Plumbing and Piping - How to remove sink drain pipe coming out of wall

The situation:
In my bathroom sink the drain pipe coming out of the wall needs replacement because it has rusted. This is a thin walled cromed pipe which comes out of the wall and then bends downwards about 1 inch. After the downwards bend is where the P-Trap attaches.

The problem:
The problem is that this thin walled 1.5 inch cromed pipe is attached to a thick cast iron pipe inside the wall and will not come loose. I cut the sheetrock around the pipe to see what was going on inside the wall and it seems to me that this pipe may be welded or perhaps just soldered to the cast iron pipe. I grabbed the thin walled cromed pipe with a pipe wrench and a pair of pliers to try to perhaps unscrew it but it won’t move. In fact, I cannot get a very good grip on it because being thin walled it deforms when I put pressure on it with the pliers and/or pipe wrench.
Do you think it is just screwed in? soldered? or even welded? Seems to me perhaps it is soldered since scratching the area where the two pipes meet seems to expose some softer metal, perhaps lead. I cannot actually see very well because this is all inside the wall, I am just looking at it through a 3 inch hole I cut into the wall around the pipe.

Any hints on how to remove it?

Thanks.

Well my neighbor told me that he had the same problem and removed his crome thin walled pipe connector by banging on it with a hammer. So I did the same and sure enough it came out. Turns out it was soldered to the cast iron pipe.

So now the broblem is how to connect again to the cast iron pipe. There are no threads on the cast iron pipe and at this point I would prefer to redo the sink drain piping in either ABS or PVC. So how do I go from a no thread cast iron hole to PVC or ABS?

Get a torch, heat the joint. Using pliers, grab the pipe, twist it as you are heating it with the torch. After removing the pipe. Sand and flux the new wall piece, flux the joint too. Heat the joint, twist wall piece in place, apply solder.

Seems like there may be threads from a broken nipple in the cast iron T joint. It seems to me that there may have been a nipple srewed into the cast iron T. Then perhaps the nipple broke, or was broken off by some previous owner and the threaded part of the nipple is still inside the T cast iron joint. Seems like the nipple broke off flush with the surface of the T.

So how do I remove these threads ? Probably rust has built on them.

Thanks for the info. I managed to replace the sink drain all the way into the cast iron T inside the wall (long story, I will not mention).

However the drain remains slow/blocked so there is a separate problem. So I posted a new thread under the title "Why is bathroom sink drain still slow?".

Thanks