Rockwell Hardness Conversion Calculator

The Rockwell hardness conversion calculator is the tool when you are looking to calculate or convert the hardness numbers across various scales. The hardness tests help evaluate a material's resistance to plastic deformation. You can do this by pressing a small ball or a cone onto the surface of the specimen. The balls or cones are usually made up of diamond or steel and are called indenters.

There are different types of tests, and they have different scales depending upon the type of load and indenter you are using. For instance, we use a diamond shape indenter to conduct a vickers hardness test (see vickers hardness number calculator), whereas a spherical indenter is used for the brinell hardness test (cf. Brinell hardness number calculator).

In the present article, we cover how to calculate Rockwell hardness and how we can convert it to different hardness scales. The calculator has two modes; you can either choose to calculate the Rockwell hardness or convert it to a different scale.

Rockwell hardness test uses the depth of penetration of the indenter to tell you a material specimen's hardness number. There are different Rockwell hardness scales such as A, B, C, D, etc. The most common ones are B and C. The scales vary as per the material of the specimen, loading force, and the indenter type and size. Unlike the Vickers hardness number, the Rockwell hardness does not use the units of stress and is dimensionless. Refer to our stress calculator for more on stresses.

The hardness scale B is primarily helpful to test copper alloys and soft steel plates, whereas we use the C scale for materials like cast iron and titanium. For any hardness scale, the hardness number is given by the equation:

where:

• $\text{HR}$ – Hardness number;
• $N$, $h$ – Scale factors; and
• $d$ – Depth of penetration (in $\text{mm}$).

Here, the $h$ value is $500$ for scales B and C. The $N$ value is 130 and 100 for scales B and C, respectively.

The test procedure for the Rockwell hardness test is covered in the standard document ISO 6508 for metallic materials and ISO 2039-2 for plastics. The overall procedure is similar to other indentation tests. The indenter is pressed into the material, loaded for a time interval (dwell time), and unloaded. The indentation depth is measured, and the above equation is used to calculate the hardness number.

The calculator has two modes — calculate and convert. The calculate mode is helpful if you have the indentation depth and want the Rockwell hardness number for either scale B or C. The convert mode is for converting Rockwell hardness numbers to a different scale like Brinell or Vickers.

The hardness data can not be presented in terms of a universal conversion formula; therefore, you need to pick a material, and based on that, the calculator applies the appropriate equation.

The conversion data relationships are adopted from the international standard document ISO E140 titled Standard Hardness Conversion Tables for Metals Relationship Among Brinell Hardness, Vickers Hardness, Rockwell Hardness, Superficial Hardness, Knoop Hardness, Scleroscope Hardness, and Leeb Hardness.

Let's calculate the Rockwell hardness B number for a specimen having an indentation depth $0.1 \text{ mm}$.

To calculate Rockwell hardness:

1. Set the calculator mode to calculate.
2. Pick a Hardness scale as B.
3. Enter the indentation depth, $d = 0.1\text{ mm}$.
4. The Rockwell hardness calculator will return the hardness number (HRB) as $80$.

Let's perform conversion of Rockwell hardness number, HRB = 65, for nickel to Brinell and Vickers hardness scale.

To convert Rockwell hardness:

1. Set the calculator mode to convert.
2. Select the material as Nickel.
3. Pick a Rockwell hardness scale as B.
4. Enter the Rockwell hardness number, $\text{HRB} = 65$.
5. The Rockwell hardness conversion calculator will return the Brinell and Vickers hardness numbers as $116$ and $117 \text{ kg/mm}^2$, respectively.

To calculate Rockwell hardness B number:

1. Multiply scale factor, 500, by depth of penetration, d.

2. Subtract the product from the scale factor 130 to obtain the Rockwell hardness B (HRB) number. Mathematically, this is:

   HRB = 130 - 500 × d.

To calculate Rockwell hardness C number:

1. Multiply scale factor, 500, by depth of penetration, d.

2. Subtract the product from the scale factor 100 to obtain the Rockwell hardness (HRC) number. Mathematically, that's:

   HRB = 100 - 500 × d.

The Rockwell hardness number (B) for brass lies in the range of 55 to 93 depending upon the composition of the alloy. Cartridge brass contains about 30% zinc by weight and has an HRB of about 93, whereas low brass has an HRB of around 55.

The steel used to make knives (such as tool steel) has a Rockwell hardness on scale C (HRC) higher than 55 and up to 66. However, the Rockwell hardness number for steel varies depending on composition.