ORIGINAL PAPER Impact of sensitization on dissolution process of AISI 304 stainless steel during intergranular corrosion evaluated using DEIS technique A. Arutunow & K. Darowicki Received: 9 May 2008 / Revised: 28 July 2008 / Accepted: 30 July 2008 / Published online: 22 August 2008 # Springer-Verlag 2008 Abstract The paper presents the results of instantaneous impedance changes measurements vs. reactivation potential performed by means of dynamic electrochemical impedance spectroscopy (DEIS) technique for AISI 304 stainless steel (SS) dissolution process during intergranular corrosion (IG) in 0.5 M H 2 SO 4 +0.01 M KSCN solution. With the use of DEIS method, it was possible to estimate dynamic changes of the examined system’ s impedance in conditions of proceeding IG process. Furthermore, the paper proposes an alternative way of evaluating AISI 304 stainless steel dissolution rate during intergranular corrosion based on approximation to theory of iron dissolution in sulfuric acid medium. Simulta- neously, based on the DEIS measurements, information about the degree of sensitization of the examined material were obtained. Performed research revealed the advantages of the DEIS technique over the classical double-loop electro- chemical potentiokinetic reactivation tests when inves- tigating intergranular corrosion process. Keywords Dissolution process . Intergranular corrosion . DEIS . AISI 304 stainless steel Introduction Austenitic stainless steels (SS)—containing 18% chromium and 8% nickel—are engineering materials widely used in many branches of industry due to their good mechanical properties and corrosion resistance at elevated temperatures. However, the precipitation of intermetallic compounds at grain boundaries affects this resistance [1–3]. Exposure to high temperatures ranging from 500 to 800 °C, during welding or service, leads to precipitation of chromium rich carbides (type Cr 23 C 6 ) or sigma phase (Fe-Cr-Mo) at grain boundaries and formation of chromium depletion regions adjacent to these carbides. Therefore, stainless steels with less than 12–13 wt.% of chromium- and chromium- depleted regions at grain boundaries are known to have undergone sensitization [1–5]. Intergranular corrosion of austenitic stainless steels is explained by the chromium depletion theory [6, 7], which shows that the extent of chromium-depleted zones at grain boundaries indicates directly the material’ s susceptibility to IG process and in the presence of residual stresses and strain to IGSCC as well in the final stage [8]. According to the ASTM standard, metallographic etching and weight-loss tests are regularly performed to assess degree of sensitization (DOS) of austenitic stainless steels [7–15]. The disadvantages of these evaluation techniques are the considerable consumption of etchant and long testing period. Since anodic dissolution of austenitic SS in an electrolyte is an electrochemical process, estimating DOS of austenitic stainless steels should be possible by means of electrochemical methods. Many electrochemical methods were proposed to determine DOS of stainless steels in the literature [16, 17]. Among them, anodic polarization tests [18] were the most commonly used approaches. The search for a rapid, quantitative, and non-destructive test method has lead many researchers to develop double- loop electrochemical potentiokinetic reactivation (DL-EPR) tests [2, 3, 19–25]. This technique was especially applied in J Solid State Electrochem (2009) 13:1687–1694 DOI 10.1007/s10008-008-0642-z Presented at the international conference CORROSION TODAY held in Gdansk-Sobieszewo, Poland, 23 to 26 April 2008. A. Arutunow (*) : K. Darowicki Department of Electrochemistry, Corrosion and Materials Engineering, Gdansk University of Technology, G. Narutowicza 11/12, 80-952 Gdansk, Poland e-mail: anka@chem.pg.gda.pl