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1.
《粉末冶金学》2013,56(4):352-357
AbstractWithin a project supported by the European Union a consortium consisting of the companies Fraunhofer Institute for Structural Durability LBF, AMES, Miba, GKN, Federal Mogul, Höganäs, RWTH Aachen, Peugeot/Citroën and Fiat worked on the realisation of heavyduty gearbox components by warm powder compaction technology. In this paper, part of this work will be reported, namely the manufacturing of synchroniser hubs by this new technology. Until now these hubs were manufactured by the double pressing and double sintering route.Based on service load measurements in a gearbox of a Peugeot 506, vehicle fatigue tests were carried out with conventionally and warm pressed hubs. The results of fatigue tests with hubs as well as the durability tests carried out in the gearboxes of Peugeot/Fiat revealed the same performance for both technologies. As a consequence, the hubs produced by warm powder compaction can substitute for the ones produced conventionally. Further, the new technology reveals economic advantages with regard to the powder price as well as production costs. 相似文献
2.
《Materials Science & Technology》2013,29(6):641-647
AbstractMultiphase stainless steels are produced for their attractive properties of mechanical strength and corrosion resistance relative to their austenite–ferrite structure. The manufacture of these steel by powder metallurgy technology presents some advantages in terms of low cost and formability of complex shapes. Mechanical and corrosion resistances are not at the level of the wrought steels due to their porous nature. In this work the fatigue and corrosion fatigue behaviour of some sintered steels obtained by sintering from 316L and 434L base powders has been studied for characterisation and comparison. The sintered steels were fatigue tested in two different environments: air and NaCl aqueous solution. The tests performed indicate that the chemical and microstructral composition has no great influence on fatigue behaviour in comparison with the manufacturing technology (sintering). This is most evident in the more aggressive environment, like seawater, in which these steels could be advantageously used. The analysis of fracture surfaces using SEM microscopy shows a peculiar crack propagation characterised by cleavage, stress intensification due to porosity, and features of localised ductility on sintering necks and base powder particles. 相似文献
3.
《Materials Science & Technology》2013,29(1):76-84
AbstractA response to the chemical or biological contamination of aircraft requires the use of a suitable decontaminant. Among possible chemical decontaminants, vapour phase hydrogen peroxide appears to be a likely candidate in terms of a combination of efficacy, low environmental impact and potential for materials compatibility. The present paper examines the effect of hydrogen peroxide, both in the vapour phase and as a liquid concentrate on two common structural materials used in aviation, namely 2024 and 7075 age hardenable aluminium alloys and on 304 austenitic stainless steel, the latter as employed in galley and lavatory surfaces. The present paper characterises both the effects of hydrogen peroxide on the microstructure of the materials and the impact that decontamination has on the tensile properties and corrosion resistance of these materials. Microstructural effects are both relatively small in magnitude and confined to a region immediately beside the exposed surface. No systematic effect is found on either the tensile properties or the post-exposure corrosion resistance of the three alloys examined. These observations are encouraging in terms of the use of vapour phase hydrogen peroxide for decontamination applications. 相似文献
4.
《Materials Science & Technology》2013,29(4):404-409
AbstractThis paper is dedicated to the memory of Professor Sir Robert Honeycombe, who examined the first author's PhD thesis on this subject in 1972. The paper reviews some of the very large improvements in the understanding of the formation of textures and microstructures in drawing quality steels in both their deformed and recrystallised states made since the 1970s, focusing in particular on deformation bending in interstitial free steels. 相似文献
5.
《Materials Science & Technology》2013,29(2):145-150
AbstractUsing a Gleeble 1500 hot simulator, the effects of hot deformation parameters and accelerated cooling conditions on the microstructural characteristics of low carbon microalloyed steels were investigated by means of compression tests. It was found that the grain refinement effect of single pass reduction in the recrystallisation or unrecrystallisation temperature ranges is weaker than that of two pass reduction in the recrystallisation and unrecrystallisation temperature ranges. However, four pass deformation in the recrystallisation and unrecrystallisation temperature ranges could result in rather fine grained microstructures and, when coupled with moderately high cooling rate, partially acicular ferrite microstructure could be obtained. With the increase of cooling rate, the microstructure becomes finer and the content of acicular ferrite increases. Under similar deformation and cooling conditions, the specimens with relatively high carbon content have more refined microstructures. 相似文献
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7.
《粉末冶金学》2013,56(4):329-334
AbstractMost of the numerical simulation software on the hot isostatic pressing (hipping) process is based on viscoplastic modelling of densification, such as the well known Abouaf's model. These constitutive equations are generally obtained from a viscoplastic potential depending on Green's equivalent stress. An implicit coupling between isotropic and deviator parts is therefore only defined by an equivalent stress. A new viscoplastic formulation proposed by Stutz introduces an explicit coupling between isotropic and deviator parts of the stress state, allowing then more flexibility to take into account the experimental results achieved from isotropic, die compaction, and creep tests. This paper deals with the presentation of this new formulation which has been implemented in the finite elements software PreCAD, and the subsequent changes observed in numerical simulations. These simulations achieved with PreCAD software, are compared with an experiment on a complex part manufactured by CEA Grenoble. 相似文献
8.
《Materials Science & Technology》2013,29(11):1431-1439
AbstractLow (0·3%) and high manganese (1·4%) plain C – Mn steels with varying sulphur levels have had their hot ductility determined over the temperature range 700 – 1000°C, both after 'solution treatment' at 1330°C and directly after casting. It has been established that the width, depth and position of the hot ductility curves after solution treatment is more related to the transformation behaviour than either the sulphur in solution or the sulphide volume fraction or distribution. The growth of deformation induced ferrite at the austenite boundaries seems to be mainly diffusion controlled, and the higher is the transformation temperature for the γ – α phase change, the faster is the growth. Large amounts of ferrite can then form, giving good ductility. Thus, high transformation temperatures Ae 3 or Ar 3 are required to produce narrow ductility troughs. It is believed that any detrimental influence of the sulphides on these 'solution treated' steels is swamped by the rapid increase in ferrite volume fraction. For the as cast state, as more sulphides are able to precipitate at the interdendritic boundaries and austenite grain boundaries than in the solution treated condition, increasing the sulphur level causes a small deterioration in ductility at the high temperature end of the trough. In the present work, only narrow troughs have been found. This is in contrast to previous work on as cast C – Mn – Nb – Al steels, which exhibited wide troughs in the ductility curves, where it was shown that higher total sulphur levels lead to considerably worse ductility and that sulphur can be as detrimental to the ductility as niobium. It is recommended that, to avoid transverse cracking during continuous casting, in addition to keeping the sulphur level low, the carbon and manganese should also be as low as possible. 相似文献
9.
《Materials Science & Technology》2013,29(4):482-486
AbstractIn this paper, fundamental concepts of ultrasonics and characteristics of distinctive microstructures have been used to simply explain the effect of microstructure on the attenuation mechanism of ultrasonic waves in carbon steels. In addition, it has been shown that application of the second medium hardness instead of the bulk hardness is more appropriate to correlate the sound velocity and the microstructure. 相似文献
10.
《钢铁冶炼》2013,40(6):473-480
AbstractThis study investigates some effects of austenite microstructure on processes leading to copper hot shortness. Low carbon steels containing 0˙55 wt-% copper were subjected to two thermal profiles in an infrared image furnace with attached confocal scanning laser microscope: hold at 1150°C for 60 s; hold at 1150°C for 60 s, quench to 400°C, reheat to 1150°C. Heat treatments were conducted in dried/deoxidised argon to image microstructures. Subsequent samples were oxidised in air. The oxide/metal interface was studied in a scanning electron microscope. Additional confocal scanning laser microscope experiments involved melting copper directly on the steel. After quench/reheat, austenite grain size decreased by a factor of ~1˙7 and grain boundaries were redistributed. Copper evolved during the first heating was no longer found at boundaries. Results from direct copper exposure reveal an apparent effect of boundary character on copper penetration rate. Possible mechanisms by which hot shortness is affected are discussed. 相似文献