Production of improved quality steel in highscale basic oxygen furnaces using vacuum treatment

Abstract

The article presents the results of the converter steel technology development using ladle treatment including portion vacuum degassing at vessel UPVS-350 and pouring at continuous casting machine. In order to improve the quality of metal products, steels of grades 3sp, 08sp, 20k, 20sp, 09G2S, 10G2S1D, 09G2S, 08GT, 17G1SU, 17G1S, 17GS, 10HSND, 15HSND, E36, pipe steels of type 09G2FB were treated by vacuum. Steel was smelted in basic oxygen furnaces with a capacity of 350 ton using technical pure oxygen (99,2–99,5% О2). The article shows that with a UPVS-350 vacuum chamber dilution to133 Pa (1 mm Hg), a metal portion weight of 20–40 tons, the number of vacuum ing cycles less than 25 and a circulation coefficient from 2 to 5, a degree of oxygen removal of up to 40%and hydrogen up to 50% can be achieved. There is an improvement in the pouring ability of vacuum treated steel, a decrease in the axial discontinuity (stratification)at the central part of the slabs from 3 to 2–2.5 grades, decrease of the nonmetallic inclusions content in the billets by 0,2–2,3 grade and their distribution in the volume of metal is more uniform. When exhaustion in a vacuum chamber reach of 1–2 mm Hg level, the impact toughness and elongation of steel in crease. For carbon steel, the production of inappropriate quality metal according to the ultrasonic control decreased by about 3 times (from 0,39 to 0,12%), and the total degree of the rejected metal decreased from 1,06 to 0,65%. During vacuuming of 08GT steel using for chemical reactors, there is a more compact and greater uniformity of the ferrite-perlite structure with the value of the actual grain no. 7–9. The internal structure at the liquation central zone of the sheets produced of this steel is also improved