Tempering 420F for Max. Tensile

[cbert]

I am getting annealed 420F barstock for making turned parts.
Tempering at 600 F then air cooling produces a tensile of 230ksi according to Mark's Handbook. I plan on doing the tempering in house in a furnace with an inert atmoshere. Can someone tell me the duration of the heat treat at 600F? Part is 3/4" round.

 

[TVP]

Tempering is usually performed for 1 hour at the temperature specified for parts less than 25 mm (1 inch) thick. You do realize that the tempering must be performed AFTER an austenitizing process (~ 980-1065 C or 1800-1950 F)? Time at temperature for austenitizing is usually 30-90 minutes.