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Corrosion behaviour of plastically deformed high-Mn austenitic steels

Grajcar A., Krukiewicz W., Kołodziej S.

Journal of Achievements in Materials and Manufacturing Engineering

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2010

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Vol. 43, nr 1

228-235

EN

Purpose: The aim of the work was the comparison of corrosion resistance in an aqueous sulfuric acid solution of two high-manganese austenitic steels of the 0.05C-25Mn-Al-Si-Nb-Ti type in a plastically deformed state. Design/methodology/approach: Investigations were carried out on specimens obtained from a thermo-mechanically rolled sheet and then plastically deformed through bending and immersed in corrosive solutions (1N H2SO4) for 100 hours. The mass decrement was calculated by the gravimetric method, whereas the character of corrosion damages was observed in metallographic investigations using light and scanning electron microscopes both in the polished and etched states. Findings: It was found that after the thermo-mechanical processing one steel is characterized by an austenitic structure with numerous annealing twins, whereas in the second steel lamellar martensitic phases in an austenitic matrix occur. The investigations showed that the examined high-manganese steels have very low corrosion resistance in normal H2SO4. Higher impact on the corrosion resistance than the phase composition has the chemical composition. The mass decrement of the steel with martensite plates is a bit higher than that with a single-phase austenitic matrix. The specimens were intensively dissolved due to general corrosion accompanying by pitting and hydrogen cracking. Research limitations/implications: To investigate in more detail the corrosion behaviour of high-manganese austenitic steels, the polarization tests and the analysis of corrosion products should be carried out. Practical implications: The obtained results can be used for searching the appropriate way of improving the corrosion resistance of high-strength high-manganese austenitic steels. Originality/value: The corrosion resistance of two types of advanced high-manganese austenitic steels with different initial structures was compared. Hydrogen impact in austenitic steels was discussed. Keywords: Corrosion resistance; high-manganese steels; gravimetric method; pitting corrosion; general corrosion; hydrogen cracking

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Corrosion resistance of high-manganese austenitic steels

Grajcar A., Kołodziej S., Krukiewicz W.

Archives of Materials Science and Engineering

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2010

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Vol. 41, nr 2

77-84

EN

Purpose: The aim of the paper is to compare the corrosion resistance of two new-developed high-manganese austenitic steels in 1N H2SO4 and 3.5% NaCl solutions. Design/methodology/approach: The steels used for the investigation were thermo-mechanically rolled and then solution heat-treated from a temperature of 850°C. Corrosion resistance of investigated steels was examined using the immersion test. The specimens were weighed and dipped in the prepared solutions for 100 h. After the test, the percentage weight loss was calculated. The metallographic investigations of corrosion damages included light and scanning electron microscope observations both in the polished and etched states. Findings: It was found that after the thermo-mechanical processing one steel is characterized by an austenitic structure with numerous annealing twins, whereas in the second steel ε and α' martensite plates in an austenitic matrix were observed. According to the results of the immersion tests it was found that the examined steels exhibit a comparable corrosion resistance. They show very poor corrosion resistance in H2SO4 solution and low corrosion resistance in NaCl medium. The weight loss in chloride solution is much lower, what is explained by different corrosion mechanisms. In both the solutions, the intensive general corrosion and corrosion pitting were observed. In acidic medium they are created in a way of hydrogen depolarization and in NaCl in the way of oxygen depolarization. Research limitations/implications: To investigate in more detail the corrosion behaviour of high-manganese austenitic steels, the investigations should include polarization tests and an analysis of corrosion products. Practical implications: The obtained results can be used to search for the appropriate way of improving the corrosion resistance of high-manganese steels with a single-phase austenitic structure as well as the austenite structure containing ε and α' martensite. Originality/value: The corrosion resistance of two types of advanced high-strength high-manganese austenitic steels with different initial structures was compared in acidic and chloride solutions.

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Korozja i pasywacja warstw azotowych na żelazie

Flis-Kaburska I., Flis J., Michalski J., Zakroczymski T.

Ochrona przed Korozją

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2009

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nr 4-5

113-116

PL

Badano korozyjne zachowanie warstw wierzchnich żelaza z azotkami ?, ?' i ? +?' otrzymanymi na drodze azotowania gazowego w 570oC. Pomiary przeprowadzono w obojętnych i zakwaszonych roztworach siarczanów oraz w buforze boranowym o pH = 8,4 bez i z dodatkiem chlorków lub amoniaku. Odporność korozyjna warstw azotkowych w roztworach siarczanów była większa niż odporność żelaza, natomiast w roztworze boranowym ich odporność była mniejsza. Pomimo zwiększonej korozji ogólnej, w boranach z dodatkiem chlorków warstwy azotkowe wykazywały bardzo wysoką odporność na korozję wżerową. Analiza powierzchni za pomocą XPS wykazała, że produkty korozji na azotowanym żelazie zawierały znacznie większe ilości tlenków żelaza, zwłaszcza magnetytu, niż na żelazie nieazotowanym. Zaproponowano wyjaśnienie, że anodowe zachowanie azotowanego żelaza w słabo- zasadowym roztworze jest określone głównie przez wpływ powstającego amoniaku. Intensywne anodowe roztwarzanie można wyjaśnić tworzeniem rozpuszczalnych kompleksów z amoniakiem, a duże ilości magnetytu można tłumaczyć zachodzeniem wspomaganej przez amoniak konwersji FeOOH + Fe(II) do Fe3O4. Zwiększona odporność na korozję wżerową azotowanego żelaza może być spowodowana powstawaniem większej ilości tlenków żelaza i wiązaniem chlorków w kompleks Fe-NH3-Cl.

EN

Corrosion behaviour of iron nitrides ?, ?' and ? + ?' ' (formed by gas nitriding at 570oC) was examined in neutral and acidifi ed sulphate solutions and in borate buffer of pH 8.4, without and with chlorides or ammonia. In chloride-free solutions, nitride layers showed in comparison with unnitrided iron higher corrosion resistance in neutral and acidifi ed solutions, but lower resistance in the borate buffer. Despite of increased general corrosion, in borate solution with an addition of chloride anions nitride layers exhibited a very high resistance to pitting corrosion. XPS analysis showed that anodic films on nitrided iron contained much larger amounts of iron oxides, in particular of magnetite, than those on untreated iron. It was suggested that the anodic behaviour of nitrided iron in slightly alkaline solution was determined mainly by the effect of evolving ammonia. Increased anodic dissolution can be explained by the formation of soluble complexes with ammonia, whereas increased amounts of magnetite can be due to the ammonia-promoted conversion of FeOOH + Fe(II) to Fe3O4. It was proposed that the enhanced pitting resistance of nitrided iron resulted mainly from the formation of large amounts of iron oxides and from binding of chloride anions into a Fe-NH3-Cl complex.

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Niestandardowe przypadki korozji wyposażenia gastronomicznego ze stali austenitycznej

Pałka K.

Inżynieria Rolnicza

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2002

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R. 6, nr 9

223--228

PL

Zaobserwowano przypadki korozji ogólnej wyposażenia gastronomicznego, wykonanego ze stali 0H18N9, objawiającej się powstawaniem rdzawego nalotu, analogicznie jak w stalach niestopowych. Przedstawiono analizę przyczyn korozji ogólnej elementów ze stali austenitycznych oraz możliwości zapobiegania jej.

EN

The cases of general corrosion were observed in gastronomic equipment made of the OH18N9 steel, the symptoms of which consisted in formation of rusty bloom, analogically like in ordinary steel. The reasons of general corrosion on the elements made of austenitic steel were analysed and the prevention possibilities were discussed.