do you mean 500 milliHz, (0.5 Hz) or 500MegaHz?
no such thing as an SCR at high frequency
they just don't turn on or off that fast
that's why they're used at line frequencies or as non-repetitive crowbars
20 ms is 0.02 s
on bottom graph, that looks like 0.1 K/W so at 600W, looks like a 60 K rise
if ambient air is room temperature, 20 deg C, the die will rise to 80 deg C
well with parameters
Figure 6 page 4 of data sheet
for 20 ms, maximum non-repetitive pulse current is 1000 A
(assuming i read the graph properly)
Figure 2 page 4 of data sheet
square wave conduction and average current
if your pulse is 0.02 sec, what is the period of the signal?
convert that to conduction angle as if the period was 360 degrees
see how much average current vs case temperature
they already applied 0.35K/W from maximum junction temperature