TIG is the most versatile kind of welding there is. You can weld 4130 chromoly, mild steel, stainless steel, tool steel, nickel alloys like inconel and hastelloy, aluminum, magnesium, titanium, and cobalt alloys like stellite .
In fact, I have used the CK tig welder (shown in the video on this page) to weld parts for a machine shop and to make over 15 videos where I welded Carbon Steel, 4130 chromoly, 4140, stainless steel, aluminum and also TIG brazing on DC and AC.
Now if that aint versatile, I dont know what is.
Heat input, travel speed, and gas shielding are key. I have some videos on discoloration of stainless here. The link above will take you to a page that breaks it down into simple terms.
There are lots of old airplanes still flying that have 4130 tubing frames that were gas welded with an oxyfuel torch.
But we know now thru lots of testing and data, that 4130 chromoly can be welded using tig welding with a pre or post heat as long as thickness is .120" or less.
But a low preheat wont hurt anything either.
seriously, if you click the link above you will see several videos that will help you to get better or even learn how to tig weld aluminum.
Or if you are just getting started, the link below might help more.
How to Tig weld magnesium
The Tig Welding links on this page will take you to pages with videos that took years to make. I hope you enjoy them and come back often for updates.