Effect of thermomechanical treatment on the corrosion behaviour of Si-and Al-containing high-Mn austenitic steel with Nb and Ti micro-additions

Abstract

The corrosion behavior of the 27Mn-4Si-2Al type austenitic steel micro-alloyed with Nb and Ti was evaluated in acidic 0.1 M H2SO4 and chloride 3.5 % NaCl environments using potentiodynamic polarization tests. The corrosion properties of solution-treated specimens were compared to thermomechanically processed specimens. In the acidic solution, the steel exhibited a lower corrosion resistance than in the chloride solution, independently of the heat treatment applied. SEM and light micrographs confirmed that the corrosion attack in the acidic solution was higher when compared to the chloride solution. The steel showed evidence of pitting and uniform corrosion in both the acidic and chloride solutions. The corrosion resistance of supersaturated specimens in both 0.1 M H2SO4 and 3.5 % NaCl media was lower when compared to the thermomechanically treated specimens. It was found that the corrosion behavior of the examined high-Mn steel depends on the passivation tendency of the alloying elements (Mn, Al) and the grain size. Keywords: high-Mn steel, austenitic steel, corrosion resistance, passivity, thermomechanical treatment, potentiodynamic polarization test Korozijsko vedenje avstenitnega jekla 27Mn-4Si-2Al, mikrolegiranega z Nb in Ti je bilo ocenjeno v kislem 0,1 M H2SO4 in v kloridnem okolju 3,5 % NaCl, s potenciodinami~nim polarizacijskim preizkusom. Korozijske lastnosti raztopno`arjenih vzorcev so bile primerjane s termomehansko izdelanimi vzorci. V kisli raztopini so bili vzorci manj korozijsko odporni kot v kloridni raztopini, neodvisno od uporabljene toplotne obdelave. SEM in svetlobni posnetki so potrdili, da je bil napad korozije v primerjavi s kloridno raztopino izrazitej{i v kisli raztopini. Na jeklu so bili dokazi za jami~asto in splo{no korozijo v obeh raztopinah, kisli in bazi~ni. Korozijska odpornost prenasi~enih vzorcev v 0,1 M H2SO4 in v 3,5 % NaCl je bila manj{a v primerjavi s termomehansko obdelanimi vzorci. Ugotovljeno je, da je korozijsko vedenje preiskovanega visokomanganskega jekla odvisno od nagnjenosti k pasivaciji legirnih elementov (Mn, Al) in od velikosti zrn.

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