From the start (1899 or so) til 1998, the steel was 1095 or something very similar. Heat treatment seemed to vary a bit, judging by hardness and the "feel" of the knife on a stone, but hardness seemed to hover around 54-55 HRC. 1998-2001 (the "Mike Stewart era") they mostly used 52100. After 2001, I lost interest but as I recall the steel switched several times.
I've had a few dozen over the years, never managed to get my hands on either of the two models I really liked: the Dall Deweese and the 4" Ideal pattern (IIRC, they called it a "canoe knife"). I've made several versions of the Dall Deweese, but seem to trade them off almost as soon as I finish them.