Can anyone help to identify this blown MOSFET? Top markings seem to include F50, "ON" in a circle, 3N and "RE4T" in a circle
There are several steps that you should be gone through by yourself:
 


First of all, I would like to say that the component shown in the image is not necessary be a MOSFET. The only thing that is clear is the package size is either DPAK or D2PAK. Please use Vernier caliper or ruler to identify, with reference of mechanical outline of DPAK and D2PAK from ON Semiconductor website.
DPAK : https://www.onsemi.com/pub/Collateral/369C.PDF
D2PAK: https://www.onsemi.com/pub/Collateral/936A-02.PDF


After decide the package, other information given in the image are "F50", "ON" and "3N". "ON" refers to ON Semiconductor. Then, for the "F50" and "3N", you need search GOOGLE. 


For example, assume that the package size shown in the image is DPAK, and it is manufactured from ON Semiconductor, then the google keywords should be: "F50"  DPAK onsemi and"3N" DPAK onsemi
"3N" or "F50" mean search engine must find the keywords include "3N" or "F50". In this case, I use keyword: "3N" DPAK onsemi
Then, the search engine shows variety results. 

Clicks the 1st link, make sure the component is made by ON semiconductor and has DPAK package. 





Scroll down to find the marking diagram

Then, maybe this component is a suitable replacement, since it include "3N" on the package

Compared marking diagrams of other choices on GOOGLE.

If still cannot decide, better collect all possible choices and ESAB manual, and passed to ON Semiconductor sales or engineering, as suggested by @KingDuken
The worst case is you need to purchase a new ESAB, as suggested by @KingDuken