Scientists Invent a New Steel as Strong as Titanium | Hacker News Reader

Scientists Invent a New Steel as Strong as Titanium

popularmechanics.com

61 pointschromaton18 comments

Steel can be stronger than titanium depending on the alloy and heat treatment. It's not uncommon to see heat treated 4130 upwards of 100ksi which is right in line with titanium. At those hardnesses it tends to be more brittle, though, unlike titanium.

The breakthrough here isn't that they can make it strong, it's that they've made it both strong and tough. Toughness is how much something deforms plastically rather than breaking. Mild steel is very tough but not terribly strong, you can easily make it 4x (or more) stronger by sacrificing toughness.

Not having to make an engineering tradeoff between strength, toughness and price would be pretty fantastic.

Aren't there issues with making extremely thin steel parts to take advantage of this new higher strength-to-weight ratio? Sure, it might exceed the mechanical properties of titanium, but steel is still twice as dense.

I thought it was because of the difficulty of making thin steel parts that aircraft use aluminum rather than steel, despite steel having a higher specific strength.

Steel can be made in thin sections very well. Examples are car bodies, music wire, etc. In fact heat treating (in some respect) can be simpler in thin parts because it is easier to control the cooling rate of the whole part, rather than just the outer skin.

It's easy to make steel that's stronger than titanium; the challenge is making steel with a higher specific strength than titanium, since titanium is so much less dense. Steel is still the clear winner by volume, which is what unqualified 'strength' refers to.

Titanium is also nice for its anti-corrosive and non-magnetic properties, and its low coefficient of thermal expansion. There's a reason it showed up in aerospace very early - its a good fit there.

And military submarines with non-magnetic hulls are considerably harder to detect.

Man, that would be an expensive sub, made completely out of titanium. At $8/lb and 6000 tons (12 million pounds) you're talking about $100mm just in materials and that's before you do anything. Titanium is very difficult to weld due to oxygen embrittling the weld so you'd have to put everyone on rebreathers and assemble the whole hull inside a giant tent with a slight positive pressure of argon only. That's the kind of project that'll give people nightmares.

Why a giant tent? Why not normal MIG/TIG welding that floods just the weld area with argon?

http://weldingdesign.com/archive/beginnings-and-development-...

The quality of the weld is extremely important, enough so to justify the 0% o2 environment.

Because I misspoke and it's actually that any hot titanium will form brittle oxides. The Heat Affected Zone (HAZ) extends far further than the weld puddle, so you need to substantially increase the coverage of your flood, usually far enough that it makes sense to do the welding inside of a bag, down in a tank, etc.

I heard that one of the titanium bicycle manufacturers actually had whole rooms that they flooded and the welders just wore masks that gave them air. Totally a "I heard it from a friend who heard it from a guy" kinda situation though.

http://www.twi-global.com/technical-knowledge/job-knowledge/...

See: Soviet "Alfa" class submarine.

https://en.wikipedia.org/wiki/Alfa-class_submarine

It seems like just the sort of project that might make it awesome to work for DoD. Unlimited budgets can let you do the craziest things. Want to intercept the whole internet? Sure. Need an entire shipyard under argon? Why not.

> At $8/lb and 6000 tons (12 million pounds) you're talking about $100mm just in materials and that's before you do anything.

The Seawolf Class submarines cost about $3.3 billion. There's 3 of those in service, they were seen as too expensive post cold war and were replaced with the Virginia Class subs that cost around $2.2 billion and are scheduled for service through 2070.

$100 million would come out to about 4.5% of the total cost for materials. . . pretty negligible.

edit

With the welding, when I worked construction on large titanium pipes they'd fill the inside of the pipe with argon. But no tents or fresh air. The welder had also had a argon tube blowing on the weld point iirc.

For larger titanium welds, they did it section by section. But still no fresh air needed.

But this was a long time ago and Titanium welds were a rare job...so my memory could be failing me on details. I'm certain no fresh air was needed.

I wasn't the welder, I was a fitter....so this was usually break time for me.

Right, but what if you're welding a 40ft long plate to another 40ft long plate? You need to cover a large portion of both the front and back in argon. At some point it becomes easier to instead of constantly rigging up and tearing down back-shields to just put up a huge tent, bring all the various sub-assemblies in there and weld everything up.

You don't have to keep the whole sub in the tent from start to finish, just while you're assembling all the various small parts into the large overall hull. If it's a 3 year build, I'd guess you'd only need it that way for a few months.

Also 12 million pounds of steel would cost you less than $12 million. And that's before you have to machine, cut, fit, weld, anything. All of those things get much, much more expensive when you're talking Ti. I suspect that an order of magnitude across all aspects is reasonable, for material cost, machining cost, welding cost, etc.

So if you had $10mm of steel and $100mm of fabrication for the Seawolf hull, you'd have $100mm of Ti and $1b of fabrication for the all titanium sub.

In addition to being old news, this story isn't all that exciting. They've made an Aluminium-based steel that's 13% lighter than ordinary steel(density of about 6.83 vs. 7.85) and that isn't brittle like previous Aluminium steels. It could have interesting uses, especially if it can be made cheap and with good properties (weldability, formability, workability, corrosion resistance), but they're just at the small-scale stage and they have a corrosion resistance problem to solve.

Shouldn't they add [Feb 2015] to the title?

Previously on HN: https://news.ycombinator.com/item?id=9001704

(Same South Korean researchers)

I wonder how it compares to "Flash Bainite" steel?

http://www.flashbainite.com

For the DARPA Armor Challenge, to stop a .30-cal APM2 armor piercing round, requires:

1/4" Flash 500 vs. 1/2" Titanium vs. 3/8" High Hard vs. 1-1/8" Aluminum

From: http://www.flashbainite.com/about/applications.html

Yes, but is it as strong as Rearden Steel?

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