The heat from the welding process and subsequent re-cooling causes changes in the HAZ. The extent and magnitude of property change depends primarily on the base material, the weld filler metal, and the amount and concentration of heat input by the welding process. The thermal diffusivity of the base material plays a large role. If the diffusivity is high, the material cooling rate is high and the HAZ is relatively small. Alternatively, a low diffusivity leads to slower cooling and a larger HAZ. The amount of heat input induced by the welding process plays an important role as well, as processes like oxyfuel welding use high heat input and increase the size of the HAZ. Processes like laser beam welding and electron beam welding give a highly concentrated, limited amount of heat, resulting in a small HAZ. Arc welding falls somewhere between these two extremes, with the individual processes varying somewhat in heat input.
Q = (V x A x 60) x efficiency
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S x 1000
Q = heat input (kJ/mm), V = voltage (V), I = current (A), and S = welding speed (mm/min). The thermal efficiency is dependent on the welding process used, with SMAW having a value of 0.75, GMAW and SAW, 0.9, GTAW, 0.8. Heat input calculated by multiplying the arc energy by the thermal efficiency factor.
The information you're looking for is out there. And plenty of it. Mountains of it. The problem is, its not all in one place. There is no one stop shopping for the info you're asking for. And for good reason. 10 cackozillion transformational alloys, and varying thicknesses, and ranges of chemistries, etc.
I think on the level of technicality you are looking for you start with a CCT diagram for your particular alloy. Determine what cooling rates yield what microstructure and prescipitations, intermetallics, carbides, etc., and then determine the effects of any heat regime imposed upon that material. Your instincts I think are correct. There is 'in general' more response due to heat input than there is preheat or interpass temps, simply because, in my opinion, heat input is a measure of an actual imposing of energy upon the weld, whereas preheat and interpass temp control is a slowing down of the dissipation of the already imposed thermal energy, and the fact that the critical transformaition temps are most often well above those temps controlled by PH and IP, though there are notable exceptions.
Sorry, CCT = Constant Cooling Transformation diagram. They superimpose transformation C curves over cooling rates. So that you can determine that at X cooling rate you will realize Y transformation products. There are volumes of these diagrams available.
Jeff,
only an extremely short input from my side, if you allow.
"Heat Input" in welding is my absolute favourite for the past few years and everything I can learn on that is being absorbed as by a sponge.
I mean to have mentioned anytime to having a "very special attitude" on "Heat Input" (what ever this means) and have often tried to find the right words for expressing this attitude.
What I was not able to find words for, you were!
Quote:
"And for good reason. 10 cackozillion transformational alloys, and varying thicknesses, and ranges of chemistries, etc."
Unquote.
Thanks for that! :-)
Best regards,
Stephan