Aerospace technic and technology

Extensive investigations of the corrosion resistance of austenitic chromium-nickel steels (with stable and unstable austenite) do not reveal the full nature of the phenomena studied. By the magnetometric method, using the specific magnetic susceptibility c₀ of austenite and low content Р_d d-ferrite (0…0.5 %), the corrosion properties of steels were studied. These parameters are determined by the chemical composition of steel, heat treatment and deformation. The pitting corrosion rate correlates with these parameters. In the scientific literature, the results of studies of the corrosion resistance of metals with variation over a wide range of carbon and nitrogen contents are given. In this work, the influence of these elements in five swimming trunks of each steel grade AISI 304 and AISI 321 is investigated. In steels AISI 304 and AISI 321, with an increase in c₀ and Р_d (under the condition low content of d-ferrite), the pitting corrosion rate К decreases. The values of c₀ and Р_d from the total content Q (wt.%) of all alloying elements for each melt are determined. The dependences of the corrosion rate K on Q for each melt of AISI 304 and AISI 321 steels are obtained. Various forms of К(Q) dependency curves are caused by a lower content of nickel, silicon and a higher content of chromium, manganese, carbon, nitrogen in AISI 304 steel. Also in AISI 321 steel, titanium is present. The dependences of К, c₀ and Р_d on the content of carbon and nitrogen, in the presence of all other alloying elements, are determined. Various (presence of a maximum or minimum) parabolic dependencies of К, c₀ and Р_d on the carbon and nitrogen contents were revealed. For melts of steel AISI 304, of the effect carbon and nitrogen on corrosion resistance are the opposite of the sum of all other alloying elements. For melts of steel AISI 321, the carbon present makes a smaller contribution to corrosion resistance compared to nitrogen. For AISI 321 steel melts, an ambiguous character of the dependence of the pitting corrosion rate K on the total content Q of all other alloying elements was found. Two values of Q (a parabolic dependence of K(Q)) can correspond to one value of K. The critical points (the content of alloying elements), before and after which the parameters c_0, P_d can increase or decrease, are determined. As a result, the paramagnetic state of austenite changes, which correlates with a change in the corrosion properties of steel.

austenitic steel; carbon; nitrogen; corrosion; ferrite; specific magnetic susceptibility of austenite; critical point

Byelikov, S. B., Narivs`ky`j, O. E., Xoma, M. S. Pitingova koroziya teploobminny`kiv v oborotny`x vodax ta yiyi prognozuvannya: monografiya [Pitting corrosion of heat exchangers in circulating waters and its forecasting]. Zaporizhzhya, NU «Zaporiz`ka politexnika» Publ., 2019. 216 p.

Narivs`ky`j, O. E., Byelikov, S. B. Suchasni uyavlennya pro pitingovu koroziyu korozijnotry`vky`x stalej i splaviv [Modern ideas about pitting corrosion of corrosion-resistant steels and alloys]. Novi materialy` i texnologiyi v metalurgiyi ta mashy`nobuduvanni [New materials and technologies in metallurgy and mechanical engineering], 2018, no. 2, pp. 14-24.

Pisarevskii, L. A., Filippov, G. A., Lipatov A. A. Effect of N, Mo, and Si on lo-cal corrosion resistance of unstabilized Cr-Ni and Cr-Mn-Ni austenitic steels. Metallurgist, 2016, vol. 60, no. 7-8, pp. 822-831. DOI 10.1007/s11015-016-0372-x

Baba, H., Kodama, T., Katada, Y. Role of nitrogen on the corrosion behavior of austenitic stainless steels. Corrosion Science, 2002, vol. 44, pp. 2393-2407.

Snezhnoi, G. V. Rol' magnitnogo sostojanija austenita v formirovanii korrozionnoj stojkosti austenitnyh hromonikelevyh stalej [Role of magnetic state austenite in the formation of corrosion resistence of austenitic chromium-nickel steels]. Aviacijno-kosmicna tehnika i tehnologia – Aerospace technic and technology, 2012, no. 8 (95), pp. 141-144.

Snezhnoi, G. V., Mishhenko, V. G., Snezhnoi, V. L. Integral'nyj fizicheskij metod identifikacii -fazy v austenitnyh hromonikelevyh staljah [Integrated physical method of -phase identification in austenitic nickel-chromium steels]. Lit'e i metallurgija – Foundry production and metallurgy, 2009, no. 3 (52), pp. 241-244.

Narivskyi, O. E. Koroziyno-elektrohimichna povedinka konstruktsiynih materialiv dlya plastinchatih teploobminnikiv u modelnih oborotnih vodah. Dis. ... kand. tekhn. nauk [Corrosion-electrochemical behavior of structural materials for plate heat exchangers working in model waters. PhD]. Lviv, Karpenko physico-mechanical institute, 2009. 200 p.