Identifying the Hardest Metal on Earth: A Technical Reference

One of the most common and expensive problems for all levels of CNC-machined parts and heavy industrial tooling is “rapid wear”. So, even if your design is optimised, your CAD work is perfect, and your supply chain and inventory management are efficient, there can be an enormous problem in production caused by a drill bit that breaks, a high-pressure valve that fails due to wear and tear of a part, etc. Our purchasing managers have seen, in fact, hundreds of descriptions regarding tungsten carbide, the hardest metal on Earth. So, here is the crucial point. Many think that “strong” and “hard” are two expressions that refer to the same characteristic. In reality, they are quite different. The tensile strength describes how strong a material is when subjected to tensile forces. The hardness, on the other hand, refers to the resistance that a material shows towards deformation by means of applied pressure.

Hardness classification is important when choosing materials for aerospace, defense, or high-performance automotive applications. In this guide, we look at the hard metal candidates and compare their hardness to more common industrial metals.

The Scientific Contenders for the Hardest Metal on Earth

Hardness is a very relative and largely dependent on the measurement scale used: Mohs scale, Vickers hardness test, or Rockwell hardness test. When we talk about the hardest metal on the planet, we have to refer to a specific measure. Pure elemental metals tend to have a chromium (Cr) hardness of 8.5 on the Mohs scale. However, this is rarely the case in B2B business.

In the industrial world, there are many options, but one of the most popular is Tungsten (W). Although pure Tungsten is quite spectacular, the form of Tungsten Carbide is what really gets the business done in the workshop. For the international trader, it is also important to remember that Tungsten is the material with the highest tensile strength, and the Vickers hardness is also significantly higher than in any type of steel. Also, a bit of knowledge about the rare earth elements can be beneficial. Especially about Osmium. It is often said to be the densest and most incompressible metal, but because of being very brittle, it is less common in machining than Tungsten.

Industrial Hardness: Tungsten Melt Temperature vs. Surface Rigidity

Many engineers often equate hardness with thermal stability. If a metal softens at some significant temperature, the value of its hardness is very limited. This is why the tungsten melt temperature of 3422 °C is such an important number.

Tungsten will remain hard and sharp, even when approaching its melt temperature, which is far higher than that of all other metals and the “red heat” to which they soften. In the cutting tool trade, hardness usually refers to resistance to heat generated from friction while cutting on a high-speed CNC spindle. Although Chromium is probably the hardest pure metal at room temperature, it is the fact that Tungsten remains by far the hardest metal in the world, during the whole process of machining, that confirms its superiority, in the heaviest of drill bits, and the most effective of armor-piercing rounds.

Comparative Hardness: Hardest Metal on Earth vs. Steel Melting Temperature

We are frequently told that “Steel is the hardest”. However, this is only true if you do not really know what you are talking about. This is because steel is an alloy of iron and carbon, and although useful in many respects, standard carbon steel is actually quite soft when compared to refractory metals. Additionally, when you compare the melting temperatures of the various steels to those of materials such as Tungsten or Chromium, you will find that steel loses its hardness long before any of these materials reach their operating temperatures.

Material	Mohs Hardness	Vickers Hardness (HV)	Melt Temperature (°C)
Tungsten	7.5	3430 (Carbide)	3,422°C
Chromium	8.5	1060	1,907°C
Titanium	6.0	970	1,668°C
Hardened Steel	5.0 – 6.0	600 – 900	~1,500°C

If we refer to the table, we can see that Chromium for the surface hardness and Tungsten for the structural component of the alloy represent a totally different level of hardness in relation to the standard hardness of steel. In the case of a B2B purchase, in fact, the hardened steel for standard parts can be a low-cost solution. But for the “impact points” of the machinery, the alloys that contain tungsten are necessary.

Why the Specific Heat of Aluminum and Hardness Metrics Diverge

We are frequently asked to contrast hardness with thermal capacity in thermal management. Aluminum is a commonly used material for heat sinks. This is primarily due to its high thermal conductivity. However, the specific heat capacity of aluminum is also 0.900 J/g·°C. As you might expect, the hardness of aluminum is near the minimum of the table.

Mohs hardness (scratch hardness) of Aluminum (Al): 2.75. I often hear “Al-Li” alloys discussed in the context of the global trade of aerospace components. These Aluminum-Lithium alloys represent a material attempt to bridge the gap, but I would never recommend Aluminum as a suitable cutting material for any reason. As we previously established, materials with high specific heat and low density will almost always have very poor hardness and therefore do not ever approach the hardest metal known to man. Materials procurement is really about one of two things, depending on the application: “heat rejection” (the characteristics of Aluminum), or “mechanical endurance” (the characteristics of tungsten and chromium).

The Role of Alloys: Brass Melting Point and the Hardness of Yellow Metals

In the world of “yellow metals”, hardness is no longer the important parameter, and machinability and corrosion resistance are more in play. As an example, the brass melting point is in the order of 900°C – 940°C, and its Mohs hardness is only about 3.0.

The workshop traders learn in is made out of brass. This is a metal that is not one of the hardest in the world. Soft enough to work with to precision on very fine detail in valves, musical instruments, or just a door handle. The traders are ordering “High-Strength Brass” — probably an alloy of copper and manganese — a metal that is tough as steel, but still resistant to corrosion.

Alloy	Major Elements	Hardness (Brinell)	Primary Use
Cartridge Brass	Cu, Zn	60 – 70	Fasteners
Manganese Bronze	Cu, Zn, Mn, Fe	150 – 200	Marine Propellers
Tool Steel	Fe, C, W	600+	Cutting Tools

Machining the Hardest Metal on Earth: CNC Challenges

For a CNC shop like ours, the hardest metal on earth is at the same time a product that we machine and a problem that we often struggle with. In order to machine Tungsten or Chromium alloyed steels, the tool that we use must be at least as hard as the material we are trying to cut. For these cases, the only alternatives to super sharp and high-performance carbide cutting tools are Polycrystalline Diamond (PCD) and Cubic Boron Nitride (CBN) inserts.

SUPER HARD TOOLING is a multi-billion-dollar-a-year international trade business. Are you engaged in the fabrication of a critical nuclear reactor part or perhaps a turbine component for a commercial or military aircraft jet engine? In such a scenario, the expense of labor is a function of “Tool Life.” A shortening of the tool life as a consequence of a material that is only marginally harder than that of the hard metals may at first seem of little significance. However, the necessity of regularly re-grinding and replacing such a tool to maintain product quality could easily impact the production efficiency and subsequently cause failure of the robot or machine automation. The Procurement specialist should be aware that a cheap or allegedly low-hardness alloy or material could prove to be more costly than the harder and superior alloys required to replace it as a result of greater quantities and values of abrasives and consumables needed in order to machine or process the component.

Visual Verification: Using the Color Guide to Copper Brass and Bronze

In the scrap and commodities market, it is often the first line of defense against scams and misleading information. The Color Guide to Copper, Brass, and Bronze is a useful tool for buyers and sellers to reference the varying shades of the softer alloys. The hardest metal on earth, candidates for Cartridge Brass samples are usually much paler and lack the warmth of the softer alloys.

Description Chromium is one of the shining “brass colored” mirror finishes. It is very hard and is commonly used in plating.

Tungsten – dull, heavy, steely grey. Its weight is the “give away” in the scrap trading world.

Titanium: A darker grey with a matte finish.

If a vendor tells you they have a “hardened alloy” and it shows a red gold color similar to the melting point sample of brass, you have to verify the metallurgy of the material. Hardness is a property of the microstructure that typically always falls within the grey-scale of light.

The Future of Metallurgy: Is There a New Hardest Metal on Earth?

HEAs are an emerging area of material science. High-entropy alloys are a class of alloys with approximately equal concentrations of five or more elements. Certain of these alloys have proven harder than Tungsten, a famously hard metal, while at the same time more ductile.

In order to be competitive in the global market, International traders are advised to monitor the development of these high-performance ceramics, materials that are required for use in equipment that can withstand temperatures of the steel of a volcano, or the re-entry temperature of space. Our status as a Business-to-Business supplier of new “super-alloys” will surely confirm your company’s status as an innovative leader in modern manufacturing technology.

Frequently Asked Questions (FAQs)

What is the hardest metal on earth?

Hardness can be defined in several ways, and Tungsten is most widely considered the hardest metal when its tensile strength and scratch resistance are compared. However, when hardness is defined from a scratch resistance viewpoint (especially for the carbide form), then again Tungsten would be one of the hardest, but not necessarily the hardest. Chromium is the hardest of the pure elements in the Mohs scale of hardness.

Is Titanium harder than Steel?

No. Pure titanium is actually a little softer than even some heat-treated grades of tool steels. But, although Titanium may not be one of the hardest metals, it certainly has a higher strength-to-weight ratio, which allows it to carry the definition of stronger for its weight — a very different measure of metal performance.

Why is Tungsten used in armor-piercing rounds?

Due to its extremely high melt temperature and its density and hardness, tungsten can simply punch through a steel plating without bending or melting.

Can you melt the hardest metal on earth with a blowtorch?

Most modelers use a standard propane torch to heat their metals before melting them in a crucible. This torch does not have enough heat to reach the melt temperature of tungsten, which is 3422° F or 1867° C. An electric arc furnace or a plasma torch would need to be used to melt these refractory metals.

Is Diamond a metal?

No. Diamond is the hardest known material on earth, but diamond is a crystalline form of carbon, a non-metal. The hardest metal on earth is still several times softer than a diamond.

References

1. Callister, W. D. (2022). Materials Science and Engineering: An Introduction.
2. ASM International. (2021). Handbook of Hardness Testing.
3. International Tungsten Industry Association (ITIA). (2023). Tungsten Technical Data.
4. National Institute of Standards and Technology (NIST). (2024). Mechanical Properties of Metals.
5. ISO 6507-1:2023. Metallic materials — Vickers hardness test — Part 1: Test method.