The tempering temperature generally employed may vary from 300 to 450°F, depending on size
and properties required. For all general purposes tempering at 350°F is satisfactory.
Temperatures above 450°F are rarely used on 01. The hardness levels produced by tempering
above 450°F can also be produced in shock-resisting grades. Therefore, where greater
toughness is required than 01 provides after tempering at 450°F, it is customary to change to a
shock-resisting steel. Small tools should be held at the tempering temperature for at least one
hour, and larger tools for two hours, per inch of greatest thickness. If a second temper is used, it
should be 25 degrees lower than the first.