"What type of steel are “K” barrels?"
Possibly I've missed the intent of Mark's question, but the names Parker used for the steel should be marked on the rib, and the composition of several Parker barrel steels is now known courtesy of Dave Suponski and published in the Summer 2014
Parker Pages.
Scroll down about 3/4 here
https://docs.google.com/document/d/1...EK8OtPYVA/edit