Weld hardness question

Ok folks, here is the situation:

I had what I thought was two identical cast hubs with worn bearing surfaces. Welded them both up with the same welder and wire. Chucked up the first one in the lathe and turned it back down to spec. Chucked up the 2nd one and burned my inserts off the tool holder. Put a file to the welded up area and it would not cut the welded area it was so hard. After trying and ruining a number of cutters I took the hub and ground the welded area down relatively smooth and tried it again, same result. Took the hub and a rosebud and heated the welded area bright red (hoping that it might anneal it somewhat) and chucked it back up. It cut but was still very hard, not to mention hard on my old lathe. Any insight on what happened? Thanks.

One hub was cast steel and the other was cast iron. As you've learned annealing helps but the real trick is to never weld cast iron if you're going to machine it later. Always braze cast iron if you're building up to machine.

One of the hubs was cast of low carbon scrap, the other of scrap springs fed into the furnace.

The rosebud anneal job may still have had enough of a heat sink effect from the remaining mass to cool the welded area fast enough to cause it to harden.

Cheers Trevor Jones

That thing has to be glowing a very bright orange if you intend to anneal it. Over 1750 degrees without checking my books. The springs were most likely loaded with carbon and that can get very hard. The low carbon had to be the soft one since with no carbon ther is no hardening... up to about 25 points... 1025 .

John

That would probably explain why the hard set looked in great used shape and the soft ones were "well used" Thanks for all the help.