Titanium Fails to Stop Corrosion in Stainless Steel

Stainless steel is widely used for its corrosion resistance, but it is not invincible. In environments containing chloride ions, such as seawater, pitting corrosion can occur. Titanium is commonly added to stainless steel to improve pitting corrosion resistance, but it does not completely prevent pitting.

The study, conducted by researchers at Tohoku University, found that residual sulfides can still trigger pitting corrosion in stainless steel despite the addition of titanium. The researchers studied a ferritic stainless steel, Fe-16%Cr alloy (Type 430), and compared four types of inclusions: MnS, (Mn,Ti)S, TiS₂, and titanium nitride (TiN).

The researchers used microscale electrochemical measurements to analyze the inclusions and found that MnS was the easiest to dissolve, followed by (Mn,Ti)S and TiS₂, while TiN did not dissolve under the conditions examined. This suggests that even with the addition of titanium, residual sulfides can still trigger pitting corrosion.

## Why it matters The findings of this study are significant because they could inform the design of more resilient stainless steel used in a wide range of applications, including home appliances, surgical tools, and car parts. Stainless steel is a critical material in many industries, and improving its corrosion resistance could have a major impact on the longevity and performance of these products.

The study's findings are published in the journal npj Materials Degradation, and provide new insight into the complex question of how titanium additions affect the corrosion resistance of stainless steel. By understanding the electrochemical properties of the various inclusions formed in Ti-containing stainless steel, researchers and manufacturers can develop more effective strategies for preventing pitting corrosion and improving the overall performance of stainless steel.