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Liquid phase sintering of M3/2 grade high speed steel (HSS) was carried out at 1270uC in high vacuum reaching near full density starting from loose packed powder. Focus is placed on the study of the effects of the addition of Si, Ni and V as elemental powder and cooling rates on the as sintered microstructure, the main objective being improving M 6 C characteristics and control of pearlite appearance. Slow cooling from the sintering temperature and Si addition in wt-% resulted in a completely fine pearlitic matrix with less elongated and more uniformly distributed M 6 C precipitates. Adding V or Ni in wt-% quantities decreased the amount of pearlite owing to MC formation and delayed pearlite formation. The study involved the use of thermodynamic modelling and sintering cycle optimisation as well as the evaluation of sintered material by means of optical and scanning electron microscopy, X-ray diffraction and hardness testing.PM/1115

This paper provides data on the effect of carbon and phosphorus levels on the density of liquid phase sintered steel and the impact of subsequent carbon removal on the mechanical properties. After sintering die pressed samples composed of liquid forming additives and coarse water atomised powder at 1250uC or below, followed by postsintering decarburisation, densities of w95% relative density and non-brittle microstructures are achieved. Tensile testing shows the important effect of the microstructure on the mechanical properties. Ductility is improved by the post-sintering decarburisation, corresponding to elongation to fracture of 12% for certain compositions. Apparent diffusion coefficients for carbon were also estimated.MST/6006

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proper quantities must be monitored. This is conventionally achieved by having a mixture of base powder and liquid Powder mixtures composed of liquid forming master forming master alloy powder constituents. The liquid formalloy powder and coarse iron powder were sintered to ing constituent can be a mixture of additives instead of a near full density by having a high amount (20 wt-%) of homogeneous master alloy powder. During liquid phase liquid phase during sintering. This was made possible sintering, a microstructure gradient will be created, as the by the use of the Fe-P-C system with or without particle boundaries may have a composition similar to Cu. Without post-sintering treatment, a brittle microthe liquid phase and the interior of the particles will have structure was obtained. By means of altered C and P the composition of the base powder. In choosing the control and decarburisation heat treatment of the as composition of the liquid phase, a low melting composition sintered material, the nal non-brittle microstructure is required and good wetting properties are needed to was achieved. Using the open porosity and liquid achieve high densi cation. The amount of liquid must be phase as a diVusion path, rapid decarburisation is just enough to ll the pores without leading to slumping created and the local combination of carbon and and the melt must also be able to penetrate easily by phosphorus in the microstructure is avoided. In this capillary action throughout the sintered body. Some well way, iron phosphide is not formed on grain and/or known binary systems are Fe-Cu, Fe-P, Fe-B.2 However, particle boundaries. Presence of pores is con rmed to these binary systems do not permit the necessary amount be bene cial for grain growth control.PM/1063 of liquid phase for high volume shrinkage when starting from loose packed or moderately pressed coarse powder.

The grey iron microstructure Fe-2C-2Si powder based compact is tailored by different kinds of in situ and post sintering processing. This has been achieved by combining thermodynamic and kinetics modelling of microstructure development with sintering and controlled heat treatment experiments of tensile test specimens die compacted at 600 MPa. Applying optimised sintering conditions led to a grey iron like microstructure with 95% relative sintered density. Sinter hardening the compacts led to 500 MPa in yield strength and 600 MPa in ultimate tensile strength in combination with ductile fracture. Quenched and tempered condition showed the same strength values, but combined with brittle fracture due to martensitic structure. Pore rounding and partial pore filling by graphite were obtained by austenising isothermal hold during the cooling of the sintering cycle.

The effects of water based shaping, by means of starch consolidation (SC), of an iron powder system regarding oxygen/carbon content and sintering performance were evaluated. Specifically, the influence of the drying conditions and the use of two different thickeners, xanthan gum and cellulose ether, were studied. The results showed that cellulose ether gave lower sintered density than xanthan gum, mainly because of less favourable rheological impact and air/gas entrapment at mould filling and consolidation. Due to less oxidation at drying and less removal of carbon at sintering, freeze dried specimens sintered to a higher density than room temperature air dried ones. The degree of oxidation and removal of carbon also influenced the as sintered microstructure. Ferrite grains surrounded by iron phosphide were found in both air dried and freeze dried specimens. However, the higher carbon content in freeze dried specimens also resulted in a significant amount of iron carbide grains (inclusions), which can be a potential strength limiting factor. PM/1135At the time the work was carried out Dr Romano

Fatigue life investigations have been made for hollow rollers in pure normal loading. Different hollowness percentages between 20 and 80% have been tested to find the optimum percentage hollowness that gives the longest fatigue life. Two main models were built for this purpose: model 1 with two identically sized rollers and model 2 with two non-identically sized rollers. In each model, two cases have been studied: when both rollers are hollow and when one roller is hollow while the other one is solid. The Ioannides–Harris (IH) theory was used to calculate the relative fatigue life of the hollow rollers with respect to solid rollers under the same loading. Investigations have been made for five different materials: CVD 52100, carburised steel, VIMVAR M50, M50NiL and induction hardened steel. The finite element package ABAQUS has been used to study the stress and deformations in the loaded rollers. In general, the optimum hollowness percentage with the longest fatigue life ranges between 60 and 70% based on the kind of the material, whether the rollers are of the same or different size and whether one or both rollers are hollow. Using the IH theory for fatigue life calculation resulted in having infinite fatigue life for those rollers made of induction hardened steel that relatively has high fatigue limit value. Rollers in the optimum range are flexible enough to get the best redistribution of stress in the contact zone. For models of a hollow cylindrical roller in contact with a solid roller, the optimum hollowness is around 70%. When both cylindrical rollers are hollow, the optimum hollowness decreases between 60 and 65%. At the optimum hollowness, small differences in the fatigue life have been found between models of one hollow roller and models of two hollow rollers, even though having both hollow rollers means less weight, thus saving more material and more stability for the system.