Gear segment welded to shaft

Hello , I have a Wheel Horse Lawn Tractor , I have the need to replace a half moon gear segment that is welded to a 3/4 in. shaft , the gear appears
to be a steel casting and was either Stick or MIG welded to the 3/4 cold rolled shaft , I checked the original weld fillet and it's as hard a diamond and the gear is likewise hard up to approx. 1/16 " from the weld line , I will probably not try to remove the old gear , will just make a new assembly and incorporate the new gear into this , I have been an Aircraft / Aerospace welder/weldor most of my working career , mostly GTAW and Electron Beam , am real curious as to what filler material was used that is as hard as a "Rock" to join a gear and shaft assembly , I may just go with Silver Braze . Thanks Phil L EAA 12873
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Phil wrote:

I'd guess that either the shaft or the gear are high carbon. Weld with any normal process will get reasonable admixture of base metal and filler. Big, solid chunks of steel in the weldments means the joint coils fast. High carbon plus fast cooling equals really hard.
Easiest fix is to destroy the easiest side to remake, weld it up again. In your case, the gear is probably harder to redo so the shaft gets sacrificed.
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