References for Steel Tech are from, but not limited to, the material specification sheets from Carpenter Technology Corporation, Steel Division and lecture material from Robb Gunters 1994 ABANA conference demonstration on scrap tool steels. 

Type Analysis

    O1 is an oil hardening, general purpose tool and die steel which is safe to harden even in intricate sections.  Its has a critical temperature of 1370 F., and a recommended forging range above 1500 F.. The maximum Rockwell hardness is 63/65 (as hardened) with the recommended hardening temperature being between 1450 and 1500 F..To anneal, heat to a uniform 1400/1450 and pack in vermiculite (or similar material).  To normalize, heat to 1600 F. and cool in still room air.  O1 can be tempered immediately after hardening with a minimum tempering time of one hour.  Sections over 2 inches thick should be tempered one hour per inch.  The tempering temperature/Rockwell hardness is as follows:

    O1 is typically used as piston material in American made automotive shock absorbers, hydraulic pistons (as on heavy machinery), blanking dies, forming dies, broaches, colletts, stamps, master tools, spindles, master taps and thread gauges.  Another common name is drill rod.  These materials/parts are good sources for scrap O1 tool steel.