GB997063A - Exceptionally-clean steel - Google Patents

Abstract

Clean steel free from inclusions, for ball-bearings or jet and missile parts, is prepared by air melting a charge of iron without adding the strong deoxidizers Al and Ti and the weaker deoxidizers Mn and Si, adjusting the carbon content of the molten melt, particularly for carbon deoxidation, such as by adding carbon, e.g. in the form of high carbon ferrochrome, as pig iron or such carbonaceous material as coke, in an amount 1-1.5 times the stoichiometric amount required to convert the oxygen in the melt into CO, then casting the melt into an ingot and melting the ingot as the consumable electrode in a vacuum electric arc furnace with the electrode region under a maximum pressure of 100 microns of mercury. The initial open steel melt may be degassed under a maximum pressure of 1000 microns of mercury. The starting charge may be of scrap iron melted in an electric arc furnace under a carbide slag covering, e.g. containing lime, fluorspar and coke fines, and a jet of oxygen may be blown into this melt from a lance, or oxygen may be introduced by adding iron oxide. Alloying elements such as Co, Ni, V and Mo may be charged into the initial melt. Alternatively, the air melting may be effected in an induction, open-hearth or L-D furnace. If necessary, a second vacuum melting step may be performed at a lower pressure than that of the first, or the melt may be subjected to vacuum lift degassing or bubbling through with argon. Specification 915,851, and U.S.A. Specifications 2,727,936, 2,818,461 and 3,033,550 are referred to.