10 Hardest Metals

Heating steel is a method of increasing its hardness.

According to the American Iron and Steel Institute, hardness refers to and is defined in terms of a substance's resistance to indentation. The American Federation of
Mineralogical Societies measures hardness using the Mohs scale, with the hardest substances rated 10. The hardest substances, the ones rating a 10 on the Mohs scale, are not metals; they are synthetic diamonds, diamonds and rubies. The Mohs scale range for the hardest metals begins around 9.5.

Tungsten Carbide

The American Iron and Steel Institute says that tungsten is a hard metallic element which, in combination with carbon, forms a metallic alloy called tungsten carbide. The metal is used in jewelry and is reported to be between 8.5 to 9.5 on the Mohs scale by Jewelry Secrets, making it the highest rated metal on the scale. Hardness ratings become somewhat arbitrary in that the hardness is actually in a specific range due to differences in the alloy ratios. Since tungsten carbide is used for jewelry and military applications, it is sometimes overlooked as the hardest metal in favor of the more widely used carbon steel alloys.

Carbon Steel Alloy

Carbon steel is sometimes called the hardest metal in the world because it has wider applications than tungsten carbide. The American Iron and Steel Institute glossary states it is a combination of steel and carbon. Substech says it has been tempered (heated or heated and cooled) and annealed (heated and then slowly cooled) to increase its strength and decrease its brittleness. Steel strength and ductility, its ability to bend without losing strength, is determined by the amount of carbon in the alloy. Dormer shows that the higher the amount of carbon, the harder the steel. Carbon steel rates between 8.5 and 9 on the Mohs scale. The hardest steel contains .03% percent carbon. It is used for shovels and plows.

Hardened Steel

The American Iron and Steel Institute explains that another way of making steel hard is to heat it and subject it to different temperatures. It can also be hardened by rolling it and subjecting it to pressure. Hammering the steel, as in a blacksmith shop, is another method for hardening steel. Hardened steel is rated at between 7 and 8 on the Mohs scale. It is used for horseshoes, nails and railroad ties.

Lesser Hard Metals

The American Federation of Mineralogical Societies and Jewelry Secrets fill out the lesser hard metals on the scale stating, iron pyrite rates at 6.5 on the Mohs scale. Titanium rates at 6 on the scale. It is used for high-strength uses, including prosthetic legs. Rhodium and chromium steel alloy are also rated at 6 on the Mohs scale. Palladium is at 4.75.
Iron rates between 4 and 5, with pig iron, an alloy made in a blast furnace that contains more than .5% carbon, as the lowest iron at 4.0. Nickel is also rated at 4. Copper, brass and bronze are tied for tenth place at 3.0 on the Mohs scale.

References

• American Iron and Steel Institute; Steelworks; Steel Glossary
• SubTech; Substances and Technology, Carbon Steel; Dr. Dmitri Kopeliovich; 2011
• Physorg; Nanotechnology; Researchers Synthesize Diamond Nanorods; Hardest and Least Compressive Material in the World
• Jewelry Secrets; The Durability and Hardness of Metals; 2011
• Dormer; Hardened Steel Application Group; 2007
• American Federation of Mineralogical Societies: 2011 Mohs Scale of Mineral Hardness