I have a constant supply of worn out and broken pipe wrench jaws and hooks. They are ridgid brand. It says steel alloy on the side but does anyone know what these are made of? They are off of pipe wrenches ranging in size from 24 inch to 60 inch. It looks like there are casting marks on the hook part but it does forge with lots of effort but when broke it looks like cast iron.  Has anyone used these for forging before?

I've never forged with them before, and i dont know exactly what they are, but I own many rigid pipe wrenches, and I'm fairly certain they are cast iron.

Have you spark tested it? Cast iron has a distinct spark, very short and non branching. That would at least point you in a general direction. You could try heating a piece to critical and quenching it, though I have no advice in that area, I have no experience heat treating cast iron. In my experience welding cast iron, it does not like rapid temperature changes (pre heat and post heat are needed) so take that for what it's worth. A more experienced metallurgist should be along shortly. 

Some pipe wrenches are forged, and some are not. If you are able to forge it, then it is forged.

Things that are drop forged have seams similar to casting lines.

It does forge. It is harder to move than mild steel of the same size. I have forged out the beginning of a knife blade with it. Might just have to experiment more to get a better feel for what it is.

So that tells you its probably not cast. I would recommend testing it before putting all the effort into a blade. That's, ultimately, your call though. Most high carbon and even mid carbon steels do not move as easily under the hammer as mild does. 

I know for sure that they were oil quenched.

When I was a kid (long time ago), my old Neighbor worked in the heat treat section at Ridge for over 30 years.

We had a field trip to Ridge tool in High school for metal shop in 1972.

I watched him shoveling pipe wrench jaws into a huge gas open oven prior to oil quench. It was like xxxx in there!

I had a newfound respect for him after that. He was Hungarian and showed me what a work ethic meant.