Materials Science and Engineering A273 – 275 (1999) 543 – 548 Corrosion behaviour of Fe–Mn–Si based shape memory steels trained by cold rolling O. So ¨ derberg a, *, X.W. Liu a , P.G. Yakovenko b , K. Ullakko a , V.K. Lindroos a a Laboratory of Physical Metallurgy and Materials Science, Helsinki Uniersity of Technology, P.O.B. 6200, FIN-02015 Hut, Finland b Institute of Metal Physics, Kie, Ukraine Abstract Fe – Mn – Si based high nitrogen steels have been studied in recent years for potential industrial applications. These steels show good shape memory properties, high strength and excellent ductility. In the present study, the effects of training history on the corrosion properties of Fe – Mn – Si – Cr – Ni based high nitrogen steels were investigated. The corrosion behaviour of shape memory alloys was analyzed by implementing anodic polarisation measurements and immersion tests. The shape memory steels in annealed, deformed and recovered conditions were studied to examine the training effect on their corrosion behaviour. The features of the anodic polarisation curves indicated a general corrosion type of these steels. The experimental results showed that Cr and Mn had a marked influence on the corrosion behaviour of the steels, followed by Ni, N and V. It was also apparent that the deformation during the shape memory training by cold rolling decreased the corrosion stability, and the recovery heating reduced further their corrosion resistance. However, further studies are needed in order to better understand the corrosion behaviour of the investigated alloys. © 1999 Elsevier Science S.A. All rights reserved. Keywords: Shape memory alloys; Fe – Mn – Si based alloys; Corrosion; Cold rolling www.elsevier.com/locate/msea 1. Introduction Since a shape memory effect in the Fe–Mn–Si sys- tem was observed by Sato et al. [1], iron based shape memory alloys have attracted increasing attention due to their potential applications. As an example, this kind of shape memory alloys has been successively used as pipe connectors in oil field tubes [2]. However, the need to improve the strength and corrosion properties of the ferrous shape memory alloys, while maintaining their shape memory effect, is obvious in order to extend their applications. According to Murakami et al. [3], silicon is beneficial for the shape memory by increasing the strength of the matrix and reducing the stacking fault energy. Si can also improve the corrosion resistance of iron in acid environment by forming a protective silica surface film, when its content is more than 14.5 wt.% [4]. However, silicon promotes also the formation of the brittle sigma phase in Fe–Cr alloys [5]. In Fe–Mn–Si shape memory alloys where the Si content is fixed to approx. 5–6 wt.%, the M s temperature of the alloy can be controlled by Mn content [6]. Zhu et al. reported that in the binary Fe–Mn alloys the addition of Mn decreases the corrosion resistance of the passive film while addition of Cr or Al improves it [7]. The beneficial effect of Cr arises from its capability of spontaneously forming a self-repairable passive film on the alloy surface. In the case of the Fe–Mn–Si shape memory alloys, with increasing Cr content the amount of Mn must be decreased to make the M s temperature constant or below room temperature [6]. However, if the amount of Cr exceeds 7% in binary Fe–Cr alloys, the susceptibility of the brittle sigma phase formation becomes high, while this can be avoided by adding Ni [4]. Nickel is also a key element in austenitic stainless steels in pre- venting chloride-stress-corrosion-cracking (CSCC) when alloyed by more than 8% [8]. The function of nitrogen in shape memory alloys has been studied by * Corresponding author. Fax: +358-9-451-2677. E-mail address: outi.soderberg@hut.fi (O. So ¨ derberg) 0921-5093/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved. PII:S0921-5093(99)00396-2