Belt abrasion resistance and cutting tool studies on new ultra-hard boride materials

Composites of AlMgB₁₄ with 0, 30, and 70 wt% of TiB₂ were prepared by mechanical alloying and hot pressing. The composites’ belt abrasion resistance and cutting tool performance were measured by gravimetric analysis of material removal at varying loads and cutting speeds. AlMgB₁₄-70 wt% TiB₂ composites had high hardness and fracture toughness and the highest abrasive resistance of the three compositions. Cutting tool performance of AlMgB₁₄-70 wt% TiB₂ showed low wear due to chipping and little reaction with the Ti-6Al-4V work-piece. Subsurface damage and adhesion of the work-piece onto the tool material were gauged by SEM.     

烧结矿单辊破碎机抗磨损技术研究

单辊破碎机是烧结矿生产线上一个重要的部件,其工作环境与性质决定其必须具有抗高温与耐磨损的特性.针对目前单辊破碎机易磨损、寿命短的问题,首先,对其失效原因与磨损机理等方面进行了研究,得出其主要磨损形式是高温环境下带有凿削形式磨损的磨粒磨损.然后,研究了其抗磨损结构设计的方法,并对其材料选择与耐磨堆焊工艺等进行了详细分析与探讨,设计了一种抗磨损的长寿命烧结矿单辊破碎机.最后,通过工程实际使用验证了提出的单辊破碎枳抗磨损技术是可行且有效的.     

Abrasive wear of high speed steels: Influence of abrasive particles and primary carbides on wear resistance

A ball cratering test has been used to investigate the abrasive wear of high speed steels with different volume fraction and size of primary carbides. Three different abrasives, SiC, Al₂O₃ and ZrO₂ were used. Wear mechanisms were investigated by scanning electron microscopy (SEM). A good correlation between the hardness of the abrasives and the abrasive wear coefficient was found. Higher abrasive wear resistance was determined for steels containing coarser primary carbides compared to those without or with smaller carbides. The most pronounced difference in abrasive wear resistance was found for Al₂O₃ abrasives. This indicates that in ball cratering the abrasive medium has to be chosen properly, i.e. with a hardness adjusted to those of both primary carbides and martensitic matrix, to obtain results suitable to rank high speed steels with respect to abrasion resistance.     

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.     

Friction and wear behaviour of sintered steels submitted to sliding and abrasion tests

Fe–C–Mo and Fe–C–Cr steels were sintered by PM processes carried out using different values of temperature and pressure, leading to different microstructures and density values. Flat specimens were submitted to tribological tests in order to evaluate their behaviour under both dry sliding and abrasive wear conditions. A flat-on-cylinder tribometer was used for the sliding tests, while a micro-scale ball cratering device was used for the abrasion tests. The dry sliding wear resistance of the PM steels was mainly influenced by the composition and sintering conditions. In this regard, the best behavior was observed for the more hardenable Fe–C–Mo steels with higher Mo content, sintered under conditions giving rise to bainitic microstructures. A determining role was also played by the porosity content and pore shape: reduction in porosity (obtained by increasing the sintering temperature and the compacting pressure), as well as an increase in pore roundness, led to a significant improvement in the resistance to sliding wear. A mild oxidative wear regime were observed for all the sintered steels under relatively low values of the applied load, while an increase of the applied load led to a delamination wear regime. The resistance to abrasive wear was low for all the tested steels, irrespective of composition and sintering cycle.     

热处理对新型贝氏体钢组织和力学性能的影响

研究热处理对新型贝氏体钢的组织与力学性能的影响.结果表明,不同冷却介质冷却,新型贝氏体钢具有较高的淬透性,正火后300℃回火具有良好的强韧性.500℃回火出现回火脆性,其原因与组织中的贝氏体、铁素体及残余奥氏体分解形成碳化物有关.提出适合新型贝氏体钢的最佳热处理工艺.     

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.     

Influence of microstructure on erosion resistance of steels

Erosive wear due to solid particle impingement is a very intensive degradation process of surface layers of metallic materials. Erosion resistance is influenced by the working conditions (impact angle, impact velocity of solid particles, size, shape, hardness and amount of impinging particles) and the parameters of the worn material like hardness and microstructure. In our experiments some structural and tool steels were tested by slurry with SiO₂ particles at a flow velocity of 20 m/s. The microstructures of the tested steels were modified in a broad range by changing the conditions of their heat treatment. Increasing pearlite share in the structure of annealed carbon and low-alloyed steels has a positive effect on their erosion resistance. The growing carbon content in the tested hardened steels increases their erosion resistance. Maximum erosion resistance was found in hardened chromium ledeburite steel. Hardened high-speed steel HS 11-0-4 in spite of its high hardness has lower erosion resistance than ledeburitic chomium steels. An increasing amount of retained austenite and decreasing carbide and martensite shares with growing quenching temperature of the tested ledeburitic chromium steels leads to the reduction of their erosion resistance.     

Influence of sliding frequency on reciprocating wear of mold steel with different microstructures

The wear resistance of a low alloy plastic mold steel has been studied under pin-on-flat reciprocating configuration against AISI 52100 steel pins, under variable sliding frequency. The as-received material (HTO; 33 HRC) was heat treated under variable conditions to obtain different microstructures and hardness (HT1, quenched 880 °C, 58 HRC; HT2, tempered 550 °C, 43.4 HRC; HT3, tempered 300 °C, 52 HRC; HT4, annealed, 26 HRC). Under low sliding frequency (1 Hz), no significant differences in the wear resistance of the different materials are observed. Only at 8 Hz, a relationship between hardness and wear resistance is found. The softer annealed material HT4 shows an increasing wear rate under increasing frequency, while the quenched steel HT1 gives the lowest wear at the highest frequency. Wear mechanisms have been studied from SEM and EDS observations. Only HT4 shows a transition from the abrasive and oxidative wear mechanisms found in all cases to an adhesive wear mechanism under the highest frequency.     

Mirror surface machining of high-alloy steels by elliptical vibration cutting with single-crystalline diamond tools: Influence of alloy elements on diamond tool damage

Elliptical vibration cutting with single-crystalline diamond tools is applied to mirror surface machining of high-alloy steels such as cold work die steels and high-speed tool steels with a hardness of more than 60 HRC. Although practical mirror surface machining of hardened die steels such as Stavax (modified AISI 420) with a hardness of 53 HRC has been realized with the elliptical vibration cutting, lives of single-crystalline diamond tools are not sufficiently long in machining of some high-alloy steels, that may be caused by a large amount of alloy elements. In order to clarify the influence of the alloy elements on the diamond tool damage, the elliptical vibration cutting experiments are conducted on six kinds of high-alloy steels and four kinds of pure metals which are the same as the alloy elements. Mechanical properties of the alloy steels, i.e. difference in hardness between carbides and matrices, and the number of small carbides, are measured, and their influence on the micro-chippings are investigated. The chemical states of the alloy elements in high-alloy steels are analyzed using an X-ray diffraction (XRD) and an electron probe micro analyzer (EPMA), and their influence on the tool wear is discussed. Based on the investigation, a mirror surface machining of DC53, which has a high hardness of 62.2 HRC and the best machinability in the tested high-alloy steels, is demonstrated, and a mirror surface with a roughness of Rt 0.05 μm is obtained successfully.     

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.     

Measurement of various properties of Southern pine and aspen as function of heat treatment

The objective of this study was to investigate the influence of heat treatment parameters, namely temperature and exposure time on surface roughness, shear strength, hardness and density of Southern pine (Pinus echinata) and aspen (Populus grandidentata) samples. The specimens were exposed to two different temperature levels of 120–200 °C for time spans of 2–8 h. A stylus type portable profilometer was employed to evaluate the surface characteristics of the samples by taking measurements across the grain orientation. Average roughness (R_a), mean peak-to-valley height (R_z) and maximum roughness (R_max) were used to evaluate surface roughness of the samples exposed to various heat treatment schedules. Comten testing unit was also used to determine shear strength and Janka hardness of the control and heat treated specimens. Based on the results of this study Southern pine samples had more enhanced surface quality but lower hardness values than those of aspen specimens with increased temperature and time of heat treatment schedules. It was found that heat treatment adversely affected hardness and shear strength properties of all types of samples. Reduction in shear strength values of Southern pine and aspen samples ranged from 23.31% to 68.59% and from 4.67% to 48.55%, respectively as compared to those of control samples. It appears that influence of heat treatment on all properties of the samples was more pronounced with increasing temperature and exposure time.     

Abrasive wear behaviour of hardened high strength boron steel

Abstract

Abrasive wear in industrial applications such as mining, materials handling and agricultural machinery constitutes a large part of the total wear. Hardened high strength boron steels are known for their good wear resistance and mechanical properties, but available results in the open literature are scarce. This work aims at investigating how different quenching techniques affect the two-body abrasive wear resistance of hardened high strength boron steels. Furthermore, the wear as a function of depth in thicker hardened high strength boron steel plates has also been studied. The material characterisation has been carried out using microhardness, SEM/energy dispersive spectroscopy and three-dimensional optical surface profilometry. The results have shown that water quenched and tool quenched high strength boron steel had similar wear resistance. The main wear mechanisms appear to be microcutting combined with microfatigue. Workhardening during the abrasion process has been found to affect the abrasive wear.     

On the wear resistance of high-speed steels

The wear resistance of cast and strained high-speed steels are evaluated and compared, and the regularities of variations in their structure and properties depending on the austenitizing temperature are described. The impact of modification on the wear resistance of tungsten-molybdenum high-speed steels has been studied. Data on the steels with improved wear resistance are reported     

Prediction of tool failure rate in turning hardened steels

This paper presents a stochastic model for predicting the tool failure rate in turning hardened steel with ceramic tools. This model is based on the assumption that gradual wear, chemical wear, and premature failure (i.e. chipping and breakage) are the main causes of ending the tool life. A statistical distribution is assumed for each cause of tool failure. General equations for representing tool-life distribution, reliability function, and failure rate are then derived. The assumed distributions are then verified experimentally. From the experimental results, the coefficients of these equations are determined. Further, the rate of failure is used as a characteristic signature for qualitative performance evaluation. The results obtained show that the predicted rate of ceramic tool failure is 20% (in the first few seconds of machining) and it increases with an increase in cutting speeds. These results indicate that there will always be a risk that the tool will fail at a very early stage of cutting. Such a possibility should not be overlooked when developing proper tool replacement strategies. Finally, the results also give the tool manufacturers information which can be used to modify the quality control procedures in order to broaden the use of ceramic tools.Nomenclature c constant - ch chamfer width of the tool, mm - d depth of cut, mm - h _i hardness value at theith location on the workpiece during machining - h mean ofh ₁,h ₂,h ₃, ...,h _nn - n hardness mean location - m Meyer exponent determined experimentally to define the nonlinear relation between the cutting force and the ratioh _i/h - f feedrate, mm rev^–1 - f(t) probability density function of tool failure - f ₁(t) probability density function of tool failure due to breakage caused by tool quality - f ₂(t) probability density function of tool failure due to breakage caused by workpiece condition - f ₃(t) probability density function of tool failure due to tool chipping caused by chemical wear - f ₄(t) probability density function of tool failure due to flank wear - f ₅(t) probability density function of tool failure due to crater wear - O() error - t cutting time, min - x ₁,x ₂,...,x _n independent variables - A _i instantaneous area of contact between the tool and the workpiece - C ₁ chip load, which can be determined as a function of the cutting conditions and tool geometry - K _I crater wear index - K _T maximum depth of crater wear on tool face, mm - K _M crater centre distance, mm - N number of failures - P(t) probability function of tool failure - P _j(t) corresponding probability of failure, such that 1j5 - R tool nose radius, mm - R(t) reliability function - R _j(t) corresponding reliability function, such that 1j5 - T _V estimate of tool life for a set value of average flank wear (V _B ^* ) - T _K estimate of tool life for a set value of maximum depth of crater wear (K _T ^* ) - V cutting speed, m/min - V _B average tool wear, mm - Z(t) instantaneous failure rate or hazard function - ₃ shape parameter in the Weibull probability density function - rake angle - ₃ scale parameter in the Weibull probability density function, min - failure rate of the cutting tool - mean of a logarithmic normal distribution function - standard deviation of a logarithmic normal distribution function - tool wear function - time corresponding to the occurrence of tool failure - (.) standard logarithmic normal distribution function     

Effect of tool pin design on the microstructural evolutions and tribological characteristics of friction stir processed structural steel

In this research, friction stir processing (FSP) technique is applied for the surface modification of ST14 structural steel. Tungsten carbide tools with cylindrical, conical, square and triangular pin designs are used for surface modification at rotational speed of 400 rpm, normal force of 5 KN and traverse speed of 100 mm min⁻¹. Mechanical and tribological properties of the processed surfaces including microhardness and wear characteristics are studied in detail. Furthermore, microstructural evolutions and worn surfaces are investigated by optical and scanning electron microscopes. Based on the achievements, all designed pins were successfully applicable for low carbon steel to produce defect-free processed material. By the microstructural changes within the stirred zone, the processed specimen is obtained higher mechanical properties. This is due to the formation of fine grains as the consequence of imposing intensive plastic deformation during FSP; however, this issue is highlighted by using square pin design. In this case, minimum grain size of 5 μm and maximum hardness of 320 VHN, as well as, maximum wear resistance are all examined for the specimen modified by square pin.     

Effect of temperature and load on three-body abrasion of cermets and steel

The effect of temperature and load on three-body abrasion resistance has been examined for stainless steel, Cr₃C₂-Ni cermet, plain WC-Co hardmetal and yttria stabilized zirconia doped WC-based composites. Series of tests at various tribo-conditions were performed on a recently developed device. Coefficient of friction and materials response to abrasive actions have been analyzed and positive effect of zirconia addition on materials wear resistance has been shown. The low wear rates of ZrO₂ containing cermets are due to lower susceptibility of zirconia to transgranular crack propagation, smaller mean free path between ceramic grains and formation of lubricating glazed silica-rich layer.     

New method to determine the mechanical properties of heat treated steels

A new numerical approach to indentation problems is developed for hardened materials. A relationship between load, displacement, flow stress and strain hardening exponent of heat treated materials with a hard film, is given.This method is based on the minimisation of the error between the experimental curve (load–displacement of the indenter) and the theoretical curve, function of the mechanical and geometrical properties of the studied materials.Comparison of the numerical results with those experimentally obtained from known materials confirms the interest of the method proposed.     

Influence of heat treatment parameters on the lubricated sliding wear behaviour of a zinc-based alloy

This investigation deals with the observations made pertaining to the influence of the duration of heat treatment (ageing) on the sliding wear response of a zinc-based alloy. The heat treatment comprised of solutionizing followed by artificial ageing for different durations. Partially lubricated sliding wear tests were carried out at a fixed applied pressure, speed and distance.The heat-treated samples attained less strength and hardness but more elongation over the as-cast one. The wear rate and frictional heating initially decreased with increasing ageing duration. This was followed by the attainment of the minimum and then a reversal in the trend at longer durations of ageing. The tensile strength and hardness decreased with increasing duration of ageing and became stable beyond certain ageing period while elongation followed a reverse trend. The response of the samples has been substantiated through the fractographic features and characteristics of wear surfaces, subsurface regions and debris.     

Investigation of tool wear suppression in ultraprecision diamond machining of die steel

Rapid tool wear in diamond machining of steel can cause catastrophic failures. Despite several approaches to reducing tool wear, diamond machining of steel for industrial applications remains limited. We investigated two solutions, namely plasma nitriding treatment for workpiece surface modification and elliptical vibration cutting for cutting process modification, to determine their effect on reducing tool wear in diamond machining of AISI 4140 die steel. Furthermore, a new approach by combining the two solutions was also explored. Experimental results showed that diamond tool wear could be reduced by several orders of magnitude and mirror-quality surface can be obtained by using either the plasma nitriding treatment or the elliptical vibration cutting. However, in contrast to our expectations, combining the two solutions did not yield further improvement of either the surface finish or the reduction of tool wear compared with that of elliptical vibration cutting alone due to microchipping. Care has been taken to investigate the mechanism responsible for microchipping, and it was found that microchipping is highly dependent on the crystal orientation of the diamond. A diamond tool with the (1 1 0) plane as the rake face and the (1 0 0) plane as the flank face was more resistant to damage, and the microchipping induced in the combined cutting process was almost completely suppressed.