Rockwell Hardness Principles
ROCKWELL HARDNESS PRINCIPLES
Referenced and compiled by Huynh Ngoc Son
Introduction of the Rockwell hardness scale
A scale indicating the hardness of materials. Stanley P. Rockwell invented it and it is first used in 1919. This measurement has no units. The symbol is HR and followed by a letter indicating one of a number of possible scales, described in the table below. The followed numbers are hardness values. For example, “HRC 68” means hardness value is 68 on the Rockwell scale. Rockwell hardness numbers are usually used to describe the hardness of metals. However, they are also used for some kind of plastics.
Rockwell hardness principles
Like the Brinell scale, the Rockwell scale is base on measuring the depth of the indent made by pressing a diamond point, or a ball, into the material.
Unlike the Brinell test, however, the Rockwell test makes two depth measurements:
- The ball was brought in contact with the surface of the material that needs to test. The preliminary test is applied for a set period of time, and then the depth of indentation is measured.
- Then the force is increased at a set rate until it reaches the total force. This force is kept constant for a predetermined period, after which the force is reduced to the preliminary force level. After a set period of time, the depth of the indentation is measured for a second time. Usually, the entire process is carried out by automatic machinery.
Rockwell hardness formulas:
The Rockwell hardness is calculated from the difference between the depth of the indentation after the application of the total force and its initial depth under the preliminary force. Calculate this difference, in millimeters, h.
Then, it the test uses a spheroconical diamond:
If the test uses a ball:
Scale of Rockwell Hardness Tester
Regular Rockwell Scales
A
- Insenter: Spheroconical diamond
- Preliminary force N (kgf): 98.07 (10)
- Total force
N (kgf): 588.4 (60)
Cemented carbides, thin steel, and shallow case hardened steel
B
- Insenter: Bi (mm/inch) 1,588 (1/16″)
- Preliminary force kgf (N): 98.07 (10)
- Total force kgf (N): 980.7 (100)
Copper alloys, soft steels, aluminum alloy, malleable iron, etc.
C
- Insenter: Spheroconical diamond
- Preliminary force kgf (N): 98.07 (10)
- Total force kgf (N): 1471 (150)
Steel, hard cast irons, pearilic malleable iron, titanium, deep case hardened steel, and other materials harder than 100 on the Rockwell B scale
D
- Insenter: Spheroconical diamond
- Preliminary force kgf (N): 98.07 (10)
- Total force kgf (N): 980.7 (100)
Thin steel and medium case hardened steel, and pearlitic bearing metals
E
- Insenter: Ball (mm/inch) 3,175 (1/8”)
- Preliminary force kgf (N): 98.07 (10)
- Total force kgf (N): 980.7 (100)
Cast iron, alumium, and magnesium alloys
F
- Insenter: Ball (mm/inch) 1,588 (1/16″)
- Preliminary force kgf (N): 98.07 (10)
- Total force kgf (N): 588.4 (60)
Annealed copper alloy, and thin soft sheet metals
G
- Insenter: Ball (mm/inch) 1,588 (1/16″)
- Preliminary force kgf (N): 98.07 (10)
- Total force kgf (N): 1471 (150)
Malleable irons, copper-nickel zinc and cupronickel alloys
H
- Insenter: Ball (mm/inch) 3,175 (1/8”)
- Preliminary force kgf (N): 98.07 (10)
- Total force kgf (N): 588.4 (60)
Aluminum, zinc, and lead
Regular Rockwell Scales (continued)
K
- Insenter: Ball (mm/inch) 3,175 (1/8”)
- Preliminary force kgf (N): 98.07 (10)
- Total force kgf (N): 1471 (150)
L
- Insenter: Ball (mm/inch) 6.350 (1/4”)
- Preliminary force kgf (N): 98.07 (10)
- Total force kgf (N): 588.4 (60)
M
- Insenter: Ball (mm/inch) 6.350 (1/4”)
- Preliminary force kgf (N): 98.07 (10)
- Total force kgf (N): 980.7 (100)
P
- Insenter: Ball (mm/inch) 6.350 (1/4”)
- Preliminary force kgf (N): 98.07 (10)
- Total force kgf (N): 1471 (150)
R
- Insenter: Ball (mm/inch) 12,70 (1/2”)
- Preliminary force kgf (N): 98.07 (10)
- Total force kgf (N): 588.4 (60)
S
- Insenter: Ball (mm/inch) 12,70 (1/2”)
- Preliminary force kgf (N): 98.07 (10)
- Total force kgf (N): 980.7 (100)
V
- Insenter: Ball (mm/inch) 12,70 (1/2”)
- Preliminary force kgf (N): 98.07 (10)
- Total force kgf (N): 1471 (150)
Scales K, L, M, P, R, S, V applied to bear metals and other very soft or thin materials. Use the smallest ball and heaviest load that does not give an anvil effect
Rockwell Superficial Scales
15N
- Insenter: Spheroconical diamond
- Preliminary force kgf (N): 29.42 (3)
- Total force kgf (N): 147.1 (15)
30N
- Insenter: Spheroconical diamond
- Preliminary force kgf (N): 29.42 (3)
- Total force kgf (N): 294.2 (30)
45N
- Insenter: Spheroconical diamond
- Preliminary force kgf (N): 29.42 (3)
- Total force kgf (N): 441.3 (45)
The application of the scales 15N, 30N, 45N is similar to A, C, and D scales, but for thinner material or thinner case depth.
15T
- Insenter: Ball (mm / inch) 1,588 (1/16″)
- Preliminary force kgf (N): 29.42 (3)
- Total force kgf (N): 147.1 (15)
30T
- Insenter: Ball (mm / inch) 1,588 (1/16″)
- Preliminary force kgf (N): 29.42 (3)
- Total force kgf (N): 294.2 (30)
45T
- Insenter: Ball (mm / inch) 1,588 (1/16″)
- Preliminary force kgf (N): 29.42 (3)
- Total force kgf (N): 441.3 (45)
The application of the scales 15T, 30T, 45T is similar to B, F and G scales, but for thinner material.
Rockwell Superficial Scales (continued)
15W
- Insenter: Ball (mm / inch) 3,175 (1/8 ”)
- Preliminary force kgf (N): 29.42 (3)
- Total force kgf (N): 147.1 (15)
30W
- Insenter: Ball (mm / inch) 3,175 (1/8 ”)
- Preliminary force kgf (N): 29.42 (3)
- Total force kgf (N): 294.2 (30)
45W
- Insenter: Ball (mm / inch) 3,175 (1/8 ”)
- Preliminary force kgf (N): 29.42 (3)
- Total force kgf (N): 441.3 (45)
15X
- Insenter: Ball (mm / inch) 6.350 (1/4 ”)
- Preliminary force kgf (N): 29.42 (3)
- Total force kgf (N): 147.1 (15)
30X
- Insenter: Ball (mm / inch) 6.350 (1/4 ”)
- Preliminary force kgf (N): 29.42 (3)
- Total force kgf (N): 294.2 (30)
45X
- Insenter: Ball (mm / inch) 6.350 (1/4 ”)
- Preliminary force kgf (N): 29.42 (3)
- Total force kgf (N): 441.3 (45)
15Y
- Insenter: Ball (mm / inch) 12,70 (1/2 ”)
- Preliminary force kgf (N): 29.42 (3)
- Total force kgf (N): 147.1 (15)
30Y
- Insenter: Ball (mm / inch) 12,70 (1/2 ”)
- Preliminary force kgf (N): 29.42 (3)
- Total force kgf (N): 294.2 (30)
45Y
- Insenter: Ball (mm / inch) 12,70 (1/2 ”)
- Preliminary force kgf (N): 29.42 (3)
- Total force kgf (N): 441.3 (45)
The scales 15W, 30W, 45W, 15X, 30X, 45X, 15Y, 30Y, 45Y were applied to very soft materials.
Rockwell hardness principles are referenced from the following documents:
1. ASTM E 18 – 2000, Standard Test Methods for Rockwell Hardness and Rockwell Superficial Hardness of Metallic Materials.
2. ISO 6508-1 Metallic Materials – Rockwell hardness test (scale A, B, C, D, E, F, G, H, K, N, T) – Part 1: Test Methods, 1999-09-01.
3. ISO 6508-2 Metallic Materials – Rockwell hardness test (scale A, B, C, D, E, F, G, H, K, N, T) – Part 2: Verification of testing machines, 1999-09-01.
4. ISO 6508-3 Metallic Materials – Rockwell hardness test (scale A, B, C, D, E, F, G, H, K, N, T) – Part 3: Calibration of reference blocks, 1999-09-01.
Types of Future-Tech Rockwell Hardness Tester
- Rockwell Hardness Tester FR-X series FR-X1, FR-X1L, FR-X2, FR-X2L, FR-X3, FR-X3L
- Analog Rockwell Hardness Tester FR-XA series
