Well it could be just about anything that they could find - cheap. It would have to be an American 400 martensitic series. The 300 series stainless steel can be "hardened" BUT only by "work hardening. That is by cold working the material, either by cold rolling down to lighter and lighter gauges, or by
"drawing" through a die or other size altering operation. "Annealing" stainless steel will REMOVE the work hardening effect. The
400 series have two different stainless steel structures. One is called
"ferritic" (409, 430, 434. 439) which cannot be hardened by heat treatment. The other is called
"martensitic" (403, 410, 416, 420, & 440 A,B,C) which CAN be hardened by heat treatment. So, if it were 400 series on a knife it would be have to be martensitic steel, 403, 410, 416, 420, or one of the 440 series.
Many read
Surgical Inst. steel on Bulldog knives and immediately they think 440C. Ain't so!
ANY of the 400 series martensitic steels could be considered Surgical Instrument steel.
Ferritic steel has 12 to 18% Chromium and almost no Carbon. Ferritic steel is relatively soft since it's mostly ferrite and it's hardness is measured on the Rockwell "B" scale.
"Martensite" most commonly refers to a very hard constituent of steel (the alloy of iron and carbon) important in some tool steels. The martensite is formed by rapid cooling (quenching) of austenite which traps carbon atoms that do not have time to diffuse out of the crystal structure. This steel is read for hardness on the familiar Rockwell "C" scale.
My guess would be 420 HC SS or 440A.
May have to call the company to find out.
It could be a proprietary steel made just for Gerber using 420 HC or 440A as a base and adding some Vanadium for toughness.