Metal hardness testing: Methods and scales

Metal hardness is a property of a metal that describes the ability of a material to resist local plastic deformation.

It’s easy to assume that all metals are hard, but there are quirky ones like mercury – which is liquid at room temperature and doesn’t even have a rigidity value – and sodium metals, which you can cut with a kitchen knife.

There are several different scales and systems for measuring metal rigidity. In this article, we provide an overview of these measurement systems.

Mohs rigidity

Speaking of hardness, most people are familiar with the Morse scale. The system determines hardness based on surface wear – scraping one material against another. If material A can scratch material B, then material A is harder than B.
This scale is used almost exclusively for minerals and gemstones, but can also be used for metals.
Rigidity of metal (Mohs)
Sodium 0.5
In 1.5
Tin 1.5
Aluminum 2.75
Copper 3.0
Bronze 3.0
Brass 3.0
The iron 4.0
Steel 4.0
Cobalt 5.0
Titanium 6.0
Tungsten 7.5
Tungsten carbide 9.0

Rockwell rigidity

Rockwell rigidity method was used to compare two indentation on the material. One is made with a small load and the other with a large load.
A unique characteristic of Rockwell rigidity is that it is linearly dependent on the tensile strength of the material; Rockwell rigidity is usually used for harder materials.
Metal rigidity (Rockwell rigidity)
Sodium –
Lead to 5
Tin –
Aluminum 20 to 25
Copper 10
Bronze 42
Brass 55
The iron 86
Steel 60
Cobalt 70
Titanium, 80
Tungsten 66
Tungsten carbide 75

Brinell hardness

This Brinellrigidity scale is a widely accepted method of measuring the rigidity of materials. It involves pressing a ball of steel (or a harder material of tungsten carbide) into the specimen with a constant and known force. The softer the material, the deeper the ball penetrates, and vice versa.
The next step is to measure the diameter of the resulting indentation and then perform calculations, usually in megapascals, to determine the Brinell rigidity scale.
Typical Brinell rigidity values for several common materials and metals are as follows:
Rigidity of material (Brinell hardness)
Sodium 0.69
In 5.0
Tin 62
Aluminum 15
Copper 35
bronze
brass
Iron, 200-1180
Steel 120
Cobalt 1265
Titanium, 716-2700
Tungsten. 2000-4000
Diamond 8000

Vickers rigidity

The Vickers hardness scale uses a square pyramidal diamond to imprint the material. Then we measure impressions; The size of the indentation determines how deep it is pressed into the material. A formula is then applied to determine the hardness of the material.
One advantage here is that the width of the square indentation is easier to measure than the circle. This means that you can use the same formula (regardless of indenter size) and the same indenter for all material types, unlike many other methods.
Rigidity of metal (Vickers hardness)
sodium
Lead to
tin
Aluminum. 160-350
Copper 343-369
Bronze 250
brass
The iron 608
Iron and steel
Cobalt 1043
Titanium, 830-3420
Tungsten. 3430-4600
Tungsten carbide 2600

The challenge of measuring metal hardness

Rigidity is not an inherent property of materials.
What does that mean? Unlike the melting point, it varies from sample to sample. This is especially true for metals like iron, which can come in many different forms.
Therefore, different methods will produce different results for the same material. It’s not uncommon to see wide differences in metal hardness values on the Internet; Hardness values for many metals under these different tests are not always published or even available.
We should note that there are conversion tables that can be used to convert between one hardness scale method and another.
Other major hardness tests not specifically listed here include Knoop and Shaw hardness.

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