National Physical Laboratory

Rockwell Hardness

In the Rockwell hardness test [8] either a 120° diamond cone with a 0,2 mm radius spherical tip or a ball indenter of a specified diameter is pressed into the surface of the test piece using a two step application - a preliminary test force F0 followed by an additional test force F1. The preliminary test force is applied and maintained for a duration that does not exceed 3 s and an indenter depth reading is recorded. The increase in force to the total test force F then occurs in between 1 s and 8 s. This force is maintained for a duration of 4 s ± 2 s, and the additional force is then removed. While the preliminary test force is still applied, a second indenter depth reading is made after a short stabilisation time. The Rockwell hardness value is calculated as:

Rockwell hardness = N - h/S

where:  h = the permanent increase in penetration depth at the preliminary test force, in mm
 N and S are constants specific to the scale (see Table 1)

Table 1 lists the various Rockwell scales covered by the ISO standard [8]. Also included in the table are additional Rockwell scales covered by the ASTM standard [2], the shading indicating these. The most commonly used scales are HRB, HRC, HR30N, and HR30T.

Table 1. Rockwell hardness scales

Scale N S Indenter Preliminary test force, F0 / N Total test force, F / N Application areas
HRA 100 0,002 Diamond cone 98,07 588,4 Sheet steel, shallow case-hardened
HRB 130 0,002 Ball 1,587 5 mm dia. 98,07 980,7 Copper and aluminium alloys, annealed low-carbon steels
HRC 100 0,002 Diamond cone 98,07 1 471 Hardened steels, cast irons, deep case-hardened
HRD 100 0,002 Diamond cone 98,07 980,7 Thin but hard steel, medium depth case-hardened
HRE 130 0,002 Ball 3,175 mm dia. 98,07 980,7 Cast iron, aluminium, magnesium, and bearing metals
HRF 130 0,002 Ball 1,587 5 mm dia. 98,07 588,4 Annealed copper alloys, thin soft sheet materials
HRG 130 0,002 Ball 1,587 5 mm dia. 98,07 1 471 Malleable cast irons, phosphor bronze, gunmetals, copper nickel alloys
HRH 130 0,002 Ball 3,175 mm dia. 98,07 588,4 Soft materials, high ferritic alloys, aluminium, lead, zinc
HRK 130 0,002 Ball 3,175 mm dia. 98,07 1 471 Aluminium and magnesium alloys
HRL 130 0,002 Ball 6,350 mm dia. 98,07 588,4 Thermoplastics
HRM 130 0,002 Ball 6,350 mm dia. 98,07 980,7 Thermoplastics
HRP 130 0,002 Ball 6,350 mm dia. 98,07 1 471 Thermosetting plastics
HRR 130 0,002 Ball 12,70 mm dia. 98,07 588,4 Very soft plastics and rubbers
HRS 130 0,002 Ball 12,70 mm dia. 98,07 980,7 -
HRV 130 0,002 Ball 12,70 mm dia. 98,07 1 471 -
HR15N 100 0,001 Diamond cone 29,42 147,1

Range of hardness tests used when measuring the hardness of thin sheets, foils, coatings, surface heat treatments, and polymers including their surface treatments.

These scales are also known as Superficial Rockwell hardness scales.

HR30N 100 0,001 Diamond cone 29,42 294,2
HR45N 100 0,001 Diamond cone 29,42 441,3
HR15T 100 0,001 Ball 1,587 5 mm dia. 29,42 147,1
HR30T 100 0,001 Ball 1,587 5 mm dia. 29,42 294,2
HR45T 100 0,001 Ball 1,587 5 mm dia. 29,42 441,3
HR15W 100 0,001 Ball 3,175 mm dia. 29,42 147,1
HR30W 100 0,001 Ball 3,175 mm dia. 29,42 294,2
HR45W 100 0,001 Ball 3,175 mm dia. 29,42 441,3
HR15X 100 0,001 Ball 6,350 mm dia. 29,42 147,1
HR30X 100 0,001 Ball 6,350 mm dia. 29,42 294,2
HR45X 100 0,001 Ball 6,350 mm dia. 29,42 441,3
HR15Y 100 0,001 Ball 12,70 mm dia. 29,42 147,1
HR30Y 100 0,001 Ball 12,70 mm dia. 29,42 294,2
HR45Y 100 0,001 Ball 12,70 mm dia. 29,42 441,3
Last Updated: 25 Mar 2010
Created: 18 Jun 2007