https://www.bodycote.com/component-journeys/hard-time/index.html
"Tegiment" is a Sinn marketing word (latin for shell/armour). The actual technology is from Bodycote, a UK company, and known as S3P (Specialty Stainless Steel Processes) which itself is based on the kolsterising process invented by Dutch professor Bel Kolster in the 1980s.