Big big Catalytic Converter problem?

The air/fuel mixture would have to be extremely rich for that to happen and although some melting damage can occur if unburned raw gasoline is burning in the cat it would take much more than just a test drive to do that and the old cat which was replaced would have had to have such a restricted flow from prolonged melting damage caused by the preexisting rich air/fuel mixture that I doubt the engine would have even run long enough to drive it to the shop. I suggest you find a good ASE certified shop to tune-up that engine and check the exhaust back-pressure for cat damage.

First, go to another mechanic. The catalytic converter melting would be the inside of it getting too hot and melting the catalyst together, which would be caused by the engine running too rich (too much unburned gasoline in the exhaust). Not a safety hazard or anything, but until this problem is repaired you will have problems with the catalytic converter. Several things could cause the engine to "run rich" so you need to let someone that knows what they are doing to find the root of the problem.

Yes, a catalytic converter problem would definetly be covered by a factory warranty since it is not a wear and tear item like your tires or breaks. It should be as simple as swapping it out for a new one.

Take it to another mechanic, then get an attorney. If this IS true, it was HIS fault anyway and he owes you for the repairs. Now, do you have a "check engine light" on? You could be having issues with your fuel system that could cause a cat to go bad. But, if it got hot enough to melt... there would have been a really nasty fire. Paladium melts at over 1700 degrees. I usually do not recomend this, but... take it t the dealer for an opinion.

Im 50 years old and have never heard of a converter melting, go to another mechanic

Get yourself a NEW mechanic FAST! This dunce has no business doing business.

Cats CAN melt inside if there is a engine malfunction throwing raw gas into the exhaust, but I'm not sure if one will melt after only one test drive.

i cant be 100% but catylitic converters dont usually melt wich leads me to belive your mechanic is full of it of the car isnt firing right in either case you shouldnt have to pay for another because it was his responsibility to fix the problem the first time so if he doesnt fix take him to small claims and dont by any means pay for a second catalytic converter they are expensive and your mechanic should make it right.

pressure test pistons first

exhaust valve may have hole burn in it