Unlubricated sliding and rolling/sliding wear behavior of continuously cooled, low/medium carbon bainitic steels

The development of low and medium carbon bainitic steels for railroad track applications is traced through investigations to understand wear behavior. Carbide-free bainite consisting of bainitic ferrite laths, with or without lath boundary retained austenite, has emerged as the best microstructure. Cast and wrought 0.25%C, 1.75%Si, Mo-B steels have exhibited wear resistance comparable with that of Hadfield's austenitic steel under severe rolling/sliding contact.     

The effects of retained austenite on dry sliding wear behavior of carburized steels

Ring-on-square tests on two kinds of low-alloy carburized steel which were AISI 8620 and 4140 were carried out to study the dry sliding wear behavior. The influence of different retained austenite level of 6% to 40% was evaluated while trying to eliminate other factors. Test results show that the effects of grain size and carburized steel species are negligible in dry sliding wear behavior. While the influence of retained austenite is negligible at 20 kg load condition, wear resistance is decreased at 40 kg load condition as the retained austenite level is increased from 6% to 30%. However, wear resistance is again increased above about 30% of retained austenite level at 40 kg load condition.     

Effect of cryogenic treatment on the matrix structure and abrasion resistance of white cast iron subjected to destabilization treatment

Effect of deep cryogenic treatment on the matrix structure and abrasion resistance of high chromium cast iron subjected to destabilization heat treatment has been investigated in this paper. The results show that, during the cryogenic treatment, the secondary carbides precipitate in austenite, which promote the transformation of retained austenite to martensite. The cryogenic treated alloys produced superior hardness and wear resistance (β) to the alloys without cryogenic treatment. When the bulk hardness and wear resistance (β) reach the maximum, there is still about 13% retained austenite in alloys. Cryogenic treatment cannot make retained austenite transform to martensite completely.     

Friction-induced martensitic transformation in austenitic manganese steels

The sliding wear behaviour of various metastable Fe-Mn-C austenites as well as that of the classic Hadfield steel is investigated. The frictioninduced martensitic transformation and work hardening of the austenite in surfaces exposed to friction are analysed using X-ray diffraction, light microscopy and scanning and transmission electron microscopies.It becomes evident that the initial hardness of the austenitic Fe-Mn-C alloys is not a useful property to predict the wear resistance. Instead of this, the hardness of the work-hardened surface layer in connection with the particular wear mechanism has to be considered.Thin martensitic surface layers induced by frictional forces considerably increase the sliding wear resistance; thick layers which have been transformed to martensite, however, can initiate failure because of brittle fracture. This depends on the degree of metastability of the austenite as well as on the applied load.     

Mechanisms of dry wear of some martensitic steels

The basic wear mechanisms operating when two identical steel surfaces are rubbed against each other were studied to determine material parameters essential for wear resistance. Three simple model alloys, with the same basic properties as tool steels, were developed, containing three different predetermined volumes of M₇C₃ carbide, having approximately the same hardnesses after hardening and annealing, and approximately the same composition of the matrix.Unlubricated sliding wear tests were performed in air, using a pin-on-ring type machine. Normal force, sliding speed and sliding distance were varied. Friction force and temperature were recorded during the test and changes in weight of specimens were measured. The worn surfaces were carefully examined by scanning electron microscopy, in an attempt to classify the different wear mechanisms.It was found that corrosive wear dominates at low sliding speeds (2 m/min). Material annealed to a lower hardness had a lower wear resistance, irrespective of carbide content. The wear is characterized as mild.At high sliding speed (100 m/min) and especially for high normal forces, the wear was dominantly by a severe adhesive mechanism. Tempering to a lower hardness gave better wear resistance, which indicates that the room temperature hardness is not significant when a high contact temperature is reached. The influence of the carbide content was complex. The results indicate that a carbide free material is the most wear resistant, because of the more extensive occurrence of corrosive wear. Abrasives such as carbides in the more carbide rich alloys may possibly tear up protective corrosive layers and expose the steel to adhesive wear.     

Effects of carbon content and sliding ratio on wear behavior of high-vanadium high-speed steel (HVHSS) under high-stress rolling–sliding contact

This study developed a wear tester to investigate the wear properties of high-vanadium high-speed steel (HVHSS) with approximately 9% vanadium and different carbon contents under rolling–sliding condition. The carbon content significantly affected microstructure of matrix and mechanical properties of HVHSS, and therefore played an important role in wear resistance. Nevertheless, the wear failure mode was mainly related to sliding ratio, which varied from fatigue wear to sliding wear with increasing sliding ratio. The wear behavior was affected by the interaction of carbon content and sliding ratio. The high-stress rolling–sliding contact not only caused severe wear but transformed austenite to martensite.     

超超临界电站锅炉关键材料的新进展

高温材料和性能是制约超超临界(电站)机组发展的关键。讨论了超超临界机组锅炉用铁素体钢、奥氏体钢与镍基合金三类材料的合金化和主要性能,指出随着机组参数的提高,材料的抗蒸汽氧化性能和抗烟气腐蚀性能愈加重要,从而促进了新型奥氏体热强钢和镍基合金的发展;指出了随着超超临界技术的采用,还需要对相关材料进行大量基础试验,特别是长期试验,以积累相关数据和经验。     

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.     

Study on relative wear resistance and wear stability of high-speed steel with high vanadium content

In this work, a new concept of wear stability was put forward by authors, and it was quantitatively expressed by factor of wear stability. Different hardness, impact toughness and retained austenite content high-speed steel with high vanadium content samples were obtained by varying heat treatment conditions. The effects of hardness, impact toughness and retained austenite content on relatively wear resistance and wear stability were studied under abrasive wear condition. Results show that relative wear resistance increases with increasing hardness or decreasing impact toughness, whereas the wear stability rises with the increasing of hardness or impact toughness. The analyzing results reveal that mechanical behaviors are only apparent factors to influence wear behaviors. Relative wear resistance substantially depends on retained austenite content (Ar). At retained austenite content of about 30 vol.%, the relative wear resistance is optimal. However, wear stability is scarcely influenced by retained austenite content, which depends on the maximum changing amount of retained austenite under certain condition (ΔAr) in essence. With increasing ΔAr, wear stability linearly decreases.     

Adhesive mechanisms in the wear of some tool steels

The adhesive wear properties of a number of tool steels have been investigated, with special emphasis on the formation and action of prows. The test pieces were worn by dry sliding in a pin-on-ring machine. A special specimen preparation technique made it possible to study the internal structure of wear fragments and prows as a function of depth under the external surface. It was found that prows form in successive steps. The initial step has been reported earlier for pure metals and low carbon steel.A detailed explanation of material deterioration in adhesive wear has been worked out. The dominating mechanism was found to be an abrasive dead zone action, rather than the shearing off or destruction of prows.Investigations by X-ray and electron microscope techniques revealed extensive transformations between the austenite and martensite phases, an extremely fine grain size and a redistribution of carbide and oxide particles during the formation of prows. Correspondingly high microhardness values, up to 1600 HV_0.15N, were measured in the transformed material. Distortion of the retained austenite lattice contributes to the high hardness.     

余氏理论在工业材料相变研究中的应用

本文应用余瑞璜的“固体与分子经验电子理论”对工业合金的奥氏结构进行了键距差（BLD）分析,结合余氏及其助手已经获得的材料价电子结构资料提出如下观点：（1）Fe－C－Me合金奥氏体中存在着C－Me偏聚区;（2）C－Me偏聚对相变有阻力,这种阻力和C－Me偏聚力交互作用可改变相变产物的结构、形态和性能;（3）从C－Me偏聚出发,对几个金属学基本问题做了新的解释：（1）奥氏体的陈留;（2）合金钢贝氏体变态及转变的不彻底性;（3）位错马氏与孪晶马氏体的成形。     

Tribological Behavior of New Martensitic Stainless Steels Using Scratch and Dry Wear Test

This paper focuses on the tribological characterization of new martensitic stainless steels by two different tribological methods (scratch and dry wear tests) and their comparison to the austenitic standard stainless steel AISI 316L. The scratch test allows obtaining critical loads, scratch friction coefficients, scratch hardness and specific scratch wear rate, and the dry wear test to quantify wear volumes. The damage has been studied by ex situ scanning electron microscopy. Wear resistance was related to the hardness and the microstructure of the studied materials, where martensitic stainless steels exhibit higher scratch wear resistance than the austenitic one, but higher hardness of the martensitic alloys did not give better scratch resistance when comparing with themselves. It has been proved it is possible to evaluate the scratch wear resistance of bulk stainless steels using scratch test. The austenitic material presented lower wear volume than the martensitic ones after the dry wear test due to phase transformation and the hardening during sliding.     

Influence of heat and thermochemical treatment on abrasion resistance of structural and tool steels

Abrasive wear is responsible for intensive degradation of machine parts or tools. This process starts as an interaction between hard, mostly mineral, particles and the working surface. Methods of increasing the lifetime are based on application of abrasion resistant materials or creation of hard, wear-resistant surface layers or coatings on the surfaces of machine parts or tools. Carbon and low-alloy steels with different types of thermochemical treatment (case hardening, nitriding) are used in cases of low abrasion. Another method of increasing lifetime is the application of ledeburitic steels. The wear resistance of these steels depends on their chemical composition and heat treatment. The results of laboratory tests of thermochemically treated steels, heat-treated ledeburitic chromium steels and high-speed steels show the effect of the microstructure of these steels on their abrasion resistance. Abrasion resistance of carburized low-alloy steels is on the same level as in high-carbon structural and tool steels. In ledeburitic chromium steel maximum abrasion resistance was achieved by quenching from 1100 °C whilst in ledeburitic chromium–vanadium steel the optimum quenching temperature was 1150 °C. Growing abrasion resistance was caused by increasing amounts of retained austenite.     

Guidelines for the selection of hardfacing alloys for sliding wear resistant applications

The work presented in this report summarizes an evaluation of the relative sliding wear characteristics of several commonly used commercial hardfacing alloys. The alloys studied include cobalt-base, nickel-base and Fe-Cr-Ni alloys which also contain small amounts of cobalt. Selecting the most effective alloy combination to withstand sliding wear is a challenge for materials engineers, equipment designers and fabricators. Accurate guidelines for selecting compatible alloys from a wear resistance point of view are not available. On the basis of the results of this work several hardfacing alloy combinations were identified which provide good sliding wear resistance. In addition, several hardfacing alloy combinations were found to exhibit poor wear resistance compatibility. The guidelines presented in this report will aid in the selection of suitable hardfacing alloy combinations with adequate sliding wear resistance. The wear guidelines are also supplemented with corrosion data in several environments of importance in the chemical process industries. These data should assist in the selection and optimization of hardfacing alloys in the presence of aggressive environments.     

Widerstand gegen abrasiven verschleiss und dynamische bruchzähigkeit weisser vanadingusseisen

The wear behaviour under abrasive sliding loading, the structure and dynamic fracture toughness of white cast iron containing (4 – 6)% V are considered in this paper. In wear systems containing hard abrasive particles (silicon carbide), the dynamic fracture toughness and wear resistance increase with increasing austenite content in the structure. In systems with less hard abrasive particles (e.g. flint, garnet) these alloys exhibit a combination of high fracture toughness and high wear resistance. The vanadium-alloyed white cast irons with a predominantly austenitic matrix show more favourable values with respect to both dynamic fracture toughness and wear resistance in comparison with a simultaneously tested chromium white cast iron.     

Influence of temperature of sub-zero treatments on the wear behaviour of die steel

This study examines the influence of temperature of sub-zero treatment on the wear behaviour of AISI D2 steel. A series of dry sliding wear studies have been made under constant normal load at varying sliding velocities. Emphasis has been laid to understand the operative modes and mechanisms of wear by the estimation of specific wear rates and detailed characterizations of the worn surfaces, wear debris and subsurfaces with the help of scanning electron microscope (SEM) examinations coupled with energy dispersive X-ray (EDX) microanalyses. The obtained results unambiguously infer that lower the temperature of sub-zero treatment higher is the improvement in wear resistance. Wear resistance can increase by 1.5–125 times depending on sliding velocity while hardness increases only by 4.2% at the lowest temperature of sub-zero treatment (77 K) compared to the conventionally treated specimens. These results corroborate well with the reduction in retained austenite content associated with simultaneous increase in the amount of secondary carbide particles with lowering of sub-zero treatment temperature. The operative modes and mechanisms of wear are identified as either mild oxidative or severe delaminative, which depends on the temperature of sub-zero treatment and the sliding velocity of the wear test.     

Wear mechanisms of laser-hardened martensitic high-nitrogen-steels under sliding wear

High-nitrogen tool steels (Fe, 15% Cr, 1% Mo, 0.3% C, 0.3% N) are applied, e.g. in bearings and gears in aeronautics and space technology. Their advantage compared to conventional, nitrogen-free tool steels is a superior corrosion resistance, which can be attributed to Cr, Mo, and N dissolved within the solid solution. In order to gain a sufficient toughness for application, these steels are tempered above 600°C bringing about precipitated carbides and nitrides, which bind Cr and N and, therefore, deteriorate the chemical properties. Within a DFG (German Research Council)-funded research project the authors show, that by means of laser hardening it is possible to dissolve a part of these precipitates — mainly nitrides resulting in improved properties under fatigue, wear and corrosion. This is brought about by a newly generated martensite with compressive residual stresses (fatigue, sliding wear), dissolution of Cr and N (corrosion) and a higher mechanical stability of the surfaces (sliding wear). This contribution focuses on the acting wear mechanisms under dry sliding wear. The investigations are carried out with pin-on-disk tests, with the disk as the actual specimen and a pin made of conventionally hardened 52100 bearing steel (100Cr6). It can be shown, that the wear properties of the high-nitrogen-steel are better than those of comparable conventional tool steels and that a laser treatment leads to a further improvement. Due to the fact that there is a tempered zone between overlapping laser-hardened areas, there is a change of acting mechanisms and, thus a distinct difference in wear rates. For the conventional corrosion resistant martensitic tool steel the difference between the tempered and the hardened zone is not as marked. Neither the wear mechanisms nor the wear rates differ distinctly. These effects and their influence on the wear behaviour is correlated with the microstructure of both steels before and after laser-hardening.     

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 behavior of bainitic steels

A systematic study of the wear properties of a series of 0.5 wt.% Mo, 0.003 wt.% B bainitic steels has been made under dry sliding conditions. In contrast to most of the established wear models and experimental data, it was found that, for eight of the nine materials, the wear rate is not a linear function of load.The wear rate data have been analyzed with respect to chemical composition, hardness, monotonic-cyclic stress strain parameters, fatigue properties, Charpy impact data and microstructure. It is shown that the chromium content has the most significant influence on wear rate. Since these bainitic steels have inherently high impact resistance, which is improved with chromium additions, it is possible to achieve an attractive combination of properties with a steel containing 0.2 wt.% C, 2.0 wt.% Cr and 1.5 wt.% Mn.The wear resistance of the bainitic steels is compared with previous work on pearlitic steels tested under the same conditions. While the best pearlitic steels stand apart, it is seen that the best bainitic steel tested to date is better than some fully eutectoid steels containing 0.7 wt.% C.     

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.