a decrease of the lattice parameters of martensite due to the precipitation of thin carbides within martensite. As a result, while the hardness of the material in the sintered condition is between 245 and 625 HV (depending on the proportion of dilution with iron), after LSM the hardness is higher than 820 HV in all the samples. Surprisingly, the abrasive wear resistance of the laser melted and of the laser melted and tempered samples is lower than that of the as-sintered ones. Observation of the wear craters by scanning electron microscopy shows that this result is due to the different wear mechanisms acting on the samples processed by different routes.