Can I replace FP50N06 with IRFZ44N?
You should see pretty much the same performance from the IRZ44Ns. That is to say, they may well cook too.

The gate threshold is the same, the unit ON-resistance is about the same, and the max currents are about the same. So the IRZ44Ns should work just about as well as the original MOSFETs. And you do remember how well they worked, right?

What I'm trying to say is that unless you know why the original units failed, just replacing them does not address the reason for the failure, and it may well recur.