The negative effects of titanium on the pitting susceptibility of commercial stainless steels has been reported, but there is no clear understanding of the precise role played by the alloying element. It is known that sulfide inclusions are deleterious and provide sites for the nucleation of pitting corrosion in stainless steels. This study has determined the manner in which titanium-containing inclusions contribute to the localized attack of stainless steels. Titanium is found to exist primarily in the form of oxides, carbides, and oxycarbides, and these are invariably different from the characteristic sulfide stringers that are commonly found in wrought stainless steels.
Scanning electron microscopy (SEM) and scanning Auger electron spectroscopy (AES) have been used to examine types 301 (UNS(1) S30100) and 316 (UNS S31600) austenitic stainless steels, both before and after corrosion under direct immersion or under anodic polarization control. The electrochemical behavior and the corrosion attack at the inclusions have been analyzed and lead to an understanding of the conditions leading to pitting corrosion. It is concluded that the titanium-rich inclusions are preferential sites for pitting attack.
