Effect of the Content and Form of Impurities and Nonmetallic Inclusions on the Metallurgical Quality of Spring Steels

Abstract

A detailed study is made of the effect of the form and content of impurities and nonmetallic inclusions on the quality characteristics of spring steels of type 60C2XA. It is established that to prevent the formation of “blowhole” defects it is necessary to limit the steel’s content of gas-forming elements as follows: [H] < < 3.5 ppm, [N] < 60 ppm, [O] < 11 ppm, and [C] < 0.54%. It is shown that the hydrogen content of the steel has the strongest effect on the formation of such defects. To make the steel cleaner in terms of its content of nonmetallic inclusions, it is best to make a metallic semifinished product with a high carbon content and a low (200–400 ppm) content of active oxygen, add carbon-bearing materials early during tapping, and proportion the additions of manganese- and silicon-bearing ferroalloys in a regime which leads to the formation of easily removed silicate inclusions. Another effective measure is to use assimilating covering slags composed of two layers in the tundish. To obtain good quality characteristics for rolled products, it is necessary ensure that the combined content of Sn, Pb, and Zn does not exceed 0.008–0.013% and to use a certain temperature-time regime for the casting operation. Here, the optimum degree to which the steel is heated above the liquidus temperature in the tundish is 23–30°C. Experimental results confirmed the adequacy of the principles that were formulated and the effectiveness of the technological measures that were developed.