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.     

热处理对奥氏体不锈钢焊接接头晶间腐蚀的影响

本文主要对奥氏体不锈钢1Cr18Ni9的焊接接头进行了不同的热处理,并根据GB/T 6394-2002中晶粒度大小评级图评定出了各区域的晶粒度;然后利用恒电流法测定了焊接接头的腐蚀电流密度.实验结果表明,焊接接头的焊缝和熔合区的晶粒度越大,腐蚀电流就越大,腐蚀速度也越大,材料的耐腐蚀性就越差.     

Wear of aluminium bronze on steel under conditions of boundary lubrication

An investigation was conducted to examine the wear of aluminium bronze against tool steel when lubricated under a boundary lubrication regime by aviation kerosene, both with and without the inclusion of a commercially available boundary additive. The objective was to isolate the mechanisms of boundary film formation, protection and wear of the metal surfaces, through mechanical measurements and analyses of surfaces and debris.A model is proposed to explain these mechanisms in terms of material transfer and subsequent competing reactions between dissolved oxygen and long chain hydrocarbon acid molecules, and the metal surface.     

Hydrodynamic lubrication of textured steel surfaces under reciprocating sliding conditions

The influence of surface topography on lubricant film thickness has been investigated for the reciprocating sliding of patterned plane steel surfaces against cylindrical counterbodies under conditions of hydrodynamic lubrication. Patterns of circular depressions, grooves and chevrons were used, and the fractional area coverage, depth, width and sliding orientation relative to the texture were systematically varied. Textured samples with features much larger than the elastic contact width gave film thicknesses, which were smaller than those for non-textured samples. This effect was more significant for larger features. For patterns composed of circular pockets, maximum film thickness was achieved for an area coverage fraction f≈0.11. Chevron patterns pointing along the sliding direction gave higher film thicknesses than those pointing across. For an area coverage ratio of ca. 0.06, maximum film thickness was achieved for a feature depth to width ratio of about 0.07. Among the patterns investigated, chevrons were the most effective and grooves the least effective in increasing hydrodynamic film thickness.     

Tribological properties of plasma nitrided stainless steel against SAE52100 steel under ionic liquid lubrication condition

1Cr18Ni9Ti stainless steel was modified by plasma nitriding. The phase composition of the plasma nitrided layer was examined by means of X-ray diffraction. The friction and wear properties of the modified and unmodified 1Cr18Ni9Ti stainless steel specimens sliding against SAE52100 steel under the lubrication of ionic liquid of 1-ethyl-3-hexylimidazolium hexafluorophosphate (L-P308) and poly α-olefin (PAO) were investigated on an Optimol SRV oscillating friction and wear tester, with the interactions among the modified surface layer and the ionic liquids and PAO to be focused on. The morphologies of the worn surfaces were observed using a scanning electron microscope. The chemical states of several typical elements on the worn surfaces of the modified steel surfaces were examined by means of X-ray photoelectron spectroscopy. Results showed that the modified sample had better anti-wear abilities than the unmodified one, but the modified sample had a slightly higher friction coefficient than the untreated one. This was partly attributed to the change in the hardness and phase composition of the stainless steel surfaces after plasma nitriding and tribochemical reactions between the steel and the lubricant. The resultant surface protective films composed of various tribochemical products together with the adsorbed boundary lubricating film contributed to reduce the friction and wear.     

Tribochemical aspects of silicon nitride ceramic sliding against stainless steel under the lubrication of seawater

Tribological behaviors of Si₃N₄ ceramic sliding against 316 stainless steel under seawater lubrication were investigated and compared with those under dry sliding and pure water lubrication. The results showed that SiO₂ colloidal particles were formed on the rubbing surface of Si₃N₄ due to the friction-induced chemical reaction of Si₃N₄ with H₂O, which were further aggregated into the silica gel with the assistance of ions in seawater. Because of the boundary lubrication of the silica gel layer, both the lowest friction coefficient and the smallest wear rates of Si₃N₄ and 316 steel were obtained in seawater.     

Tool wear and tool life in end milling of 15–5 PH stainless steel under different cooling and lubrication conditions

Most of the machining operations on stainless steel alloys are carried out with cutting fluid due to the poor machinability of this kind of material. Tool wear mechanisms are directly influenced by the cooling and lubrication condition to which the tool is exposed, especially in interrupted cutting processes. This work investigates tool wear mechanisms for an end milling operation of a precipitation-hardened martensitic stainless steel under four different cooling and lubrication conditions. The results demonstrated that the cooling and lubrication condition strongly influences tool life and the tool wear mechanism, and furthermore, that tool lubrication rather than cooling should be the purpose for using cutting fluid in this kind of operation, in order to avoid damage caused by tool temperature variations.     

The effect of surface chemistry in lubrication on the tribological behaviour of steel rollers under rolling-sliding contacts

Experiments were carried out on a wear test machine utilising a gearcam adapter to simulate line-contact lubrication. Due to the formation of a surface adsorption layer on the steel substrate, the tribological performance was detected by measuring the voltage for a lubricant with various additive concentrations. The roller wear rate was found to be strongly dependent upon both the rising rate of voltage in the wear process and the time period needed to create a positive voltage. The antiwear effect of differing additive concentrations was evaluated using the measurements of voltage for various operating conditions. An increase in rotational speed, with a lubricating oil with a low additive concentration, decreases the wear rate. A lubricating oil with a high additive concentration does little to decrease the wear rate at low rotational speeds.     

Wear resistance by copolymers with controlled structure under boundary lubrication conditions

Lubricants are of paramount importance in protecting metallic contact surfaces and reducing friction. The viscosity of lubricating oil can be engineered by introducing long linear polymers, such as poly(lauryl methacrylate) (PLMA). In particular, the formation of adsorption films by using polymers with hydroxy or amino side groups has attracted much attention in recent years. In this study, copolymers with controlled structure were synthesised by SARA ATRP, which can be used in large scale production. A comparison of friction and wear under boundary lubrication was conducted using both statistical and block copolymers with low Ð. Friction test results using a reciprocating sliding machine (SRV) showed that the block copolymers were less likely to desorb from the metal surface than the statistical copolymers. In addition, the wear evaluation after the SRV test showed that the block copolymer had less wear and less wear debris.     

The reaction layer formed on steel by additives based on sulphur and phosphorus compounds under conditions of boundary lubrication

Sliding experiments were carried out under constant load and under continuously increasing load using a combination of a high carbon steel and a ball bearing steel with a mineral oil containing a commercial S-P compound under conditions of boundary lubrication. The reacted films formed on the carbon steel under conditions of severe boundary lubrication were examined by light microscopy, electron probe microanalysis and Auger emission electron spectroscopy. The surface products were composed essentially of dispersed thin films containing a high concentration of phosphorus and little sulphur and discontinuously distributed pits containing much more sulphur than the surrounding area. The element distribution on worn surfaces varied considerably with the applied load and the temperature of the contact.     

Forming characteristics of austenitic stainless steel sheet alloys under warm hydroforming conditions

Stainless steel sheet alloys have been increasingly used in heating, ventilating, and air conditioning; appliance; sanitary and medical devices; as well as several structural and transportation applications, due to their high strength-to-weight ratio, corrosion resistance, biomedical compatibility, and esthetic appearance. Among various stainless steel alloys, austenitic stainless steels are the most commonly used type. Due to the forming limitations into complex shapes at room temperature conditions and stress-corrosion cracking issues, forming at elevated temperature has been considered as an enabling technique. Formability of stainless steels is affected by strain rate and temperature due to martensitic transformation of meta-stable austenite microstructure. In this study, deformation characteristics of three common austenitic stainless steels (AISI 201, 301, and 304) were investigated using closed-die hydroforming under different process conditions. Specifically, effects of pressure, temperature, and die/part geometry on the material forming characteristics quantified using cavity filling ratio and thinning distribution were investigated. Results suggested that, in terms of cavity filling, pressure and material grade are significant factors while temperature is not in the case of axisymmetric part. For the non-axisymmetric case, all parameters were found to be significant. In addition, finite element (FE) modeling was performed to simulate several forming cases that were experimentally conducted in this study. The FE model was simulated based on material flow curves obtained from previous studies under similar conditions (strain rate and temperature) by the authors. FEA results were shown to be in good agreement with experimental findings, particularly for cavity filling and part profile predictions. Hence, the FE model and the material models can be used for further predictions of complex and different parts with confidence.     

不锈钢的ELID磨削实验研究

在实验的基础上,对磨削不锈钢时磨削力的变化规律进行分析,并将磨削力、工件表面粗糙度与普通磨削进行比较.结果表明,采用铸铁基金刚石砂轮进行ELID磨削时,磨削力随时间的增加量较小,而采用普通磨削方式进行磨削时,磨削力随时间的增加量较大.在线电解修整使砂轮在磨削中始终保持良好的磨削状态,有利于节省砂轮修整时间,提高加工效率.采用相同砂轮进行磨削实验,ELID磨削可获得更低的表面粗糙度值,实现了对不锈钢的精密镜面磨削.     

Fretting fatigue behavior of SUS304 stainless steel under pressurized hot water

Fretting fatigue behavior of the sensitized SUS304 stainless steel under a pressurized hot water at 7.3 MPa and 288 °C was investigated. The tests were carried out under a contact pressure of 100 MPa and a frequency of 20 Hz. From the experimental result, combined effect of pressurized hot water and localized high tangential stress due to fretting resulted in nucleation of intergranular crack along the outer edge of contact region at lower stress amplitudes, while a fretting fatigue crack was nucleated at the highest tangential force point independently from these intergranular cracks at higher stress amplitudes. No intergranular crack nucleation was observed for fretting fatigue at the same temperature in air. The higher stress ratio reduced the fatigue strength, where the crack tip was exposed more in corrosive environment due to the high mean stress compared to the lower stress ratio.     

Influence of non-smooth surface on tribological properties of glass fiber-epoxy resin composite sliding against stainless steel under natural seawater lubrication

With the development of bionics, the bionic non-smooth surfaces are introduced to the field of tribology. Although non-smooth surface has been studied widely, the studies of non-smooth surface under the natural seawater lubrication are still very fewer, especially experimental research. The influences of smooth and non-smooth surface on the frictional properties of the glass fiber-epoxy resin composite(GF/EPR) coupled with stainless steel 316 L are investigated under natural seawater lubrication in this paper. The tested non-smooth surfaces include the surfaces with semi-spherical pits, the conical pits, the cone-cylinder combined pits, the cylindrical pits and through holes. The friction and wear tests are performed using a ring-on-disc test rig under 60 N load and 1000 r/min rotational speed. The tests results show that GF/EPR with bionic non-smooth surface has quite lower friction coefficient and better wear resistance than GF/EPR with smooth surface without pits. The average friction coefficient of GF/EPR with semi-spherical pits is 0.088, which shows the largest reduction is approximately 63.18% of GF/EPR with smooth surface. In addition, the wear debris on the worn surfaces of GF/EPR are observed by a confocal scanning laser microscope. It is shown that the primary wear mechanism is the abrasive wear. The research results provide some design parameters for non-smooth surface, and the experiment results can serve as a beneficial supplement to non-smooth surface study.     

Comparative evaluations of machining performance during turning of 17-4 PH stainless steel under cryogenic and wet machining conditions

Productivity in machining of 17-4 PH stainless steel is adversely affected by the premature failure of tool and poor surface finish as a consequence of high cutting temperatures. Conventional cutting fluids not only create environmental and health problems but also fail to overcome the high cutting temperatures during machining. Cryogenic cooling is an environmentally clean cooling technology for attractive management of machining zone temperatures. The present study investigates the effect of cryogenic liquid nitrogen (LN₂ at ?196°C) on cutting temperatures, cutting forces (main cutting force, feed force), surface roughness, tool flank wear and chip morphology in turning of 17-4 PH stainless steel with AlTiN PVD-coated tungsten-coated carbide inserts and results were compared to wet machining. In overall, cryogenic machining reduces the cutting temperature, cutting forces, surface roughness and tool flank wear to a maximum of 73.4, 17.62, 44.29 and 55.55%, respectively. Improved chip breakability was found in cryogenic machining.     

Wear of AISI 4340 steel under boundary lubrication

Wear tests were conducted using AISI 4340 steel sliding on AISI 01 tool steel under boundary lubrication conditions. The AISI 4340 steel was heat treated to obtain different microstructures and hardness levels. The results indicated that the wear behavior depends on the heat treatment procedure. It was found that hardness alone cannot be used as a measure of wear and that the microstructure and other mechanical properties should also be used. Chemical reaction products containing phosphorus, sulfur and zinc were found on the wear surfaces lubricated with a fully formulated light oil containing zinc dithiophosphates. The chemically reacted film was nonuniform and consisted of patches 1–1500 μm in size. The larger patches were formed on the surface of steel with a pearlite-ferrite microstructure and resulted in a high wear rate. In contrast, the small patches and the thin blue and brown films were formed on the wear surface of tempered martensite steel and produced low wear rates.     

微量油膜水滴切削加工不锈钢的效果试验研究

主要应用微量油膜水滴切削液,在C620-1普通机床上,通过改变切削速度、进给量以及调整喷嘴的喷射角度,对奥氏体1Cr18Ni9Ti不锈钢材料进行切削加工的效果试验研究。试验结果表明,与干切削、乳化液切削相比,微量油膜水滴切削不仅能够有效地降低切削力和加工表面粗糙度,而且其刀具寿命分别是干切削、乳化液切削的2.28倍和1.6倍。在喷射方向效果研究中,微量油膜水滴在对刀具后刀面和侧面进行喷射的切削加工效果更佳。试验研究表明,微量油膜水滴切削液具有一定的冷却效果和良好的润滑效果。     

Process performance of micro-EDM drilling of stainless steel

An experimental campaign based on the execution of through micro-holes on stainless steel plates was carried out using a micro-EDM machine Sarix SX-200. The experimental campaign was carried out by varying several process parameters, namely peak current, voltage and frequency. Tubular electrodes made of two different materials (tungsten carbide and brass) were used. A study of the in progress material removal rate (MRR) and tool wear ratio (TWR) during the drilling process was performed. Some mathematical laws governing the relation between process parameters and performance indexes were defined. Two technological windows representing TWR and MRR as a function of the hole depth, for different electrode materials, were obtained.     

Temperatures of meshing gears under conditions of elastohydrodynamic lubrication

Formulae which have been derived previously were used to determine the temperatures in the contact zone of spur gears meshing under conditions of elastohydrodynamic lubrication.