preheating the work in stick welding

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hello expert guys,i wanted to ask if does make it a difference if you preheat the work with a (propane) torch just before the stick weld  -  is it then the heat affected zone narrower and less material stress, due to a lower temperature gradient between the weld zone and the rest of the work or the overall heat input becomes high enough to burn through? is it possible to weld hotter material with a lower amp setting?thank you for any advice
Reply:I have never seen a wps requiring preheating of mild steel unless the steel was below 30 degrees F.Getting a uniform temperature would be impossible unless you have an oven.We constantly do destructive bend tests on mild steel and have no heat affected zone issues unless;the weld is quenchedthere is excessive interpass temperature multiple pass weldsthe weld is excessively slow and large therefore creating HAZJust my 2 centsgood luckLast edited by ZTFab; 12-09-2010 at 05:21 PM.
Reply:in my personal opinion using this technique is fine if you dont have the amps to quite get where you want.  Basicallly its a cheater method.  It will work.  As far as yielding better results, I dont think so.  But as far as helping you out when you have a machine that just doesnt quite cut the mustard...yeah it will do.  It will bring the temps up so you would wantto watch out for burn through depending on thow thin, but usually if burn through is an issue you dont need to preheat.  Just my two centsIF it Catches...Let it Burn
Reply:This method works for me, before I bought my big machine.  I had a Century 130class machine.  To get anywhere close to the thickness on the doorplate, I had to propane torch preheat.  It really helped in wetting out, but not with penetration.  My personal experiences!  Good Luck!  Brian Lee  Sparkeee27
Reply:Preheat is required for some procedures to reduce distortion (due to t he lower temperature differential), reduce risk of cracking in the HAZ, maintin ductility of the weld metal by slowing the cooling, and to make it practical to perform welds with sufficient fusion using less heat than otherwise needed. There are other reasons as well.Example of the last case: welding lifting lugs to a locomotive. The lugs are about 6" long by 3/4 thick, are engineered to support 25 tons, and are welded full penetration  to 4.5" thick deck plate. The deck plate is heavy enough that getting sufficient fusion to the plate at the weld root  is sketchy without preheat. Running hot enough to burn into the deck is way too hot for the lug. So, preheat the deck to about 250 or 300 in the weld area, and 1/8 7018 was fine in its proper heat range. Without the preheat, the weld metal would stand up on the heavy plate, leaving hte weld toes open, and grinding through the weld showed poor fusion. Attached ImagesLast edited by enlpck; 03-17-2006 at 05:20 PM.
Reply:Of course post heating is also commonly used in the prevention of cracking as well IF it Catches...Let it Burn