laboratory 2 hardness test of materials -...

MME222/Jan 17 Term/Expt. 02: Hardness Testing of Materials of 12

Department of Materials and Metallurgical Engineering

Bangladesh University of Engineering and Technology, Dhaka

MME222 Materials Testing Sessional 1.50 Credits

January 2017 Term

Laboratory 2

Hardness Test of Materials

1. Objective

Hardness is usually defined as resistance to cause localise permanent deformation in material. Hardness,

however, is not a fundamental property of material, because the resistance to indentation depends on the

shape of the indenter and on the load applied. This laboratory experiment is designed to introduce the

principles of different methods of hardness testing, emphasizing the limitations and significance of the

results in each method.

After completion of this experiment, students should be able to

1.1 understand the principles of a different methods of hardness testing and gain their practices on

operating the hardness testing machines to achieve the required hardness value following a specific

standard,

1.2 estimate the tensile properties of materials from their hardness values.

2. Materials and Equipment

2.1 Hardness specimens

2.2 Automatic Rockwell hardness tester

2.3 Automatic Brinell hardness tester and Brinell microscope

2.4 Automatic Vickers (Microhardness) hardness tester

2.5 Different indenters

3. Experimental Procedure

3.1 Rockwell hardness testing

3.1.1 Keep the loading and unloading lever at the unloading position.

3.1.2 Select the suitable indenter and weights according to the scale.

3.1.3 Fix the indenter in the hardness tester and switch ON the power supply of the machine. Place the

specimen on testing table anvil.

3.1.4 Turn the hand wheel clockwise to raise a job until it makes contact with indenter and continue

turning till the dial gauge reads between 290 and 299 and the SET indicator becomes lighted. This

indicates that the ‘minor load’ (usually 10 kg) is now applied to the indenter.

3.1.5 Press the button START to apply the ‘major load’ (usually 60, 100 or 150 kg depending on the scale

selected). The dial readings will continue changing and, after about 15 second intervals, the reading

will become stationary and OK indicator will be lighted.

3.1.6 Note down the reading.

3.1.7 Turn back the hand wheel anti-clockwise and remove the job.

3.1.8 Similarly repeat the step from 3.1.1-3.1.8 for different trials and for different samples.

3.1.9 Complete Data Sheet 2.1.


3.2 Brinell hardness testing

3.2.1 Keep the loading and unloading lever at the unloading position.

3.2.2 Fix the indenter in the hardness tester and switch ON the power supply of the machine. Select the

suitable load and dwell time according to the scale.

3.2.3 Place the specimen on testing table anvil.

3.2.4 Turn the hand wheel clockwise to raise a job until it makes contact with indenter and continue

turning till the load indicator becomes green.

3.2.5 The load will now be applied on to the sample by the machine and when the full load is applied,

time will start counting.

3.2.6 After the application of load for the required amount of time, the orange indicator will lid indicating

unloading. Turn back the hand wheel anti-clockwise to remove the job.

3.2.7 Read the diameter of the indentation using Brinell microscope and using appropriate formula

calculate BHN.



3.3 Vickers hardness testing

3.3.1 Clean and polish the surface of the specimen.

3.3.2 Select the load using manual handle (from 1 to 50 kg). Switch ON the power supply.

3.3.3 Place the specimen with cleaned surface facing the indenter on the anvil at the work table.

3.3.4 Focus the work piece surface for clean visibility by rotating the hand wheel at the work table

upwards and downwards. Once focused, remove the lens and move the indicator at the top of the

sample.

3.3.5 Set the dwell time and press RESET to erase previous history of data from the machine memory.

Press START to apply load. After the pre-set dwell time, the indicator will move automatically and

the lens will move at the top of the sample.

3.3.6 For the first reading, D1, of the indentation, adjust the display at the indentation made by the

indenter to coincide with the micrometer on the display screen. Press READ to store the first

reading of the indentation. For the second reading, D2, of the indentation, rotate the micrometer

head to 90 degrees and press READ again to store the second reading of the indentation.

3.3.7 The measurement is to be made for two opposite corners of the diagonal indentation. Using

appropriate formula calculate VHN.



4. Results

4.1 List hardness values and determine the average hardness number of each specimen. Compare your

result with those published in reference book.

4.2 Predict the tensile strength of steel sample from its hardness value.

5. Discussion

5.1 Answer the following questions:

(a) How do the Rockwell and Brinell tests actually measure hardness? Give any appropriate sketches

and formulae. Are there any units involved? Explain the reason for the pre-load applied in the

procedure for the Rockwell test.


(b) What is the limitation on the thickness of specimens for a hardness test? Explain. Calculate the

minimum thickness for one specimen for the Rockwell test and one for the Brinell test.

(c) What are the limitations for distance from specimen edge to indentation and distance between

indentations? Explain why these limitations exist in both cases.

(d) What surface condition is necessary for Brinell, Rockwell and Vickers?

(e) What are the advantages of Vickers test against Brinell test? Of Brinell test against Rockwell test?

(f) Would you suggest conducting Rockwell-Type hardness tests on ceramic or polymeric materials?

Why or why not?


Table 2.1: Data Sheet for Rockwell Hardness Number

Material Type of Indenter Rockwell Hardness

Number

Average Rockwell

Hardness Number

1

2

3

4

5

Table 2.2: Data Sheet for Brinell Hardness Number

Material Diameter of

Indenter, D

Applied

Load, F

Diameter of

Indentation, d

Average Diameter

of Indentation

Average Brinell

Hardness Number

mm kgf mm mm BHN

1

2

3

4

5

Table 2.3: Data Sheet for Vickers Hardness Number

Material Applied

Load, F

Length of Indentation Vickers Hardness

Number

Average Vickers

Hardness Number D1 D2 Average D

kgf mm mm mm VHN VHN

1

2

3

4

5


6. Theoretical Background

6.1 Introduction

Hardness is a measure of a material’s resistance to localized plastic deformation (by scratching or

indentation). Methods to characterize hardness can be divided into three primary categories:

1. Scratch Tests. These are the simplest form of hardness tests. In this test, various materials are rated

on their ability to scratch one another. If two materials are compared, the harder one is capable of scratching the softer one, but not vice versa. Mohs hardness test is of this type. This test is used mainly

in mineralogy.

2. Dynamic Hardness or Rebound Tests. Here an object of standard mass and dimensions is bounced

back from the surface of the test specimen after falling by its own weight. The hardness number is proportional to the height of rebound of the standard mass. Shore hardness is measured by this method.

3. Static Indentation Tests. Test tests are based on the relation of indentation of the specimen by a

penetrator under a given load. The relationship of total test force to the area or depth of indentation

provides a measure of hardness; the softer the material, the larger and deeper the indentation, and the

lower the hardness index number. The Rockwell, Brinell, Knoop, Vickers, and ultrasonic hardness

tests are of this type. For engineering purposes, static indentation tests are mostly used, Fig. 6.1.

Figure 6.1: General characteristics of hardness-testing methods and formulas for calculating hardness.

Indentation tests actually produce a permanent impression in the surface of the material. The force and size

of the impression can be related to a quantity (hardness) which can be objectively related to the resistance

of the material to permanent penetration. Because the hardness is a function of the force and size of the

impression, the pressure (and hence stress) used to create the impression can be related to both the yield

and ultimate strengths of materials. For materials that undergo plastic deformation primarily via slip (e.g.,

metals for which dislocation motion requires shear stress), it has been demonstrated empirically and by

“slip line theory” that:

𝐻 ~ 3 𝜎𝑦 (6.1)


Thus, as hardness increases so does the yield strength and the ultimate tensile strength. For this reason,

specifications often require the results of hardness tests rather than tensile tests.

Several different types of hardness tests have evolved over the years. These include macro hardness test

such as Brinell, Vickers, and Rockwell and micro hardness tests such as Knoop and Tukon. Rockwell and

Brinell testing is the most commonly applied materials test in industry due to several factors:

1. Simple to perform and does not require highly skilled operators;

2. Through the use of different loads and indenters, hardness testing can be used for determining the

hardness and approximate strength of most metals and alloys including soft bearing materials and

high strength steels;

3. Hardness readings can be taken in a few seconds with minimal preparation; and

4. For Rockwell hardness testing, no optical measurements are required; all readings are direct.

Factors influencing hardness include microstructure, grain size, strain hardening, etc. Measured hardnesses

are only relative (rather than absolute) thus care must be taken when comparing values determined by

different techniques.

6.2 Brinell Hardness Test

Introduced by J. A. Brinell in 1900, this test involves pressing a hardened steel or tungsten-carbide ball 10

mm in diameter against a flat surface of a workpiece, with a load of 500, 1500, or 3000 kg. Brinell hardness

is evaluated by taking the mean diameter of the indentation (two readings at right angles to each other) and

calculating the Brinell hardness number (HB) by dividing the applied load by the curved surface area of the

indentation according to the expression:

𝐻𝐵 = 2 𝑃

𝜋𝐷 (𝐷 − √𝐷2 − 𝑑2) (6.2)

where P is the load in kilograms, D is the diameter of the ball in millimetres, and d is the average diameter

of the indentation in millimeters. Calculations have already been made and are available in tabular form

for various combinations of diameters of impressions and load.

As shown in Eq. (6.2), hardness has units of [N/m2], but is not physically equivalent to stress because the

measured projected area of the indentation is not the actual area normal to the applied load of the 3-

dimensional indenter.

The Brinell hardness number followed by the symbol HB without any suffix numbers denotes standard test

conditions using a ball of 10 mm diameter and a load of 3000 kg applied for 10 to 15 s. For other

conditions, the hardness number and symbol HB are supplemented by numbers indicating the test

conditions in the following order: diameter of ball, load, and duration of loading. For example, 75 HB

10/500/30 indicates a Brinell hardness of 75 measured with a ball of 10 mm diameter and a load of 500 kg

applied for 30s.

The 500-kilogram load is usually used for testing nonferrous metals such as copper and aluminium alloys,

whereas the 3000-kilogram load is most often used for testing harder metals such as steels and cast irons.

The load is held for a specified time (10 to 15 seconds for iron or steel and about 30 seconds for softer

metals), after which the diameter of the recovered indentation is measured in millimeters. This time period

is required to ensure that plastic flow of the work metal has stopped.

The harder the material to be tested, the smaller the impression; hence, a 1500-kg or 3000-kg load is usually

recommended in order to obtain impressions sufficiently large for accurate measurement. Depending on

the condition of the material, one of two types of impression develops on the surface after the performance

of this test (Fig. 6.2) or of any of the other tests described in this section. The impressions in annealed

metals generally have a rounded profile (Fig. 6.2a); in cold-worked metals, they usually have a sharp

profile (Fig. 6.2b). The correct method of measuring the indentation diameter, d, is shown in the figure.


Figure 6.2: Indentation geometry in Brinell

hardness testing: (a) annealed metal; (b) work-

hardened metal. Note that the depth of the

permanently deformed zone is about one order

of magnitude larger than the depth of

indentation. For a hardness test to be valid, this

zone should be fully developed in the material.

Highly hardened steel (or other very hard metals) cannot be tested by a hardened steel ball by the Brinell

method because the ball would plastically deform and flatten during penetration. One method for

minimizing this effect is to use tungsten carbide balls because of their higher modulus of elasticity, they

distort less than steel balls do. Tungsten carbide balls are recommended for Brinell testing materials of

hardness from 444 HB up to 627 HB (indentation of 2.45 mm in diameter). However, higher Brinell values

will result when using carbide balls instead of steel balls because of the difference in elastic properties. The

degree of accuracy that can be attained by the Brinell hardness test is greatly influenced by the surface

smoothness and therefore the test surface should be filed, ground, machined or polished with emery paper

such that the indentation diameter is clearly enough defined to permit its’ accurate measurement.

Typical advantages of Brinell hardness measurements are:

1. This measurement uses one scale for virtually all materials.

2. Brinell hardness is good for averaging heterogeneities over a relatively large area, thus lessening the

influence of scratches or surface roughness, or presence of small defects.

3. It can be used to estimate yield strength of steel:

y (psi) ≈ HB * 515 (for HB < 175) (6.3)

y (psi) ≈ HB * 490 (for HB > 175) (6.4)

General precautions of Brinell hardness testing include the following:

1. Indentations should not be made on a curved surface having a radius of less than 25 mm.

2. The load should be applied in such a way that the direction of loading and the test surface are

perpendicular to each other within 2°.

3. The thickness of the workpiece being tested should be such that no bulge or mark showing the effect of

the load appears on the side of the workpiece opposite the indentation. In any event, the thickness of

the specimen shall be at least 10 times the depth of the indentation

The Brinell hardness test has the following principal limitations:

1. Size and shape of the workpiece must be capable of accommodating the relatively large indentations.

2. Because of the relatively large indentations, the workpiece may not be usable after testing.

3. Because of the spherical shape of the indenter ball, the BHN for the same material will not be the

same for different loads if the same size ball is used. Thus, geometric similitude must be imposed by

maintaining the ratio of the indentation load and indenter diameter (P1/D1 = P2/D2 = P3/D3 etc.).

3. The limit of hardness range -- about 11 HB with the 500-kg load to 627 with the 3000-kg load -- is

generally considered the practical range.

6.3 Rockwell Hardness Testing

This hardness test uses a direct reading instrument based on the principle of differential depth

measurement. Rockwell hardness differs from Brinell hardness testing in that the indentation size is

measured by the diameter of the indentation in Brinell testing while Rockwell hardness is determined based

on the inverse relationship to the difference in depths of indentation produced by minor and major load.


For thin test samples or samples for which the relatively large Brinell or Rockwell indentations must be

avoided, the Superficial Rockwell hardness test is often employed. Superficial Rockwell hardness testing

employs lower loads to the indenter in order to minimize penetration.

The Rockwell Hardness Test consists of measuring the additional depth to which an indenter is forced by a

heavy (major) load beyond the depth of a previously applied light (minor) load as illustrated in Fig. 6.3.

Application of the minor load eliminates backlash in the load train and causes the indenter to break

through slight surface roughness and to crush particles of foreign matter, thus contributing much greater

accuracy in the test.

The Rockwell hardness test method consists of indenting the test material with a diamond cone or

hardened steel ball indenter. The indenter is forced into the test material under a preliminary minor load F0

(Fig. 3A) usually 10 kgf. When equilibrium has been reached, an indicating device, which 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, resulting from the application and removal of the additional major load is used to calculate

the Rockwell hardness number.

Figure 6.3: Principle of Rockwell testing.

The minor load is applied first, and a reference or “set” position is established on the measuring device or

the Rockwell hardness tester. Then the major load is applied at a prescribed, controlled rate. Without

moving the workpiece being tested, the major load is removed and the Rockwell hardness number is

indicated on the dial gage. The entire operation takes from 5 to 10 seconds. In Rockwell testing, the minor

load is 10 kgf, and the major load is 50, 90 or 140 kgf. In superficial Rockwell testing, the minor load is 3

kgf, and major loads are 12, 27 or 42 kgf. In both tests, the indenter may be either a diamond cone or steel

ball, depending principally on the characteristics of the material being tested.

The 120° sphero-conical diamond indenter is used mainly for testing hard materials such as hardened steels

and cemented carbides. Hardened steel ball indenters with diameters 1/16, 1/8, 1/4, 1/2 in. are used for

testing softer materials such as fully annealed steels, softer grades of cast irons, and a wide variety of

nonferrous metals.

There are 30 different Rockwell scales (regular and superficial), defined by the combination of the indenter

and minor and major loads, Table 6.1. The suitable scale is determined due to the type of the material to be

tested. The majority of applications are covered by the Rockwell C and B scales for testing steel, brass, and

other materials.

Hardness values taken for round samples need to be corrected because the material flows more easily to the

edge and, in effect, creates a lower hardness value. Rockwell Round Correction Charts (Table 6.2) can be

used for such correction.

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 0.002 mm

E = a constant depending on form of indenter: 100 units for diamond indenter, 130 units for steel ball indenter

HR = Rockwell hardness number = E – e

D = diameter of steel ball E

e

Stage A

F0 applied

Stage B

F0 + F1 = F applied

Stage C

F0 applied (F1 Withdrawn)


Table 6.1: Rockwell hardness scales.

Scale Indenter Minor

Load, F0

Major

Load, F1

Total

Load, F

Typical Applications

kgf kgf kgf

A Diamond cone 10 50 60 Cemented carbides, thin steel and

shallow case hardened steel

B 1/16" steel ball 10 90 100 Copper alloys, soft steels,

aluminium alloys, malleable irons

C Diamond cone 10 140 150

Steel, hard cast irons, pearlitic

malleable iron, titanium, deep case

hardened steel and other materials

harder than 100 HRB

D Diamond cone 10 90 100

Thin steel and medium case

hardened steel and pearlitic

malleable iron

E 1/8" steel ball 10 90 100 Cast iron, aluminium and

magnesium alloys, bearing metals

F 1/16" steel ball 10 50 60 Annealed copper alloys, thin soft

sheet metals

G 1/16" steel ball 10 140 150

Phosphor bronze, beryllium copper,

malleable irons. Upper limit is

HRG 92, to avoid flattening of ball.

H 1/8" steel ball 10 50 60 Aluminium, zinc, lead

K 1/8" steel ball 10 140 150

Bearing metals, plastics and other

very soft or thin materials

L 1/4" steel ball 10 50 60

M 1/4" steel ball 10 90 100

P 1/4" steel ball 10 140 150

R 1/2" steel ball 10 50 60

S 1/2" steel ball 10 90 100

V 1/2" steel ball 10 140 150

No Rockwell hardness value is expressed by a number alone. A letter has been assigned to each

combination of load and indenter, as indicated in Table 6.1. Each number is suffixed first by the letter H

(for hardness), then the letter R (for Rockwell), and finally the letter that indicates the scale used. For

example, a value of 60 in the Rockwell C scale is expressed as 60 HRC, etc. One Rockwell number

represents an indentation of 0.002 mm (0.00008 in.). Therefore a reading of 60 HRC indicates an

indentation from minor to major load of (100 - 60) x 0.002 mm = 0.080 mm or 0.0032 in. A reading of 80

HRB indicates an indentation of (130 - 80) x 0.002 mm = 0.100 mm.

The metal immediately surrounding the indentation from a Rockwell hardness test is cold worked thus

multiple readings cannot be taken at the same point on a material’s surface. If multiple tests are conducted

on a single part the indentations should each be a minimum of 3 indentation diameters apart. The depth of

material affected during testing is on the order of ten times the depth of the indentations. Therefore, unless

the thickness of the metal being tested is at least ten times the depth of the indentation, an accurate

Rockwell hardness test cannot be expected. In addition to the limitation of indentation depth for a

workpiece of given thickness and hardness, there is a limiting factor on the minimum material width. If the

indentation is placed too close to the edge of a workpiece, the edge will deform outward and the Rockwell

hardness number will be decreased accordingly. Experience has shown that the distance from the centre of

the indentation to the edge of the workpiece must be at least 3 times the diameter of the indentation to

ensure an accurate test.

A fundamental requirement of the Rockwell hardness test is that the surface of the workpiece being tested

be approximately normal to the indenter and that the workpiece must not move or slip in the slightest

degree as the major load is applied. As one point of hardness represents a depth of only 0.0008 inches, a

movement of only 0.001 inches could cause an error of over 10 Rockwell numbers. The support must be of


sufficient rigidity to prevent its permanent deformation in use. Indenters are not calibrated below values of

20 or above values of 95, thus if readings are outside of this range then a different indenter must be

selected. Minimum thickness requirements, conversions between various Rockwell scales and round work

corrections

Table 6.2: Rockwell Round Correction Chart

ROCKWELL C, A, D SCALES

Diameter .25" .375" 0.5" .625" .75" .875" 1" 1.25" 1.5"

Result 6.4 mm 10 mm 13 mm 16 mm 19 mm 22 mm 25 mm 32 mm 38 mm

20 6.0 4.5 3.5 2.5 2.0 1.5 1.5 1.0 1.0

25 5.5 4.0 3.0 2.5 2.0 1.5 1.0 1.0 1.0

30 5.0 3.5 2.5 2.0 1.5 1.5 1.0 1.0 0.5

35 4.0 3.0 2.0 1.5 1.5 1.0 1.0 0.5 0.5

40 3.5 2.5 2.0 1.5 1.0 1.0 1.0 0.5 0.5

45 3.0 2.0 1.5 1.0 1.0 1.0 0.5 0.5 0.5

50 2.5 2.0 1.5 1.0 1.0 0.5 0.5 0.5 0.5

55 2.0 1.5 1.0 1.0 0.5 0.5 0.5 0.5 --

60 1.5 1.0 1.0 0.5 0.5 0.5 0.5 -- --

65 1.5 1.0 1.0 0.5 0.5 0.5 0.5 -- --

70 1.0 1.0 0.5 0.5 0.5 0.5 0.5 -- --

75 1.0 0.5 0.5 0.5 0.5 0.5 -- -- --

80 0.5 0.5 0.5 0.5 0.5 -- -- -- --

85 0.5 0.5 0.5 -- -- -- -- -- --

90 0.5 -- -- -- -- -- -- -- --

ROCKWELL B, F, G SCALES

Diameter .25" .375" 0.5" .625" .75" .875" 1"

Result 6.4 mm 10 mm 13 mm 16 mm 19 mm 22 mm 25 mm

0 12.5 8.5 6.5 5.5 4.5 3.5 3.0

10 12.0 8.0 6.0 5.0 4.0 3.5 3.0

20 11.0 7.5 5.5 4.5 4.0 3.5 3.0

30 10.0 6.5 5.0 4.5 3.5 3.0 2.5

40 9.0 6.0 4.5 4.0 3.0 2.5 2.5

50 8.0 5.5 4.0 3.5 3.0 2.5 2.0

60 7.0 5.0 3.5 3.0 2.5 2.0 2.0

70 6.0 4.0 3.0 2.5 2.0 2.0 1.5

80 5.0 3.5 2.5 2.0 1.5 1.5 1.5

90 4.0 3.0 2.0 1.5 1.5 1.5 1.0

100 3.5 2.5 1.5 1.5 1.0 1.0 0.5


6.3 Vickers Hardness Test

The Vickers hardness test method consists of indenting the test material with a diamond indenter, in the

form of a right pyramid with a square base and an angle of 136 degrees between opposite faces subjected to

a load of 1 to 100 kgf. The full load is normally applied for 10 to 15 seconds. The two diagonals of the

indentation left in the surface of the material after removal of the load are measured using a microscope

and their average calculated. The area of the sloping surface of the indentation is calculated. The HV

number is then determined by the ratio F/A, where F is the force applied to the diamond in kilograms-

force and A is the surface area of the resulting indentation in square millimeters, Fig. 6.4.

Figure 6.4: Hardness impression on to the sample during Vickers hardness test.

A can be determined by the formula

𝐴 = 𝑑2

2 sin(136/2) =

𝑑2

1.8544

(6.5)

where d is the average length of the diagonal left by the indenter. Hence

𝐻𝑉 = 𝐹

𝐴 = 1.8544 (𝐹

𝑑2⁄ ) kgf/mm2 (6.6)

Here F is in kg, and d is in mm.

When the mean diagonal of the indentation has been determined the Vickers hardness may be calculated

from the formula, but is more convenient to use conversion tables. The Vickers hardness should be reported

like 800 HV/10, which means a Vickers hardness of 800, was obtained using a 10 kgf force. Several

different loading settings give practically identical hardness numbers on uniform material, which is much

better than the arbitrary changing of scale with the other hardness testing methods. The advantages of the

Vickers hardness test are that extremely accurate readings can be taken, and just one type of indenter is

used for all types of metals and surface treatments. Although thoroughly adaptable and very precise for

testing the softest and hardest of materials, under varying loads, the Vickers machine is a floor standing

unit that is more expensive than the Brinell or Rockwell machines.

There is now a trend towards reporting Vickers hardness in SI units (MPa or GPa) particularly in academic

papers. To convert the Vickers hardness number to SI units the force applied needs converting from kgf to

newtons to give results in MPa (or N/mm2) using the formula above and furthermore divided by 1000 to

get the hardness in GPa. For example, 700 HV/30 changes into HV/294 N = 6.87 GPa.


6.4 Hardness Conversion

The facility to convert the hardness measured on one scale to that of another is most desirable. However,

because hardness is not a well-defined material property, and because of the experimental dissimilarities

among the various techniques, a comprehensive conversion scheme has not been devised. Hardness

conversion data have been determined experimentally and found to be dependent on material type and

characteristics. The most reliable conversion data exist for steels, some of which are presented in Figure 6.5

for Knoop, Brinell, and two Rockwell scales; the Mohs scale is also included.

Figure 6.5: Comparison of several hardness scales.

laboratory 2 hardness test of materials -...

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