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.     

Impact of Metastable Austenite on the Wear Resistance of Tool Steel

The possibility of increasing the abrasive wear resistance of tool steels by obtaining a multiphase structure including tempering martensite, carbides, and metastable austenite undergoing dynamic deformation martensitic transformation (DDMT) under abrasive action is shown.     

Comparison of wear properties of tool steels AISI D2 and O1 with the same hardness

Two commercial cold work tool steels, AISI D2 and O1, were heat treated in order to obtain the same hardness 700 HV (60 HRc) and were subsequently tested in three different modes of wear, namely in adhesion, three-body and two-body abrasion, by using pin-on-disk, dry sand/rubber wheel apparatus and pin abrasion on SiC, respectively. Even though AISI O1 and D2 steel are heat treated to the same hardness, they perform differently under the three modes of wear examined. The results show that the steel microstructures play the most important role in determining the wear properties. For relatively low sliding speeds AISI O1 steel performs up to 12 times better than AISI D2 steel in adhesive wear. For higher sliding speeds, however, this order is reversed due to oxidation taking place on the surface of the AISI D2 steel. The wear rate of both tool steels in three-body and two-body abrasion wear is proportional to the applied load. In three-body abrasive wear, AISI D2 exhibits a normalised wear rate about two times lower than the AISI O1 tool steel, and this is due to the presence of the plate-like hard carbides in its microstructure. Both tool steels perform 3–8 times better in three-body abrasive wear conditions than in two-body abrasive wear.     

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.     

激光强化参数对40Cr钢表面组织及摩擦性能影响的研究

采用CO2横流式激光器对40Cr材料进行表面强化处理研究;使用S-360型扫描电镜观察激光硬化区金相组织及成分并观察金属表面磨损形貌;采用CHX-1超显微硬度计测量激光强化区断面的显微硬度;然后在MPX-2000盘销式摩擦磨损实验机上进行干摩擦和油润滑实验。结果表明:激光参数对表面硬度和硬化层深度有很大影响,较大的功率可使奥氏体转变充分而获得更多的马氏体,激光扫描速度越快,功率越大,显微硬度越高,硬化层越深;少量针状马氏体组织化引起表层强化,经激光硬化的表面其耐磨性可大大提高;40Cr在干摩擦条件下的平均磨损量是润滑时的5倍,40Cr和20MnSiV的磨损主要以磨粒磨损为主,同时也有粘着磨损。     

Coercive-force and eddy-current testing of the abrasive wear resistance of quenched and tempered hypereutectoid carbon steels: II. Steels subjected to different quenching regimes,subzero treatment,and tempering after high-temperature quenching

The effects of the carbon concentration in martensite from 0.70 to 1.35 wt %, the presence of up to 70 vol % residual austenite, the degree of coagulation, and the volume fraction of tempering carbides on the specific features of the application of eddy-current and magnetic methods for testing abrasive wear resistance are studied. The case of high-carbon (0.83–1.53 wt % C) steels quenched from 790–1200° C, treated with cold at ?196°C, and tempered in the temperature range 75–700°C is considered.     

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.     

42CrMo钢振动磨料磨损研究

为研究振动对材料磨损的影响,对经过低温、中温、高温回火的42CrMo钢在自制的振动磨料磨损试验机上进行了振动磨损实验.结果表明,试样的塑性、硬度及磨料的振动参数综合影响其耐磨性,磨损量并不与磨料的振动频率成正比,磨粒的振动影响材料的磨损形貌.     

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.     

Tribological Behavior of a 0.33% C Dual-Phase Steel with Pre I/C Hardening and Tempering Treatment under Abrasive Wear Condition

The present study investigates the effect of prior hardening and tempering treatment on the microstructure, mechanical properties, and high-stress abrasive wear response of 0.33% carbon dual-phase (DP) steel. For this purpose, two different DP steels were produced by subjecting the as-received steel to hardening (DP-H) and hardening + tempering (DP-HT) treatments prior to the intercritical (I/C) annealing treatment. These steels along with the as-received steel were subsequently characterized by optical and scanning electron microscopy (SEM) metallography. Furthermore, tensile properties were evaluated along with microhardness measurements. The fracture surfaces of the failed tensile specimens were studied under SEM. Prior hardening and tempering treatment resulted in the formation of a nearly spherical martensite (aspect ratio = 1.2 ± 0.13) phase along with fine iron carbides in DP-HT steel. These fine iron carbides and spherical martensite act as the void nucleation sites in DP-HT steel. Therefore, DP-HT steel exhibits good ductility along with reasonable strength. On contrary, DP-H steel exhibits the presence of a fine elongated martensite (aspect ratio = 6.1 ± 3) phase, which causes poor ductility. Furthermore, abrasion tests were carried out at varying sliding distances at three different applied loads. Dual-phase treatment results in improved overall wear response. Moreover, tempering of prior hardened steel leads to improvement in wear resistance in DP-HT steel under all conditions studied in comparison with DP-H steel. This is attributed to higher strain hardening and greater resistance to particle scooping in DP-HT steel.     

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.     

Abrasive wear study of white cast iron with different solidification rates

The abrasive wear resistance of white cast iron was studied. The iron was solidified using two solidification rates of 1.5 and 15 °C/s. Mass loss was evaluated with tests of the type pin on abrasive disc using alumina of different sizes. Two matrices were tested: one predominantly austenitic and the other predominantly martensitic, containing M₃C carbides. Samples with cooling rate of 15 °C/s showed higher hardness and more refined microstructure compared with those solidified at 1.5 °C/s. During the test, the movement of successive abrasives gave rise to the strain hardening of the austenite phase, leading to the attainment of similar levels of surface hardness, which explains why the wear rate showed no difference compared to the austenite samples with different solidification rates. For the austenitic matrix the wear rate seems to depend on the hardness of the worn surface and not on the hardness of the material without deformation. The austenitic samples showed cracking and fracture of M₃C carbides. For the predominantly martensitic matrix, the wear rate was higher at the solidification rate of 1.5 °C/s, for grain size of 66 and 93 μm. Higher abrasive sizes were found to produce greater penetration and strain hardening of austenitic matrices. However, martensitic iron produces more microcutting, increasing the wear rate of the material. The analysis of the worn surface by scanning electron microscopy indicated abrasive wear mechanisms such as: microcutting, microfatigue and microploughing. Yet, for the iron of austenitic matrix, the microploughing mechanism was more severe.     

Influence of cryosoaking period on wear characteristics and surface topography of M35 tool steel

Cryogenic treatment affects tool steels wherein alteration in microstructural features like phases, uniform precipitation of carbides is observed. In this work, improvement in wear resistance of cryotreated material with microstructural features and surface roughness of material has been correlated. Samples of AISI M35 steel were hardened at 1200°C, followed by triple tempering at 555°C in the salt bath, subsequently subjected to cryogenic treatment at minus 185°C for varying cryosoaking period (4–32?h) followed by soft tempering at 100°C. Such samples were characterized for hardness, microstructure, carbide density, wear rate and surface roughness. A correlation of carbide density and roughness has been established with wear resistance.     

Tribology and surface mechanical properties of the oxide film formed by excimer laser surface treatment of AISI 304 stainless steel

The surface hardness and tribological properties of the surface oxide formed by excimer laser surface processing of AISI 304 stainless steel have been examined. It is found that laser processing initially anneals the stress-induced martensite on the surface of the stainless steel, resulting in a softening of the surface. After more than 100 cycles of melting and resolidification, a surface oxide film develops which is harder than the austenite of the annealed substrate and comparable in hardness to the stress-induced martensite. The thickness of the oxide film is dependent on the number of laser pulses, so that arbitrarily thick films can be produced. The dry-sliding friction of the oxide film against a steel pin is substantially lower than that of the untreated polished surface with only the native oxide film and there is substantially less damage in both the wear track and the pin. The hard surface oxide is underlain by relatively soft austenite. The tribological behavior is thus not obviously the result of the surface mechanical properties of the film-substrate combination but is ascribed to changes in the chemical interaction between the pin and the disk.     

基体组织对高钒高速钢干滑动摩擦磨损行为的影响

利用销环式滑动磨损试验机测试了具有不同基体组织的高钒高速钢的干摩擦磨损性能,并利用扫描电子显微镜对其失效行为进行了分析。结果表明：以低碳板条马氏体为主要基体组织的高速钢可同时较为有效地抵御显微切削与疲劳磨损,其组织中均匀分布的高硬度VC能够充分发挥抗磨骨架作用,因而具有最优的耐磨性。基体组织为铁素体时,基体无法对VC提供有效的支撑,磨损失效形式为严重的显微切削及表面粘着磨损,耐磨性很差。基体以面碳马氏体为主时,抵抗循环疲劳和热疲劳的能力较差,导致耐磨性下降。     

Refinement of tempered martensite structure and its effect on wear mechanism in SAE 8620

All mechanical components that undergo sliding or rolling contact are subjected to some degree of wear. Carburising treatment is important in improving wear characteristics of AISI 8620 gear steel. An experimental investigation was conducted on carburised AISI 8620 steel. Gas carburising of the specimens was carried out in sealed quenched furnace at 1198 K for 6 h followed by hardening at 1133 K, oil quenching at 393 K and followed by tempering at 453 K. Carburised cryotreated samples were cooled in a controlled manner soaked at 88 K for 16 h in a cryoprocessor subsequently followed by soft tempering at 373 K. Specimens were characterised by microhardness test, wear test and retained austenite content by XRD. 3D wear surface response and 2D contour map showed that wear rate decreased by 32% in the case of carburised cryotreated specimens as compared to only carburised specimens. It was concluded that there was an improvement in hardness and wear resistance of carburised cryotreated steel as compared to only carburised steel. Refinement and densification in martensitic structure resulted in shift in wear transition from severe wear regime to mild wear regime.     

An evaluation of the wear behaviour of a dual-phase low-carbon steel

Wear behaviour of dual-phase AISI 1020 steel was investigated. The steel was austenitized at critical transformation temperature and rapidly quenched. Thus, the structure of the steel consists of martensite and ferrite phases in different proportions. Heat treated samples were subjected to wear with a cylinder-on-cylinder sample configuration under dry sliding conditions. Wear resistance was determined as functions of hardness and proportion of martensite phase, and elongation of the steel. The wear resistance of the dual-phase 1020 steel was also compared with those of hardened and tempered AISI 1040 and 8640 steels. It was indicated that the wear resistance of the test steel decreases with martensite proportions, and increases with martensite hardness and elongation of the steel.     

The Microstructure and Abrasive Wear Resistance of Fe–Cr–C Hardfacing Alloys with the Composition of Hypoeutectic,Eutectic, and Hypereutectic at $$ \frac{Cr}{C} = 6 $$

In this investigation, three Fe–Cr–C hardfacing alloys with different carbon and chromium contents and in constant ratio of ( \fracCrC = 6 ) \left( {\frac{Cr}{C} = 6} \right) were fabricated by GTAW on AISI 1010 mild steel substrates. The OES, OM, SEM, and XRD techniques and Vickers hardness method were used for determining chemical composition, hardness, and studying the microstructure of the hardface alloys. The OES, OM, and XRD examination results indicated that different carbon and chromium contents of hardface alloys produced hypoeutectic/eutectic/hypereutectic structures. By increasing the carbon and chromium contents in the chemical composition of hardface alloys, the volume fraction of the total (Cr, Fe)₇C₃ is increased resulting to decreasing in total the austenite volume fraction and increasing the hardness of the surface. Studying the microstructure after wear test (ASTM G65) shows that at the edge of the worn surface, the transformation of austenite to martensite had occurred in all the samples. The wear test results indicate that the highest wear resistance is gained in the hypoeutectic structure with maximum hardness after the wear test. In addition, abrasive wear micromechanisms in hypoeutectic/eutectic/hypereutectic were recognized as: ploughing + cutting/ploughing + cutting + cracking/cracking + cutting, respectively.     

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.     

无缝线路磨损钢轨激光熔覆自动修复方式的研究

由于列车的高速化和重载化,钢轨磨损问题越来越严重,采用修复质量高、修复速度快的激光熔覆技术可以对其进行在线快速修复。为此,采用三维扫描仪首先对磨损钢轨进行扫描,然后将扫描点云数据进行三维重构、路径规划及数据格式转换,最后利用优化的数据驱动机器手臂和激光熔覆装置对磨损钢轨进行自动修复。修复工艺结果表明,对5 mm的磨耗层进行7层修复,利用修复道与道之间和层与层之间的回火作用,修复层的组织马氏体含量少,硬度为330~360 HV;经过600℃回火处理10 min后,加入钒元素的铁基合金粉末激光熔覆修复后钢轨母材、热影响区、修复层硬度均在300~340 HV,组织为回火索氏体;修复钢轨的耐磨性约为钢轨母材的87%,达到修复目的。