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.
Powder metallurgy technology at the service of diamond-impregnated tool production
ABSTRACT Different approaches to take advantage of powder metallurgy in the manufacturing of diamond-impregnated components were studied. Three different powders were used as starting materials; two pre-alloyed powders, based on Fe–Cu and Fe–Cu–Sn systems, and one pre-mixed Fe-based powder. Different manufacturing routes as a strategy to obtain tailored mechanical properties were studied, with the influence of alloying elements such as graphite, iron phosphide and Mn–Ni–B master alloy to reinforce the iron-based powders. Both uncoated and coated commercial synthetic diamonds were introduced in the systems to analyse the surface reactions that depend on both metallic matrix and processing parameters. Hardness values from 88 to 105 HRB were obtained with a wide range of transverse rupture strength values from 1250 to 1640 MPa. An appropriate combination of metallic matrix, alloying elements and processing parameters makes the materials analysed here suitable powders for the manufacturing of diamond-impregnated tools.
Changes in Quartz During Heating and the Possible Effects on Si Production
In Si and FeSi production, the main Si source is SiO2, in the form of quartz. Reactions with SiO2 generate SiO gas that further reacts with SiC to Si. During heating, quartz will transform to other SiO2 modifications with cristobalite as the stable high-temperature phase. Transformation to cristobalite is a slow process. Its rate has been investigated for several industrial quartz sources and has been shown to vary considerably among the different quartz types. Other differences in behavior during heating between these quartz sources, such as softening temperature and volume expansion, have also been studied. The quartz-cristobalite ratio will affect the rate of reactions involving SiO2. The industrial consequences and other implications of the observed difference between quartz types are discussed. Initial studies of industrial quartz were published by Ringdalen et al. In the current work, a new experimental method has been developed, and an investigation of several new quartz sources has confirmed the earlier observed large variation between different sources. The repeatability of the data has been studied and the effect of gas atmosphere investigated. The results from the earlier work are included as a basis for the discussion.