PROPERTIES OF MATERIALS LAB

(BTM 2412)

REPORT

HARDNESS AND MICSTRUCTURE OF MATERIALS TESTS

INSTRUCTOR’S NAME: MADAM SITI AISHAH BINTI RUSDAN

SECTION: 03

SEMESTER/YEAR : 2/2

GROUP MEMBERS:

1) NOR HIDAYATUL AKMAL BINTI AZAHAR TA12003

2) NOR AZIZAH BINTI MOHAMAD SHOBIR TA12012

3) MUHAMAD HAFIZ BIN FATAHUDDIN TA12007

4) RAHMAD BIN SUDIRMAN TA12016

HARDNESS TEST

ABSTRACT

Hardness as defined by The Metals Hand book is “Resistance of metal to plastic deformation”, usually by indentation. However, the term may also refer to stiffness or temper, or to resistance to 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. In this experiment there will include Brinell, Vickers and Rockwell tests.

The Brinell hardness test method most 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. The Brinell test for this experiment uses steel ball as indenter which is pressed into a specimen by a 100 kgf load that is maintained for 15 seconds. Since the Brinell number is based on the area of indentation, the diameter of the indentation must be measured. This is done with a microscope. The larger diameter indentation corresponds to a softer material and lower Brinell number.

Next is Rockwell test. 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 hardness test method consists of indenting the test material with a diamond cone. The indenter is forced into the test material under a load of 150 kgf.

The Vickers hardness test method is mostly used for small parts, thin sections, or case depth work. The Vickers method is based on an optical measurement system. 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.

METHODOLOGY

BRINELL HARDNESS TEST

All Brinell tests use a carbide ball indenter. The test procedure is as follows:

The indenter is pressed into the sample by an accurately controlled test force.

The force is maintained for a specific dwell time, normally 10 - 15 seconds.

After the dwell time is complete, the indenter is removed leaving a round indent in the sample.

The size of the indent is determined optically by measuring two diagonals of the round indent using either a portable microscope or one that is integrated with the load application device.

The Brinell hardness number is a function of the test force divided by the curved surface area of the indent. The indentation is considered to be spherical with a radius equal to half the diameter of the ball. The average of the two diagonals is used in the following formula to calculate the Brinell hardness.

ROCKWELL HARDNESS TEST

The specimen is correctly placed on the anvil of the Rockwell Hardness instrument. The base of the instrument is slowly rotated the LED will started to move until it

reaches ‘SET’. The test is automatically started. The reading is taken after ‘TI’. Step 1-4 is repeated for the other area of the steel.

VICKERS HARDNESS TEST

The specimen is correctly place on anvil of the Vickers Hardness instrument.

The specimen is being focused and changed it below the indenter exactly.

The ‘START’ button is pressed and the machine will shine with the sound showed that the machine is readily operated.

When the ‘START’ light goes off, the indenter is assured that it doesn’t touches the specimen’s surface.

Change t he i nden t e r w i th t he l en s . The w id th o f t he co rne r i s measu red and no t ed . Step 1-6 is repeated for the other area.

RESULT AND DISCUSSION

BRINELLS

Load = 100kgf

Reading Brinnel Hardness Test number (BHN)

1 32.3 2 58.7 3 20.7 4 53.4 5 37.9 Average 40.6

A good sampling size due to a large steel ball diameter is advantageous for materials with highly

different microstructures or microstructural heterogeneity. Scratches or surface roughness have

very small effects on the hardness values measured. However, there are some disadvantages of

Brinell hardness test. These are errors arising from the operator themselves (from diameter

measurement) and the limitation in measuring of too small samples.

ROCKWELL

Load = 150kgf

Reading Rockwell Hardness Test number 1 Out of range 2 Out of range 3 Out of range 4 Out of range 5 Out of range

All the result from reading 1-5 are out of range. This is because daily indirect performance verification of the testing instrument is also important; the scales being used should be verified using standardized test blocks or coupons. If possible, it is recommended that the system is verified with each scale change and at each shift start-up. Blocks should be selected that are in the approximate range of the material being tested and used only on the calibrated side. Two “seating” indents should be made to set the anvils, block and indenter. These values should be discarded prior to actual recording of results. Five total readings should be made in the verification process; the measured values must fall within the tolerance stated on block and the block certificate. If verification fails, the machine should be removed from operation until the appropriate adjustments or repairs are made. Periodic visual inspection of the diamond and ball indenters for damage that could occur during testing should be carried out and compromised they should be replaced.

VICKERS

Load =100kgf

READING d1 d2 HVN 1 37.38 37.38 132.7 2 41.81 41.81 106.1 3 35.69 35.69 145.6

Average 192.2

The Vickers hardness is the quotient obtained by dividing the kgf load by the square mm

Area of indentation.

VHN = 2P sin

1362

d2

P is the load and it can be varied from to grams

d is the average diagonal diameter of indentation [mm].

When the mean diagonal of the indentation has been determined the Vickers hardness may be calculated from the above formula. The Vickers hardness should be reported like 192.2HV/10, which means a Vickers hardness of 192.2, was obtained using a kgf force.

CONCLUSION

There are several reasons that makes hardness test be performed more frequently than any other mechanical test. Some of them are they are simple and inexpensive which normally no special specimen needed to be prepared, and the testing apparatus is less expensive. Next is the test is non-destructive where the specimen is neither fractured nor excessively deformed (only a small indentation). Last is the other mechanical properties often may be estimated from hardness data, such as tensile strength.

From the experiment, the Brinell, Vickers and Rockwell are tests that are designed to test the hardness of a metal sample. The Brinell test measures the diameter of an indentation in order to obtain a hardness number, the Rockwell test measures the depth of penetration and returns a hardness number and the Vickers test measures small parts of metal with a diamond indenter.

In conclusion, the lab illustrates that each test can measure the behavior of the material however some lack the ability to measure all materials. Those who can measure on a large scale involve a greater amount of estimation and have greater room for error. The best scenario would be one tool that could measure all materials with great accuracy but since none exist you should use the right tool for the right job.

RECOMMENDATION

BRINELL

Very hard metals, over 450BHN may also cause the ball to deform resulting in an

inaccurate reading. To overcome this limitation a tungsten carbide ball is used instead

of the hardened steel ball but there is also a hardness limit of 600BHN with this indenter.

The oxide layer should be remove from the sample by using sand paper or grinders

otherwise it would cause variation in hardness number.

Cannot perform the operation on a very thin sheet of metal usually having thickness less

than 10mm.For this we need to pile few sheets accurately without any impurity or oxide

layer.

Both surface of the specimens was ensure that flat and positioned securely on the anvil.

The elevating was rotated gently during elevation of the anvil. Otherwise, the indenter

may be destroyed due to the abrupt strike of the indenter tip with the specimen.

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

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

are perpendicular to each other within 20

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.

ROCKWELL

The indenter and anvil should be clean and well seated.

The surface to be tested should be clean and dry, smooth, and free from oxide. A rough-ground surface is usually adequate for the Rockwell test.

The surface should be flat and perpendicular to the indenter.

Tests on cylindrical surfaces will give low readings, the error depending on the curvature, load, indenter, and hardness of the material. Theoretical and empirical corrections for this effect have been published.

The thickness of the specimen should be such that a mark or bulge is not produced on the reverse side of the piece. It is recommended that the thickness be at least 10 times the depth of the indentation. The spacing between indentations should be three to five times the diameter of the indentation.

The speed of application of the load should be standardized. This is done by adjusting the dashpot on the Rockwell tester. Variations in hardness can be appreciable in very soft materials unless the rate of load application is carefully controlled.

VICKERS

When doing the hardness tests the minimum distance between indentations and the distance from the indentation to the edge of the specimen must be taken into account to avoid interaction between the work-hardened regions and effects of the edge.

Ensure that contact surfaces such as the indenter attachment face, between the specimen and specimen platform, and between the specimen platform and raising/lowering screw are continually maintained in a clean state. Accurate hardness values may not be obtained if foreign matter such as dust, rust, or oil is included on contact surfaces.

The specimen measurement location must be spaced at least 4d (where d is the indentation diameter) from the center of indentations already present. The measurement location must also be separated at least 2d from the edge of the specimen.

The surface (test face) and reverse face of the specimen must be kept as horizontal aspossible. When measuring specimens which are not horizontal, maintained the test faceperpendicular to the indenter axis using special jigs. Care is also needed in providing a satisfactory finish to the reverse face of the specimen, and not just the test face. Correct hardness values will not be obtained if the specimen surface is concave, as deformation will occur under the load.

The specimen thickness or hardened layer thickness must be at least 8 times theindenter penetration depth. Correct hardness values will not be obtained if below this and so either the test load must be reduced or else measurements must be performed using a different type of hardness tester. Otherwise, try measuring with a different scale having a large steel ball indenter.

REFERENCES

http://uqu.edu.sa/files2/tiny_mce/plugins/filemanager/files/4220193/lab02- Hardness_Test.pdf

http://www.mslab.boun.edu.tr/hardness.pdf

http://dcomm.cxc.lsu.edu/portfolios/09fall/jboard2/Hardness_report.pdf

http://engineeringdiary.wordpress.com/2008/09/13/hardness-testing/

http://www.wilson-hardness.com/Resources/PressandPublications/ BestPracticesforRockwellHardnessTesting.aspx

http://en.wikipedia.org/wiki/Vickers_hardness_test#Precautions

http://www.mse.iastate.edu/files/2011/07/Buehler_Hardness-Tester.pdf

APPENDIX