Theory and Technology of Metallurgical Production

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Mokritsky M.I., Velikotsky R.E., Sumets A.V., Shabratsky S.V. MATHEMATICAL AND PHYSICAL MODELING OF DETERMINATION OF CORROSION CONSTANT FOR REAL AND ZERO CARBON CONTENT OF FERRITE-BAINITE-PEARLITE PIPE STEEL

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Abstract

The paper presents a metallographic analysis of the causes of pitting corrosion on the surface of hot-rolled pipe steels of the ferrite-perlite-bainitic class of strength category from K56 to K60, with elements of mathematical and physical modeling of pitting formation depending on the heating temperature and holding time of the metal. The mathematical apparatus for predicting pitting corrosion of pipe steel, strength classes K56-K60, was further developed. The results of mathematical and physical modeling made it possible to expand the ideas on determining the corrosion constant in the temperature range of 900-1300ºC for real and zero carbon content. Morphological features of corrosion-active nonmetallic inclusions are considered. It was established that corrosion-active non-metallic inclusions consist of sulfide and oxysulfide parts. The presence of alumina-calcium inclusions 12CaO7Al2O3 in solid metal, not removed during smelting and casting, has the most negative effect not only on pitting corrosion, but also on the viscosity and ductility of steel, compared to alumina-calcium inclusions of a different composition. The most preferable type of inclusion for pipe steel of strength category K52-K60 is corrosion-active non-metallic inclusions, consisting of 3CaOAl2O3, since such a composition has the maximum sulfide capacity, a sufficiently high melting point and a relatively good coefficient of thermal expansion. The purity of steel according to corrosion-active non-metallic inclusions is ensured by optimizing the process parameters of out-of-furnace treatment with Ca-containing materials, a set of production measures aimed at reducing the oxygen and hydrogen content in liquid steel, as well as minimizing the formation of non-metallic inclusions. Pre-treated metal (shot blasting + surface priming) prevents the development of pitting. The depth of pitting depends on two main factors: the magnitude of surface heterogeneity (minimization of corrosion-active non-metallic inclusions) and the heating temperature, with the first factor being decisive.

Keywords:

pitting, corrosion-active non-metallic inclusions, pitting corrosion, mathematical modeling of pitting, non-metallic inclusions, pitting depths, pitting corrosion resistance

Mokritsky Maksim I. – Executive Director limited liability company «Southern Mining and Metallurgical Complex», Alchevsk. Velikotsky Roman E. – Head of the Patent Department limited liability company «Southern Mining and Metallurgical Complex», Alchevsk.

Sumets Andrey V. – candidate of technical sciences, Senior Lecturer, Department of Mechanical Engineering and Construction, Severodonetsk Technological Institute, Severodonetsk.

Shabratsky Sergey V. – candidate of technical sciences, head of Department Mechanical Engineering and Construction, Severodonetsk Technological Institute, Severodonetsk.

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