What mosfet do I use in induction heater?
Two things for you to check.

1) Ensure that the power supply rise time is FAST. Generally don't switch the power supply on with the inverter connected, the inverter can get into a linear mode that prevents fast switching of the MOSFETS and leads to destruction. Connect the inverter to an already powered and enabled supply.

2) Check your inductors are not saturating at your maximum current, as saturating inductors effectively look like a short. So you get full power supply voltage across a MOSFET in the ON state - leading to overheat and destruction. The circuit will work OK at idle, and low power, but at high power will self destruct. Did you make the inductors? Commercial inductors specify the saturation current, but if you just used any old toroid, you will not necessarily be able to predict the saturation point.