AC measurements of B-H properties were made and it was observed that the coercivity of cobalt ferrite was below 1600 A/m in the 10–100 Hz range.

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The deoxidation of steel with complex deoxidisers was studied at 1550°C and compared with silicon, aluminium and silicon/aluminium alloys as standards. The deoxidation alloy systems, Ca/Si/Al, Mg/Si/Al and Mn/Si/Al, were chosen for the low liquidus temperatures of many of their oxide mixtures and the potential deoxidising power of their constituent elements. Product separation rates and compositional relationships following deoxidation were examined. Silicon/aluminium alloy deoxidation resulted in the product compositions and residual oxygen contents expected from equilibrium and stoichiometric considerations, but with the Ca/Si/Al and Mg/Si/Al alloys the volatility of calcium and magnesium prevented them participating in the final solute equilibrium, despite their reported solubility in liquid iron. Electron-probe microanalysis of the products showed various concentrations of lime and magnesia, possibly resulting from reaction between the metal vapours and dissolved oxygen. The consequent reduction of silica activity in the products due to the presence of CaO and hgO produced an indirect effect of calcium and magnesium on the residual oxygen content. Product separation rates, indicated by vacuum fusion analyses, were not significantly influenced by calcium and magnesium but the rapid separation of products having a high Al2O3Si02 ratio was confirmed. Manganese participated in deoxidation, when present either as an alloying element in the steel or as a deoxidation alloy constituent. The compositions of initial oxide products were related to deoxidation alloy compositions. Separated products which were not alumina saturated, dissolved crucible material to achieve saturation. The melt equilibrated with this slag and crucible by diffusion to determine the residual oxygen content. MnO and SiO2 activities were calculated, and the approximate values of MnO deduced for the compositions obtained. Separation rates were greater for products of high interfacial tension. The rates calculated from a model based on Stoke's Law, showed qualitative agreement with experimental data when corrected for coalescence effects.

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A study has been carried out of the resistance to molten zinc of a series of candidate materials. The object was to identify those that might be capable of increasing the service life of hot-dip galvanising bath hardware rolls. The testing involved immersing samples in a molten zinc alloy, representative of that used in commercial operations, at 455° and 480°C for periods up to 360 hours. For some programmes of tests the samples were rotated during immersion. The candidate materials ranged from uncoated low carbon steel, commercial and experimental stainless steels and cobalt-base superalloys to some of the same products covered with a variety of non-metallic and ceramic coatings. Although an Fe-18%Cr experimental alloy had poorer resistance to liquid zinc than low carbon steel, the further addition of 9%Ni to produce an experimental Type 304 stainless steel generated better liquid zinc resistance than low carbon steel. It is suggested that structure rather than compositional effects play an important part in this. Microstructures containing significant amounts of martensite appear to be particularly susceptible to zinc attack. There is, however, a compositional effect from silicon which, when varied in experimental cases of a Type 316 stainless steel, showed the same ability to influence coating microstructure as in carbon steels. The effectiveness of coatings was related to two factors: their inertness and their integrity. Some coatings, for example nitrided and titanium nitrided steel, appeared to be attacked by liquid zinc. Tungsten carbide/cobalt were also attacked unless an inert sealant had been applied. Ceramic oxide coatings consisting of a mixture of fine particles of alumina, chromia and silica proved highly effective in countering zinc attack. However discontinuities in inert coatings arising from the manufacturing process or from microsfissuring during periods of sharp temperature change promoted opportunities for zinc attack and undercutting of the coating. An unexpected phenomenon was observed on some semi-immersed samples. Liquid zinc attack occurred progressively <U>above</U> the liquid zinc meniscus to the formation of thick intermetallic layers. In some cases these layers engulfed the sample and sample holder. The phenomenon has been termed 'supermeniscus intermetallic climb' (SMIC).

The mechanical properties of die-compacted sintered nickel compacts prepared from closely sized sieve fraction of annealed Sherritt-Gordon wore determined The properties, especially fatigue properties, were found to be dominated by the presence of film like porosity in the grain boundaries. The occurrence of this porosity was at the original particle boundaries and its form was attributed to botryoidal shape of the original powder particles. A mechanism for the propagation of the fatigue crack is suggested. Several iron powders were carefully characterised. Thin steel strip was prepared from these samples using a slurry technique. Binder was used in the slurry to give coherent strip before rolling. The properties of the green strip were found to be affected by the particle size and particle size distribution of the original powder. The presence of binder in the strip contributed towards the green strength especially at high roll loads. strength was observed to develop quickly during sintering, for sintering times of the order of sixty seconds duration although little or no densification occurred. Specimens of near-theoretical density were prepared by re-rolling and re-sintering. Despite the high density of these specimens the mechanical properties were poor.

No description available.