Yeah, it looks like welding will be too robust. And soldering is just too weak. I’m going to go with the “grind down the Tiniest Screw Ever” method.
So, Padeye, and guesses as to what I might be making/fixing/working on? I’d think you’d be one of the few Dopers that might catch on.
I have an idea. What caliber is it, anyway? 
Sorry *Bear_Nenno, I’m drawing a blank. I’ve either mentally constructed the desciption incorrectly or need more information. Beyond guessing that it has to do with firearms because you think I might have a good guess I got nothin’
[weld engineer hat on]
Yes, you can solder steel. You can solder anything that doesn’t melt, and that the solder will stick to.
[weld engineer hat off]
You have a good candidate for friction stir welding. Probably not something you can do in your garage. Drawn arc stud welding is perfect for your application, and there may be a weld shop that can do this for you for a couple of bucks. I don’t recommend any type of wire weld for this, although yeah, it can be done. If you can get a nut-type of material through your “base” from the bottom, then a resistance projection weld is a good candidate. Again, this is something you’re going to want to go a weld shop for, and then, not just any weld shop.
