Welding Tips and Tricks

How would I go on about repairing a pumphouse made out of tungstencarbide?
The pumphouse has been cladded internally, and I've been told to repair the cracks. I've also been told it's cast, including anything from 1-3% Carbon.

Any genereal advice? Like heat input, pre - post heat? Tips on wire, as well as welding method?

So which part are you trying to fix, the overlay or the body?
Some hard face overlays will crack no matter what, just the nature of what they are.
lots of preheat, a high nickle filler, and post heat/slow cooling for the cast iron.
Best of luck...

Edit: I'm fixing cracks in a tungsten carbide pumphouse!

Do you have a pic? Where the crack is in the housing may make your repair approach a little different.

Tungsten Carbide components are not weldable in the ordinary sense. As others have said, they can be brazed, with silver solders.

Tungsten Carbide is actually a mixture of cobalt and tungsten carbide, a metal matrix composite, with cobalt acting as a 'glue' to hold the carbide particles together. Like any two phase mixture, it's a poor candidate for welding, as the two phases have very different melting temperatures.

http://en.wikipedia.org/wiki/Tungsten_carbide

I suppose you could weld them with cobalt filler metal, assuming such is available, but the mechanical properties of the tungsten carbide are a function of the cobalt and carbon content. Welding with cobalt filler is sure to degrade the materials hardness and other mechanical properties. Brazing keeps the temperature low enough that it doesn't cause any changes in the tungsten carbide composite

The thing is, it has been welded. The cracks came DUE to welding. The cracks are kinda like slim line that you can barely see with the bare eye. Im sorry I can't be more descriptive! Won't be able to get a picture till Tuesday!

Pics are needed... something sounds weird about this.
WC can be brazed/soldered but arc welding is out...
Some of the overlays lay down a cobalt base with WC sprinkled into it as they weld it(automated with lasers or plasma arc welding)... is that what your up against? Cobalt can be welded but its REALLY sensitive to contamination and heat stresses...
I've had an arc hit a WC insert before... it flares off in a fuzzy yellow flame and blows a black sooty mess all over the part and your tungsten (I was tigging it). Then it cracks.
A customer wanted a well drilling head modified and it had a bunch of carbide balls stuffed into it, well some of them were too close to the parts I was welding in...

Update!
Forgot to take pics, but I'm tig welding it with a Cobalt based filler, Stellite 6 I believe. (Got more info today)
Has apparantly been welded with MAG, should be said that this pumphouse has been used in Chlorine production.
They've already welded a sort of "ware coating" which I'm repairing the cracks in.
I've welded similair pumphouses before, cast in Super Duplex, which have been used in Zinc production.
Should I be expecting something similair?

Photos are of the Zinc "Attacked" pumphouses.

The pictures cleared up some ambiguity for me... Now I see what you mean by "pumphouse"... The volute of a centrifugal pump.

I can't contribute on this one, as it's outside my experience, but I'll be following to see how it goes and learn what I can.

Steve S

Ok, now I see and I have very little to offer. Never gotten to play with stellite, just heard stories about it.
I'd start with grinding most of that old stuff off to start with clean base metal.
Sounds like its in a nasty environment.

Looks like ware from pump cavitation. They may want to rethink what type of pump they use for the application. Chlorine will be embedded in the pores of the metal, and the casting, and in any cracks. Get good ventilation. Grind out anything questionable and if they tell you a pre heat and interpass temp I'd get temp sticks to keep it in range. Good chance you will have to have the mating faces remachined when your done. Cool project not a common one. I welded hard surface beads inside a housing like that once for a place that pumped a sand slurry for a pit operation. They brought in a company that specialized in heat treat and preheat. They wrapped it in sensors and heat blankets and used cpu controls to maintain correct temps.

Still waiting for wire.
Will definetively keep you guys updated!
I'll see if I cant get some photos pre-during-after weld.