What is the service temperature for the impact testing on this?
Look at matweb.com
Input 4140 in the search bar. I assume that the heat treatment is a Q&T? Look around in the 900F - 1000F tempering range for a matching hardness, though if the test temperature is not within a few degrees of your service temperature, then the impact properties do not apply to your application.
HOWEVER:
1) I would avoid using cast materials for impact loading. Use a forged material.
2) If you cannot avoid the use of a casting for your application, use an alloy with a higher nickel content like 4340 or 6820. Nickel does a lot to improve toughness, although 8620 cannot be hardened through Q&T.
Engineering is not the science behind building. It is the science behind not building.
Information on Matweb is sometimes incomplete. You may also find this information in other sources such as Machinery's Handbook or ...I forget the name of that old book with all the metals in it.
Unfortunately there aren’t any ‘typical’ impact props at a given hardness.
Unlike UTS and YS, you cannot dial in a hardness and expect a correlation to either impact strength, elongation, RA, fx toughness, etc. It all depends on the microstructure: phases present and the morphology. These are dependent on the path taken to get to 35 HRC or other (steelmaking process, chemistry, refining, HT). A good reference is ASM Hdbk, Vol 1. Also ditto what EngineerTex said, plus lower carbon, e.g. 4130.
