ABSTRACT

The strain-induced accelerated corrosion has been reported for many alloys used in structural and functional applications. Strain is expected to increase the metals internal energy, hence increasing the oxidation tendency of metals. However, significant work has generally been concentrated on stress corrosion cracking and effect of plastic strain on corrosion. It is widely known that strained steels undergo a higher active dissolution rate than the unstrained ones. Under unstable passivity conditions, strain is also expected to alter the characteristics of passive film, leading to more frequent breakdown of passive film. In this study, the influence of elastic strain on general corrosion and metastable pitting is investigated for steels through in-situ test setup. In the active state, steels undergo activation-controlled general corrosion, the in-situ elastic strain is applied to carbon steel A516 (UNS K02100) to assess its quantitative influence on general corrosion. Under unstable passivity conditions, stainless steel 316L (UNS S31603) specimens are tested for the metastable pitting resistance under in-situ elastic strain conditions. Results from electrochemical tests on specimens with different amounts of in-situ elastic strain are discussed in this paper.

INTRODUCTION

Metallic structures in the chemical process industry as well as in other structural applications show accelerated corrosion in areas with deformation. During manufacturing, assembly, or service, deformation is inevitably inflicted to the metals. When investigating the interplay of internal strain energy and corrosion reactions, it is generally suspected that the excess internal strain energy can accelerate general corrosion. Depending on different environmental parameters (pH, temperature, ion species/concentration) and potentials, alloys can be under activation-control or in a passive state below the transpassive potential or pitting potential. Activation controlled corrosion reactions are expected to be affected by the available strain energy, especially in carbon steels in acidic environments where the material is more likely to be in the active state. However, for stainless steels in which a stable passive film usually forms on the surface, the strain energy may also be expected to influence the repassivation behavior and the characteristics of the resultant passive film. Therefore, localized corrosion, for example pitting, can also be affected by the strain. Although much research has concentrated on the stress corrosion cracking (SCC) and plastic deformation influenced corrosion [2, 6, 7], but the effect of elastic strain on general corrosion and metastable/stable pitting in different alloy/environment systems have not been systematically investigated.

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