Corrosion of an austenite and ferrite stainless steel weld

Abstract

Dissimilar metal connections are prone to frequent failures. These failures are attributed to the difference in the mechanical properties across the weld, the coefficients of thermal expansion of the two types of steels and the resulting creep at the interface. For the weld analyzed in this research, it was shown that corrosion measurements can be used for a proper evaluation of the quality of weld material and for the prediction of whether or not the material, after the applied welding process, can be in service without failures. It was found that the corrosion of the weld analyzed in this research resulted from the simultaneous activity of different types of corrosion. In this study, electrochemical techniques including polarization and metallographic analysis were used to analyze the corrosion of a weld material of ferrite and austenitic stainless steels. Based on surface, chemical and electrochemical analyses, it was concluded that corrosion occurrence was the result of the simultaneous activity of contact corrosion (ferrite and austenitic material conjuction), stress corrosion (originating from deformed ferrite structure) and inter-granular corrosion (due to chromium carbide precipitation). The value of corrosion potential of -0.53 V shows that this weld, after the thermal treatment, is not able to repassivate a protective oxide film.

Spojevi različitih metala dobijenih zavarivanjem skloni su propadanju uglavnom usled pojave različitih vidova korozije. Fizičko-hemijska, mehanička svojstva, kao i koeficijenti toplotnog širenja različitih čelika najčešći su uzrok pucanja materijala na zavarenim spojevima. Istraživanja u ovom radu su pokazala da se ispitivanje korozije materijala može koristiti za procenu kvaliteta spojeva zavarenih materijala. Različite analitičke, metalografske i elektrohemijske tehnike i metode analize su primenjene za ispitivanje korozije zavarenog spoja nerđajućih čelika feritne i austenitne strukture. Ustanovljeno je da do pojave korozije na zavarenom spoju ispitivanih materijala prevashodno dolazi usled: kontaktne korozije, naponske korozije (koja potiče od deformisane strukture ferita) i međukristalne korozije (posledica izluživanja hrom-karbida) u feritnom delu zavarenog spoja.