What is the Hardest Metal?

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  • Originally Written By: Michael Anissimov
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The hardest known metal is steel alloy, which is often made even harder by adding carbon and other elements. With a tensile strength of 0.84 GPa (122,000 psi) and a yield strength of 0.64 GPa (67,000 psi), carbon steel is surpassed in hardness only by very hard nonmetals, such as rubies, diamonds, or aggregated diamond nanorods. Hardness is defined as the resistance of a matter to abrasion or indentation. The Mohs scale ranks elements according to comparative hardness, on a scale from 1 to 10, 10 being the hardest. The best high-carbon steels rate an 8 to 9 on the scale, relative to ruby at 9 and diamond at 10. The hardest metals are still somewhat soft in comparison to the strongest nonmetals, based on the strongest bonds in chemistry, the sp2bond between carbon atoms.

Carbon Steel

High-strength carbon steel goes through a process of tempering and annealing, which uses heat, to make it harder. While heat makes the metal stronger, it also makes it less ductile, meaning it is less able to bend and move when under stress. Carbon is also added to the steel, at which point the steel alloy metal becomes carbon steel, or strengthened steel, the hardest metal available. Carbon contents as great as 2 percent may be present in the hardest metal.

Carbon steel is one of the most common types of steel, the other most common type being stainless steel. Due to it's high melting point of 2,800°F (1,537°C), most carbon steels are used in construction tools such as rock drills and construction dowels. Sometimes very hard metals, such as carbon steel, are undesirable because of their other properties; carbon steel, for instance, is notoriously prone to corrosion. While it is the hardest metal, it is not necessarily the most useful material for every job.

Other Hard Materials

While often mistaken to be the hardest metal, tungsten carbide, is actually a composite material made of tungsten and carbon, often with cobalt added. It is used in both the military and for gun reloading equipment, and is also a popular choice for men's wedding rings.

Iridium and titanium are also sometimes incorrectly called the hardest metals; though they are hard, they are not the hardest. Titanium has been used to build the world's deepest-diving submarines, however, and iridium is known to be the most corrosion-resistant metal. Chromium, which rates 8.5 on the Mohs scale, is also extremely hard, and is often added to alloy steels for this quality. Depleted uranium, the metal of choice for tank shells, is not harder than tungsten carbide or carbon steel but it is more dense, which is preferable for projectiles. The strongest single element is carbon, but only when it is in the form of a diamond.


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Post 68

Single wall carbon nanotube is the hardest material. Young Modulus around 1-5 TPa, Tensile strength 13-53 GPa

Post 67

The hardest alloy probably CPM REX 121 steel, hardness achieved 72 RC. Hardest pure metal probably "beta tantalum", hardness Knoop is 1000-1300 HN. The hardest material is ADNR (aggregated diamond nanorod), Vickers hardness ~300 GPa.

Post 65

@ceramic tile guy: that's probably meant for home tile, like you would use on your floor. By ceramic standards, that's soft. To shape TC, you're best off using something with industrial diamond.

Post 64

Would a cutting wheel for ceramic tile be right for cutting tungsten?

Post 62

Tungsten carbide is not a ceramic, is a metal alloy. Ceramics are defined by their composition and mixing method, and while tungsten carbide and carbon steel might have a few similarities to the definition of ceramic, they do not have enough to be even remotely classified as a ceramic.

Diamond is the hardest substance on earth (*not* a metal). The Americal Iron and Steel institute recognizes that some tungsten carbide alloys are the hardest (commercially viable/useful) metals. Now, just like there are elements that are man-made in the laboratory (that exist only for a short time), I am sure that there are or have been alloys constructed in labs that rival even the tungsten carbide alloys, but many, if not all, of these would most likely be impractical for any useful purpose base on any number of factors (brittle, dangerous/toxic, unstable, expensive, etc.). So, if we just consider common, useful materials, then tungsten carbide is the agreed-upon "winner".

Post 58

Elemental Tungsten (NOT tungsten carbide) is the hardest metal.

In theory steel could be made harder than tungsten, but it'd be so brittle that it'd have so few applications, whereas tungsten is both hard, dense and ductile.

Moderator's reply: On the Mohs scale, which is used in this article, tungsten has a hardness rating of 7.5. Other metals, like chromium, are higher.

Post 57

what is the alloy steel used in manufacturing drill pipes and drill collars?

Post 56

If you ask a Scientist/chemist they will say Tungsten is the hardest metal. Steel may be classified as a metal in the industry but if you go by the periodic table definition then steel is an alloy.

And 1090 is not the hardest steel in any case.

Post 55

@Post 53: "pure diamond is the densest material known to man."

Diamond is not dense. It has a density of 3.5 grams per cubic centimeter, compared to 1g/cc for water, 2.7 for aluminum or 4.5 for titanium. Steel hovers around 7.8, lead 11.3, gold 18.9, tungsten 19.3, osmium 22.6. Osmium, notably, is over 6 times as dense as diamond.

Returning to the article.

I'm a bit baffled by the claim that 1090 steel is the hardest metal. It has a Brinell hardness when severely quenched of up to 600, which is about 57 on the Rockwell C scale. Tool steels (AISI M- or T-series) generally reside in the HRC 65-67 range. Maraging steels - which are vastly stronger than

1090 (up to 350,000psi) - have hardnesses in the same range as hard-quenched 1090, but with much greater toughness. Satellites also have a good reputation for hardness.

As for the overall hardest metal? I'm not sure, because there are many obscure metals (i.e., rarely seen outside of a lab or niche applications) with which I'm not familiar. Heavy metals like tungsten (not tungsten carbide) can alloy into quite strong and probably hard alloys, and osmium is famously hard. I think its 4GPA hardness is off the Rockwell C chart, but don't quote me.

@Post 11: "How high a temperature would you need to forge Alloy 1090? Would you want the hottest flame to get the hardest steel?"

Forging - specifically, the act of squishing a solid metal into a desired shape - can be done at room temperature, though higher temperatures may be preferable (if the forging die can handle it) because the metal is softer. For a metal like 1090, you'd probably want to forge it in a soft, annealed state to avoid the cracking you'd find in the fully-hardened state. Subsequently, you'd reheat the forged 1090 and then quench it to a desired temperature (the lower the quench temperature, the harder and more brittle the part). The problem with this approach is the unevenness of heat removal - thin outer sections will be cooled faster than thicker sections, resulting in uneven hardening. You're also likely to see some distortion in the part.

The "hottest flame" doesn't matter. After a certain point, the metal will simply melt (and 1090 does not have an impressive melting point.) There are specific changes to metals' crystal structures (varying by alloy) that happen at certain temperatures and at certain speeds. You pick the temperatures, heating rates, hold times, and cooling rates based on the alloy. The methods and conditions selected will differ enormously between alloys and desired properties: a carbon steel's austenitizing/quench-and-temper cycle is much different than the aging process used in maraging steels. Further, for a given alloy, you can often alter properties significantly by changing the heat treating (as I implied above about different cooling rates impacting hardness).

Post 54

Blah, blah, blah. Ignorance is to be found everywhere on "what is the hardest this or that article."

There are several new alloys that are harder than the conventional 1090 carbon steel alloy.

Check out any metal supplier and ask for harder than 1090 steel.

Elemental tungsten is softer than several steel alloys, it's only the ceramics based on tungsten that are harder than steel alloys, by far.

Osmium is not "the strongest." It's the densest, non-radioactive element (not metal alloy) known to man, and it's a metal. It is also the hardest element, but it is extremely brittle. It's not "tough" (fracture resistant) at all compared to softer metals or alloys.

Tungsten carbide is a carbide, and all carbides

are ceramics, so tungsten carbide is not a metal. Tungsten carbide = WC : one atom of tungsten (W) for one atom of carbon (C) .

Steel, for example, is one of many metals with a fine dispersion of carbides, but the amount of metal is so great in proportion to the amount of dispersed carbides (carbide is a ceramic) that it is still considered a metal alloy (carbon can be up to 2 percent in steel more or less).

When you up the amount of carbide or any other ceramic in a metal alloy and you reach a certain limit, it is called a metal matrix or metal-ceramic-matrix material (engineering materials that are tough and hard for very specific use).

Tungsten carbide is as much a metal as aluminum oxide a.k.a. alumina a.k.a. corundum a.k.a. ruby or sapphire (when found in nature), and everyone knows alumina is a ceramic, even if it's based on aluminum.

It doesn't mean because there's a metal in the formula that the end product is a "metal", and the example I gave shows it very well.

Post 53

pure diamond is the densest material known to man, however diamond has cracks in it so it is not invincible it is often brittle. The true strongest material on earth is super diamond. Super diamond has tiny bubbles in it which makes one crack only a small irritation and is extremely hard to destroy.

Post 48

Diamond is the strongest substance but it is not a metal.

Post 39

rhenium diboride.

Post 35

Boron Nitride.

Post 33

I thought that tungsten was the strongest metal.

Post 32

How about titanium diboride and titanium aluminide alloys?

Post 29

People, stop posting whatever sounds right to you. Look up numbers in engineering sources.

Pure Osmium can have a HRC of up to 64 which is higher than any other pure metal I found. It is true that it's not very tough because it's so brittle but it is the hardest.

Really old metallurgy texts list 1090 as the hardest steel but modern high speed steels are much harder.

One high speed steel called Rex 121 has an HRC of over 70 when heat treated right.

I'm sure it is possible to have even harder alloys.

Finally, as other people have said, carbides are not metals.

Post 28

KD11S Tool Steel has an HRC of about 61.

Post 27

Tungsten carbide is a ceramic.

Tungtsen is a metal, not an oxide or carbide or whatever; these are ceramics.

And tungsten carbide is not the hardest ceramic. It's only one of the most.

Osmium isn't "tough" at all, it's very hard and brittle. Iridium is used much more often than osmium for pen tips. And it's not for toughness, but for hardness and wear properties.

If you don't believe me, just check out any recent ceramics engineering book.

Post 26

What about weight? Which metal would be ideal choice, say, for a customized Land Rover Defender? (spare no expense)

Post 25

Actually tungsten carbide pressed into a solid form is the strongest metal you can find. No steel even comes close. Unless they made some kind of mythic discovery, the hardest steel can be is Rockwell 58 if even that high; it might only be a 56. I can't remember.

Post 24

Titanium is not the strongest metal. It is often thought of as the strongest but actually it has one of the highest strength to weight ratios. I.e., for a metal that is so light-weight, it is extremely strong.

Typically it has a ultimate tensile strength of up to 170,000 psi. Another unique property is that its strength does not deteriorate in high temperature applications. This makes it ideal for use in aerospace, especially engine components.

There are many metals much stronger than this. Two stainless steels that come to mind are 17-4PH and 15-5PH which can achieve Ftu of 180,000 to 200,000 psi through heat treatment.

Inconel 625 which is used in the aerospace industry, typically in the production of

high-strength fasteners used in critical joints can achieve ultimate shear strengths of 220,000 psi.

Intermediate alloy steels such as 5Cr-Mo-V has an Ftu of up to 280 ksi. Also low alloy steel such as AISI 4130 used in aircraft landing gear has extremely high bearing strength, tensile and compression strength.


Aircraft metal strength tables and the Mil-Hdbk-5

Post 23

the melting point for normal titanium is 3034f, and the boiling point is 5949f. But titanium carbide is much harder lighter less brittle and doesn't rust.

Titanium carbide is ranked 9-9.5 on the mohs scale and its density is 4.93 g/cm3.

Titanium carbide's melting point and melting point only is 5720f -- almost as much as normal titanium's boiling point. And, titanium carbide's boiling points is a staggering 8708f.

Yes, normal titanium is much weaker than carbon or high carbon steel but when you add carbon to titanium, then you have what i think is the world's strongest, lightest metal.

Post 20

For what temperature alloy steel will be used in process piping?

Post 17

what can I use to make a knife that I can find around the shop? I'm looking for carbon and nickel.

Post 15

1090 is not by any means the hardest metal or even the hardest steel. 1090 is very ductile, and in the normalized, quenched and tempered state, has a very high modulus of elasticity. This alloy is primarily used for springs. Maximum attainable Rockwell "c" scale is about 42. I know this because I am a tool and die maker and federally certified.

Post 14

What are the difference between carbon steel and mild steel. advantage and disadvantage, strength and others. thanks

Post 11

How high a temperature would you need to forge Alloy 1090? Would you want the hottest flame to get the hardest steel?

Post 10

The melting temperature of titanium is 1820F 3308C

Post 8

haha.. DragonForce is a metal band

Post 3

So, you mean to tell me that Dragonforce is not the hardest metal known to man?

Post 2

1668°C. Lots of element properties can be found at chemicalelements and webelements.

Post 1

Please can you tell me what is the melting temperature of titanum.

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