Welding 4130 Bar

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I will be welding a .75" dia u-shape (4" across) solid bar to a 1.0" dia straight solid bar (10" long), centered, both out of 4130 CF normalized stock.  We have done this before and with various results, like cracking in the 1.0 dia bar, some short, near the weld at the .75" dia bar, some the entire length of the 1.0" dia bar.  We tried to preheat with a rosebud, weld (ER70S-2 wire) and cool as slow as possible.  After reading various articles and comments, one thing we did not do is prep the parts at the are to be welded.Any, all, comments, suggestions are very welcome.Thanks...
Reply:413041404150Really should be pre heated and post heated during the welding process..(Get it almost red)They call it "Stress Releiving" and it will stop all the cracking you are encountering.. ...zap!I am not completely insane..Some parts are missing Professional Driver on a closed course....Do not attempt.Just because I'm a  dumbass don't mean that you can be too.So DON'T try any of this **** l do at home.
Reply:Like Zap said, make it HOT before welding, weld it, and keep it HOT and let it cool s-l-o-w-l-y in the furnace/oven.  There should be no cracking that way.  Those are some moderately thick sections to weld.  If you are just TIG fusing the edges together would be different than doing full penetration welds of the 3/4 bar from the standpoint of how much HEAT you are putting into the workpieces.Whatcha makin?
Reply:Preheat the material.  There are tables available.  My guess for only one inch you don't need much more than 300 F.  The more important point is to slowly cool.  In one shop were we did a lot of small castings and tool steel parts we had a barrel of "vermiculite".  It is a mica chip material often used as plant bedding material or pourable insulation for brick walls.  A one inch bar 10 inches long in the stuff will be too hot to handle for many hours if it is buried in the stuff.  That is what you want in order to prevent cracking.  Pull your pieces out the next day.  A post heating with the rosebud before burying it will also help.  Full post weld normalizing is around 1100 F.   Don't heat to full red because you chance grain growth.