What steel...

[JoeBusic]

..is the worst without cold treatment? Precisely, steel with the largest amount of RA at room temp, using normal HT protocols, before cryo and tempering.

 

[DevinT]

Most high alloy steels. D2 and A2 have quite a bit of RA.

High speed steels can have most of the RA eliminated with the upper temper.

440-C has a hard time with attainable hardness without a cryo.

Hoss

 

[Alex Topfer]

Would the answer here technically be various austenitic stainless steels, as they're engineered to be in the austenitic phase at room temperature? 300 and 400 series, probably others too
A lot of alloy elements stabilise austentite, so as Devin said anything with lots of alloying elements