The role of titanium in the initiation of localized corrosion of stainless steel 444

Localized corrosion: Understanding stabilised stainless steel Using a suite of techniques, the role of Ti-rich inclusions in the localized corrosion of stainless steel has been better understood. For some applications ferritic stainless steels are a good low-cost option because they contain low levels of relatively expensive nickel, however, they are vulnerable to intergranular corrosion. There are methods by which to minimize such unwanted corrosion chemistry, such as creating alloys with stabilizing agents like Ti and Nb. Now, a team, led by Janine Mauzeroll at McGill University, Montreal, Canada, has used a battery of techniques, such as X-ray energy dispersive spectroscopy and scanning electrochemical- and electron- microscopies, to understand the role of Ti-rich inclusions in the Ti-stabilized stainless steel 'SS 444'. Specifically they found that, while Ti does improve bulk corrosion properties, Ti-rich inclusions act as initiation sites for localized corrosion. Titanium has been added to ferritic stainless steels to combat the detrimental effects of intergranular corrosion. While this has proven to be a successful strategy, we have found that the resulting Ti-rich inclusions present on the surface play a significant role in the initiation of other forms of localized corrosion. Herein, we report the effect of these inclusions on the localized corrosion of a stainless steel using macro and micro electrochemical techniques. Through the use of scanning electrochemical microscopy, we observe the microgalvanic couple formed between the conductive inclusions and passivated metal matrix. The difference in local reactivity across the material's surface was quantified using a 3D finite element model specifically built to respect the geometry of the corrosion-initiating features. Combined with electron microscopy and micro elemental analysis, localization of other alloying elements has been reported to provide new insight on their significance in localized corrosion resistance.