Just off de cuff here, every piece cast is a whole new adventure, but what do I know, only been doin such since I learned to back when done with war surplus airplane piston rings and a O/A torch. Pretty much how it done back den. Course we didn't know it couldn't be done so dat how it was done.
Ders 2 kinds cast iron, good and CRAP. You generally tell by lookin at what casting was designed for to do. 7 dollar word 'metalurgy' gets thrown around a lot. Dat generally translate to your guess as god as mine. Go back to design purpose and calculate what was cheapest for maker. Engine blocks is good quality cause dey gotta be, pots & dutch ovens generally crap. Stove parts wid baked on porcelain absolutely NOT gonna weld or braze. You dont wanna know how dat porcelain fly off and stick to you either. Whole special group wood & coal burning stoves and boilers. You only gonna know how good casting was when it cold and hopefully not cracked to #e!!.
How you gonna connect hunks back together absolutely depends on how much customer willing to spend and how mad he gonna be if repair don't work. Next step in job is knowing or figuring out what process got best chance of success dat gonna endure when put back in service. I can stick together pot can be ground up and painted to sit in corner for decoration probably 90% of time, but same pot going back to work on top of stove or in fire success be maybe 5%. Either way gonna take time and time = money. Got a old cast iron coal fired water heater sittin on porch wid a plant growin out of it. Price was no object when fellow dropped off for fixin to make his wife happy. No way was he payin for 10 hours of fittin & fussin when he came to get, so I kept.. OK, I find a use, and I chalk dem hours up to tuition.
Flange on blower in picture, we can all see it broke. Can I 'fix' it? SURE Before I start tho, what does flange do? Is it suport dat holds blower to bottom of forge or just connection between blower & tyre? Makes big difference in fix.
How I make repair? Depends. What flange does and what mate looks like kind of governs decision. How much $$$ you want to spend big part of decision too. Come to pick up and yell at me how you could have bought new for less and my 18 pound hammer make it real easy for you to go buy new. Truth is if casting stays below 400f, best & cheapest repair is JB Weld.
Choices = Brass, 309ss rod, high nickel rod, Everdur either gas or carbon arc applied, and ever present E70-s6 MIG wid Co2.
Which choice is function of end result required, nothin else.
BTW, casting in picture looks like real crap dat foundry cast cheap as possible. Flange was designed to fail.