5 ms·

Scientists Invent a New Steel as Strong as Titanium

61 points by chromaton 11y ago

msandford 11y ago
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.
- ycuctctc 11y ago
  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.
  - ebrewste 11y ago
    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.
- Armisael16 11y ago
  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.
  - simonh 11y ago
    And military submarines with non-magnetic hulls are considerably harder to detect.
    - msandford 11y ago
      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.
      - durkie 11y ago
        Why a giant tent? Why not normal MIG/TIG welding that floods just the weld area with argon?
        mtreis86 11y ago
        http://weldingdesign.com/archive/beginnings-and-development-pressure-hull-welding-united-kingdom-submarines http://weldingdesign.com/archive/beginnings-and-development-... The quality of the weld is extremely important, enough so to justify the 0% o2 environment.
        msandford 11y ago
        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/welding-of-titanium-and-its-alloys-part-1-109/ http://www.twi-global.com/technical-knowledge/job-knowledge/...
alricb 11y ago
Previously on HN: https://news.ycombinator.com/item?id=9001704 https://news.ycombinator.com/item?id=9001704 (Same South Korean researchers)
jsonmez 11y ago
Yes, but is it as strong as Rearden Steel?
alricb 11y ago
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.
- wrsh07 11y ago
  Shouldn't they add [Feb 2015] to the title?
pjkundert 11y ago
I wonder how it compares to "Flash Bainite" steel? http://www.flashbainite.com 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 http://www.flashbainite.com/about/applications.html

61 points by chromaton 11y ago

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.

ycuctctc 11y ago
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.
- ebrewste 11y ago
  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.
Armisael16 11y ago
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.
- simonh 11y ago
  And military submarines with non-magnetic hulls are considerably harder to detect.
  - msandford 11y ago
    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.
    - durkie 11y ago
      Why a giant tent? Why not normal MIG/TIG welding that floods just the weld area with argon?
      - mtreis86 11y ago
        http://weldingdesign.com/archive/beginnings-and-development-pressure-hull-welding-united-kingdom-submarines http://weldingdesign.com/archive/beginnings-and-development-... The quality of the weld is extremely important, enough so to justify the 0% o2 environment.
      - msandford 11y ago
        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/welding-of-titanium-and-its-alloys-part-1-109/ http://www.twi-global.com/technical-knowledge/job-knowledge/...

alricb 11y ago

Previously on HN: https://news.ycombinator.com/item?id=9001704 https://news.ycombinator.com/item?id=9001704 (Same South Korean researchers)

jsonmez 11y ago

Yes, but is it as strong as Rearden Steel?

alricb 11y ago

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.

wrsh07 11y ago
Shouldn't they add [Feb 2015] to the title?

pjkundert 11y ago

I wonder how it compares to "Flash Bainite" steel? http://www.flashbainite.com 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 http://www.flashbainite.com/about/applications.html