By Franklyn D. Garland Originally published in the UMBA Newsletter Vol. 17 Issue No. 1

O1 is an oil hardening, general purpose tool steel and die steel which is safe to harden even in intricate sections. The element breakdown is as follows:

Element Percentage
Carbon 0.90%
Manganese 1.20%
Chromium 0.50%
Vanadium 0.20%
Tungsten 0.50%
Iron Balance

It 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 F. and pack in vermiculite (or similar material). To normalize, heat to 1600 F. and air 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 temperatures/Rockwell hardness is as follows:

in Degrees
Fahrenheit Rockwell
(C scale)
200 63/65
300 63/65
350 62/64
400 60/63
450 60/62
500 58/60
600 55/57
700 52/54
800 48/50

O1 is typically used as piston material in American made automotive shock absorbers, hydraulic pistons (as on heavy machinery), blanking dies, forming dies, broaches, collets, 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.

Author's Notice: References for this article are from, but not limited to, the material specification sheets from Carpenter Technology Corporation, Steel Division and lecture material from Robb Gunter's 1994 ABANA conference demonstration on scrap tool steels.

Copyright 1994, 1995 ArtMetal

Author: Franklyn Garland
HTML Editor: Roger Schmitt
ArtMetal Editor/Curator: Enrique Vega
Last Updated: 1/19/2012