Current limiter circuit is damaging MOSFETs
Safe operating area. Repeat after me &quot;look at the safe operating area graph&quot;: -

According to the data sheet SOA graph for the IRF630 it would survive less than 1 ms with 5 amps and 160 volts across it. Looks like it managed to survive 3 ms though: -


What´s is going on here?

It's called operating the device below its zero temperature coefficient point. The ZTC is best shown in this graph of the IRF630: -

I've taken the liberty of adding a few bits in red. In particular, I draw your attention the the red circle; the ZTC point. At gate voltages above 6.5 volts, if the device warms a little then the drain current falls. This is inherently safe. If the gate voltage is below 6.5 volts (say 5.75 volts) then if the device warms the drain current rises from 5 amps to 6 amps pretty quickly as the device hits a junction temperature of 150 °C but it won't stop getting warmer. If the picture above had graphs at higher junction temperatures, you would see higher drain currents and, now, you should be able to see that this spirals out of control. It can happen in less than 1 ms with certainty.