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Rockwell Hardness

Rockwell hardness is a measure of the resistance of a material to permanent indentation under a specific static load. It is defined based on the depth of indentation produced by a penetrator (either a diamond cone or a hardened steel ball) under two sequential loads: an initial minor load and a major load.

UnitedTest Rockwell Hardness Testing Machine

Feature:

  • Rockwell & Superficial Rockwell
  • Touching screen

Key parameter:

  • Force: 150kg and 45kg
  • Max. height: 300mm
Details

Feature:

  • Rockwell & Superficial Rockwell
  • Touching screen

Key parameter:

  • Force: 150kg and 45kg
  • Max. height: 220mm
Details

Touching Screen Rockwell Durometer

Model: HRS-150, HRMS-45

Feature:

  • Rockwell
  • Touching screen

Key parameter:

  • Force: 150kg
  • Max. height: 200mm
Details

Feature:

  • Rockwell & Superficial Rockwell
  • Dial needle scale, motorized loading

Key parameter:

  • Force: 150kg and 45kg
  • Max. height: 200mm, 380mm available.
Details

Feature:

  • Rockwell & Superficial Rockwell
  • Dial needle scale

Key parameter:

  • Force: 150kg and 45kg
  • Max. height: 200mm
Details

What's Rockwell hardness test?

Rockwell hardness is a measure of the resistance of a material to permanent indentation under a specific static load. It is defined based on the depth of indentation produced by a penetrator (either a diamond cone or a hardened steel ball) under two sequential loads: an initial minor load and a major load.


Unlike Brinell or Vickers hardness (which rely on indentation area), Rockwell hardness is expressed as a numerical value combined with a scale symbol (e.g., HRC, HRB). The higher the value, the harder the material (with exceptions for some soft materials on specific scales).

Rockwell Hardness Test: Principle

The Rockwell hardness test follows a standardized, four-step process, with its core principle centered on indentation depth difference measurement:

1, Apply initial minor load (preload)

  1. A small fixed load (usually 10 kgf) is first applied to the penetrator. This step eliminates surface irregularities and ensure the penetrator is in stable contact with the test sample, establishing a reference depth position (zero point for depth measurement).

2, Apply major load

  1. After the initial load is stabilized, the major load is added (the total load = minor load + major load). The penetrator presses further into the material, causing plastic deformation.

3, Remove the major load (retain minor load)

  1. The major load is removed, while the minor load remains. The material will undergo elastic recovery, reducing the indentation depth slightly.

  2. Measure the residual indentation depth

    The key measurement is the permanent indentation depth increment (denoted as e) after elastic recovery. The Rockwell hardness value is calculated using the formula:

    • K = constant (100 for diamond cone penetrators, 130 for steel ball penetrators)

    • e = residual indentation depth increment (in mm)

    • The denominator 0.002 means each Rockwell hardness unit corresponds to a 0.002 mm change in indentation depth.


Common Penetrators and Loads (Typical Scales):


Rockwell Scale   

Penetrator 

Total Load      

Application Scope

HRC

120° diamond cone     

150 kgf

Hardened steels, alloys (hard materials)

HRB

1.588 mm steel ball

100 kgf

Mild steels, copper alloys, aluminum   alloys (medium-soft materials)

HRA

120° diamond cone

60 kgf

Thin hard materials, surface-hardened   layers, cemented carbides


Applications of Rockwell Hardness Test

The Rockwell test is one of the most widely used hardness testing methods in industrial and laboratory settings, thanks to its speed, simplicity, and non-destructive nature (indentations are small). 


Key applications include:

  • Metal manufacturing and processing: Quality control of steel, aluminum, copper, and their alloys. For example, testing the hardness of quenched and tempered steel parts (HRC scale), or checking the hardness of cold-rolled steel sheets (HRB scale).

  • Surface treatment evaluation: Measuring the hardness of surface-hardened layers (e.g., carburized, nitrided layers) using the HRA or superficial Rockwell scales (e.g., HR15N, HR30N).

  • Tool and die industry: Verifying the hardness of cutting tools, molds, and wear-resistant components to ensure service life.

  • Aerospace and automotive sectors: Testing critical components like engine parts, gears, and shafts to confirm they meet design hardness requirements.

  • Research and development: Comparing the hardness of new materials or evaluating the effect of heat treatment processes on material hardness.


Standards for Rockwell Hardness Test

Standards specify test procedures, equipment requirements, sample preparation, and data interpretation to ensure accuracy and repeatability across different laboratories.

ASTM Standards

  • ASTM E18: Standard Test Methods for Rockwell Hardness and Rockwell Superficial Hardness of Metallic Materials

    This is the most authoritative standard for Rockwell testing in North America. It covers:

    • Requirements for test machines (load accuracy, indentation depth measurement precision).

    • Sample preparation (surface flatness, thickness—samples must be thick enough to avoid indentation through the material).

    • Procedures for different scales (HRC, HRB, HRA, superficial scales).

    • Acceptance criteria and error correction methods.

ISO Standards

  • ISO 6508: Metallic materials — Rockwell hardness test

    This is the international counterpart to ASTM E18, divided into three parts:

    • ISO 6508-1: Test method, principles, and definitions.

    • ISO 6508-2: Verification and calibration of test machines.

    • ISO 6508-3: Calibration of reference blocks.

      ISO 6508 aligns with most of ASTM E18’s technical requirements, with minor differences in terminology and some test parameters (e.g., load application time).

Superficial Rockwell Standards:

For thin materials or shallow surface layers, superficial Rockwell tests are used (lower loads: 15, 30, 45 kgf). Corresponding standards include:
  • ASTM E18 (includes superficial scales)

  • ISO 6508-1 (covers superficial Rockwell methods)


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