Utilization of scrap for production of steel 000Kh18N12 in the vacuum induction furnace

Abstract

The low-carbon stainless steel 000Khl8Nt2 is made in vacuum induction furnaces either by melting pure charge materials (NZh, iron, nickel, FKh001 ferrochrome, or metallic chromium) or by blowing the surface of the melt with oxygen, using a melting charge with a higher carbon content (ferrochrome FKh010).However, home scrap (top and bottom crops, and also crops formed in forging and rolling) was as a rule not individually segregated under the conditions prevailing at Chelyabinsk and was used in making steels containing chromium and nickel in open arc furnaces.A study was made of the possibility of using home scrap in the vacuum induction furnace production of lowcarbon stainless steel 000KhlSN12 with a limited oxygen, hydrogen, nitrogen, and non-metallic inclusions content. The steel was made in a semicontinuous vacuum induction furnace of 0.5 tons capacity, using two methods: charge material melting, and blowing the melt with argon. The charge materials used were NZh low-carbon iron, N-1 nickel, FKh001 ferrochrome, and home scrap (top and bottom crops produced during ingot forging). When the head crop norm for an ingot weighing 500 kg is 22% scrap is formed as lumps weighing 90-120 kg. The charge wasloaded into the crucible by buckets in two stages, the scrap being charged with the second load. All the heats utilized one or two lumps, which amounted to 18, 20-25, or 36% scrap in the total amount of charge.In making steel 000Kh18N12 by the melting method, the metal was deoxidized with aluminum by 0.15% after heating to I580-1600~ andthe electromagnetic mixer was switched on for 1-3 rain. The metal was then held for 25 rain and poured. Prior to pouring, the melting chamber of the furnace was filled with argon to a pressure of 40-50 mm Hg.In the vacuum induction furnace the metal was blown with argon through porous plugs installed in the bottom of the crucible. The standard magnesite plugs which are employed for blowing metal in the ladle were used. They were in the form of a truncated cone 300 mm high, diameter of the lower base 180 mm and of the upper, 144 ram; their porosity was 40-45%, and the diameter of the predominant pores was 50-30 g.The technology for making steel 000Kh18N12 with argon blowing consisted of the following: after the charge had melted and a temperature of 1590-1600"C had been reached the metal was deoxidized with aluminum by 0.10-0.15%, the melting chamber was filled with argon to a pressure of 5-10 mm Hg and the metal blown with argon for 30 rain. Argon consumption in the blowing process amounted to 20-25 normal liters/rain with a pressure of 1.5-2.0 gauge atmospheres at the cylinder outlet. These conditions ensure intensive boiling of the metal without splashing from the crucible. After the conclusion of the blow the melt was held for 10-15 rain and poured. In some heats the aluminum for deoxidizing was added after the conclusion of the blow.The making of steel 000Kh18N12 with utilization of scrap yields metal with a 0.019-0.026% carbon content, which guarantees fulfillment of the requireme...