What is the strongest metal?
How can you test the strength of metal?
The strength of metal can be measured using different scales; tensile strength, compressive strength, yield strength, surface hardness, and impact strength. Each of the different ways to measure strength have their benefits and disadvantages, so it is worth taking the time to understand the difference between the techniques to help you choose the most appropriate metal for the project depending on which strength characteristic you need.
Tensile strength is a measure of resistance of metal before it breaks, deforms, or fails under pressure. The metal is clamped between two sets of clamps which are then pulled apart to apply a tensile load to the metal, measurements are recorded at differing points of the plastic deformation process; plastic deformation is when a material is permanently distorted and deformed by torsion stress, compression, and bending that causes elongation, twisting, and buckling. Tensile strength tests report three types of tensile strengths.
Tensile yield strength is the strength recorded before the sample begins to plastically deform.
Ultimate tensile strength is a measure of the maximum strength of the metal after plastic deformation has been recorded.
Fracture tensile strength is the recorded strength at the point of complete metal failure. This resistance is measured in psi (pounds per square inch).
Impact strength is the amount of energy a metal can absorb via impact before it shatters, deforms, or snaps. The most commonly used test to determine impact strength is the Charpy V-notch test where a sample of metal has a notch cut into it to correspond with the test standard criteria and is then secured in the V-notch testing equipment. The notch is the specific place the metal will fail when a weighted pendulum is released, and the energy absorbed by the impact is recorded. This test is useful for applications where the metal will be used intentionally to receive repeated impact stress.
Compressive strength is the limit of compression a metal can tolerate before it reaches the point of failure. The metal is placed between two plates and compressed between them, the range of deformation in the metal is compared to the measure of the load applied to give a reading of the maximum load capacity. Compression testing is useful for components made from metals that will be load bearing as maintaining their integrity under compressive force is of paramount importance.
Yield strength is the measurement of the metal’s elasticity. The material is tested for the ability to withstand bending and its ability to return to its original form before reaching the point of failure. The strength scale relates to the point at which the metal is permanently deformed and will not return to its original form once the stress has been removed.
Mohs hardness is an ordinal scale that measures the surface hardness of minerals and materials, this is often also referred to as ‘scratch testing’. Knowing the surface hardness or scratch resistance is useful when selecting materials where damage from abrasion would hinder the desired aesthetic or when wear would compromise the integrity of the component. The Mohs hardness scale ranks talc at 1 as being the softest surface and diamond as 10. The scale has been modified by geologists since it was first used back in 1820, some versions placing diamond at 15- but the convention of Mohs scale remains the most used.
The strongest metals.
Tungsten is often alloyed with steel to create ‘high speed steel’ due to having the top tensile strength of any metal at around 142,000 psi. It is, however, very brittle in its rare form and can shatter with a relatively low impact strength compared to some other metals.
Iridium is a high-density element that belongs to the platinum group of metals, it is extremely brittle and has a melting point in excess of 2,000°C which makes it extremely difficult to work with, however, it has a very high resistance to corrosion which makes it a valuable alloying element.
Steel is probably the best known of the strongest metals and is widely used across industries worldwide. Steel is an alloy of iron and carbon which can be alloyed with a wide range of elements to produce a range of metal grades of varying mechanical and chemical properties suitable for a range of different uses. For example, stainless steel is extremely resistant to corrosion and chromoly steel is stronger than regular low carbon steel because of the added chromium and molybdenum. These additions increase hardenability, corrosion resistance, toughness, and resistance to temperature fluctuations. Two of the strongest grades of steel are EN24T and T45 which are widely used across engineering, aeronautics, and motor sport due to their reliable mechanical properties.
EN24T is a high strength engineering steel that can be heat-treated to produce a variety of different strength alloys for use in harsh environments and heavy-duty industries. EN24T is very popular for use in industries where hardness, tensile strength, and resistance to wear are important such as bolts and shafts, gears and cams, and heavy-duty vehicle axles.
T45 is a seamless manganese steel tube known for its strength and can withstand high levels of G force before failure making it an extremely popular steel for the aeronautical industry as well as for racing cars. It is used for manufacturing anti-roll bars and roll cages where significant strength is needed for safety, however, its incredible strength means the tubes can be manufactured with thinner walls to reduce weight without compromising strength.
Osmium is an extremely dense metal with a very high melting point. Found predominantly in platinum ores, Osmium is extremely strong but brittle, but when alloyed with other platinum group metals it provides high levels of hardness.
Chromium is commonly alloyed with steel because of its hardenability and its resistance to corrosion.
Titanium is a low-density metal with a moderate tensile strength of 63,000 psi. It has the highest ratio for tensile strength versus density of any metal. It is often alloyed with iron or aluminium to make extremely light but extremely strong alloys for use in aeronautics, racing cars and in the cycling industry.
So, which is the strongest metal?
Whilst there are several extraordinarily strong metals, the answer to the question of which is the strongest metal comes down to which metal is most suitable for the proposed application. It is not possible to do a direct comparison between the metals listed because strength and mechanical properties are measured in a variety of ways.
Steel, although not as strong as tungsten or iridium for example, is widely considered to be the metal of choice across engineering, construction, aviation, and transport infrastructure globally. By utilising different strengths and properties of alloying elements, it is possible to produce a grade of steel that meets all the criteria for a project; strength, corrosion resistance, weldability, weight, machinability, and durability without costing the earth as steel can also be repeatedly recycled without losing any of its mechanical or chemical properties.
