What is the Rockwell Hardness Scale?

Understanding the physical properties of metals is crucial to effectively utilising them, and ensuring manufactured components are fit for purpose. Alongside tensile strength and ductility, the hardness of a metal often is critical to its successful application in an assembly.

In this article, we explain what tests are used to measure hardness, and why the Rockwell Hardness Scale is one of the most commonly used units of hardness.

What is Hardness in Metals?

Metal hardness is a physical property of a material, it refers to the material’s resistance to abrasion and indentation from impact and wear. There are a few different ways to measure hardness, including the Rockwell, Vickers and Brinell scales.

Hardness varies greatly between metals, with some being extremely soft, such as Lead, and some having a very high hardness rating, such as Tungsten.

What is the Rockwell Hardness Scale?

Rockwell hardness is one of the most commonly used hardness scales and involves pressing a hardened indenter into a coupon of the material to be tested. A Rockwell hardness figure can be given from the data captured.

The Rockwell hardness test is unique in that it applies two levels of load to the indentation tool, creating a pre-load and main load pressure, this helps to eliminate variations in the material surface finish and provide accurate results.

The test and resultant figures are dependent on the scale used too, there are many Rockwell hardness scales, the most commonly used ones for steel and similar metals are Rockwell B and Rockwell C, the unit for each HRB and HRC respectively.

Using multiple scales allows for a wide range of materials to be tested, including differing hardnesses, thicknesses and heat treatment levels.

The below table shows the first 5 Rockwell scales and their uses. There are 17 scales in total, each covering a slightly different range of hardnesses and material types.

How to Read Rockwell Hardness Values?

Rockwell hardness values are used to define and convey the hardness of a metal, with the higher the number the higher the hardness, but when reading Rockwell hardness numbers, you must take into account the scale used.

As the table above shows, there are a number of different scales, so in order to compare two materials, ensure the scales are the same. For instance, 65 HRC may be harder than 70 HRB, and vice versa.

Typical Rockwell Hardness of Metals

As the most prominent method of measuring hardness, the Rockwell scale is useful for comparing materials if they need to be resistant to wear or abrasion. Here are some examples of metal hardness values:

Other Ways to Measure Hardness

The Rockwell process is not the only way to measure and test a material’s resistance to wear and abrasion, due to the nature of the test it is not applicable to all materials and components, thankfully there are a number of other methods:

Mohs Hardness

Mostly used for minerals and gemstones, instead of using a calibrated machine, the Mohs hardness test compares materials against each other, e.g. if one material can indent or scratch another, it is deemed harder than it. Mohs hardness tests can be very easy to carry out but do not give as precise data as other methods.

Vickers Hardness

Usable for both macro and micro hardness testing, the Vickers test uses a slightly different apparatus to indent a sample with a pyramid-shaped indenter, using the same force each time, the indentation left behind is measured and used to determine the hardness of the material.

The Vickers test is harder to carry out and read when compared to the Rockwell test and is traditionally used on harder materials such as carbides and ceramics.

Brinell Hardness

In a similar way to the Vickers test, the Brinell test indents the material using a hardened sphere, the indentation is then measured in both directions, and the size of the indentation correlated to a hardness level.

The nature of the indenting shape means variations in the surface finish affect the end result less and allow the method to be used on parts produced by casting or forging.

Get the Right Metal for Your Project at Metals Supermarkets

For more information on metal hardness, check out our guide, which covers all the measuring systems in depth. If you’re ready to order your material, find exactly the type, size and shape of metal online, or collect from one of our nationwide stores.