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Is Steel Harder Than A Diamond?

Is Steel Harder Than A Diamond?

Apart from being one of the most beautiful gemstones in the world, diamonds are also famous for their exceptional hardness. Despite that, there are people who are concerned about the diamond’s durability and if there is something that can scratch this gorgeous gemstone. 

That’s why today’s topic is going to be: Is steel harder than a diamond?

When you look at the Mohs scale of hardness, you can see that the diamond is a perfect 10, meaning it’s the hardest material there is. But what about steel? Is steel something that can scratch a diamond?

In this article, we’ve covered everything you need to know about steel and diamonds and their correlation. Without further ado, let’s jump right into it.

Let’s Talk About Steel 

Steel is one of the world’s most crucial construction and engineering materials. It’s used in the everyday aspects of human lives – in the making of various products, including cars, washing machines, and refrigerators, cargo ships, and surgical scalpels. 

It can be recycled – several times, might we add – without loss of its properties, too.

You get iron by removing oxygen and other impurities from the iron ore. And when the iron is combined with carbon, recycled steel, and some other elements, it becomes steel. 

So, steel is essentially an alloy of carbon and iron, containing less than 2% carbon and 1% manganese, along with small amounts of phosphorus, sulfur, silicon, and oxygen.

Steel is produced via two main routes – the electric arc furnace route and the blast furnace-basic oxygen furnace. The main difference between the routes is the type of raw materials they use: 

One route primarily uses recycled steel, while the other uses iron ore, coal, and recycled steel. Most steel products can be used for decades before they are recycled. 

Steel isn’t a single type of metal; there are more than 3500 different grades of steel with different chemical and physical properties.

The Four Main Types Of Steel 

Since steel properties and the different steel alloys are so vast and varied, it might be a shocker that steel is composed of just iron and carbon. 

However, the real difference starts when additional carbon and alloying elements come into the picture. Steel’s durability and strength are determined by added elements, such as phosphorus and manganese. 

So, let’s take a look at four fundamental steel types.

1. Carbon Steel

This variant of steel looks dull, matte-like, and is known to be vulnerable to corrosion. There are three subtypes of carbon steel – low, medium, and high. 

Low carbon steel contains about 0.30% of carbon, medium about 0.60%, and high 1.5%. 

The name comes from the fact that they contain just a small amount of other alloy elements. Carbon steel is exceptionally strong, which is why it’s often used to make things like automotive parts, high-tension wires, and knives.

2. Alloy Steel

Next, we have alloy steel, which is a mixture of a few different metals such as nickel, copper, and aluminum. This kind of steel tends to be more on the cheaper side. 

Also, it’s more resistant to corrosion and is favored for some car parts, mechanical projects, and ship hulls. The strength of alloy steel depends on the concentration of the elements that it contains, though.

3. Tool Steel

This type of steel is famous for being hard, and both scrape- and heat-resistant. Its name comes from the fact that it’s commonly used to make metal tools – for example, hammers.

Tool steel is made up of cobalt, tungsten, and molybdenum, which is why tool steel has such durability and heat resistance.

4. Stainless Steel

Stainless steel is probably the most well-known type of steel out there. Having around 10 to 20% chromium for their alloying element means this steel is shiny. It’s also resistant to corrosion – and easily molded into different shapes. 

Due to its easy manipulation, quality, and flexibility, stainless steel generally finds its place in home applications, silverware, and surgical equipment.

Related Read: Why Is Diamond Not Used for the Machining of Ferrous Material?

How Hard Is Steel?

Steel is considered a synonym for strength, and it’s surprising how many situations make use of it. You can have a steely determination, have nerves of steel, or have a mind as sharp as a steel trap. It’s easy to see why, when we think “hard,” we think “steel.”

However, with so many types of steel out there, it can be challenging to decide which one suits your engineering project the best. Even under the term “steel,” there are many different specs and characteristics – some of which are better suited to withstand certain conditions.

There are several tests to measure the hardness of steel that can help you determine which type of steel suits your needs the best.

First, we have the Brinell Hardness Test. It is a test of deformation under pressure, where a hardened steel ball is indented onto the surface of the test steel. 

After 15 seconds, the indentation made from three different types of force load is measured – and hardness values are calculated. 

The Brinell test is useful as it measures a sustained and applied pinpoint weight, giving reliable and accurate results. 

The Vickers Diamond hardness test works similarly. However, instead of placing a ball, the diamond pyramid is placed onto the test surface and under standard load for a specified time. 

This method allows different grades of material to be tested – the so-called Vickers Number, calculated by dividing the load (in kilograms) by the indentation left and the test in millimeters squared.

The third test is called The Rockwell Hardness test, which involves a dual test of the material. The procedure starts by placing a diamond cone or hardened steel ball under a specific load of 10 kilogram-force. 

The depth of indentation made under the light load is taken before another load of 150-kilogram force is applied. The difference between these two tests is then measured and used to determine the Rockwell number. 

This test can also be applied as a superficial test for thinner materials. 

With each of these tests, the higher the number is, the harder material you have. The hardness rating is a crucial piece of knowledge when dealing with materials like steel, as they must be able to withstand impact without deforming or breaking.

The good thing is that modern technologies are able to measure more accurately than before, which allows engineers confidence that they’ve chosen the right material for a specific job.

What About A Diamond’s Hardness? 

The hardness of a certain object determines its resistance to damage in the form of scratches – and diamonds are the hardest substance there is. 

While some may think of diamonds as fragile, that perceived fragility has more to do with their mythologized rarity than their vulnerability to surface impact. 

The hardness of a substance can’t be compared to toughness. A material’s strength involves its resistance to fracturing or breaking. Nothing but another diamond can scratch or cut a diamond

However, a diamond’s moderate toughness means it can still shatter. 

Uncertainty between diamonds’ hardness and toughness can be tested with a simple hammer. Diamond will fracture – or break – if hit with a hammer. On the flip side, the metal surface of a hammer won’t scratch a diamond.

Learn More:

Measuring Hardness 

Hardness relies on the bonds that hold the atoms together within a crystal structure. That bonding is obvious in the ease with which the layers of atoms at the surface can be divided when you apply pressure with a sample of another material.

If the second material is harder than the first, it’ll leave a scratch. That scratch represents the breaking of millions of atomic bonds on a microscopic scale. 

And every mineral can be ranked based on other minerals it can scratch.

In order to measure the hardness of a diamond, or any other substance, we use the Mohs scale of mineral hardness. This method involves testing one mineral by seeing if another mineral has the potential of producing a scratch on its surface.

Mohs scale is a ten-point scale, where 1 is the softest and 10 is the hardest. 

Mohs scale revealed some unexpected results and changed how you might normally think of certain substances. You see, dust, which can corrode surfaces, is hard enough to cut glass. Glass is actually rather soft according to this scientific scale.

The Mohs scale works by comparisons, in four simple possibilities:

  1. If the first substance can scratch the second substance, the first one is harder.
  2. If the first substance can’t scratch the second, the second is harder.
  3. If two substances are equal in hardness, neither of those two will be able to make much of a scratch on the other.
  4. If the first substance can be scratched by the second but can’t be scratched by the third substance, the hardness of the first substance is between the second and the third.

Gemologists often use this scale to identify a mineral. In the field, they conduct the scratch test on a certain mineral with a stainless steel knife (5 to 6.5 on the Mohs scale) and come to a conclusion on whether the mineral is softer or harder than stainless steel.

It’s common practice to utilize a set of hardness picks made from metals and alloys that are equal to various numbers on the Mohs scale to perform the same test on minerals with more precise results.

A certain mineral will usually result in a consistent hardness. However, some minerals can vary in composition – like garnet, which can have few different compositions and will vary in hardness from 6.5 to 8. 

Some minerals have different hardness at different angles because of their crystal formation.  For example, kyanite has a Mohs scale of 5 if tested at a certain angle and 7 if tested from another angle.

As we mentioned, there are several other more controlled tests where a tool is scratched into the surface to determine the hardness. These tests take into account the force used and the size and depth of the indentation left by the tool.

However, the Mohs scale continues to be a popular test for hardness. It’s essential to note that these tests only tell you how hard a certain material is, though – not how strong or tough the material is.

Let’s look at the Mohs scale of hardness for some of the most common gemstones:

  • Diamond – 10
  • Sapphire and ruby – 9
  • Spinel and topaz – 8
  • Aquamarine and emerald – 7.5 to 8
  • Citrine, amethyst, and smoky quartz – 7
  • Tanzanite and peridot – 6.5 to 7
  • Jade and moonstone – 6 to 6.5
  • Opal 5.5 to 6.5
  • Turquoise 5 to 6
  • Pearl 2.5 to 4.5
  • Amber 2 to 2.5

Metals can be ranked on the Mohs scale, too, even though they possess other properties which make them durable and long-lasting. 

Let’s see some of the examples:

  • Tungsten carbide – 8.5 to 9
  • Tungsten – 7.5
  • Hardened steel – 7 to 8
  • Titanium – 6
  • Palladium – 4.75
  • Iron – 4.5
  • Steel – 4 to 4.5
  • Copper – 3
  • Bronze – 3
  • Aluminum, gold, and silver – 2.5 to 3
  • Zinc – 2.5
  • Tin – 1.5

As you see, where metals stand on the Mohs scale can also give us some info regarding which other metal can scratch it. That can also be useful when deciding which pieces of jewelry you can wear together – or which items you shouldn’t store in the same box.

Learn More: Are Diamonds The Hardest Substance On Earth?


If you’re still wondering, “Is steel harder than a diamond?” let us break it down for you:

Steel is known to be one of the most important engineering materials out there. It is an alloy of iron and carbon with a little bit of phosphorus, sulfur, silicon, and oxygen. 

Even though steel has amazing properties, it still ranks between 4 and 8 on the Mohs scale of hardness, depending on the type of steel. On the other hand, diamond ranks with a perfect 10 on the Mohs scale of hardness, meaning it is harder than steel. 

So, the answer to our question would be: No, steel isn’t harder than a diamond. And, in turn, that means steel couldn’t scratch a diamond, either.

Learn More: Is There A Gem Harder Than Diamond?