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
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.
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