10/12/2010

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Structure and Properties of Materials

Eighth LectureDr. Nahid Abdel Salam

Hardness Testing

The hardness test measures the resistance to

penetration of the surface of a material by a hard

object.

Hardness can represent resistance to scratching or

indentation and a qualitative measure of the

strength of the material.

Hardness numbers are used primarily as a

qualitative basis for comparison of materials,

specifications for manufacturing and heat treatment,

quality control, and correlation with other

properties of materials.

October 12, 2010

ENGR 230

Structure and Properties of Materials

Nahid Abdel Salam2

10/12/2010

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HARDNESS SCALES

There are five major hardness scales:

Brinell - HB

Vickers - HV

Microhardness

Knoop - HK

Rockwell - HR

Shore - HS

October 12, 2010ENGR 230

Structure and Properties of Materials

Nahid Abdel Salam3

Indentors for Hardness Tests

Brinell Rockwell

Hard steel of 10 mm diameter or

tungsten carbide ball

Diamond cone or hardened steel

ball

October 12, 2010

ENGR 230

Structure and Properties of Materials

Nahid Abdel Salam4

10/12/2010

3

Rules of Hardness Test

October 12, 2010ENGR 230

Structure and Properties of Materials

Nahid Abdel Salam5

Brinell Rockwell

A, C, D Diamond cone

B, F, G1/16 in diameter

steel sphere

Where:

P = applied force (kgf)

D = diameter of indenter (mm)

d = diameter of indentation (mm)

E1/8 in diameter

steel sphere

F

1/16 in diameter

steel sphere

Rules of Hardness Test

October 12, 2010ENGR 230

Structure and Properties of Materials

Nahid Abdel Salam

6

1. The indenter moves down

into position on the part

surface

2. A minor load is applied and

a zero reference position is

established

3. The major load is applied

for a specified time period

(dwell time) beyond zero

4. The major load is released

leaving the minor load

applied

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Rockwell Hardness Scales

Scale IndenterMinor Load

F0 (kgf)

Major Load

F1 (kgf)

Total Load

F (kgf)

A Diamond cone 10 50 60

B 1/16" steel ball 10 90 100

C Diamond cone 10 140 150

D Diamond cone 10 90 100

E 1/8" steel ball 10 90 100

F 1/16" steel ball 10 50 60

October 12, 2010ENGR 230

Structure and Properties of Materials

Nahid Abdel Salam7

Comparison

Brinell Rockwell

• HB is related to area of the

impression;

• HB can be obtained in just

a few minutes;

• Virtually no preparation of

the specimen is needed;

• It provides a close

approximation of the

tensile strength;

• Reading needs special

microscope.

• HR is related to the depth

of impression;

• HR cannot be directly

related to strength of

metals and alloys;

• The test is rapid;

• It is easily performed;

• It is popular in industry;

• Optical measurement of

indention dimension is not

needed

October 12, 2010

ENGR 230

Structure and Properties of Materials

Nahid Abdel Salam8

10/12/2010

5

Relation between strength and

Hardness

October 12, 2010ENGR 230

Structure and Properties of Materials

Nahid Abdel Salam9

HB in kg/mm2

σTS in psi