MIG welding, base metal and resulting hardness / wear characteristics

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This is the scenario:A worn roller shaft has hardened ends which constitute a bearing surface that revolve within a brass (bronze?) bushing.  Hardness is in the 35-40 RHC scale.  The material is, say, 4140.  The hardened, worn ends are built up with a MIG weld and turned back to original dimensions and tolerances.What is the practical result?  Is the weld as hard, harder or less than the original surface?  If equally hard or harder, is it more brittle or prone to wear?My inclination is that any material exposed to a welding operation will anneal.  I also know that the resulting weld beads are quite hard.  Can anyone give insight into the possible metallurgical characteristics of the resulting repair versus the original?  What kind of test(s) could be performed other than a straight-forward Rockwell hardness test to determine the result?  Is the answer dependent on the filler wire used?My sincere and gracious thanks for the education on this particular issue!   For context, my background is largely in machining rather than welding.  I was referred to this forum by a helpful member of Practical Machinist who felt the query would be better addressed here.  Thank you again for any insight or technical references appropriate to this repair!
Reply:Practical result in mig welding the worn shaft could be optimized if you go with Er80, or even ER90 in a small 2lb spool. Personally I doubt a standard filler would achieve as hard a surface as the original hardened 4140 unless you had a great deal of base metal dilution into the weld.Weld like a "WELDOR", not a wel-"DERR" MillerDynasty700DX,Dynasty350DX4ea,Dynasty200DX,Li  ncolnSW200-2ea.,MillerMatic350P,MillerMatic200w/spoolgun,MKCobraMig260,Lincoln SP-170T,PlasmaCam/Hypertherm1250,HFProTig2ea,MigMax1ea.