When people ask for the strongest metal, they are seeking a single answer for a concept that is complex in materials science. The term “strength” does not refer to one single property, but rather a collection of measurable behaviors a material exhibits when subjected to force. Answering this question requires understanding how a material is being tested, because the metal that resists a scratch is entirely different from the one that resists being pulled apart. Therefore, the strongest metal depends entirely upon the specific metric used to measure its performance.
Defining Strength: The Key Metrics
Engineers characterize material strength using three primary metrics that describe different forms of resistance to stress. The first is hardness, which measures a material’s resistance to localized plastic deformation, such as scratching, indentation, or abrasion. Hardness is often measured using scales like the Mohs scale or by indentation tests, such as the Brinell or Vickers methods.
The second measure is yield strength, which is the point at which a material begins to deform permanently, or plastically, and will not return to its original shape once the stress is removed. This property is important for structural components that must maintain their exact dimensions under heavy loads, such as building beams. Below the yield point, the material is elastic and will recover, but exceeding it means the component has failed its function.
The third metric is tensile strength, often called ultimate tensile strength (UTS), which represents the maximum stress a material can endure before it fractures or breaks completely when being stretched. High tensile strength is necessary for applications like cables, ropes, and chains that must survive extreme pulling forces. While yield strength prevents permanent bending, tensile strength prevents catastrophic failure.
The Hardest Materials: Resisting Deformation
When strength is defined by the ability to resist surface damage and compression, a different set of metals rises to the top, often characterized by high density and high melting points. Chromium is considered the hardest pure metal due to its exceptional resistance to abrasion and scratching. This hardness is why chromium is commonly used as a plating material, giving stainless steel its scratch-resistant surface and high corrosion resistance.
Tungsten is another contender in the hardness category, possessing the highest melting point of any unalloyed metal. This allows it to maintain its structure and hardness even at extremely high temperatures. Though pure tungsten is hard, it is also brittle, a trade-off often seen in hard materials. To overcome this, tungsten is frequently combined with carbon to create tungsten carbide, an incredibly hard ceramic alloy used in high-speed cutting tools and armor plating.
Other hard metals include Osmium and Iridium, both belonging to the platinum group metals. Osmium is the densest naturally occurring element and is highly resistant to melting and wear. Iridium shares similar characteristics, including a high melting point and resistance to corrosion, making these rare elements valuable in specialized engineering.
The Toughest Alloys: Resisting Pull and Yield
For structural applications requiring a material to resist being pulled apart or permanently deformed, specialized alloys engineered for high tensile and yield strength are the champions. Maraging steels, a class of ultra-high-strength iron alloys, consistently rank among the strongest metallic materials in terms of ultimate tensile strength. These materials can achieve ultimate tensile strength values exceeding 2,500 megapascals (MPa), with some grades approaching 3,500 MPa.
The exceptional strength of maraging steels is achieved through a unique heat-treatment process called “aging,” which causes the precipitation of tiny intermetallic compounds within the iron-nickel matrix. Unlike conventional steels that rely on carbon for hardness, maraging steels contain very low carbon. They use alloying elements like nickel (15–25%), cobalt, molybdenum, and titanium to form these strength-imparting precipitates, providing a superior combination of strength and toughness.
Another class of high-performance materials are Bulk Metallic Glasses (BMGs), also known as amorphous alloys, which exhibit a disordered, non-crystalline atomic structure. BMGs, particularly those based on titanium or zirconium, offer a unique combination of high strength and surprising elasticity. Titanium-based BMG composites have achieved ultimate tensile strengths around 1,600 MPa. Their low density makes their specific strength—strength relative to weight—highly competitive with traditional structural alloys.
Beyond Metals: Nanomaterials and Theoretical Strength
While traditional metals and alloys provide structural integrity, the theoretical limit of strength is found in materials beyond conventional metallic classification. Graphene, a single layer of carbon atoms arranged in a two-dimensional honeycomb lattice, is often cited as the strongest material ever tested. Its intrinsic tensile strength is calculated to be around 130 gigapascals (GPa), approximately 100 times stronger than structural steel.
Graphene’s strength comes from the powerful sp² carbon-carbon bonds that form its structure, which are resistant to being pulled apart. Carbon Nanotubes (CNTs) are closely related, essentially a sheet of graphene rolled into a seamless cylinder. These nanotubes also boast high tensile strength, often cited around 100 GPa, and are effective as reinforcing fibers in composites. Although their theoretical strength is immense, the practical challenge of manufacturing them without defects and incorporating them into large structural components means they remain separate from traditional engineering metals.