亜鉛メッキ鋼板は磁性を持つ

亜鉛メッキ鋼板は磁性を持つか?詳しく見る

How susceptible is galvanized steel to magnetism?

Well, as a professional ネオジム磁石メーカー, I set out on a mission to uncover the truth.

And in this post, you’ll see what I discovered. You’re also going to learn:

  • A bit about the history and use of galvanized steel
  • Why some types of steel are magnetic while others are not
  • What exactly happens during the galvanization process
  • Is galvanized steel magnetic
  • The degree to which common magnets are attracted to galvanized steel

So if you’re looking for a definitive answer to this very question, you’ll find it here.

亜鉛メッキ鋼板は磁性を持つ

Let’s start by understanding galvanized steel a bit better.

What is Galvanized Steel?

Galvanized steel gets its name from the galvanization process used to make it.

Galvanization is the process of applying a protective zinc coating to steel, in order to prevent rusting. The term comes from the name of Italian scientist Luigi Galvani.

In the galvanization process, clean steel is submerged in a kettle or vat containing molten zinc. The steel is said to be “hot-dipped”. As it is removed from the zinc, a coating adheres uniformly to the steel’s exterior.

This zinc coating protects corrosive substances from reaching the steel itself. It does by acting as a sacrificial layer, corroding before the actual steel does.

  • The zinc layer corrodes at a steady rate, acting as a buffer between the environment and the steel’s surface.
  • As long as this layer remains intact, the base metal’s vitality is preserved.

Initially developed in 18th century France for shipbuilding, galvanized steel gained widespread use in the 20th century across various sectors like construction, energy, infrastructure, and more.

Key properties of galvanized steel include:

  • 手頃な価格 – Hot-dipped galvanizing of steel is a lot more economical than other alternatives like stainless steel. It adds only 2% to steel’s cost.
  • Corrosion resistance – The zinc coating offers reliable protection, especially in wet environments.
  • Longevity – Galvanizing makes steel last over 50 years in submerged conditions and 100+ years above ground. All without further maintenance.

Now we know what galvanized steel is and what’s so useful about it. But what about its magnetic properties?

Which Types Of Steel Are Magnetic?

Before we analyze whether galvanized steel is magnetic or not, it helps to first understand why steel is magnetic in general.

The magnetic properties of steel have everything to do with its composition. Let’s look at how the three main types of steel interact with magnets:

1. Carbon Steel

Carbon steel, made mostly of iron and small amounts of carbon, is highly magnetic. We’re talking fridge magnet type of magnetic.

That’s because the carbon levels are low enough to not impede the magnetic forces of iron, which makes up 98%+ of this steel.

A carbon steel product will “stick” quite strongly to a magnetic surface. Strong permanent magnets especially have no problem picking up thinner sheets of carbon steel.

2. Low Carbon/Mild Steel

What if carbon steel gets additional alloying elements like manganese or silicon added to it? The resulting low-carbon or mild steel is less magnetic than regular carbon steel.

While mild steel is still attracted to magnets, it won’t stick as firmly compared to high-carbon versions. The additional metals modify the internal structure just enough to dilute iron’s magnetism.

A permanent refrigerator magnet will pick up a mild steel item too. Although dropping or tugging on the piece might separate it from the magnet.

3. Stainless Steel

Stainless steel has high levels of metals like chromium, nickel, and manganese. At least 10-20% chromium content makes stainless steel entirely non-magnetic.

The large portion of non-ferrous metals modifies stainless steel’s crystalline structure to make it paramagnetic. So there’s no magnetic attraction whatsoever between a magnet and stainless steel.

要約すると

  • Carbon steel – Highly magnetic
  • Mild/low carbon steel – Less magnetic
  • Stainless steel – Non-magnetic

Now we know what makes steel magnetic. The more iron it has, the more magnetism it exhibits. Additional elements weaken the effect to varying degrees.

This brings us back to the central question – how does the zinc coating used to make galvanized steel impact its magnetism?

How Does Galvanization Affect Steel’s Magnetism?

We know that galvanized steel involves applying a zinc coating to steel. Now what exactly happens at a microscopic level when zinc and steel meet?

What The Zinc Coating Does

Hot-dip galvanizing results in zinc bonding metallurgically with steel’s surface. When the molten zinc alloy comes in contact with steel, a series of zinc-iron alloy layers form on the steel’s outer surface.

Together, these zinc-iron alloys form an outer skin that completely encapsulates the steel.

So while the original steel still exists underneath this coating, the outermost layer consists of zinc-iron compounds.

The resulting barrier helps by:

  1. Physically separating corrosive agents from the actual steel
  2. Sacrificing itself via corrosion before the steel gets corroded

How The Coating Impacts Magnetism

Okay, so the zinc coating ends up layered on top of the steel, shielding it physically. This coating is also metallurgically bonded to the steel’s original surface.

But what effect does this have on the base steel’s magnetic properties?

The key thing is that the steel itself is unchanged. Hot-dipping doesn’t modify or sterilize steel’s inherent ability to get magnetized.

Regardless of what covering gets added later, the steel retains characteristic magnetic behavior:

  • Carbon steel remains highly magnetic
  • Mild steel is weakly magnetic
  • Stainless steel stays non-magnetic

However…

Adding a zinc layer on the outside does end up shielding some of the magnetism at the surface.

Think of the coating acting like a blanket placed over a warm object. The concealed part stays warm while outer side ends up cooler.

Here, even though the steel stays magnetic underneath, the zinc surface can’t convey the magnetic force to the same degree.

So technically, a piece of galvanized steel IS still magnetic. It’s just that the zinc weakens the apparent magnetism by blocking the steel’s magnetic lines of flux.

What Type of Steel Gets Galvanized Typically?

For galvanization purposes, low/mild carbon steel is most commonly used. That’s because it offers the best combination of formability and strength once galvanized.

On the other hand, high carbon steel tends to become too brittle after adding zinc. And stainless steel already has corrosion resistance so galvanizing it is unnecessary.

So in most real-world applications, mild carbon steel is the starting material that gets transformed into corrosion-resistant galvanized steel.

And as we found above, mild steel HAS magnetic properties to begin with (unlike stainless steel, for example). It’s just not as intensely magnetic as regular carbon steel.

So IS Galvanized Steel Magnetic?

Given its mild steel roots and the physics behind the hot-dipping process…

The answer is, yes – galvanized steel is magnetic. Just not quite magnetic enough to align iron filings or attract a nail from several inches away. But enough to weakly stick paperclips, pins, steel wool, and small iron objects to it.

Common fridge magnets DO lightly cling to galvanized steel. Although they also fall off the surface quite easily.

So if your criteria for magnetism involves pieces of metal firmly sticking to each other – galvanized steel qualifies. Just keep your expectations in the “weak magnetism” department instead of expecting full-blown metallic cling!

But The Magnetic Force Varies…

As discussed earlier, the zinc barrier DOES end up limiting the magnetic forces. And a thicker galvanized layer can further dilute the apparent magnetism at the very surface.

But just underneath, the magnetic steel still exists unchanged.

So for a newly galvanized item with minimal surface corrosion, the magnetic response will be moderate. Gentle attraction and some sticking force on lightweight objects.

On the other hand…

An old rusted galvanized piece will have a more corroded zinc layer with the magnetic steel more exposed. So its magnetic effects will seem more pronounced.

When Would The Magnetism Come In Handy?

I found a couple of neat ways galvanized steel’s magnetism can be harnessed in regular situations:

Picking Up Stuff That Accidentally Fell In

If you drop a steel hardware item like a screw or nail onto a galvanized steel rooftop, you may be able to retrieve it with a magnet wand.

Provided the item lands on an exposed spot rather than a seam or lapped joint.

Making Signs

Small steel letters/logos applied on an exterior galvanized steel surface will weakly cling on directly. Avoiding the need to drill holes for hanging them.

Mounting Decor Items Outdoors

Similar to signs, implementing thin magnetic sheets behind decorative pieces allows cleanly installing them on galvanized walls or fences.

These applications work precisely because galvanized steel DOES exhibit minor magnetism despite its zinc cladding. Now if it was stainless steel, none of this would be possible!

テイクアウェイ

Let’s recap the key facts:

  • Galvanized steel is steel coated with a zinc layer for enhanced corrosion resistance
  • Different types of steel have varying magnetic properties depending on their composition
  • The base steel itself retains innate characteristics even after galvanization
  • Mild steel and high carbon steel exhibit magnetic attraction; stainless steel does not
  • Mild steel is commonly used to produce galvanized steel
  • The zinc coating makes galvanized steel less apparently magnetic at the surface
  • But YES, galvanized steel IS still attracted to magnets weakly due its magnetic steel core
    So there you have it – a complete lowdown into galvanized steel and magnets.

Now you know exactly why galvanized steel demonstrates modest magnetic effects thanks to its underlying steel layer.

Leave a comment if you have any other questions! I may just address them in an updated version of this post.

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