Don't tell my welds ain't strong!

Well Guys; Don't tell me my welds ain't strong!
I got done strippin a truck for parts and wanted to get rid of the body so I called a tow truck guy that pays you for the weight or car.
I had alot of old scrap metal thats been laying around here for years.
So I threw all that junk in the bed of the truck. I had one more piece of junk
to get rid of, it's always in the way and to heavy to keep moving around all the time. It was a 4 X 4 foot safe that I got from a guy that had his own rental company some years ago. When I got it, I picked it up with a engine hoist and bent the hoist. At first I put it on the back of my double axle trailer but when I did it picked up the back of my 89 full size bronco right off the ground. So I had to move it forward over the axles.
Anyway this thing was 2in. thick all the way around except for the door,
that was 4 inches with 6 - 2in rods that would lock in to the side.
This thing is solid steel no cement in it. I figured I would get rid of this too since it's always in the way and so hard to move. Well when I started to build my car frame I had boxed in both ends of the rear section of the frame
then had grounded the welds smooth to make it look purtty!!! HE! HE!
Well I decided that I wanted to bing the back put out further to the sides of the car, so I cut that boxed end off and widened the rear.
I didn't want to pick the safe up from the lip like I did the last time and bend my new hoist. So I welded the old frame end on the top of the safe and centered it. I then welded some metel on both the sides of the safe to be able to jack it up with a floor jack. This way I could put the safe on bricks
so the legs of the hoist could go under the safe. The safe is to wide for the legs to go around it. Now it took me longer to get the stuff out to weld than it took me to weld it up. I didn't have much time since I had already called the tow guy. So I just threw some quick welds down, probably 5 minutes at the most. Anyway I started thinking that frame end would be alot stronger if I had not ground them welds down. So I picked it up and drug it half way acrossed the back yard. The tow guy gets here picks it up with the truck
and is got it buy the frame trying to balance it on a corner so he can let it fall
into the bed of the other truck from his truck. Anyway the safe slips and falls about two feet out of the back of his truck but didn't hit the ground before he could get backed up against the other truck bed. It bent the crap out of the 10 gage 2 X 3 boxed steel, but non of my welds even cracked.
Even the welds that I had ground down so much to look smooth no cracks.
I have wondered how strong those ground down welds really were, not any more. I also wondered how good my lincoln 250 volt mig - gas welder worked.
I spent alot of time making sure my welds on my frame are good, after grinding the welds down I look for cracks or any low spots, then fill them in and re - grind. The welds on the safe and the ends of the frame were just some fast welds thrown on in a hurry and they didn't crack.
Now that I have seen this I feel alot better about my welds and my Lincoln welder. So no one better tell me that my welds ain't strong!!! I know better, now. Kurt