Hardness Test

Saka Oluwadamilola

110404085

Mechanical Engineering

University Of Lagos

An Industrial Visit to:

Federal Institute of Industrial Research, Oshodi (FIIRO)

Oshodi, Lagos

Table of Contents Hardness Test ......................................................................................................................................................... 1

I. ABSTRACT ................................................................................................................................................... 3

II. INTRODUCTION ..................................................................................................................................... 4

III. THEORY .................................................................................................................................................. 5

A. HARDNESS .............................................................................................................................................. 5

B. HARDNESS MEASUREMENT ................................................................................................................ 5

C. HARDNESS MEASUREMENT METHODS ............................................................................................. 7

1. BRINELL HARDNESS TEST ............................................................................................................... 8

2. VICKERS HARDNESS TEST............................................................................................................. 10

3. ROCKWELL HARDNESS TEST ........................................................................................................ 12

D. RELATION OF HARDNESS TO OTHER MATERIAL PROPERTIES ................................................... 14

E. IMPORTANCE OF HARDNESS TEST .................................................................................................. 15

F. CUTTING TOOLS .................................................................................................................................. 16

1. CHARACTERISTICS OF CUTTING TOOL MATERIALS ................................................................ 16

2. TYPES OF CUTTING TOOL MATERIALS ....................................................................................... 17

3. HIGH SPEED STEELS ....................................................................................................................... 18

IV. APPARATUS .......................................................................................................................................... 19

1. The Rockwell Tester ............................................................................................................................ 19

V. EXPERIMENTAL PROCEDURE ........................................................................................................... 20

VI. EXPERIMENTAL RESULTS ................................................................................................................. 21

VII. ANALYSIS ............................................................................................................................................. 22

A. Mean Hardness Value .............................................................................................................................. 22

B. Standard Deviation of Readings ............................................................................................................... 22

VIII. DISCUSSION OF RESULTS .................................................................................................................. 24

IX. INDUSTRIAL APPLICATIONS ............................................................................................................. 25

X. VISIT TO FIIRO OSHODI ...................................................................................................................... 26

A. THE UNIVERSAL TESTING MACHINE ............................................................................................... 26

B. THE ROCKWELL TESTER.................................................................................................................... 27

C. THE BRINELL TESTER ......................................................................................................................... 28

XI. RECOMMENDATIONS ......................................................................................................................... 29

XII. CONCLUSION ....................................................................................................................................... 30

XIII. REFERENCES ........................................................................................................................................ 31

I. ABSTRACT

The mechanical properties of materials are ascertained by performing carefully designed tests like the hardness

test. Particularly, cutting tools are ensured to meet a specified standard value of hardness. Hardness is one of the

essential characteristics for cutting tools to withstand the heavy conditions of the cutting process, avoid excessive

wear and to produce high quality and economical parts. This experiment determined the hardness number of the

high speed steel cutting tool using the Rockwell machine with diamond cone indenter. The hardness number was

found to be 57.9HRC and the corresponding tensile strength from Material Properties Table was estimated to be

2068N/mm2. Finally, the applications of the hardness test in industry were highlighted.

II. INTRODUCTION

Hardness testing has existed for more than one century. Hardness tests have always been important in the

metalworking industry and in materials research, because the specified mechanical properties for further processing,

or of defined final conditions, can be obtained during or after industrial production. This method of testing is the

quickest and least expensive way to obtain information about the mechanical property of metal. The hardness test is,

by far, the most valuable and most widely used mechanical test for evaluating the properties of metals as well as

certain other materials. The hardness of a material usually is considered resistance to permanent indentation. In

general, an indenter is pressed into the surface of the metal to be tested under a specific load for a definite time

interval, and a measurement is made of the size or depth of the indentation. The principal purpose of the hardness

test is to determine the suitability of a material for a given application, or the particular treatment to which the

material has been subjected. The ease with which the hardness test can be made has made it the most common

method of inspection for metals and alloys.

Why is hardness test so valuable? Principally, the importance of hardness testing has to do with the relationship

between hardness and other properties of material. For example, both the hardness test and the tensile test measure

the resistance of a metal to plastic flow, and results of these tests may closely parallel each other. The hardness test

is preferred because it is simple, easy, and relatively nondestructive. A hardness test consists of pressing an indenter

of known geometry and mechanical properties under pre-defined conditions into a test material. In order to obtain

comparable test results, all important test parameters must be within strictly defined tolerances and kept constant. In

other words, hardness is not a fundamental parameter of the material, but depends on the test method being utilized.

Hardness is not a fundamental property of a material. Hardness values are arbitrary, and there are no absolute

standards of hardness. Hardness has no quantitative value, except in terms of a given load applied in a specified

manner for a specified duration and a specified penetrator shape. Hardness is one of the essential characteristics for

cutting tools to withstand the heavy conditions of the cutting process, avoid excessive wear and to produce high

quality and economical parts. The hardness of a cutting tool must be maintained in high cutting temperatures (hot

hardness). Various steel grades of cutting tools and other alloys can be optimized by using the data from hardness

tests. From such data, the integrity of a product, its ability to be machined, abrasive properties, ductility and

potential lifetime can be deduced. Furthermore, a meaningful and reliable result can be retrieved quickly. As the

testing process makes only a small indentation in the material, it is considered to be a quasi-non-destructive test.

III. THEORY

A. HARDNESS Hardness has a variety of meanings. To the metals industry, it may be thought of as resistance to permanent

deformation. To the metallurgist, it means resistance to penetration. To the lubrication engineer, it means resistance

to wear. To the design engineer, it is a measure of flow stress. To the mineralogist, it means resistance to scratching,

and to the machinist, it means resistance to machining. Hardness may also be referred to as mean contact pressure.

All of these characteristics are related to the plastic flow stress of materials.

Hardness is the property of a material that enables it to resist plastic deformation, usually by penetration. It is the

mechanical resistance that a body opposes to the penetration of another body. Hardness is not only the resistance

against harder bodies; it is also the resistance against softer and equal hard bodies. However, the term hardness

may also refer to stiffness or temper or to resistance to bending, scratching, abrasion or cutting. It is the property of a

metal, which gives it the ability to resist being permanently deformed (bent, broken, or have its shape changed),

when a load is applied. The greater the hardness of the metal, the greater resistance it has to deformation.

B. HARDNESS MEASUREMENT Hardness measurement can be defined as macro-, micro- or nano-scale, according to the forces applied and

displacements obtained. Measurement of the macro-hardness of materials is a quick and a simple method of

obtaining the mechanical property data for the bulk material from a small sample. It is also widely used for the

quality control of surface treatment processes. However, when concerned with coatings and surface properties of

importance to friction and wear processes for instance, the macro-indentation depth would be too large relative to

the surface scale features. Where materials have a fine microstructure, are multi-phase, non-homogenous or prone to

cracking, macro-hardness measurements will be highly variable and will not identify individual surface features. It is

here that micro-hardness measurements are appropriate.

Microhardness is the hardness of a material as determined by forcing an indenter such as a Vickers or Knoop

indenter into the surface of the material under 15 to 1000gf load; usually, the indentations are so small that they

must be measured with a microscope capable of determining hardness of different microconstituents within a

structure, or measuring steep hardness gradients such as those encountered in case hardening. Conversions from

microhardness values to tensile strength and other hardness scales (e.g. Rockwell) are available for many metals and

alloys. Micro-indenters work by pressing a tip into a sample and continuously measuring: applied load, penetration

depth and cycle time.

Nano-indentation tests measure hardness by indenting using very small, on the order of 1nN (nano-Newton),

indentation forces and measuring the depth of the indentation that was made. These tests are based on new

technology that allows precise measurement and control of the indenting forces and precise measurement of the

indentation depths. By measuring the depth of the indentation, progressive levels of forcing are measurable on the

same piece. This allows the tester to determine the maximum indentation load that is possible before the hardness is

compromised and the film is no longer within the testing ranges. This also allows a check to be completed to

determine if the hardness remains constant even after an indentation has been made.

There are various mechanisms and methods that have been designed to complete nano-indentation hardness tests.

One method of force application is using a coil and magnet assembly on a loading column to drive the indenter

downward. This method uses a capacitance displacement gauge. Such gauges detect displacements of 0.2 to 0.3nm

(nanometer) at the time of force application. The loading column is suspended by springs, which clamps external

motion and allows the load to be released slightly to recover the elastic portion of deformation before measuring the

indentation depth.

Generally, hardness is indicated in a variety of ways, as indicated by the names of the tests that follow:

i. Static indentation tests: A ball, cone, or pyramid is forced into the surface of the metal being tested. The

relationship of load to the area or depth of indentation is the measure of hardness, such as in Brinell,

Knoop, Rockwell, and Vickers hardness tests.

ii. Rebound tests: An object of standard mass and dimensions is bounced from the surface of the

workpiece being tested, and the height of rebound is the measure of hardness. The Scleroscope and

Leeb tests are examples.

iii. Scratch file tests: The idea is that one material is capable of scratching another. The Mohs and file

hardness tests are examples of this type.

iv. Plowing tests: A blunt element (usually diamond) is moved across the surface of the workpiece being

tested under controlled conditions of load and shape. The width of the groove is the measure of

hardness. The Bierbaum test is an example.

v. Damping tests: Hardness is determined by the change in amplitude of a pendulum having a hard pivot,

which rests on the surface of the workpiece being tested. The Herbert Pendulum test is an example.

vi. Cutting tests: A sharp tool of given shape is caused to remove a chip of standard dimensions from the

surface of the workpiece being tested.

vii. Abrasion tests: A workpiece is loaded against a rotating disk, and the rate of wear is the measure of

hardness.

viii. Erosion tests: Sand or other granular abrasive is impinged on the surface of the workpiece being tested

under standard conditions, and loss of material in a given time is the measure of hardness. Hardness of

grinding wheels is measured by this testing method.

ix. Electromagnetic testing: Hardness is measured as a variable against standards of known flux density.

x. Ultrasonic testing: The ultrasonic test is another type of indentation test

However, the focus of this report is on static indentation tests (particularly Rockwell Test), because they are the

most widely used. Rebound testing is also used extensively, particularly for hardness measurements on large

workpiece or for applications in which visible or sharp impressions in the test surface cannot be tolerated.

C. HARDNESS MEASUREMENT METHODS Hardness is not an intrinsic material property dictated by precise definitions in terms of fundamental units of

mass, length and time. A hardness property value is the result of a defined measurement procedure. Hardness of

materials has probably long been assessed by resistance to scratching or cutting. An example would be material B

scratches material C, but not material A. Alternatively, material A scratches material B slightly and scratches

material C heavily. Relative hardness of minerals can be assessed by reference to the Moh's Scale that ranks the

ability of materials to resist scratching by another material. Similar methods of relative hardness assessment are still

commonly used today. An example is the file test where a file tempered to a desired hardness is rubbed on the test

material surface. If the file slides without biting or marking the surface, the test material would be considered harder

than the file. If the file bites or marks the surface, the test material would be considered softer than the file.

The above relative hardness tests are limited in practical use and do not provide accurate numeric data or scales

particularly for modern day metals and materials. The usual method to achieve a hardness value is to measure the

depth or area of an indentation left by an indenter of a specific shape, with a specific force applied for a specific

time. Testing is made by pressing or indenting one material into another with a known amount of mechanical force.

Since the ability of the material to resist deformation is related to the yield point and the material's capacity for

work-hardening, the result is actually a measurement of relative hardness.

Indenters are produced from the hardest materials available, such as diamond, and the deformation is limited to

the testing material. The shape of indenters is defined by the respective standard of hardness testing and can be very

defined by the respective standard of hardness testing and can be very different, depending on whether the indenter

is a cone, pyramid or sphere. At the point of contact between the indenter and tested material, the stress easily

exceeds the yield strength of the tested material, which is plastically deformed as the indenter moves into the

material. All hardness tests are based on the same principle. Applying the same test load to stainless steel and

aluminum, the indentation in stainless steel is smaller. This means that stainless steel's hardness reading will be

higher.

There are three principal standard test methods for expressing the relationship between hardness and the size of

the impression, these being Brinell, Vickers, and Rockwell. For practical and calibration reasons, each of these

methods is divided into a range of scales, defined by a combination of applied load and indenter geometry.

1. BRINELL HARDNESS TEST

The Brinell hardness test is a method used to determine the hardness of engineering materials. Most commonly it

is used to test materials that have a structure that is too coarse or that have a surface that is too rough to be tested

using another test method, e.g., castings and forgings. Brinell testing often use a very high test load (3000 kgf) and a

10mm wide indenter so that the resulting indentation averages out most surface and sub-surface inconsistencies. The

Brinell method applies a predetermined test load (F) to a carbide ball of fixed diameter (D) which is held for a

predetermined time period and then removed. The resulting impression is measured across at least two diameters

usually at right angles to each other and these result averaged (Di). A chart is then used to convert the averaged

diameter measurement to a Brinell hardness number. Test forces range from 500 to 3000 kgf. A Brinell hardness

result measures the permanent width of indentation produced by a carbide indenter applied to a test specimen at a

given load, for a given length of time. Typically, an indentation is made with a Brinell hardness testing machine and

then measured for indentation diameter in a second step with a specially designed Brinell microscope or optical

system. The resulting measurement is converted to a Brinell value using the Brinell formula or a conversion chart

based on the formula. Most typically, a Brinell test will use 3000 kgf load with a 10mm ball. If the sample material

is aluminum, the test is most frequently performed with a 500 kgf load and 10mm ball. Brinell test loads can range

from 3000 kgf down to 1 kgf. Ball indenter diameters can range from 10mm to 1mm. Generally, the lower loads and

ball diameters are used for convenience in combination testers, like Rockwell units, that have a small load

capacity. The test standard specifies a time of 10 to 15 seconds, although shorter times can be used if it is known

that the shorter time does not affect the result. There are other conditions that must be met for testing on a round

specimen, spacing of indentations, minimum thickness of test specimens, etc.

D = Ball diameter

Di = impression diameter

F = load

HB = Brinell result

Typically the greatest source of error in Brinell testing is the measurement of the indentation. Due to disparities

in operators making the measurements, the results will vary even under perfect conditions. Less than perfect

conditions can cause the variation to increase greatly. Frequently the test surface is prepared with a grinder to

remove surface conditions. The jagged edge makes interpretation of the indentation difficult. Furthermore, when

operators know the specifications limits for rejects, they may often be influenced to see the measurements in a way

that increases the percentage of good tests and less re-testing.

Two types of technological remedies for countering Brinell measurement error problems have been developed

over the years. Automatic optical Brinell scopes use computers and image analysis to read the indentations in a

consistent manner. This standardization helps eliminate operator subjectivity so operators are less-prone to

automatically view in-tolerance results when the samples result may be out-of-tolerance.

Brinell units measure the samples using Brinell hardness parameters together with a Rockwell hardness method.

This method provides the most repeatable results (and greater speed) since the vagaries of optical interpretations are

removed through the use of an automatic mechanical depth measurement. Using this method, however, results may

not be strictly consistent with Brinell results due to the different test methods an offset to the results may be

required for some materials. It is easy to establish the correct values in those cases where this may be a problem.

2. 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 Vickers hardness is the quotient obtained by dividing

the kgf load by the square mm area of indentation.

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.

F= Load in kgf

d = Arithmetic mean of the two diagonals, d1 and d2 in mm

HV = Vickers hardness

3. ROCKWELL HARDNESS TEST

The Rockwell hardness test method is the most commonly used hardness test method. The Rockwell test is

generally easier to perform, and more accurate than other types of hardness testing methods. The Rockwell test

method is used on all metals, except in condition where the test metal structure or surface conditions would

introduce too much variations; where the indentations would be too large for the application; or where the sample

size or sample shape prohibits its use.

The Rockwell method measures the permanent depth of indentation produced by a force/load on an indenter.

First, a preliminary test force (commonly referred to as preload or minor load) is applied to a sample using a

diamond indenter. This load represents the zero or reference position that breaks through the surface to reduce the

effects of surface finish. After the preload, an additional load, call the major load, is applied to reach the total

required test load. This force is held for a predetermined amount of time (dwell time) to allow for elastic recovery.

This major load is then released and the final position is measured against the position derived from the preload, the

indentation depth variance between the preload value and major load value. This distance is converted to a hardness

number.

Preliminary test loads (preloads) range from 3 kgf (used in the Superficial Rockwell scale) to 10 kgf (used in

the Regular Rockwell scale) to 200 kgs (used as a macro scale and not part of ASTM E-18; see ASTM E-1842).

Total test forces range from 15kgf to 150 kgf (superficial and regular) to 500 to 3000 kgf (macrohardness).

A variety of indenters may be used: conical diamond with a round tip for harder metals to ball indenters ranges

with a diameter ranging from 1/16 to for softer materials.

When selecting a Rockwell scale, a general guide is to select the scale that specifies the largest load and the

smallest indenter possible without exceeding defined operation conditions and accounting for conditions that may

influence the test result. These conditions include test specimens that are below the minimum thickness for the depth

of indentation; a test impression that falls too close to the edge of the specimen or another impression; or testing on

cylindrical specimens. Additionally, the test axis should be within 2-degress of perpendicular to ensure precise

loading; there should be no deflection of the test sample or tester during the loading application from conditions

such as dirt under the test specimen or on the elevating screw. It is important to keep the surface finish clean and

decarburization from heat treatment should be removed.

Sheet metal can be too thin and too soft for testing on a particular Rockwell scale without exceeding minimum

thickness requirements and potentially indenting the test anvil. In this case a diamond anvil can be used to provide a

consistent influence of the result. Another special case in testing cold rolled sheet metal is that work hardening can

create a gradient of hardness through the sample so any test is measuring the average of the hardness over the depth

of indentation effect. In this case any Rockwell test result is going to be subject to doubt, there is often a history of

testing using a particular scale on a particular material that operators are used to and able to functionally interpret.

D. RELATION OF HARDNESS TO OTHER MATERIAL PROPERTIES

Hardness covers several properties: resistance to deformation, resistance to friction and abrasion. The well-

known correlation links hardness with tensile strength, while resistance to deformation is dependent on modulus of

elasticity. The frictional resistance may be divided in two equally important parts: the chemical affinity of materials

in contact, and the hardness itself. A correlation may be established between hardness and some other material

property such as tensile strength. Then the other property (such as strength) may be estimated based on hardness test

results, which are much simpler to obtain. This correlation depends upon specific test data and cannot be

extrapolated to include other materials not tested.

Moreover, the mechanical properties of small mechanical parts cannot be easily determined by tensile tests or

other forms of tests because it is impossible to cut standard samples from small parts. In this case, it is of interest to

determine the mechanical properties of a material, not directly but indirectly, by hardness test. The standard

hardness tests are relatively simple, do not require cutting of samples, and make it possible to determine the

properties of small sections. Naturally, the relationship between the hardness and the mechanical properties makes it

possible to determine the mechanical properties of semi-finished products as well as finished parts.

As a result of many tests, comparisons have been prepared using formulas, tables, and graphs that show the

relationships between the results of various hardness tests of specific alloys. There is, however, no exact

mathematical relation between any two of the methods. Hardness conversion between different methods and scales

cannot be made mathematically exact for a wide range of materials. Different loads, different shape of indenters,

homogeneity of specimen, cold working properties and elastic properties all complicate the problem. All tables and

charts should be considered as giving approximate equivalents, particularly when converting to a method or scale

which is not physically possible for the particular test material and thus cannot be verified. For this reason, the result

of one type of hardness test converted to readings of another type should carry a notation like "352 Brinell converted

from Rockwell C-38". Another convenient conversion is that of Brinell hardness to ultimate tensile strength. For

quenched and tempered steel, the tensile strength (psi) is about 500 times the Brinell hardness number (provided the

strength is not over 200,000 psi). The table below is a sample hardness conversion table.

E. IMPORTANCE OF HARDNESS TEST

1. The hardness of a Ductile Material determined by the indentation test, is related with its other mechanical

properties (in particular with the ultimate tensile strength). The ultimate tensile strength of most steels

(except for those having austenitic or martensitic structure) and many nonferrous alloys can be assessed

quickly by hardness measurements. Though the Brittle Materials undergo plastic deformation in indentation

tests, a correlation between hardness and ultimate strength is not observed for brittle materials. A limited

exception is the gray iron for which a qualitative relationship exists. High indentation hardness is usually an

indication of high ultimate compressive strength for this material (gray iron).

Hardness, as determined by indentation tests, is also shown to be correlated with the "fatigue strength"

of some metals such as annealed steels, copper and duralumin.

These correlations, both for Su and fatigue strengths, apply only over a range of materials on which

tests have previously been made. Therefore, users should refrain from making over generalization.

2. Hardness tests are substantially simpler than other mechanical tests. Specially prepared specimens are not

needed. The machine parts can usually be tested directly. Though depends on the size of the part and type

of test, the parts tested are not damaged. Furthermore, hardness tests can be made quickly, taking about in

the order of seconds to few minutes.

3. Similar materials may be graded according to hardness, thus making specifications for a certain type of

application clear-cut. Likewise, the quality level of materials or products may be controlled effectively by

hardness tests.

4. Hardness can be measured on parts of small thickness and in very thin layers, or over microscopic sections.

F. CUTTING TOOLS A metal cutting tool is a device used in metal cutting processes on machine tools, for removing layers of material

from the blank, to obtain a product of specified shape and size with specified accuracy and surface finish.

Depending upon the number of cutting edges, the metal cutting tools are classified as follows: Single-point cutting

tools, Multi-point cutting tools and Form tools.

Machining operations which required 105 minutes in the year 1900 can be done today within 1 minute. This

improvement has been made possible because of the immense sophistication in machine tools and remarkable

progress in cutting tool materials.

1. CHARACTERISTICS OF CUTTING TOOL MATERIALS The following are the most essential requirements of a good cutting tool material to give maximum production

with minimum maintenance and trouble:

i. Hot hardness: It is the ability of the cutting tool to withstand high temperatures without losing its cutting

edge. The hot hardness of the tool materials can be increased by adding chromium, molybdenum, tungsten

and vanadium, all of which form hard carbides.

ii. Abrasion resistance: It is the ability to resist wear. Abrasion resistance not only depends on hardness but

also on the extent of hard, undissolved carbides present. This characteristic increases as the carbon and

alloy contents increase.

iii. Toughness: Toughness is the ability to resist shock and/or impact forces and also to resist a high unit

pressure against the cutting edge. The term actually implies a combination of strength and ductility.

iv. Frictional coefficient: In order to have low tool wear and better surface finish, the coefficient of friction

between the chip and tool should be as low as possible in the operating range of speed and feed.

v. Thermal conductivity and specific heat: It is very much desired that tool material should possess high

thermal conductivity and specific heat, so that the materials may conduct away the heat generated at the

cutting edge.

vi. Machinability: This is the property of a material which defines the ease with which a material would

machine. The tool material should be comparatively easier to machine.

vii. Cost and ease of fabrication: The cost and ease of fabrication should be within reasonable limits.

Resistance to deformation: The tool steel material should retain shape and size during the heat treatment

process.

viii. Resistance to decarburization: Decarburization causes soft spots on the tool surface, which may get

cracked due to quenching by the application of cutting fluid.

ix. Quality: The tool material must produce acceptable quality parts in terms of surface finish.

x. Ease of grinding: The tool material should be easy to form, grind and sharpen to the desired geometry.

2. TYPES OF CUTTING TOOL MATERIALS

As a result of research, the following types of tool materials, each suitable for specific ranges of application,

have been evolved:

i. High speed steels

ii. Plain carbon steels

iii. Low alloy steels

iv. Non-ferrous cast alloys

v. Cemented carbides

vi. Ceramics

vii. Cermets

viii. Diamonds

ix. Abrasives

3. HIGH SPEED STEELS

High-speed steel (HSS) is a subset of tool steels, commonly used in tool bits and cutting tools. It is often used in

power-saw blades and drill bits. It is superior to the older high-carbon steel tools used extensively through the 1940s

in that it can withstand higher temperatures without losing its temper (hardness). This property allows HSS to cut

faster than high carbon steel, hence the name high-speed steel. At room temperature, in their generally

recommended heat treatment, HSS grades generally display high hardness (above HRC60) and abrasion resistance

(generally linked to tungsten and vanadium content often used in HSS) compared with common carbon and tool

steels. The main use of high-speed steels continues to be in the manufacture of various cutting tools: drills, taps,

milling cutters, tool bits, gear cutters, saw blades, planer and jointer blades, router bits, etc., although usage for

punches and dies is increasing. High speed steels also found a market in fine hand tools where their relatively good

toughness at high hardness, coupled with high abrasion resistance, made them suitable for low speed applications

requiring a durable keen (sharp) edge, such as files, chisels, hand plane blades, and high quality kitchen, pocket

knives, and swords. High speed steel tools are the most popular for use in woodturning, as the speed of movement of

the work past the edge is relatively high for handheld tools, and HSS holds its edge far longer than high carbon steel

tools can. The main use of high speed steel is in the manufacture of HSS cutting tools including drills, taps, end

mills. HSS bits and other high speed steel cutting tools are the workhorse of American Industry, providing

outstanding sharp cutting edges that withstand vibration and the limitations of many of todays machine tools. The

next generation of HSS cutting tools uses particle metallurgy and improved designs to enhance productivity, and

with many multi-layer coatings available, superior performance is expected.

IV. APPARATUS

1. The Rockwell Tester

V. EXPERIMENTAL PROCEDURE

i. I selected the anvil most suitable for supporting the specimen, bearing in mind that the specimen must

be stable and supported immediately beneath the point of indentation for a successful test.

ii. I inserted the appropriate indenter and proportional weights.

iii. I raised the weights clear off the main level by pulling the hand lever at the right hand side of the

machine towards myself.

iv. I placed the specimen on the anvil and raised it by rotating the hand wheel clockwise until contact was

made with the indenter.

v. I continued carefully rotating the hand wheel until the small indicating hand on the dial indicated SET

and the main indicating hand is approximately vertical.

vi. I pushed the handle towards weight slowly allowing the pre-weights to descend onto the specimen rod.

vii. I applied the indenters for a period of 10seconds with the aid of stopwatch.

viii. I pulled the handle back so that the top of handle was away from the weights.

ix. I read the hardness value from the scale.

VI. EXPERIMENTAL RESULTS

High Speed Steel (HSS) Cutting Tool

S/N Hardness Value (HRC)

1. 56

2. 56

3. 58

4. 57

5. 59

6. 61

7. 60

8. 61

9. 62

10. 55

11. 54

12. 56

VII. ANALYSIS

A. Mean Hardness Value

B. Standard Deviation of Readings

S/N

1. 56 57.9167 -1.9167 3.6737

2. 56 57.9167 -1.9167 3.6737

3. 58 57.9167 0.0833 0.0069

4. 57 57.9167 -0.9167 0.8403

5. 59 57.9167 1.0833 1.1735

6. 61 57.9167 3.0833 9.5067

7. 60 57.9167 2.0833 4.3401

8. 61 57.9167 3.0833 9.5067

9. 62 57.9167 4.0833 16.6733

10. 55 57.9167 -2.9167 8.5071

11. 54 57.9167 -3.9167 15.3405

12. 56 57.9167 -1.9167 3.6737

=76.9162

VIII. DISCUSSION OF RESULTS

The experimental results above show remarkable deviation from the mean value. This can be attributed to

The estimated ultimate tensile strength is checked from Steel Properties Table at a corresponding hardness value

of 57.9HRC. The Ultimate Tensile Strength was given as 2068N/mm2. The standard deviation of the hardness values

obtained during the test was 2.6443HRC. The deviations in the values can be traced to several reasons which may

include:

i. Inhomogeneity of material surface

ii. Oil film, grease or dirt on material surface

iii. Indentation on previous holes on material surface

iv. Vibration of test equipment

v. Loading mechanism

vi. Load applied time

IX. INDUSTRIAL APPLICATIONS

i. Aerospace In the aerospace industry, hardness tests are widely employed for structural and component development, testing and

inspection of materials and parts.

ii. Airplane manufacturing For maintenance and repair involving substitution of metals, hardness tests are employed to prevent parts being

replaced with sub-standard parts, leading to rapid wear and finally crash of the aircraft.

iii. Lawnmower blades Hardness tests are employed to test the wear resistance of the blades

iv. Machining Hardness tests are used quite extensively to determine the resistance to scratching of engineering materials before

and after machining.

v. Metrology In the field of metrology, hardness tests find application to verify the accuracy of the instruments

vi. Racing and Cars In design and production of automobile cars for personal use or sport, hardness tests are employed for testing of

wheels, brake pads, and clutch disks

vii. Bullets manufacturing For ammunition and armory, hardness are extensively applied to test the lead harness of produced bullets of

firearms.

viii. Steel warehouses Product testing is an important process in steel warehouses. The mechanical properties of the products are

determined usually by hardness tests.

X. VISIT TO FIIRO OSHODI

The Federal Institute of Industrial Research, Oshodi (FIIRO) is a parastatal under the agency of the Federal

Ministry of Science and Technology. FIIRO is the foremost centre for Science and Technology-based research and

development for the industrialization and socio-economic advancement in Nigeria. It conducts, coordinates and

promotes market-driven research and development (R&D) for the industrialization and socio-economic development

of the country, with focus in Food and Agro Allied Processing Technologies, Pulp and Paper Processing,

Packaging and Product Design as well as Design and Fabrication of Equipment Prototype.

It is located at FIIRO road, off Agege Motor road, Oshodi, Lagos. I was taken round to the different testing

equipment in their materials section by one Mr. Mike, the head of the Materials section. It was a firsthand

experience as I was opportune to see different means of testing engineering materials.

A. THE UNIVERSAL TESTING MACHINE

The universal hardness testing machine I saw was very

similar to the one used in the mechanical laboratory but

this worked on the principle of hydraulics. The

Universal Testing Machine is capable of performing

different hardness tests (both Brinell and Rockwell

hardness tests). Specific load is to be forced into test

material based on material type. The indenter has a

diameter mostly 10mm for ferrous metals it is 10000N

(10kgf). The material is rotated until the gauge reaches

this force and the material becomes indented

automatically. There are two ways of obtaining hardness

values of materials either by calculations or with direct

gauge readings. Universal hardness testing machines can

be used for more than just one testing method their

versatility makes them suitable for a wide range of

applications.

B. THE ELECTRONIC ROCKWELL TESTER

The Rockwell tester that was used in FIIRO is

electrically powered, unlike the equipment in the school

laboratory which is hydraulically powered. The

Rockwell tester uses a direct reading instrument based

on the principle of differential depth measurement.

Initially a minor load is applied, and a zero datum

position is established. The major load is then applied

for a specified period and removed, leaving the minor

load applied. The resulting Rockwell number represents

the difference in depth from zero datum as a result of the

application of major load. The entire procedure requires

only 5 to 10 seconds. Use of a minor load greatly

increases the accuracy of this type of test, because it

eliminates the effects of backlash in the measuring

system and causes the indenter to break through slight

surface roughness.

C. THE BRINELL TESTER

The Brinell hardness tester was hydraulically actuated. It

is commonly used to test materials that have a structure

that is too coarse or that have a surface that is too rough

to be tested using another test method, e.g., castings and

forgings. Brinell testing often use a very high test load

(3000 kgf) and a 10mm wide indenter so that the

resulting indentation averages out most surface and sub-

surface inconsistencies. The Brinell method applies a

predetermined test load to a carbide ball of fixed

diameter which is held for a predetermined time period

and then removed. The resulting impression is measured

across at least two diameters usually at right angles to

each other and these result averaged. A formula was

given to me, which is to be used to calculate the Brinell

hardness value from the diameters and force applied.

XI. RECOMMENDATIONS

Based on the industrial visit to FIIRO, I would make the following recommendations for the hardness test unit in

the school laboratory:

i. Machine Table: If the bench or table on which a Rockwell hardness tester is mounted is subject to

vibration, such as is experienced in the school laboratory as a result of transmitted vibration of other

machines in the Mechanics of Machines laboratory, the indenter will indent farther into the material

than desired. I therefore recommend that the tester should be mounted on a metal plate with sponge

rubber at least 2.5 cm (1 in.) thick, or on any other type of mounting that will effectually eliminate

vibrations from the machine. Otherwise the indenter will indent farther into the material than when such

vibrations are absent.

ii. Cleanliness of Indenter: Dust, dirt, grease, and scale or rust affect the results of the hardness tests

produced when they are allowed to accumulate on the indenter. I recommend that the indenters used in

the laboratory should be kept in special housings. Also, steel ball indenters that have nicks, burrs, or are

out of round shall not be used.

iii. Care of the Equipment: The condition of the test equipment is an important factor in the accuracy of

the tests. Dust, dirt, or heavy oil act as a cushion to the load supporting members of the test equipment

and cause erroneous readings of the instrument dial. I recommend that the shoulders of the instrument

housing, indenter chuck, ball seat in the instrument housing, capstan, capstan screw, and anvil shoulder

seat should be kept clean and true. In addition, the capstan and screw should be lightly oiled.

XII. CONCLUSION

Hardness test is an important test for cutting tools. It helps to ascertain whether the cutting tools can withstand

the heavy conditions of the cutting process, avoid excessive wear and to produce high quality and economical parts.

In addition, the hardness test is a quick method of determining the mechanical properties of metallic tools based on

the relationship between hardness and other material properties.

XIII. REFERENCES

Books

[1] Harry Chandler, Hardness Testing, 2nd Edition, ASM International, 1999, ISBN: 978-0-87170-640-9

[2] Jain K.C. & Chitale A.K., Textbook of Production Engineering, New Age International Publishers, 2010, ISBN-

978-81-203-3526-4

[3] Juneja B.L. & Sekhon G.S., Fundamentals of Metal Cutting and Machine Tools, 2nd Edition, New Age

International Publishers, 2003, ISBN: 81-224-1467-2

[4] Konrad Herrmann, Hardness Testing: Principles and Applications, ASM International, 2011, ISBN-978-1-

61503-832-9

[5] Rao P.N., Manufacturing Technology: Metal Cutting and Machine Tools, McGraw-Hill, 2000