ASTM E18-Rockwell Hardness Testing

Standard Test Methods for Rockwell Hardness of Metallic Materials

ASTM E18 specifies the procedures for determining the Rockwell hardness and Rockwell superficial hardness of metallic materials using standard and nonstandard test methods.

It is applicable to a wide range of products:

Bars, rods

Plates, sheets

Tubes and wires

Castings and forgings

1. What is Rockwell Hardness?

Rockwell Hardness is a non-destructive indentation hardness test that measures the depth of penetration of an indenter under a specific load.

There are multiple Rockwell scales, depending on:

Material hardness (soft metals vs. hard alloys)

Thickness of the specimen

Indenter type (steel ball or diamond cone)

2.Common Rockwell Scales

For titanium alloys (e.g., Gr 5 / Ti-6Al-4V), Rockwell C scale (HRC) is commonly used.
For CP titanium (Gr 1–4), HRB or HRF may be more appropriate depending on hardness.

3. Equipment Requirements

Indenter: Diamond cone (Brale) or steel ball (1/16", 1/8", 1/4")

Load System: Applies minor (10 kgf) + major (60, 100, or 150 kgf) loads

Hardness Tester Machine: Must meet precision, alignment, and force application specs

Calibration Blocks: Certified reference blocks for periodic verification

4. Testing Procedure Summary

Prepare the surface-Flat, clean, and smooth (no oil, scale, or defects).

Place sample on anvil-Ensure good contact and stability.

Apply minor load (10 kgf)-Set zero reference.

Apply major load (60, 100, or 150 kgf)-Held for dwell time (typically 2–6 seconds).

Remove major load-Read depth increase from minor load.

Read Rockwell value-Direct reading from machine scale.

5. Sample Thickness & Indentation Rules

Minimum thickness: At least 10×the depth of indentation.

Spacing from edge: At least 2.5×the diameter of the indentation.

Spacing between indentations: At least 3×the diameter of the indentation.

6. Acceptance Criteria and Reporting

Test reports should include:

Rockwell hardness scale and value (e.g., 36 HRC)

Indenter type and applied loads

Test location and orientation (if relevant)

Number of tests and average value

Material designation (e.g., Ti Gr5)

Calibration verification info (optional but recommended)

7. Example Results (Titanium Alloys)

Note: Actual hardness varies based on processing, heat treatment, and thickness.

8. Related Standards

Standard  Description

ASTM E384-Microhardness testing (Vickers, Knoop)

ASTM E10-Brinell hardness testing

ASTM E92-Vickers hardness testing

ISO 6508-International Rockwell hardness equivalent

9.Applications of ASTM E18

Quality assurance and mill certification

Material comparison (e.g., alloy vs. CP titanium)

Heat treatment verification

Surface hardness control after forming/machining