Pre-heating heavy steel before welding

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Here in about 20 min I'm going to be welding some 4x6 with 1/4" sidewall to a chunk of 1" plate. The 1" plate will be laying horizontal and the 4x6 will be vertical on too of it. My understanding is that to prevent a cold weld with the MM252 I should preheat the plate so that it doesn't cool to rapidly and result in a weak weld. How hot does the plate need to be? I've got an infrared gun to measure the temp.Thanks.
Reply:is this a home project or work? If work, you should have a welding procedure to go by. If not, I would think 200 degrees would do.
Reply:I'm a farmer so I guess you would classify it as a home project. It is way overbuilt for what it is but I still want to make it as good as I can. Thanks.
Reply:For mild steel, around  150º F and you should be fine.ESAB Migmaster 250 Hobart Ironman 230Multimatic 215TWECO Fabricator 181i & 211iHH125EZ - nice little fluxcore only unitMaxstar 150 STH - very nice
Reply:Thanks for the help guys. Got it all done. Hopefully it holds up now.
Reply:If somebody tells you not to pre-heat anything that's 1/2" and up, they're wrong.   I think 250 degrees would be good for 1/2".