1. 1. Standard Test Method for Vickers Hardness of Materials E92-82(reapproved 1997) BY:- NAMAN SONI(12BME051) NIMESH SUTHAR(12BME052) ABHISHEK THAKKAR(12BME53) NAISHAL THAKKAR(12BME054) ADITYA VAGHASIYA(12BME55)
2. 2. Scope This test method covers the determination of the Vickers hardness of metallic materials, using applied loads of 1 kgf to 120 kgf, the verification of Vickers hardness testing machines, and the calibration of standardized hardness test blocks. Two general classes of standard tests are recognized : Verification, Laboratory or Referee Tests. Routine Tests.
3. 3. Reference Documents ASTM Standards: E 4 Practices for Force Verification Testing Machines. E 140 Hardness Conversion Tables for Metals (Relationship between Brinell Hardness, Vickers Hardness Rockwell Hardness, Rockwell Superficial Hardness, Knoop Hardness and Seleroscope Hardness). E 384 Test Method for Microhardness of Materials.
4. 4. Terminology Vickers hardness number, HV a number related to the applied load and the surface area of the permanent impression made by a square-based pyramidal diamond indenter having included face angles of 136 can be calculated by : HV = 2P sin (/2)/d2 =1.8544P/d2
5. 5. Formula HV = 2P sin (/2)/d2 =1.8544P/d2 Where: P = load, kgf d = mean diagonal of impression, mm = face angle of diamond = 136
6. 6. Terminology Vickers hardness test an indentation hardness test using calibrated machines to force a square-based pyramidal diamond indenter having specified face angles, under a pre-determined load, into the surface of the material under test and to measure the diagonals of the resulting impression after removal of the load. VH test are made at test loads of 1 kgf to 120 kgf.
7. 7. Contd For practical purposes the Vickers hardness number is constant when a square-based diamond pyramid with a face angle of 136 is used with applied loads of 5 kgf and higher. At lower test loads Vickers hardness numbers may be load dependent. In table 2 the Vickers hardness numbers for a test load of 1kgf are given.
8. 8. Contd For obtaining hardness numbers when other test loads are used, the Vickers hardness number obtained from table 2 is multiplied by the test load in kilograms- force.
9. 9. Using table 3 determine: HV = 4.47 at 0.644 mm diagonal length at 1kgf load. 50*4.47 = 224 HV for 50 kg test load
10. 10. A)GENERAL DESCRIPTION & TEST PROCEDURE Apparatus Test specimen Verification of apparatus Procedure Measurement of Impression Accuracy Conversion to other Hardness scales or tensile strength values Report Precision and Bias
11. 11. 1)APPARATUS A. Testing machine:- supports the specimen. Permits the indenter and the specimen to be brought into contact gradually and smoothly under a predetermined load,which is applied for a fixed period of time. Design should be such that no rocking or lateral movement of indenter or specimen is permitted while load is applied or removed Measuring microscope is usually mounted in such a manner that the impression in the specimen may be readily located in the optical field.
12. 12. B. Indenter:- Should be Highly polished, pointed, square-based pyramidal diamond with face angles of 136 30min. All four faces shall be equally inclined to the axis of the indenter(within 30min) and meet at sharp point , i.e. the line of junction between opposite faces shall not be more than 0.001 mm in length. It should be examined periodically and if it is loose in the mounting material, chipped or cracked,it should be discarded or reconditioned.
13. 13. NOTE:- Point of the indenter is of considerable importance where the test load is light and the impression is small. It should be periodically checked by examining an impression made in a polished steel block, under a magnification of 600 or more, using a vertical illuminator ,and extent of defect is measured with a filar micrometer. Diamond pyramid indenter should not be used for tests in which the maximum length of such a defect exceeds 5% of the length of the impression diagonal
14. 14. C. Measuring Microscope:- Divisions of micrometer scale of measuring microscope shall be so constructed that the length of the diagonals of an impression in a properly surface finished specimen can be measued to within 0.0005 mm or 0.5% , whichever is larger.
15. 15. 2)TEST SPECIMENS A. Thickness:- It should be at least one and half times the length of the diagonal of an indenter. It should be such that,no bulge or marking showing the effect of the load appears on the side of the specimen opposite the impression. B. Finish:- It should be so prepared that the ends of the diagonals are clearly defined and can be read with precision of 0.0005 mm or 0.5% of the length of the diagonals , whichever is larger.
16. 16. C. Alignment:- Surface of specimen should be normal to the axis of the indenter within 1 of angle. Opposite side should be parallel upto maximum extent. D. Radius of curvature:- It is a special case for spherical and cylindrical surfaces. Correction factor must be applied to the vicker hardness values obtained. Correction factor are given in standard table corresponding to the ratio of mean diagonal d of indentation to the diameter D of the sphere or cylinder .
17. 17. Example: Diameter of sphere, D = 10 mm Load =10 kgf Mean diagonal of impression, d =0.150 mm d/D = 0.150 / 10 = 0.015 From Tables 2 and 3 , HV= 824 From Table 4, correction factor = 0.983 Hardness of sphere = 824 * 0.983 =810 HV 10
18. 18. 3)VERIFICATION OF APPARATUS TWO METHODS: Separate verification of load application , indenter , measuring microscope. Verification by standardized test block method.
19. 19. 4)PROCEDURE A. Magnitude of Test Load:- Test load of 1 kgf to 120 kgf may be used, depending upon the requirements of the test. Tests on homogeneous materials indicate that the Vickers hardness number is nearly independent of the test load, but this condition will not be present in cases where there is a hardness gradient from the specimen surface to the interior of the specimen. Therefore magnitude of the test load should be stated in the test report.
20. 20. B. Application of Test load:- The time of application of the full test load shall be 10 to 15 sec. , unless otherwise specified. It should be applied and released smoothly without shock or vibration. C. Spacing of Indentation:- It should not be closer to any edge of the test specimen or to another impression than a distance equal to two and half times the length of diagonal of the impression.
21. 21. 5)MEASUREMENT OF IMPRESSION Both diagonals of the impression shall be measured and their mean value is used as a basis for calculation of the vicker hardness number. In case of anisotropic materials ,such as heavily cold worked , there may be a difference between the lengths of the diagonals.In such cases,test specimen should be reoriented so that the diagonals of a new impression are approximately of equal length.
22. 22. 6)ACCURACY It depends upon accuracy of test load , indenter , measuring device , support surface etc. Under optimum condition of these factors the accuracy that can be expected is equivalent of 4% of the vicker hardness number of the standardized reference hardness test blocks.
23. 23. 7) CONVERSION TO OTHER HARDNESS SCALES OR TENSILE STRENGTH VALUES
24. 24. 8)REPORT It shall include:- The Vicker Hardness number, The test load used, The loading time , if other than 10 to 15 seconds. 9)PRECISION AND BIAS Due to wide variety of materials tested by this method and the possible variations in test specimens, the precision of this method has not been established. Generally it can be established by employing statistical methods.
25. 25. B) VERIFICATION OF VICKERS HARDNESS TESTING MACHINE
26. 26. 1)SCOPE This part covers the procedure for verification of Vickers Hardness Testing Machine and the procedure that is recommended for use to confirm that the machine is not properly adjusted in the intervals between periodical routine check. The two methods are: 1. Separate Verification of Force Application, Indenter, and Measuring Microscope which is used for new and rebuilt machines. 2. Vertification by Standardized Test Block Method which is used for verifying machines in service.
27. 27. 2)GENERAL REQUIREMENTS Before a Vickers hardness testing machine is verified the machine shall be examined to ensure that The machine is properly set up. The indenter holder is mounted normally in the plunger. The force can be applied and removed without shock or vibration in such a manner that the readings are not influenced.
28. 28. contd.... If the measuring device is integral with the machine, the machine shall be examined to ensure that the change from loading to measuring does not influence the readings. The method of illumination does not affect the readings. The center of the impression is in the center of the field of view.
29. 29. 3)VERIFICATION A. Force Application The applied force shall be checked by the use of dead weights and proving levers, or by an elastic calibration device . Vickers hardness testing machines shall be verified at a minimum of three applied forces including the test force specified. A minimum of three readings should be taken at each force. A Vickers hardness testing machine is acceptable for use over a loading range within which the machine error does not exceed + 1 %.
30. 30. contd..... B. Measuring Microscope The measuring microscope or other device for measuring the diagonals of the impression shall be calibrated against an accurately ruled line scale. The errors of the line scale shall not exceed 0.05 m (0.00005 mm) or 0.05 % of any interval, whichever is greater. The measuring microscope shall be calibrated throughout its range of use and a calibration factor chosen such that the error shall not exceed + 0.5 %.
31. 31. C. Verification by Standardized Test Block Method A Vickers hardness testing machine used only for routine testing may be checked by making a series of impressions on standardized hardness test blocks. A minimum of five Vickers hardness reading shall be taken on at least three blocks having different levels of hardness using a test force or forces as specified by the user with the test force applied for 12 s.
32. 32. 4)PROCEDURE OF PERIODIC CHECKS BY THE USER Make at least one routine check each day that the testing machine is used. Before making the check, verify that the zero reading of the measuring apparatus is correctly adjusted. Make at least five hardness readings on a standardized hardness test block on the scale and at the hardness level at which the machine is being used. If the values fall within the range of the standardized hardness test block the machine may be regarded as satisfactory; if not the machine should be verified by the Standardised Block Method
33. 33. 5)REPEATABILITY AND ERROR Repeatability For each standardized block, let d1, d2, d5 be the arithmetic means of the two diagonals of the indentations, arranged in increasing order of magnitude. The repeatability of the machine under the particular verification conditions is expressed by the quantity d5 d1. Error The error of the machine under the particular verification conditions is expressed by the quantity d d, where d= (d1 + d2 + d5)/5, and d is the reported mean diagonal of impressions on the standardized hardness test block.
34. 34. 6)ASSESSMENT OF VERIFICATION Repeatability The repeatability of the machine verified is considered satisfactory if it satisfies the conditions givenin Table 7. Error The mean diagonal for five impressions should not differ from the mean diagonal corresponding to the Vickers hardness of the standardized test block by more than 2 % or 0.5 m (0.0005 mm), whichever is greater.
35. 35. C. CALIBRATION OF STANDARD HARDNESS TEST BLOCKS FOR VICKERS HARDNESS MACHINES
36. 36. 1)SCOPE This part covers the calibration of standardized hardness test blocks for the verification of Vickers Hardness Test machines as described in previous parts.
37. 37. 2)MANUFACTURE Each metal block that is to be standardized should not be less than 0.25 inch in thickness. Each block should be specially prepared and heated to give the necessary homogeneity and stability of structure. If the block is of steel, it should be demagnetized from manufacturer and also mantained by user. The lower surface of the test block shall have a fine ground finish.
38. 38. The test surface should be polished and free of scratches which would interfere with measurements of the diagonals of the impression. The mean surface roughness height rating should not exceed 4 micro inch center line average. To ensure that no material is subsequently removed from the test surface of the standardized test block, an official mark of the thickness at the time of calibration shall be marked on the test surface to an accuracy of --- -0.005 to +0.005 inch.
39. 39. 3)STANDARDIZING PROCEDURE The standardized hadness test blocks shall be calibrated on a Vickers hardness testing machine as per the requirements of described in previous part ie.separate Verification of Force Application, Indenter, and Measuring Microscope The control mechanism of Application of Load should be of two type 1. A device such as spring to reduce velocity of indentation 2. A device that can maintain a constant velocity of indentation The full load shall be applied for 12 seconds.
40. 40. 4)NUMBER OF INDENTATIONS Preferably ten randomly distributed indentations shall be made on each test block. If not possible, atleast five indentations shall be made.
41. 41. 5)MEASUREMENT OF THE DIAGONAL OF THE INDENTATION The illuminating system of the measuring microscope shall be adjusted to give uniform intensity over the field of view and maximum contrast between the indentation and the undistributed surface of the block. The Measuring microscope shall be graduated to read 0.001mm with estimates made to nearest 0.0002mm. The Measuring microscope shall be checked by a stage micrometer , or by other suitable means , to ensure that the difference between reading corresponding to any two division of the instrument is correct within 0.0005mm. Indentation should be measured by two observers.
42. 42. 6)REPEATABILITY Let be the mean values of the measured diagonals arranged in increasing order of magnitude. Repetability is defined as for Ten readings or for Five reading.
43. 43. 7)UNIFORMITY OF THE HARDNESS The repetability of hardness readings as measured by mean of five-ten impressions should be within limits as given in Table. Unless repetability is within limits , the block cannot be regarded as sufficently uniform for standardization purposes.
44. 44. 8)MARKING After determining Hardness of the material , each block should be marked with the following : Arithmetic mean of the hardness values found in standardization test. The name or mark of the supplier. Serial number of the block. Thickness of the test block or and official mark on the top surface. All of the markings except the official mark or the thickness should be placed on the side of the block , the marking being upright when the test surface is the upper face.