Welding A36 steel to 4140 steel advice needed

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Working on a current project requiring welding A36 structural steel tubing to heat treated 4140 steel plate, I need recommendations on proper weld procedure and what filler metal should be used.
Reply:Hello Killswith1987, if I have this correct you are going to be welding A36 to 4140 that is already heat-treated. Is the 4140 going to be heat-treated afterwards to provide the same level of hardness that you had present prior to the welding of these parts? I was going to try to go off of memory to address parts of your question but thought better of that and instead found a link with some valuable and applicable information that I believe does answer it pretty good.http://weldingdesign.com/welding-qa/...-stress-reliefGood luck on your project. More details might help to receive more detailed answers too though. Best regards, Allanaevald
Reply:I think Allens rright, hardened 4140 is an insane idea.   how hard or its  rockwell may play a factor.   ETD150 i think is pretty close to a prehardened 4140, and i've gotten away w/ welding that, when trying hard, but wouldnt do it on anything formal w/ a consience.      but i've used 7018 w/ good results w/ 4140 before the oven.    i mean really good.  and it was trencher frost teeth pockets, a36 to 4140. it was 4140 tubing to mild flat, and brought them up to a high 40s - low 50 rockwell c afterward.