America's Cup 4340 welding procedure development

Foreshadowed at the end of the layer 2 cut — Tom is about to launch into the case where a client wanted to use 4340 (a high-hardenability, >180 ksi steel requiring 600°F preheat and post-weld heat treatment) for racing yacht components. Will be developed in the next portion of the lecture. ## Figures referenced

With the weld metal you get martensite, and you try to keep your hardness in your weld metal below Rockwell C 30 — the petroleum guys like to keep it below Rockwell C 22, but they can't use the higher strength. It turns out the bridge guys, when you're building a bridge, can use steels up to 100 ksi, but we don't use steels any stronger than that, because you'd have to do post-weld heat treatment. You can't post-weld heat treat a bridge, not economically anyway. If you go above 180 ksi — so this is up to 120, this is like 120 to 180, if you're greater than 180, it's hard martensite. Now we're talking preheats of 600 degrees Fahrenheit and post-weld heat treatment required, very expensive. This is the problem when they came to me and said, oh, we want to use 4340 in our America's Cup yachts —

Used to introduce the hardenability concept. A four-inch-thick keel beam couldn't be made from HY-130 (too soft, plastically deforming in trials) so they wanted 4340, but didn't know how to weld it in that section thickness. Tom showed them how.

Then there's hardenability, which is how deep you can harden it. I was asked once by a professor — would be now mechanical engineering, but at the time he was naval architecture — working on the America's Cup. He had a four-inch-thick keel beam. The keel beam is not just on a big ship; the keel is the thing you build everything up from. There's a keel beam on a 747, a big aluminum beam they build everything up from. But on a sailboat — that particular America's Cup — they had a big steel piece that created the resistance to being blown sideways. This was supposed to be four inches thick.

Tom's consulting case with Prof. Jerry Ingram (MIT Course 13) on a David Koch–funded America's Cup yacht. Four-inch HY-80 centerboard was bending in sea trials; Tom developed a 4340 welding procedure with 600°F preheat. Used to teach the cost/weldability tradeoff in high-strength alloy steels.

I don't think I've told you the story of Professor Ingram — I think it was Jerry Ingram, who I think is retired. This is back when we had a Course 13, which was the ocean engineering program, Naval Architecture and Ocean Engineering. He was working on one of the America's Cup yachts. In fact this was the year that two MIT professors in Course 13 were designing the competing yachts for the America's Cup. I had to lock their offices from each other, I guess. This is also I think the year that David Koch — David Koch got a degree from the chemical engineering department, he and his brother inherited Koch, inherited a couple of billion from their father, and they've turned it into a couple of tens of billions, so they've got a fair amount of money.