Rockwell Superficial Hardness Test

The Rockwell Superficial hardness test method consists of indenting the test material with a diamond cone (N scale) or hardened steel ball indenter. The indenter is forced into the test material under a preliminary minor load F0 (Fig. 1A) usually 3 kgf. When equilibrium has been reached, an indicating device that follows the movements of the indenter and so responds to changes in depth of penetration of the indenter is set to a datum position. While the preliminary minor load is still applied an additional major load, is applied with resulting increase in penetration (Fig. 1B). When equilibrium has again been reach, the additional major load is removed but the preliminary minor load is still maintained. Removal of the additional major load allows a partial recovery, so reducing the depth of penetration (Fig. 1C). The permanent increase in depth of penetration, e, resulting from the application and removal of the additional major load is used to calculate the Rockwell Superficial hardness number.

HR = E - e

F0 = preliminary minor load in kgf
F1 = additional major load in kgf
F = total load in kgf
e = permanent increase in depth of penetration due to major load F1, measured in units of 0.001 mm
E = a constant of 100 units for diamond and ball indenters
HR = Rockwell hardness number
D = diameter of steel ball

Larger View

Fig. 1.Rockwell Principle

Fig. 1 Rockwell Superficial Principle

Rockwell Superficial Hardness Scales

Scale	Indenter Type	Minor Load F0 kgf	Major Load F1 kgf	Total Load F kgf	Value of E
HR 15 N	N Diamond cone	3	12	15	100
HR 30 N	N Diamond cone	3	27	30	100
HR 45 N	N Diamond cone	3	42	45	100
HR 15 T	1/16" steel ball	3	12	15	100
HR 30 T	1/16" steel ball	3	27	30	100
HR 45 T	1/16" steel ball	3	42	45	100
HR 15 W	1/8" steel ball	3	12	15	100
HR 30 W	1/8" steel ball	3	27	30	100
HR 45 W	1/8" steel ball	3	42	45	100
HR 15 X	1/4" steel ball	3	12	15	100
HR 30 X	1/4" steel ball	3	27	30	100
HR 45 X	1/4" steel ball	3	42	45	100
HR 15 Y	1/2" steel ball	3	12	15	100
HR 30 Y	1/2" steel ball	3	27	30	100
HR 45 Y	1/2" steel ball	3	42	45	100

Rockwell superficial scales are used to test materials too thin or small for the regular scales or outside the regular ranges. Generally Diamond Indenters are used for hard materials while Ball Indenters are used on soft materials. The HR 15 N scale is useful for testing hard thermal spray coatings like ceramics and carbides, while at the other extreme the HR 15 Y scale is used to test very soft abradable coatings.

Hardness Conversion Tables and Charts:

Gordon England Independent Thermal Spray Coating Consultant

Telephone: +44 (0)1252 405186

Email: tsc@gordonengland.co.uk

Site Links

Introducing

Nature of Thermal Spray Coatings

Surface Engineering in a Nutshell

Surface Engineering Forum

Thermal Spray Gun Repair Service

Plasma Consumable Parts

Thermal Spray Powder Supplies

Applications:

Thermal Spray Coatings on Carbon and Glass Fibre Reinforced Polymers

HVOF Coating of Paper Making Roll

Abradable Coatings

Photomicrographs

Rockwell Superficial Hardness Test

Links To:

Hardness Conversion Tables and Charts:

Site Links