Titanium is used in the manufacture of AISI 316L austenitic stainless steel as a deoxidizer. Titanium is considered a residual element, and limits are often not specified. As a residual element, titanium most often appears in complex oxide inclusions, usually in conjunction with aluminum and other deoxidizers. Titanium-bearing inclusions have been found to initiate pitting during electropolishing. The present work was performed to evaluate the acceptable upper limit for titanium as a residual element in AISI 316L.
Metallographic specimens were prepared from seven commercial heats of AISI 316L (Table 1) with titanium contents varying from 0.003 % to 0.014 %. A quantitative metallographic analysis of each specimen was performed using an SEM/EDS system with an automated stage. Operating parameters are given in Table 2. Data was obtained with the system in the backscatter (BS) mode, producing a high-contrast image based on differences in chemical composition. Once each inclusion was identified by its difference in gray scale, it was also analyzed by EDS for elements present.