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Related to this: Any Better Alternatives to Steel?

I have found that any alternatives to steel are not so easy to obtain or practice. Aluminum is lighter than steel, but it's not as strong and more brittle. Titanium is stronger, but it's more expensive and it reacts rather poorly to oxygen. Palladium glass is not immediately possible because it's too ridiculously expensive.

So if, from the 1880s to the 1930s, someone made the skeleton of the skyscraper from an alloy made of iron, carbon, chromium, aluminum and titanium, would this be practical?

If yes, then would this be allowable for larger buildings than we already have, and will they let the building stand for longer than a century in a Life After People?

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    $\begingroup$ If we knew these things put together would be practical, then wouldn't we be using it? $\endgroup$ – Xandar The Zenon Jan 20 '16 at 23:53
  • $\begingroup$ I think you should go with some futuristic type of carbon. After all, carbon can be one of the strongest materials on earth. Although it can also be the weakest. $\endgroup$ – Xandar The Zenon Jan 21 '16 at 0:02
  • $\begingroup$ Aluminum, like steel can be made into many different alloys. The alloys of both metals range from brittle to ductile. I would not say that Al is "more brittle" than steel. Titanium (like Al) is not as strong as steel but has better strength to weight ratios. Steel alloys also retain their strength to higher temperatures. With all the possible alloys and its low cost, steel remains the preeminent structural metal. Other metals are only used when the application requires properties not provided by steel alloys (e.g. light weight) AND it is cost effective to do so. $\endgroup$ – Jim2B Jan 21 '16 at 2:08
  • $\begingroup$ You can't just mix them together like that. If it worked, they would be doing that! However, maybe you would get the desired result using composites instead. Often, composites do combine desirable properties and support each other's shortcomings. $\endgroup$ – JDługosz Jan 21 '16 at 9:43
  • $\begingroup$ Can you clarify what your question is? Are you asking whether there were any alloys/composites we know about now that they could have used in that era to make stronger skyscraper frames, or whether if we made the same skyscrapers now with the benefit of modern technology, that we would be able to use a stronger material? Or are you just asking what material a skyscraper would need to be made of in order to still be standing more than a 100 years without maintenance? $\endgroup$ – Ieuan Stanley Jan 22 '16 at 9:09
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Alloying metals is not just as simple as smooshing them together and getting a mix of the properties of the underlying metals. In particular, steel is a fascinating material dominated by grain boundaries and precipitation and all sorts of complex processes. You can almost get a masters degree in Steel.

Could you find a mix that works? Who knows. Maybe. I'm no materials expert. But it wouldn't be easy. Consider your mixture of aluminum and steel. There has been a desire to do this for a while (at least back to the 1970s, according to the linked article). Aluminum and steel, alloyed together, had great promise as a light weight ultra-strong material. However, the reality of steel manufacturing prevented any success. Aluminum and steel, when mixed, form a crystalline structure known as B2, which made the product unusably brittle. Just this year, a team announced that they had developed a complicated process to control the B2 crystals after years of work. The new product is apparently 13% lighter than steel, but as strong as titanium.

So you can imagine, after how much trouble they had to go through to find an alloy of aluminum and steel, how hard balancing an aluminum+steel+titanium alloy would be. It certainly would not have simple properties that you could guess from the base materials.

As a general rule, we use carbon steel and stainless steel because they are the optimal alloys we have found. They have very good properties, so they get used. It will be difficult to guess an arbitrary mixture of metals which, when alloyed together, will outperform what generations of scientists and engineers have spent painstakingly optimizing.

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  • $\begingroup$ "You can almost get a masters degree in Steel." - Not exactly true. You can certainly get a master degree in Steel, available as specialization under Materials Science, Material Engineering, Metal Technologies and similar courses. $\endgroup$ – Mołot Nov 20 '18 at 8:30
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Different alloys are created to provide different properties, so perhaps you should recast this differently. What, exactly do you want your material to do (what properties are important?) and the alloy might already exist for you to select from a materials handbook.

Your particular idea (iron, carbon, chromium, aluminum and titanium) is unlikely even today because the vastly differing properties of the materials, in particular aluminum. Aluminum has very different density than the iron, as well as different melting points etc. The inclusion of carbon (to make iron into steel) is usually done in minute amounts so the carbon can diffuse through the melt and the crystallization of the iron is affected by the presence of the carbon (generally no more than 2%). The addition of 10%+ chromium to the melt makes stainless steel.

I'm not entirely clear what the inclusion of aluminum will do to iron, (or for that matter, adding iron to aluminum mixtures), but since this does not seem to have been done to date, I suspect there is a reason for that.

WRT wanting to make a stronger steel structure, you can see that adding enough chromium to make stainless steel would probably make the steel skeleton prohibitively expensive. Carbon steel is much harder, but also more brittle, and can tend to rust quickly. Once specifications are made, metallurgists can start to experiment to create new formulations to meet the standard. Generally the state of the art will advance incrementally, in OTL the demand for strong, inexpensive and "tough" steel grew as more and more skyscrapers were being ordered (and this was due to a combination of land prices, the invention of the elevator and the prestige associated with tall buildings from the late 1800's to about the late 1960's). So the steel follows the demands rather than leads them.

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  • $\begingroup$ "In OTL"? What is that? $\endgroup$ – JDługosz Jan 21 '16 at 9:45
  • $\begingroup$ In our timeline. $\endgroup$ – JohnWDailey Jan 21 '16 at 13:09

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