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The technological innovation is to solve the problem of why this wasn't done previously - preventing corrosion with stainless steel coating seems obvious, so wh

by mmooss 1y ago

The technological innovation is to solve the problem of why this wasn't done previously - preventing corrosion with stainless steel coating seems obvious, so what held people back? Unfortunately, the article doesn't describe the problem or how they solved it - does anyone know?

abakker 1y ago
this is costly and difficult. The reason they didn't do this before is that it is only necessary in some construction, and because rebar has to be as cheap as possible.
cyberax 1y ago
Stainless steel is not _completely_ stainless. It corrodes just fine if it doesn't have access to oxygen to form a protective oxide film (crevasse corrosion). But the bigger problem is that stainless steel has significantly worse mechanical characteristics, _and_ it's significantly more expensive. Regular steel can also be protected from corrosion using paint, zinc coating, cathodic protection, etc. Engineering is always an exercise in trade-offs. And it's almost always better to build four bridges that can stand for 100 years, instead of one bridge that can stand for 500 years.
- amluto 1y ago
  > But the bigger problem is that stainless steel has significantly worse mechanical characteristics This is a common claim, but I’m not sure I really believe it. Even for applications that require especially good mechanical characteristics, e.g. tool steels, good stainless alloys can be very good. I would believe that the stainless alloys that are widely available in large quantities at somewhat reasonable prices for structural use (e.g. 304 and 316 stainless steel) have mediocre mechanical properties.
  - cyberax 1y ago
    ??? Tool steels are not stainless, as anyone who forgot to stow away tools properly can confirm.
  - cyberax 1y ago
    Ah, got it. You mean modern stainless steels are good enough even as tool steel replacements? It's indeed true, but at the same time, non-stainless steels are getting even better.
    - amluto 1y ago
      I don’t have a good, accessible source for traditional tool applications, but knives are basically tools, and knifesteelnerds.con is a fantastic resource from an author who is a genuine expert: https://knifesteelnerds.com/2021/10/19/knife-steels-rated-by-a-metallurgist-toughness-edge-retention-and-corrosion-resistance/ https://knifesteelnerds.com/2021/10/19/knife-steels-rated-by... Compare the toughness vs hardness charts for non-stainless and stainless. You’ll find some low alloy non-stainless steels with excellent toughness at a given hardness level, but those have poor wear resistance. Other than that, the charts are just not very different. Note that even some of the very most wear-resistant steels are stainless (but you’ll have to recognize the names or look them up to tell). Of course, this says nothing about price, availability in large quantities, weldability, or ability to form them in the ways that people building large structures might want.
      - cyberax 1y ago
        Hardness is not really the weakest point of stainless steels, anybody who tried high-carbon knives and got disappointed with them can attest to it. Stainless steels have lower yield strength compared to carbon steels, meaning that the stainless steels bend under stress more easily. This is not an issue for knives, but it is a big issue for construction materials.
        amluto 1y ago
        Steel hardness and yield strength are very strongly correlated: https://wpfiles.mines.edu/wp-content/uploads/aspprc/ResearchMaterials/Publications/386-Pavlina.pdf https://wpfiles.mines.edu/wp-content/uploads/aspprc/Research... I’m fairly confident that what’s going on here is that no one builds buildings out of high-hardness stainless steel. On the other hand, you can buy excellent construction screws made from 400 series stainless steel if you’re willing to pay for them —- the main problem is that they’re even more expensive than hot-dip-galvanized or fancy coated non-stainless equivalents.
- mmooss 1y ago
  So what changed that allowed this innovation and made it attractive, at least to some extent?
  - cyberax 1y ago
    They somehow made stainless steel _coating_. So theoretically you should be able to get the mechanical benefits of high-carbon steel, and corrosion resistance of stainless steel.
Glyptodon 1y ago
Based on the process being roller driven and not involving drawing,I'd infer that it's probably similar to wrapping the bar with another layer at some point in the process and continuing to roll it. I'd also infer that they don't care about having the ends "capped" with stainless since everyone tends to assume that rebar can be cut off when needed. But YMMV, I'm mostly familiar with much smaller scale fabrication.

by mmooss 1y ago

abakker 1y ago

this is costly and difficult. The reason they didn't do this before is that it is only necessary in some construction, and because rebar has to be as cheap as possible.

cyberax 1y ago

Stainless steel is not _completely_ stainless. It corrodes just fine if it doesn't have access to oxygen to form a protective oxide film (crevasse corrosion). But the bigger problem is that stainless steel has significantly worse mechanical characteristics, _and_ it's significantly more expensive. Regular steel can also be protected from corrosion using paint, zinc coating, cathodic protection, etc. Engineering is always an exercise in trade-offs. And it's almost always better to build four bridges that can stand for 100 years, instead of one bridge that can stand for 500 years.

amluto 1y ago
> But the bigger problem is that stainless steel has significantly worse mechanical characteristics This is a common claim, but I’m not sure I really believe it. Even for applications that require especially good mechanical characteristics, e.g. tool steels, good stainless alloys can be very good. I would believe that the stainless alloys that are widely available in large quantities at somewhat reasonable prices for structural use (e.g. 304 and 316 stainless steel) have mediocre mechanical properties.
- cyberax 1y ago
  ??? Tool steels are not stainless, as anyone who forgot to stow away tools properly can confirm.
- cyberax 1y ago
  Ah, got it. You mean modern stainless steels are good enough even as tool steel replacements? It's indeed true, but at the same time, non-stainless steels are getting even better.
  - amluto 1y ago
    I don’t have a good, accessible source for traditional tool applications, but knives are basically tools, and knifesteelnerds.con is a fantastic resource from an author who is a genuine expert: https://knifesteelnerds.com/2021/10/19/knife-steels-rated-by-a-metallurgist-toughness-edge-retention-and-corrosion-resistance/ https://knifesteelnerds.com/2021/10/19/knife-steels-rated-by... Compare the toughness vs hardness charts for non-stainless and stainless. You’ll find some low alloy non-stainless steels with excellent toughness at a given hardness level, but those have poor wear resistance. Other than that, the charts are just not very different. Note that even some of the very most wear-resistant steels are stainless (but you’ll have to recognize the names or look them up to tell). Of course, this says nothing about price, availability in large quantities, weldability, or ability to form them in the ways that people building large structures might want.
    - cyberax 1y ago
      Hardness is not really the weakest point of stainless steels, anybody who tried high-carbon knives and got disappointed with them can attest to it. Stainless steels have lower yield strength compared to carbon steels, meaning that the stainless steels bend under stress more easily. This is not an issue for knives, but it is a big issue for construction materials.
      - amluto 1y ago
        Steel hardness and yield strength are very strongly correlated: https://wpfiles.mines.edu/wp-content/uploads/aspprc/ResearchMaterials/Publications/386-Pavlina.pdf https://wpfiles.mines.edu/wp-content/uploads/aspprc/Research... I’m fairly confident that what’s going on here is that no one builds buildings out of high-hardness stainless steel. On the other hand, you can buy excellent construction screws made from 400 series stainless steel if you’re willing to pay for them —- the main problem is that they’re even more expensive than hot-dip-galvanized or fancy coated non-stainless equivalents.
mmooss 1y ago
So what changed that allowed this innovation and made it attractive, at least to some extent?
- cyberax 1y ago
  They somehow made stainless steel _coating_. So theoretically you should be able to get the mechanical benefits of high-carbon steel, and corrosion resistance of stainless steel.

Glyptodon 1y ago

Based on the process being roller driven and not involving drawing,I'd infer that it's probably similar to wrapping the bar with another layer at some point in the process and continuing to roll it. I'd also infer that they don't care about having the ends "capped" with stainless since everyone tends to assume that rebar can be cut off when needed. But YMMV, I'm mostly familiar with much smaller scale fabrication.