Im welding a mild steel flange for a wastegate, to a cast iron log manifold. I searched online and it said it was fine, if done correctly. pre heating, slow cooling. does anyone have experience in this? suggestions? more ways that i wont get the weld to crack?

 

What welding process are you using?

 

i've done it a few times. the first time i did it the cast iron cracked a few times before i got it right.
basicly all you need to do is preheat to a decent temperature hard to say how hot but i just do it until i can feel the heat off the piece kindof like after you have been welding on something for a while. then weld with i dunno silicon bronze rod, mild steel rod or preferably something high in nickel content like monel or inconel if you have any lying around but stainless is ok i think they also make a rod for cast iron but im not sure. the after you weld it up you should insulate it to slow the cooling rate. i use old leather gloves to cover up small pieces then wrap them with a towel or something. you dont really need to cover it up because the energy input from the preheat will slow the cooling rate already but its insurance i guess.

 

Why not just have a 40lb bag of sand and a 5gal pail ready? Works for most slow cooling needs.

 

isn't SMAW preferred for cast iron welding?

would it be possible to "stick" weld this?

:S what i learned in school awhile back, since cast iron is pourous, and with TIG , the teach said it will be easier to get porosity with gas welding.

but you guys are a hell-of-alot-better than i am with gas.

 

oh yea you can do that. i just dont like the mess related to sand.
come to think of it the cast iron rod i used was a SMAW electrode. i just broke off the shielding and sanded it down in water to clean and used the TIG. then i went over it with a monel rod.

 

You can get nickel rods specifically for GTAW

 

i usually use mild rod, but it depends on how crappy the casting is. the worse the casting, the more your going to need nickel rod. you can get nickel rod, but its usually 1/8" which is a pain in the *** and its super expensive.

a friend of mine took an electrode and scraped off all the shielding and used that with tig. turned out pretty nice.

if your welding cracks, make sure to drill a small hole on each side of the crack. it will keep it from cracking further.

i usually pre-heat with a map gas torch and then let it cool down on the bench. seens to work fine. kinda depends on how thick the casting is. the thinner it is, more more you want to slow down the cooling process.