Complex perfection of the 20KT steel production technology, which basic results are increase in the stability of technological parameters, decrease in oxidation degree of semiproducts of arc steel-melting furnace and rise in desulfurization, led to favorable changes in the composition of nonmetallic inclusions. However the mentioned correction of the production technology did not solve one of the most significant technological problems - effective modification of oxide phases for the purpose of raising steels casting ability because it retained the reduced level of calcium content in nonmetallic inclusions. It was possible to solve this technological problem substantially by transferring to the modification technology before vacuum processing at the final stages of treatment at ladle refining installation.