The references I've read said they were using 440C, and that was what they trademarked as "Queen Steel". I've seen some spots of rust here and there on mine, but nothing general.
Queen also used 1095 carbon steel on some, notably on their Workhorse series, but the carbon steel blades will rust or patina generally rather than just spotting.
It is possible that some of the rust spots seen on stainless blades are the result of carbon steel being transferred by the tooling when it had been used on carbon steel previous to stainless. It is certain that "stain less" steels can rust. Especially over the course of forty or fifty years.
