Suggestions for welding on 8620 hardened tool steel

[WeldThis]

I may be joining an 8620 pinion gear to an 8620 shaft soon. Both pieces have been hardened, (case hardening) done to them. Does anyone have any suggestions on filler rod/ pre-heat or PWHT temps if necessary for this welding procedure? I have been researching all week, and many suggested 400 F for pre-heat, with slow post weld cooling. Rods suggested so far have included 312 SS, and Eutectic 680S, and 9018. I've also been told that this may have had a oil quench, and thus does not require a pre-heat/post heat process. I thought all tool steel should be pre-heated. Hm......I'm hoping to find out more on the heat treatments next week, but any advice in the meantime would be greatly appreciated. The application will be a temporary part to be used until a full billet part is produced. It is strictly for testing purposes right now. I plan on GTAW process, using ARgon shield, and grinding the case hardening off.

 

[metengr]

WeldThis;
I am trying to understand this connection in your post. Is this a solid pinion gear that will be welded to an end of a steel shaft or is this a pinion ring that will slip on the shaft OD surface and welded circumferentially? Can you provide a sketch?