Wear characteristics of HSLA steel

HSLA steel being a promising material in numerous applications, was subjected to wear studies under dry sliding conditions at varying conditions of loads and sliding speeds. Wear debris were extensively studied under optical, stereo- and scanning electron microscopes and also by X-ray diffraction. In order to understand the wear mechanism, wear tracks were examined under optical and scanning electron microscopes. In addition, depth of strain hardened zone below sliding surface was measured under different conditions of loads. This study showed that wear rate initially increased either with increased load or sliding speed and debris generated was a mixture of oxide and metal powders, but after attaining a peak in wear rate, a decreasing trend was observed for load as well as sliding speed studied. This decreasing trend has been attained due to domination of oxidation process as a result of rise in temperature at higher values of loads and sliding speeds. These oxides formed with temperature rise covered the wear tracks and wear rate decreased. Finally, depth of strain hardened zone beneath the sliding surface was observed to increase with load.     

Cutting of corrosion-resistant steel using a tool with a short front surface

This study addresses the influence of shortening the cutter’s front surface on the buildup, the chip departure, the shear angle, the chip shrinkage, the cutting-force components, the unit work of deformation, and the energy expenditure in converting the cut layer to a chip.     

钢结硬质合金ELID磨削表面的AFM分析

研究了采用ELID磨削技术磨削钢结硬质合金,使其表面粗糙度Ra≤0.02μm。并通过原子力显微镜(AFM)对其微观表面形貌、表面缺陷及钢结硬质合金难加工机理进行分析。     

Wear characteristics of ceramic cutting tools in machining steel

Some ceramic materials such as Al₂O₃ which have a high compressive strength, hardness and chemical stability came into use industrially in the middle of this century as powder metallurgy produced indexable cutting tool inserts. These early ceramic tools were inherently weak in tension, impact and dynamic loading owing to their low tensile strength, toughness and transverse rupture strength; because of this their application was limited to medium productivity operations and work materials of softer grades. However, the technology of ceramic cutting tools has made great strides in the last few years through substantial improvements in their strength, toughness and wear resistivity. These modern ceramic tools have found wide and economic applications in high production machining of both cast iron and steels.In this paper the constructional characteristics of some modern ceramic tools and their wear behaviour and overall performances in machining mild steel at both low and high speeds are presented. The comparative results obtained are reported and discussed.     

Wear behaviour of a steel weld-joint

A series of experiments has been carried out to examine the dry sliding wear behaviour of the different regimes of a single pass steel weld-joint vis-à-vis their microstructures and micro-hardness characteristics. Wear tests have been performed on two types of specimen configurations: first, on limited regions of the weld-joint exhibiting a specific microstructure, and second, continuously from the weld metal to the base metal via the heat affected zone (HAZ). The former type of experiments was found capable in delineating the wear characteristics of the base metal, weld metal and the different regimes of the HAZ. The wear behaviour of the varied regimes of the weld-joint, specifically that of the different sub-zones of the HAZ, has been explained using their microstructures, initial micro-hardness, work hardening during wear and their inherent residual stresses. This is a first report on the sequential wear behaviour of a weld-joint.     

Wear resistance of cutting tools with a plasma-modified surface layer

An analytical model is obtained for calculating the working life of a cutting tool with a plasmamodified surface layer. It permits calculation of the conditions ensuring increased wear resistance of the tool and hence increased reliability in manufacturing on numerically controlled machine tools.     

基于网络能力的钢铁企业短期生产能力计划模型求解算法

根据钢铁企业流程式生产的特点,以有限生产能力、库存和工艺制程为约束,利用约束规划方法建立了短期生产能力计划的约束满足模型。针对常规约束规划求解大规模问题过程中不存在可行解时大量回溯对求解效率产生的影响,提出一种基于约束的网络生产能力计算方法,首先对产品／订单的生产流程网络进行预处理,快速计算可用能力,然后利用网络生产能力约束辅助约束规划裁剪搜索空间,实现在短时间内找到解并进行订单／产品的能力承诺以及生产排程。通过算例实验证明了算法的复杂性与问题规模增长呈近似线性关系,而且可适用于不同生产模式,算法具有通用性。     

Interfacial properties of diffusion bonded Ti-6Al-4V to AISI 304 stainless steel by inserting a Cu interlayer

The joining characteristics of Ti-6Al-4V with AISI 304 stainless steel by inserting a Cu interlayer was investigated in a vacuum-free diffusion bonding process. The diffusion bonds were carried out in the temperature range of 820, 850 and 870°C for 50, 70 and 90 minutes, respectively, under 1 MPa load in argon atmosphere. The joining performances of diffusion bonded Ti-6Al-4V to AISI 304 were studied experimentally. The influence of the insert layer on the microstructure-formed interface region, bonding quality and mechanical properties have also been estimated. The microstructures formed in the diffusion region were observed and determined by scanning electron microscopy (SEM). The microhardness across and perpendicular to the interface were measured and the strength of the joints were also determined with lap-shear test.     

Wear behaviour and failure mechanism of bonded solid lubricants

A test rig and a test procedure have been developed using a ring-block system as a test specimen in order to evaluate the wear behaviour of bonded solid lubricating films by laboratory methods. Bonded films have been used as test lubricants containing MoS₂, graphite and Sb(SbS₄) as two- and three-component systems.     

Wear of steel by rubber

Wear of a steel blade used as a scraper to abrade rubber surfaces has been found to take place much more rapidly on a cis-polyisoprene (natural rubber) surface than on a cis-polybutadiene surface, and much more rapidly in an inert atmosphere than in air. These observations are attributed to the direct attack upon steel of free-radical species generated by mechanical rupture of elastomer molecules during abrasion.     

Wear behaviour of carbonitrided steel

A pin and disk study of carbonitrided steel revealed different types of wear. The best results were with carbonitrided material rubbing on carbonitrided material. The effect of load and the role of brittleness on wear has been studied. Differences in structure, hardness and work-hardening of the various surface layers as well as debris in the interface caused the difference in wear behaviour of the layers.     

The effect of some surface treatments on the life of high speed steel tools

Surface treatments are very important, especially for high speed steel cutting tool tips. After the cutting edges become dull the cutting tip becomes useless.In this paper three groups of cutting tools were used to turn a mild steel workpiece; the cutting tool groups are conventional high speed steel tools, cromhardened tool steels and tufftrided cutting tool steels.A response surface methodology was used to investigate the effect of speed and feed on tool life.Tool life can be increased by these types of surface treatment on high speed steel tools for practical values of the cutting speed.     

Wear of steel in rolling contact with silicon nitride

Wear of steel (AISI M-50 and AISI 52100) bearing balls in lubricated rolling contact with ground and ground-and-lapped silicon nitride rods was studied using a ball-on-rod rolling-contact-fatigue (RCF) tester. The steel balls suffered significant wear in rolling contact with the as-ground (R_a = 0.18 μm) silicon nitride rods. The wear volume loss was approximately linear with the rolling distance. The wear rate increased linearly with the initial Hertzian contact stress in the range, 3–6.5 GPa. Examination of the wear tracks in a scanning electron microscope revealed surface features that suggested a wear mechanism that involved plastic deformation of the steel surface, squeezing of the metal symmetrically outward and rupture of the metal layers at the edges. The steel balls suffered negligible wear but failed by spalling in rolling contact with the ground-and-lapped silicon nitride rods (R_a = 0.08 μm) at an initial contact stress of 5.5 GPa. The as-ground silicon nitride rods exhibited neither wear nor spalling in the RCF tests, while the ground-and-lapped silicon nitride rods showed no wear but occasional spalling failure.     

Effect of laser surface hardening on magnetic characteristics of a carbon steel under loading

Comparative studies of the structure and mechanical and magnetic characteristics of a Steel 45 subjected to laser treatment and the same steel subjected to hot rolling and volume hardening were performed. Staging changes in magnetic characteristics during tension were shown to reflect the order of involvement of individual structural components into the plastic deformation of the material.     

碳纤维布胶接修复含裂纹钢管仿真分析

在胶接修复工艺中,裂纹的形式和不同的胶接方案影响结构的修复效果.以裂纹尖端应力强度因子(Stress Intensity Factor,SIF)为依据,分别对含有2种裂纹形式的钢管进行了仿真分析,探讨钢管的裂纹大小、碳纤维布的长度和层数对胶接修复强度的影响.分析结果表明,增加碳纤维布长度可以有效提高修复结构的强度,当长度超过有效胶接长度后,提高幅度不明显.裂纹面积所占比例越大,裂纹处应力集中程度越高,胶接碳纤维布的修复效果越显著.2层碳纤维布胶接修复对SIF的增长抑制效果比1层碳纤维布提高了10％以上,对于圆周裂纹损伤程度较小时,使用1层碳纤维布修复已能有效改善钢管的结构性能,对于圆弧裂纹和损伤程度较大的圆周裂纹,建议使用2层碳纤维布修复.     

碳纤维布胶接修复含裂纹钢管仿真分析

在胶接修复工艺中,裂纹的形式和不同的胶接方案影响结构的修复效果.以裂纹尖端应力强度因子(Stress Intensity Factor,SIF)为依据,分别对含有2种裂纹形式的钢管进行了仿真分析,探讨钢管的裂纹大小、碳纤维布的长度和层数对胶接修复强度的影响.分析结果表明,增加碳纤维布长度可以有效提高修复结构的强度,当长度超过有效胶接长度后,提高幅度不明显.裂纹面积所占比例越大,裂纹处应力集中程度越高,胶接碳纤维布的修复效果越显著.2层碳纤维布胶接修复对SIF的增长抑制效果比1层碳纤维布提高了10％以上,对于圆周裂纹损伤程度较小时,使用1层碳纤维布修复已能有效改善钢管的结构性能,对于圆弧裂纹和损伤程度较大的圆周裂纹,建议使用2层碳纤维布修复.     

Machining of sintered steel under different lubrication conditions

Cutting experiments of sintered steel Fe–2Cu–0.8C under different lubrication/cooling conditions and with different tool materials were performed in order to clarify the reasons for the low machinability of the sintered steel, and investigate the applicability of minimum quantity of lubricant (MQL) to the machining of sintered steel. As a theoretical approach to the short tool life in machining sintered steel, the impacts to the cutting edge caused by micro-voids were theoretically modeled, and it was revealed that the cutting edge suffered from impacts at a very short interval causing high cycle fatigue. Extremely short tool life in dry machining of sintered steel already used for wet machining proved that coolant definitely increased the stress amplitude in high cycle fatigue. Application of the air jet to a tool showed the positive effect in reducing tool wear. This indicated the possibility that micro-cracks nucleated by high cycle fatigue were healed by oxidation. MQL cutting with small amount of oil and air jet is proved to be acceptable for machining sintered steel from the results of cutting experiments using uncoated and coated carbide and cermet tools. Finally, it is confirmed that thick coating of a carbide tool is effective for dramatically improving the machinability.     

Wear characteristics of metals

Although there are still many gaps in our knowledge of the factors involved in tribological interactions, there is sufficient information available to characterise the commonly encountered wear mechanisms. Many techniques are currently available to modify surfaces to improve their wear characteristics, but these are usually applied after a problem has become apparent in service. These techniques are not usually included in the original design because most engineers do not appreciate the effect of operating conditions on the life of components. The precise role of physical and mechanical properties of metals in wear is little understood. Much effort has been expended in our understanding of bulk properties. Considerably more effort is now required to understand surface properties. Halling has stated that the major growth area for the next decade lies in the role of surface treatments for improving tribological characteristics²⁴. These, however, are already becoming available faster than our rate of understanding of their precise tribological properties.Design guides for widely used engineering metals in different conditions of treatment are required under specific wear conditions. Few materials combinations have been examined in the metallurgical detail demonstrated by Lea. This approach should be further extended to produce wear maps with their associated atlas of surface and sub-surface microstructure showing both satisfactory and unsatisfactory wear behaviour.An appreciation of the cost wear would bring about a greater awareness of the problems involved and greater effort would be applied to producing long term solutions instead of the concentration on short term expediencyThe major problem, however, is the lack of communication between those with the knowledge and those who should be using it in their designs. The tribologist should produce more information related to the behaviour of materials in service. He should be encouraged to publish more case studies and solutions related to specific engineering components or systems.     

Tool wear and tool life characteristics of unconventional sintered carbides in the intermittent cutting of hardened steel

Carbides coated with TiC, TiN, TiC/TiN or TiC/Al₂O₃ coatings on a tough hard material base and TiC-containing hard material of modified composition and structure were used to investigate tool-wear and tool-life characteristics in face milling of martensitic steel of hardness 300–600 HV. Tool-life behaviour with increasing hardness and cutting speed was determined. Characteristic wear mechanisms are discussed on the basis of light and scanning electron microscopy observations.     

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.