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Mild steel rod

I need to protect mild steel (steel with low carbon) from corrosion even any crack or scratch on it. I searched on internet, I found recommendation like this:

  • Keep it clean,
  • Apply protective coatings like paint or wax,
  • Store it in an area free from excessive moisture and temperature fluctuations,
  • Avoid cracks or scratches, or/and
  • Control the humidity,
  • Use galvanized metal,
  • Blueing technique,
  • Provide proper and regular maintenance.

I am interested with the galvanization. Then I used chatGPT to know further and I asked, "Does galvanization protect steel even if it's damaged?"

And the answer is like below:

Yes, galvanization does protect steel even if it’s damaged. The process of galvanization applies a layer of zinc to the steel. This zinc coating acts as a barrier that prevents corrosive substances from reaching the underlying steel.

Even if the zinc coating is scratched or damaged, the exposed steel will still be protected by the remaining zinc. This is because zinc serves as a sacrificial anode, meaning that the zinc will corrode before the steel does.

In the event of severe mechanical damage and exposure of the base steel to the environment, galvanizing also provides cathodic protection. This means that even if the coating is breached, the zinc’s sacrificial behavior protects the steel.

So, even where damage or a minor discontinuity in the coating occurs, the steel is still protected. This is one of the reasons why galvanization is a widely used method for corrosion protection.

My question then, is that explanation true? Is galvanization protects mild steel even any crack or scratch on its surface?

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  • $\begingroup$ Consider to edit your question to include duration of protection of the steel as well as the eventual intended use. Using galvanized steel can create complications if welding is expected in the future. In certain inhospitable environments, galvanizing slows corrosion but does not eliminate it. $\endgroup$
    – fred_dot_u
    Nov 5, 2023 at 22:30
  • $\begingroup$ The zinc coating tends to self-heal, to at least some degree. sciencedirect.com/science/article/abs/pii/S0013468608002971 $\endgroup$ Nov 6, 2023 at 0:40
  • $\begingroup$ @fred_dot_u, indeed, during the searching, I asked also whether I can weld a galvanized mild steel. And according to chatGPT, using MIG is the best welding method. But whether it will be rusted after the welding, I think the answer is yes as the welded area is not protected. So, need to be galvanized again, at least the welded part. $\endgroup$ Nov 6, 2023 at 3:01
  • $\begingroup$ @JerryCoffin, I am very weak on chemistry. Can you please give a simple explanation what is the conclusion in that article? $\endgroup$ Nov 6, 2023 at 3:16
  • $\begingroup$ @AirCraftLover: In a battery, you have two dissimilar metals: an anode and a cathode. Metal travels through the electrolyte from the cathode, and gets deposited on the anode. Where rust happens, it's basically a tiny battery forming (with water as the electrolyte). But with zinc nearby, the zinc will act as the cathode, and the steel as the anode--so the scratch (or whatever) leaving exposed steel will get electroplated with some zinc. $\endgroup$ Nov 6, 2023 at 5:50

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Yes it does via galvanic protection. The zinc layer protects it mechanically by sealing the steel from the environment, but if scratched the zinc corrodes sacrificially to protect the exposed steel.

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  • $\begingroup$ So if a mild steel rod like in that picture I cut, I lathe, I drill, I weld, will not make any corrosion? Those works will make exposure out of that galvanized surface. $\endgroup$ Nov 6, 2023 at 3:19
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    $\begingroup$ @AirCraftLover Not ideal but the zinc will still offer some degree of protection. Note that for the zinc to sacrificially corrode, there needs to be a path for ions to travel between the zinc and steel. That means that the wet steel being protected needs the water to extend to make contact with zinc. $\endgroup$
    – DKNguyen
    Nov 6, 2023 at 19:44
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    $\begingroup$ This means a huge area of exposed steel is, ironically, less protected if there is a small amount of water than a very large amount of water. If the exposed end of the rod is submerged or inserted into wet soil, it means the zinc layer will sacrificially corrode but you can be ensured that the steel will be fully protected while it does. On the other hand, if it is exposed outdoors in air, the steel may not corrode at all, or it may slowly corrode if small isolated droplets of water form that do not bridge the steel and zinc. $\endgroup$
    – DKNguyen
    Nov 6, 2023 at 19:49
  • $\begingroup$ Very useful information, I never though about it previously. So, if galvanizing is not completely protecting, what is then the best way to protect a mild steel? I saw like my frying pan, it is not corrode. Is that different? $\endgroup$ Nov 8, 2023 at 0:57
  • $\begingroup$ @AirCraftLover That'd probably to chrome plate or powder coating or paint or black-oxide, in order of decreasing effectiveness. But if you're DIY then paint is the most accessible but this won't work where tolerances or abrasion are important, or inside threads. Really, only black-oxide or plating will work in that case. Black-oxide being the best for tolerances but being inferior to plating in terms of protection. Black-oxide isn't very effective corrosion protection to begin with. It mainly holds onto oil better. $\endgroup$
    – DKNguyen
    Nov 8, 2023 at 1:04

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