Electric Boat HY80 weld forensics

Physical-object teaching move. Tom acquired this single-side weld with backing bar from Electric Boat ~30–35 years before the lecture; uses it to show distortion (V-shape pulls top edges in), the HAZ size relative to a quarter-inch in carbon steel, and the rationale for clear-coating black iron samples.

Any questions on preheat? We're going to go through preheating now, because I just handed around part of the structural welding code, and we're talking about welding something like this. [Tom holds up a welded HY80 sample.] I got this from Electric Boat about thirty or thirty-five years ago. This is an actual weld in one-inch-thick HY80 made by Electric Boat. It has a backing bar because they welded from one side. If you measure it very carefully you actually see some distortion here — if I drew a straight line here it wouldn't be straight. The thing is V-shaped, because it's a V-shape weld. You can also see the size of the heat affected zone: this is weld metal in the slightly lighter gray, the darker blacker region is the heat affected zone of the weld. You've got a heat affected zone down here. This piece is probably not HY80 — HY80 is expensive steel; if you're just using a backing bar and you're going to cut it off later, use a piece of cheap old carbon steel. And this is not rusted — anybody want to know why it didn't rust? Because it's black iron. It's actually got a layer of other stuff on it, but the surface — we sprayed it with a clear coat, clear lacquer, so it wouldn't rust.