734. Vacuum blast sintering

Classified Abstracts 732--737 established that after the charge had been smelted at a pressure of 10-3 m m Hg the Cr content was reduced by 1.96 per cent, which agrees closely with the calculation given. The determination of the losses o f the components of alloys alloyed with Cr, A1, Ti, Co, W and M o was carried out in an OKB-497 vacuum induction furnace at a vacuum of 1.5× 10-2 and 1 × 10-3 m m Hg. The temperature of the liquid metal was measured by an immersion thermocouple and in the majority of cases was 1600 °. The use of inert gas during smelting of the charge reduces the losses of alloying elements to a minimum. The greatest variation during residence of the melt under vacuum is that of the Cr content ; the Ti and A1 contents show minimum variation. With a change in the vacuum from 1 to 1 × 10-3 m m Hg the losses of the alloy components are roughly the same. This is explained by the fact that, together with an increase in the vacuum in the furnace and also the increase in losses as a result of evaporation, the losses due to oxidation are reduced. The presence of Co in the alloy does not affect the variation of the losses of Cr. Addition of 6 per cent AI to the charge reduced the Cr losses, probably as a result of the formation of a protective film on the surface of the metal. In fusions with Ti, Mo and W the effect of A1 is less marked than with fusions without these elements (in Russian). P. Ya. Ageyev and B. G. Chernov, Nauchno-tekh. Inform. Byul. Leningrad. Politekh. Inst., (11), 1960, 7-16. 37 732. Degassing molten steel continuously. Great Britain. The British Iron and Steel Research Association has been experimenting with a process for continuous vacuum degassing of steel. A refractory lined vessel, 6 ft diameter and 6 ft high is heated to 1300°C and evacuated rapidly to a pressure of approx. 1 torr. When molten steel is allowed to enter this vessel from below, the vacuum gives rise to a fountain, the molten steel breaking up into droplets which are projected several feet upwards before dropping back into the bottom of the vessel. Any gases liberated during this process are pumped away, whilst the degassed steel is drawn off from the lower end of the vessel. The introduction and subsequent removal of the steel require the provision of special devices, such as aluminium rupture discs or glass seals, w.J.s. Anon., New Scientist, 15 (306), 27 Sept. 1962, 674. 37 733. Xenon compounds. United States. The chemical inactivity of the noble gases is usually explained by the fact that the outer shells of electrons surrounding the atoms are complete and cannot accept further electrons from different atoms. Recently, however, the Argonne National Laboratory has succeeded in obtaining a chemical compound of Xe and F by heating x e n o n and fluorine in a sealed nickel container at 400°C for one hour followed by rapid cooling. The resultant product, XeF4, is in the form of colourless crystals which are stable at room temperatures. This new kind of chemical bond is explained by the discrepancy in the number of atomic shells of the two elements, 5 for Xe and only 2 for F. It is thus possible for the F nuclei to attract the outer electrons of the Xe atoms more strongly than do the corresponding Xe nuclei, w.J.s. Anon., New Scientist, 16 (308), 11 Oct. 1962, 104. 37 734. Vacuum blast sintering. U.S.S.R. The disadvantage of the method of sintering when air is blown through from below, preventing its wide distribution, consists in the formation of zonal blowouts and ejection of the charge after the " equilibrium " pressure of the compressed air has been exceeded. Four variants of the use of special media preventing blowouts and ejections were studied in the laboratory in a sintering cup 225 m m in diameter. On the layer of charge with a basicity of 1.0, consisting of a fine magnetite concentrate

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and limestone, 500-600 mm high, including 35-40 mm of an " ignition layer ", a grating with 6 mm openings (active section 20 per cent) was placed, or a layer (50 mm) of crude pellets 12-15 mm in diameter from the same concentrate, or a layer of salvage 5 0 - 6 0 m m high of 15-16mm l u m p s ; a variant was also tried with the formation of a fine protective crust of sinter cake on the layer of charge. The air for sintering was supplied under a pressure of 1000-1100 mm H20. The most effective variant was that with the use of a layer of salvage, giving a 44 per cent increase in output, and a 20 per cent increase in gas penetrability; moreover, the total salvage consumption is 24--30 per cent ; the strength of a sinter cake obtained in this way does not differ from the ordinary (in Russian). I. M. Arkhipov, Obogashcchniye Rud, 2 (32), 1961, 26-30. 37 735. Determination of the vapour pressure of tin sulphide. U.S.S.R. The vapour pressure of synthesized SnS was determined by the effusion method in vacuo, followed by cooling of the condensate in an atmosphere of nitrogen. The experimental results and the available literature data are brought together in the equation, log p = - - ( 1 0 4 7 0 / T ) - ~ 7.088, applicable in the 936-1084°K range (in Russian). A. A. Benunin and A. A. Tseidler, Symposium: Trud. Gos. Nauchno-issled lnst. Tsvet. Met., 15, 1959, 198-204. 37 736. Problem of the effect of vacuum smelting and casting on the properties of metal and the quality of an ingot. U.S.S.R. Mildly magnetic F e - C o alloy (K50F2) of the percentage compositions, 9 0 . 0 5 C, 9 0 . 2 Si, 9 0 . 2 Mn, 49-51 Co, 1.5-2 V, 9 0 . 5 Ni, 90.025 S and P, remainder Fe was smelted in a h.f. vacuum furnace of the experimental works of the Central Scientific Research Institute of Ferrous Metallurgy. A vacuum of the order of 1 × 10-3 mm Hg was attained in the space of the furnace in the cold state. The melts were carried out in crucibles of ZrO2, which were made directly in the furnace. The stability of one crucible was ~ 4 0 melts. The weight of the smelted ingots amounted to 30-45 kg. In metal smelted in a vacuum the content of gases and non-metallic inclusions, and also the magnetic properties, were determined. It was found that smelting of alloy K50F2 in a vacuum of the order 500-50 mm Hg is not accompanied by a change in the chemical composition of the alloy, except in Si, the amount of which is reduced by 50 per cent. The content of gases in the metal varies from I0 to 2 0 m l . / 1 0 0 g instead of 60 ml.,/100 g, found in metal smelted by the ordinary technology. The amount of non-metallic inclusions in the alloy is substantially decreased, but its magnetic properties are improved. A study of the effect of vacuum smelting and casting of low C nickel steel containing 0.1-0.15 per cent C and 2-3 per cent Ni on the formation of gas bubbles in the ingot showed that when steel subjected to short term vacuum treatment in a ladle at a pressure of 30-40 mm Hg is cast into vacuum moulds, the formation of gas bubbles in the ingot takes place, and therefore the casting of metal treated under vacuum in a ladle should be carried out in an inert atmosphere (in Russian). A. V. Yemyashev, A. M. Zubko and V. Ye. Neimark, Symposium: Trud. Inst. Metalloved. i Fiz. Metal. Tsent. Nauchno-issled. Inst. Chern. Metallurg., 6, 1959, 169-186. 37 737. The pumping effect and the characteristics of the evaporation of chromium metal under vacuum by electron bombardment. U.S.S.R. Cr atomized by electron bombardment improves the vacuum in experimental 2.41. tubes from 10-6 to 10-7 mm Hg. The vacuum in the tubes is retained for 4-6 hours by the pumping effect of the Cr film. The effect of the Ti film is similar to that of Ti atomized at the melting point. Growth of filiform crystals of Cr203 on the atomized Cr sample is observed. This indicates