Free Rockwell Hardness Conversion Calculator

Rockwell Hardness Conversion Calculator Overview

The Rockwell hardness conversion calculator is a free online tool designed to simplify the process of converting hardness measurements between different scales. Whether you need to determine the HRB or HRC value from an indentation depth or convert a Rockwell number into its Brinell (HBS) or Vickers (HV) equivalent, this material hardness calculator provides quick and reliable results. By covering multiple scales and material types, it serves as a comprehensive hardness scale converter for engineers, metallurgists, and quality control professionals.

Understanding Rockwell Hardness Testing

Hardness tests evaluate a material's resistance to permanent indentation, typically by pressing a specific indenter—such as a diamond cone or hardened steel ball—into the surface. The Vickers test employs a diamond pyramid, while the Brinell test uses a spherical indenter. The Rockwell method differs by using the depth of indentation rather than the size of the impression, making it a fast and direct reading technique. The result is a dimensionless number that does not incorporate stress units.

The Rockwell Hardness Formula

Rockwell hardness is reported on various lettered scales (A, B, C, D, etc.), with B and C being the most widely used. Scale B is typically employed for softer materials like copper alloys and low‑carbon steel, whereas scale C is suitable for harder materials such as cast iron, titanium, and hardened steel. For all scales, the hardness number is derived from:

$$\text{HR} = N - h \times d$$

where $\text{HR}$ is the hardness number, $N$ and $h$ are scale‑dependent constants, and $d$ is the residual indentation depth measured in millimeters after the major load is removed. For scales B and C, $h = 500$; $N$ equals 130 for scale B and 100 for scale C.

Standards and Procedure

The Rockwell test procedure is governed by ISO 6508 for metallic materials and ISO 2039‑2 for plastics. The process involves applying a preliminary minor load to establish a reference position, then adding a major load held for a specified dwell time, and finally removing the major load. The increase in indentation depth resulting from the major load is used as $d$ in the formula.

Using the Calculator: Two Modes

This calculator operates in two distinct modes:

• Calculate mode: Input the measured indentation depth and select a scale (B or C) to obtain the corresponding Rockwell hardness number.
• Convert mode: Enter a known Rockwell value together with the material type, and the tool outputs the equivalent hardness on the Brinell or Vickers scale. Because conversion relationships depend on the material's elastic recovery properties, the calculator applies the appropriate correlation from the international standard ISO E140, which covers tables for Brinell, Vickers, Rockwell, superficial Rockwell, Knoop, Scleroscope, and Leeb scales.

Step‑by‑Step Examples

Example 1: Computing HRB from Indentation Depth

Suppose a specimen yields an indentation depth of $d = 0.1\ \text{mm}$. In the calculate mode with scale B selected, the calculator performs:

$$\text{HRB} = 130 - 500 \times 0.1 = 80.$$

The result, HRB 80, is displayed instantly.

Example 2: Converting HRB to Brinell and Vickers

For a nickel alloy with HRB 65, choose the convert mode, set material to Nickel and scale B, then enter 65. The calculator returns:

• Brinell hardness (HB): approximately 116;
• Vickers hardness (HV): approximately 117 $\text{kg/mm}^2$.

The data are sourced from the ISO E140 conversion tables.

Typical Hardness Ranges for Common Materials

Although specific values depend on composition and heat treatment, common materials fall within characteristic Rockwell ranges. In particular, brasses exhibit HRB values from roughly 55 (low‑zinc varieties) up to 93 (cartridge brass with about 30% Zn). Tool steels used in blades often show HRC between 55 and 66. These reference ranges help users gauge the plausibility of measured or converted values.