Surface structure of stainless and Hadfield steel after impact wear

After impact wear, the very surface of stainless austenitic CrMnCN steel and austenitic MnC Hadfield steel revealed a thin fully amorphous layer followed by a layer of nanocrystals embedded in an amorphous surrounding, which was supported by a severely cold worked layer of austenite below. The new high-strength stainless steel contained C + N = 0.82 mass% and exceeded Hadfield steel in respect to proof strength, elongation, work to fracture and wear rate.     

The effect of fretting on the fatigue behaviour of plasma nitrided stainless steels

The plain fatigue and fretting fatigue behaviour of a plasma nitrided dual phase stainless steel known as 3CR12 and an AISI 316 austentic stainless steel have been studied in the present work, using a modified Wohler rotating-bending configuration. Test specimens were produced at two nitriding temperatures, namely 400 and 520 °C, representing low temperature and conventional nitriding temperature, respectively. The test results demonstrate that both nitriding processes can enhance the plain fatigue limit of these steels by approximately 10-25%, with the high temperature process being slightly more effective. Under fretting fatigue conditions, the beneficial effect of plasma nitriding is even more significant and the fretting fatigue limit is increased between 50 and 100% for 3CR12 and at least 50-150% for the AISI steel as the nitriding temperature is raised from 400 to 520 °C.     

An examination of the electrochemical characteristics of two stainless steels (UNS S32654 and UNS S31603) under liquid-solid impingement

The erosion-corrosion resistance of high alloy stainless steel UNS S32654 and standard stainless steel UNS S31603 has been assessed under liquid-solid impingement conditions. The electrochemical characteristics of the two stainless steels have been examined via free corrosion potential measurements, anodic polarisation, linear polarisation and potentiostatic control in erosion-corrosion.It has been shown in this paper that high alloy stainless steel UNS S32654 exhibits better corrosion and erosion-corrosion performance than lower grade alloy UNS S31603. A general linear relationship between two electrochemical parameters (E_corr and R_p) has been shown in this study. A critical solid loading between 60 and 100 mg/l, at which there is a transition from corrosion to erosion-corrosion for the two stainless steels under different conditions, has been determined.     

The microstructure and wear behaviour of friction stir processed AISI 430 ferritic stainless steel

ABSTRACT

The microstructure and wear behavior of Friction Stir Processed (FSPed) AISI 430 ferritic stainless steel were analyzed in the present study. FSP was performed with a tool rotation and advancing speeds of 1400?rpm 16?mm/min respectively by employing a tungsten carbide tool. The FSPed microstructure consisted of a mixture of ferrite and martensite. After FSP, microhardness increased with respect to that of the as-received material. The wear resistance of the FS processed material was significantly enhanced if compared to that of the as-received substrate. According to the SEM analyses of the worn surfaces and wear debris, a combination of adhesive wear and delamination was observed in the case of the base metal. The wear mechanism shifted to mild adhesive wear after FSP. The superior wear resistance of the FS processed AISI 430 steel was attributed to the pronounced grain refinement and to martensite formation in the stir zone.     

The relevance of wear-mechanism maps to mild-oxidational wear

The presence of oxygen in the environment in which a steel sliding system operates will promote a mild form of wear with wear debris consisting mainly of iron oxides. Of the oxidation-dominated mechanisms, mild-oxidational wear (the prefix describes the extent of oxidation and not the wear rate) has been most extensively investigated. In this paper, examples will be used to show that the wear-mechanism map for the unlubricated sliding of steels can adequately predict the occurrence of mild-oxidational wear and the trend of wear rates as well as describe the resultant features on the worn surfaces. It is also shown that this map is relevant to delamination wear and to test geometries other than the pin-on-disk configuration. It is suggested that the more-recently constructed wear maps for aluminium and magnesium alloys could similarly be used to predict the wear characteristics of these alloys during sliding.     

Friction of PM ferritic stainless steels at temperatures up to 300 °C

Two ferritic stainless steels (409Nb and 434L) manufactured through powder metallurgical techniques were wear tested at different temperature conditions (up to 300 °C). Two sliding speeds were used, and tests were carried out against a wrought austenitic stainless steel. Materials’ wear performance was characterized through friction coefficients and analysis of wear tracks was carried out through scanning electron microscopy. Results have shown an adhesive wear mechanism. Oxidized ferrite particles have also been found on wear tracks.     

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.     

Friction and wear behaviour of stainless steel rubbing against copper-impregnated metallized carbon

A series of experimental tests were carried out using stainless steel rubbing against copper-impregnated metallized carbon under electrical current on a pin-on-disc test rig. The test parameters include the sliding speed of 60-100 km/h, normal force of 40-80 N and electrical current of 0-50 A. During testing, the friction coefficient and wear volume were recorded. The topography of worn surfaces was also observed with SEM. The cross sectional profiles of worn surfaces of stainless steel were measured with Ambios profiler. The result displays that electrical current, normal load and sliding speed have a distinct effect on the friction and wear behaviour of stainless steel rubbing against copper-impregnated metallized carbon. Without electric current, the friction coefficient is largest but the wear volume of copper-impregnated metallized carbon is lowest. With increasing electric current, the friction coefficient decreases while the wear volume of copper-impregnated metallized carbon increases. Through the whole test, it is found that the wear loss of stainless steel was light. The wear of copper-impregnated metallized carbon becomes severe when electrical current or sliding speed is high. When the electrical current or sliding speed is high, arc ablation is a dominant wear mechanism of copper-impregnated metallized carbon.     

Effect of sliding wear on tribocorrosion behaviour of stainless steels in a Ringer's solution

The dependence of the tribocorrosion of stainless steels AISI 304L and SS 3M^® orthodontic archwires sliding against corundum in a Ringer's solution on applied normal force, and sliding velocity, has been investigated using in situ electrochemical noise measurements. Applied normal force and sliding velocity were found to greatly affect current and potential during fretting-corrosion. An increase in normal force and sliding velocity induce an increase in current and a decrease in potential accelerating the depassivation rate of the tested stainless steels. The fluctuations in potential and current during fretting-corrosion are more pronounced at increasing sliding frequency than at increasing applied normal force. Sliding wear affects the repassivation behaviour of the tested materials by increasing the anodic current in the wear track area.     

Sliding wear behavior of stainless steel parts made by metal injection molding (MIM)

The wear resistance of stainless steel parts, which were fabricated by a metal injection molding (MIM) process, was studied under self-mating, dry sliding conditions, using a pin-on-disk type wear configuration. The materials used were an austenitic stainless steel 316L (of MIM and wrought steel), a precipitated stainless steel 17-4PH (of MIM and wrought steel) and a widely used ball-bearing steel (DIN 100Cr6). Two surface conditions, i.e. as sintered and as polished, were considered in the wear tests of the MIM samples. In summary, the wear resistance of 316L was lower than 17-4PH, and the latter was almost the same as 100Cr6. Further, the wrought materials showed a better wear resistance than the MIM materials. The mechanisms responsible for these tendencies were discussed by means of microscopical observations and chemical inspections of the worn surfaces and the microstructures of the samples.     

The effect of nitrogen on the scratch resistance of austenitic stainless steels

High nitrogen stainless steels (HNSS) are being considered a new promising class of engineering materials. When nitrogen is added to austenitic steels it can simultaneously improve fatigue life, strength and wear and localized corrosion resistance. In this work, a single pass pendulum scratch test was used to study the effect of nitrogen on the scratch resistance of an UNS S30403 austenitic stainless steel. Samples with increasing nitrogen contents at the surface were obtained through high temperature gas nitriding. The thermochemical treatments were performed at 1473 K in (N₂+Ar) gas atmospheres for 36.0 ks, obtaining fully austenitic cases (surface nitrogen contents up to 0.5 wt%) ca. 1.5 mm in depth. The scratch tests were performed in a single-pass pendulum, equipped with strain gages to measure normal and tangential forces during scratching. The specific absorbed energy was calculated as the ratio between the measured absorbed energy and the amount of mass removed from the specimen. An increase of the specific absorbed energy with increasing nitrogen content was observed. The results of the scratch tests were analyzed taking into account the stress–strain behavior during depth sensing indentation tests and the energy absorbed during Charpy impact tests. The improvement in scratch resistance due to nitrogen alloying was attributed to the strong hardening effect of nitrogen in solid solution, which does not affect significantly work hardening and toughness. A comparison between the scratch resistance and the cavitation-erosion resistance, measured in previous work, was made too.     

Mapping the role of Cr content in dry sliding of steels: Comparison between maps for material and counterface

In this work, a study of the wear transition regimes was carried out for a pin-on-disk sliding couple, involving two steels of different hardness and Cr contents. Dry sliding wear behaviour of the more highly alloyed stainless steel was dominated by adhesive wear and tribo-oxidation at relatively low sliding speeds and by mixed and adhesive wear at high speeds and loads. In contrast, oxidative wear was more predominant for the lower alloyed steel. The individual wear maps generated for the individual components i.e. material and counterface are discussed in the context of the wear mechanisms observed in the tribological contact.     

Tribocorrosion behaviour of Fe–17Cr stainless steel in acid and alkaline solutions

The effect of applied potential, load and frequency on the tribocorrosion behaviour of a ferritic stainless steel in aqueous solution is investigated under sliding wear conditions using a reciprocating motion tribometer including an alumina pin sliding on a metal plate. The tribometer is equipped with a reference electrode and a counter electrode for electrochemical experiments. The total metal removal rate of the stainless steel is determined from the rate of penetration of the pin and from an analysis of the wear track at the end of a wear experiment while the fraction of electrochemically removed metal is deduced from the current measured during the wear experiments. Two electrolytes are used, 0.5 M H₂SO₄ and 1 M NaOH. Applied potentials are in the passive potential region except for a few experiments performed under cathodic polarisation. The obtained results demonstrate the interdependence of electrochemical and mechanical mechanisms and the importance of the passivation behaviour of the metal in the electrolyte used. In sulphuric acid the electrochemical metal removal rate depends strongly on the value of the applied potential in the passive region, but not in NaOH because in the latter electrolyte the anodic charge serves only for film formation rather than dissolution. The effect of mechanical parameters on the rate of electrochemical metal removal is in qualitative agreement with a previously developed model. The presence of debris in the contact after test was found to depend on the prevailing electrochemical conditions.     

Synergy between corrosion and wear of electrodeposited Ni-P coating in NaCl solution

An immersion block-on-ring tester was employed in this study to investigate the interaction between wear and corrosion of electroplated Ni-P coating in 5% NaCl solution. The weight loss and the coefficient of friction of the specimen under different bath temperatures and overpotentials were measured. The results showed that at temperature of 50 °C and overpotential of +600 mV_SCE, which was within the transpassive region of its polarization curve, a severe synergy between corrosion and wear was observed. However, at lower temperatures and overpotentials, the interaction between wear and corrosion was hardly noticed.     

Tribological behaviour of stainless steel with respect to that of DLC in terms of energetic aspects

Abstract

The tribological behaviour of stainless steel (SUS 440C) relative to that of diamond-like carbon (DLC) was investigated in terms of tribometer input energy. The DLC was prepared on tungsten carbide (WC) substrates using radio frequency plasma chemical vapour deposition with benzene (C₆H₆) as a gas source. The stainless steel ball, as the counterpart, was tribotested. The input energy was calculated using the applied load, friction coefficient and sliding distance obtained from each tribotest. The wear loss of the ball increased as the sliding distance increased, whereas wear loss of the DLC was not directly observed. During evaluation of the input energy, the wear rate of the stainless steel ball decreased as the input energy increased. We propose a method for evaluating tribological properties using the input energy and discuss the wear behaviour of the stainless steel based on the input energy.     

Effect of tangential force on wear behaviour of steels in reciprocating rolling and rolling–sliding contact

A new rolling testing apparatus was developed on a tension–compression hydraulic machine with a high precision. The aim of this paper is to study the transition of wear mechanisms of steels with the increase of tangential friction force between contact surfaces in rolling. The wear modes were particularly analyzed during the passage from rolling to mixed rolling–sliding contact.     

The role of lubrication and corrosion in abrasion of materials in aqueous environments

A rubber wheel type test apparatus has been constructed which allows abrasion testing to be conducted in slurry or dry environments in otherwise identical conditions. Abrasion tests of a steel, a sintered tungsten carbide–cobalt hardmetal and an HVOF sprayed nickel chrome–chromium carbide cermet coating have been performed in dry and aqueous slurry conditions, the latter with both neutral and acidic carriers. It has been shown that the aqueous carrier acts as an effective lubricant and thus significantly reduces the abrasion rate over that observed in dry conditions. However, enhancement of corrosion by use of an acid slurry lead to an increase in the rate of material removal over that of the neutral aqueous conditions in all cases. Increases were small for the corrosion resistant cermet coating and moderate for the steel. Significant enhancement of wear was observed for the sintered WC–Co hardmetal where rapid removal of the cobalt binder by the acid resulted in a change in dominant mechanism of carbide removal from attritive wear to pullout.     

The abrasive wear of steels in South African soils

A high carbon steel was heat treated to produce a range of microstructures and mechanical properties. These steels were subjected to abrasion testing in stony, clay, and sandy soils. Wear rates were found to be twenty times higher in stony soil than in sandy soil and seven times greater than in clay. It was found that the relative wear resistance increased in sandy and clay soils with increase in steel hardness. In stony soils the relative wear resistance of all steels was found to be similar. An explanation for such behaviour was formulated on the basis of surface temperature heating and work hardening effects. The aggressive nature of abrasion found in stony soils was also found to give rise to the appearance of very hard white layers on the steel surfaces.     

The characterization of wear transitions in sliding wear process contaminated with silica and iron powder

When a machine is in operation, two moving surfaces interact to generate a large amount of wear particles. The wear debris generated inside the machine or contaminants from outside plays important roles in both two-body and three-body wear. For all mining and port machinery, their lubricants are very likely to be polluted by contaminants such as silica and other metallic debris such as iron and nickel. In order to seek a deeper understanding of the effects of different contaminants on wear process, this project investigated sliding wear processes when silica powder and iron powder exist in lubricants.Four sliding wear tests were conducted on a pin-on-disc tester with and without the contaminants. Visual inspection, ferrography analysis, particle quantity analysis using a particle analyzer, and numerical surface analysis using confocal laser scanning microscopy (CLSM) were conducted to study the wear particles and wear surfaces. Supported by the data generated from the comprehensive analyses on the wear particles and wear surfaces, the investigation of the effects of the added contaminants to the wear processes and wear mechanisms have been carried out and presented in this paper.     

Influence of microstructure of HC CoCrMo biomedical alloys on the corrosion and wear behaviour in simulated body fluids

The corrosion and tribological behaviour of an as-cast High Carbon CoCrMo alloy subjected to different thermal treatments in simulated body fluids has been analyzed by electrochemical techniques. After the microstructural characterization of the alloy, the samples were studied electrochemically and tribo-electrochemically. Thermal treatments influence the corrosion behaviour, passive dissolution and tribological response. An increase of grain boundaries accelerates the anodic reaction in all solutions. A higher carbide volume fraction generates a lower wear-rate. Microscopic observation by means of Optical and SEM microscopy showed that presence of proteins modified the debris behaviour. In non-protein containing solutions particles are dispersed away from the track while in protein solutions particles tend to agglomerate and sediment around the wear track.