The spec sheet provided by Sapper is correct as far as it goes, but here is some advice you should keep in mind.

1) 8620 is low carbon and as such it will be sold in the unannealed state in the USA and Canada. (despite what the link provided by Sapper says). If you buy it as hot rolled bars, it will be in the as rolled condition.If you buy it cold drawn, it will be sufficiently cold worked to boost the yield strength probably 20% or so and increase the yield /tensile ratio and decrease ductility somewhat. I have data in my office, but I am stuck in Califrnia for a couple of days. Only if you buy it as annealled will you get annealled. (My direct personal experience making drawing and selling the stuff.)

2) The case depth is controlled by time at temperature. Diffusion of carbon in carburizing is time dependent. Given the depth, the heat treater will calculate the cycle to get the carbon into the parts. You will need to specify the case depth needed if that is going to be a rejection criteria. That info is from your design requirements, not the steel's spec sheet. So what Case depth do you need? You won't find that on the spec sheet!

3) Tempered is the name for the final thermal treatment process to relax the martensite formed in Quenching. The tempering temperature used determines the hardness /mechanical properties of the steel after the heat treatment. This too is a design decision. What hardness do you need the case to be? That will determine the tempering temperature to be used.

4) You can optimize for hardness, in the case; You can optimize for toughness in the core; You can try to get highest hardness with toughest case. These all imply different heat treat cycles.

5) Depending on the case depth and hardness, You may or may not need to carburize to get the extra carbon for the case. You have not given us size/section thickness, hardness required, nor case depth desired, so right now the advice you have is well meaning but unfocused.

What is your timeline? I will return to my office thursday, when I can provide you with additional data Specifics given your particular requirements. Is that soon enough?

On a more general note, to specify on the drawing, i would expect to find a caption such as " Rockwell C XX-XY case depth .0XX" minimum" or "Carburize and Q&T to HRC XX -XY case depth .0XX-.0YY". If toughness is really the issue, A caption such as "HRC ZZ maximum at midradius" might also be included, if you know that hardnesses greater than HRC ZZ are associated with lower toughness and more brittle failure modes.

Beware using the jominy charts without seeing the quench and dimensional equivalents . The charts provided do NOT tell you what section thickness, for example , "J4" equates to in a mild oil quench. Nor do they give you any insight into as tempered properties.

Heres hoping that you have a couple of days...

milo