GB1002106A - Process for production of ultra clean steel - Google Patents

Abstract

Steel low in inclusions is produced from iron powder containing not more than 0.01% each of sulphur and phosphorus by forming the powder into a consumable electrode, melting in a furnace at a pressure not exceeding 1000 microns, the molten metal being collected in a water-cooled metal crucible, and using the resultant ingot as a consumable electrode in a second melting stage carried out at a pressure not exceeding 100 microns. Sufficient carbon is present in the initial mixture, either as a constituent of the iron or added thereto, to convert all the oxygen present to carbon monoxide and to provide the desired carbon content in the product; altenatively the required carbon content may be obtained by mixing appropriate amounts of powders of differing carbon content. Should the iron powder contain an undesired excess of carbon this may be eliminated by adding a controlled amount of iron oxide to the starting mixture. Alloying additions such as nickel, molybdenum, cobalt, manganese, vanadium, silicon and chromium may be added in powder form to the iron powder, while aluminium and titanium are preferably added by inserting them in holes drilled in the electrode of the second stage melting. Sulphur may be removed from the iron powder by annealing in wet hydrogen (e.g. saturated with water vapour at 150 DEG F.) at 1500-1700 DEG F. for 2-4 hours; this may be followed by annealing in dry hydrogen at 1500-1750 DEG F. for 2-4 hours to partially eliminate oxygen. The electrode may be formed from the initial powder by pressing at 40000-50000 p.s.i. followed by vacuum sintering at 1750 DEG F. under a pressure of 1-500 microns, or by sintering in an inert atmosphere at temperatures up to 2200 DEG F.