Phosphorus as sintering activator in powder metallurgical steels: characterization of the distribution and its technological impact
Powder metallurgy is a highly developed method of manufacturing reliable ferrous parts. The main processing steps in a powder metallurgical line are pressing and sintering. Sintering can be strongly enhanced by the formation of a liquid phase during the sintering process when using phosphorus as sintering activator. In this work the distribution (effect) of phosphorus was investigated by means of secondary ion mass spectrometry (SIMS) supported by Auger electron spectroscopy (AES) and electron probe micro analysis (EPMA). To verify the influence of the process conditions (phosphorus content, sintering atmosphere, time) on the mechanical properties, additional measurements of the microstructure (pore shape) and of impact energy were performed. Analysis of fracture surfaces was performed by means of scanning electron microscopy (SEM). The concentration of phosphorus differs in the samples from 0 to 1% (w/w). Samples with higher phosphorus concentrations (1% (w/w) and above) are also measurable by EPMA, whereas the distributions of P at technically relevant concentrations and the distribution of possible impurities are only detectable (visible) by means of SIMS. The influence of the sintering time on the phosphorus distribution will be demonstrated. In addition the grain boundary segregation of P was measured by AES at the surface of in-situ broken samples. It will be shown that the distribution of phosphorus depends also on the concentration of carbon in the samples.
Sintering and Microstructure of Phosphorus Steels
The effect of chemical composition on the sintering mechanisms and microstructure of Fe-C-P alloys was studied by metallographic and thermal analysis and by secondary ion mass spectroscopy. Pore morphology was found to tend to spheroidisation with an increase in the phosphorus and, more particularly, in the carbon content. In addition, phosphorus was found to be heterogeneously distributed in ferrite and in pearlite. These results are explained by proposing a sintering mechanism, based on two main processes. The first leads to the formation of phosphorus rich ferrite through the reaction between phosphides and low carbon austenite. The second produces transient liquid through a eutectic reaction between phosphides and carbon rich austenite
Magnetic properties of Lu2Fe17 crystals
Abstract We present the results of crystal structure and magnetization studies of three single crystals grown from melts of different nominal compositions in the vicinity of the Lu2Fe17 stoichiometry. The ferromagnetic state of the crystals is strongly dependent on the real sample composition and the local atomic ordering. A drastic difference is observed in the behaviour of the ferro–antiferromagnetic transition, even in crystals for which almost identical composition and crystal parameters were determined by microprobe and X-ray analysis.