Study of the Effect of Process Parameters in Steel Production on the Content of Corrosion-Active Nonmetallic Inclusions in Corrosion-Resistant Pipes

The main reason for the accelerated local corrosion of tubes is contamination of the steel by corrosion-active nonmetallic inclusions (CANI), which determine the metallurgical properties of tube steel in terms of their corrosion resistance. Studies have shown that there are two main types of corrosion-active nonmetallic inclusions: CANI^sub 1^ -- inclusions based on calcium aluminates; CANI^sub 2^ -- complex inclusions that contain calcium sulfide. In order to master to production of tubes of steel 20-PKS at the Volga Pipe Plant (VTZ), a study was made of the effect of the parameters of out-of-furnace treatments on the contamination of steel by CANI. 1. The mechanisms and main sources of formation of CANI in tube steels made by the VTZ were determined. The main reasons for the formation of CANI^sub 1^ in furnace slag containing thermodynamically active CaO are mixing of the metallic and slag phases during the argon blow and the simultaneous introduction of additions to correct the chemical composition of the steel. Inclusions of the CANI^sub 2^ type may be formed by deoxidation operations carried out with suboptimal proportions of added aluminum and calcium (lime). 2. The following measures are recommended to ensure that steel 20-PKS made by the VTZ is clean with respect to both types of CANI: * optimize the composition of the ladle slag (increase the average content of Al^sub 2^O^sub 3^, increase the average content of SiO^sub 2^ as much as possible, and in any case decrease the average concentration of CaO); * keep the mass ratio of added CaO to added Al within the range 1.5-2; * continue the argon blow done after addition of the last batch of ferroalloys for at least 15-20 min; * ensure that the intensity of the blow is at least 0.5-1.5 m^sup 3^/min. 3. Vacuum-degassing steel in the ladle after treatment on a ladle-furnace unit makes it possible to distribute the CANI more uniformly over the volume of the steel.[PUBLICATION ABSTRACT]