| 摘要 |
<p>An all-pearlitic (which may be partly or wholly sorbitic) structure with possible traces of cementite, but no free ferrite whatsoever, is produced in grey iron castings made in cold moulds of sand or other refractory material or in hot or cold metal moulds and containing materials which inhibit and promote the formation of ferrite, by altering (a) the quantity of ferrite-promoting material (which must always be so high as normally to produce a ferritic casting), (b) the quantity of ferrite-inhibiting material, and (c) the rate of cooling of the casting as determined by its section and, in the case of metal moulds, the mould-temperature, the method being carried out without superheating the mixture to such a high temperature before pouring the casting that its structure would be affected thereby. The ferrite-promoting material may be one or more of silicon, nickel, or copper in amount equivalent to 2-7 per cent of silicon, it being reckoned that 0,4 per cent of silicon is equivalent to 1 per cent of nickel and 0,35 per cent of silicon is equivalent to 1 per cent of copper, no more than 3,5 per cent of nickel and 4 per cent of copper being, however, present. The ferrite-inhibiting material may be one or more of chromium, manganese, or molybdenum in amount up to 6 per cent, up to 3,5 per cent, and up to 1,5 per cent respectively, it being reckoned that 0,3 per cent of molybdenum is approximately equal to 0,2 per cent of chromium and 0,25 per cent of manganese (after the first 1,75 per cent of manganese which is stated to be without effect) being equal to 0,15 per cent of chromium. The inhibiting-material may be added to the cast in the pouring-ladle, the cast preferably containing a quantity of scrap from a previous operation. British Specifications 147,933, [Class 82 (i)], 495,475, and 495,820, and U.S.A. Specification 1,910,034 are referred to. Reference has been directed by the Comptroller to Specification 245,196, [Class 82 (i)].</p> |
