America's Cup yacht center board (Jerry Milgram consulting)

Twenty-years-ago consulting call from MIT Professor Jerry Milgram (Course 13, now 2N): a six-inch-thick HY-80 (or HY-130) center board bent on first sea trials. Tom consulted on the move to 4340 and the 600°F preheat needed to weld it. Used to introduce both the high-end of alloy steel hardenability and the consequences (preheat protocols) for welding.

Student: What are you making that's even —

I'll give you an example. They were using HY-80 — this is Jerry Milgram, who was a professor in 13, which is now Course 2N. He was designing America's Cup yachts. He called me up — this is twenty years ago — and they had a problem. They designed the keel, not keel, but the — what do you call it, the dorsal fin upside down —

Student: The center board?

The center board, thank you. They were designing the center board. It was six inches thick, HY-80, or it may have been HY-130, I don't remember — it was an HY steel. And when they went on the first sea trials, the center board bent. A lot of force. This was five or six feet long and six inches thick, and had a big lever arm. So he called me. That's when I first realized there were a couple of other faculty who were here at 6:00 a.m. — he called me at 6 a.m. one morning and offered to hire me as a consultant. They were going to go to 4340. 4340 has lots of nickel, chrome, moly, and vanadium. John Lippold in his chapter on hydrogen cracking has the same plots — for a 1046, this is martensite high hardness, over here is bainite plus pearlite when you cool slow. And he's got the same Jominy quench hardenability for 4340. The hardness is nearly 100% martensite full thickness. You extrapolate this out, you can go to eight or ten inches thick. So to your question, if you want to spend enough money and put enough alloy content in, you can harden pretty thick.