How to Do Rockwell Hardness Test | ferrous and non-ferrous metals

In this article, we explained how To measure the Rockwell hardness of ferrous and non-ferrous metals such as hard alloy, carbon steel, alloy steel, cast iron, brass, aluminium, etc.

 

SCOPE OF ROCKWELL HARDNESS TEST

Hardness is defined as resistance to penetration or resistance to abrasion. The test involves determining the depth of the sample caused by a certain indentation under a certain constant load.

In the Rockwell hardness test, an indentation is formed on the surface of the test specimen in two operations. In the first process, a small initial or datum (small) load of 10 kg is applied to one penetration to observe the surface roughness of the sample; Whereas a large or constant load (60,100,150 kg) is added in the second process. The permanent increase in the depth of penetration from the depth at which the data reaches under load due to static load is measured after it is removed. Indicates the hardness of the material read on the dial-in inverse proportion to the depth of penetration; So that the higher the penetration, the lower the hardness number and vice versa. A 120 degree angled steel ball or diamond cone made of black diamond is used. Indentation is selected depending on the nature and position of the object. This induction test used on small samples and hard materials is conducted in accordance with IS 1586: 2000.

The Rockwell hardness test machine is widely used for its simple test method, which reads the hardness number directly. This machine can be used to test materials such as hard steel, mild steel, aluminum, cast iron and brass. Indentation or penetration is a steel ball or diamond cone with a small rounded point. A steel ball weighing 100 kg is used to test soft materials such as brass and hardness number. A diamond cone weighing 150 kg is used to test hard materials such as hard steel and hardness number (C scale).

 

APPARATUS

Rockwell hardness testing machine; Ball and Brale (diamond) Indentors; 0.0 Emery paper.

Description of Apparatus

The Rockwell Hardness Testing Machine Affects a constant load on a steel ball or brale (diamond) indentor. Depth of indentation is recorded on the dial gauge based on Rockwell hardness numbers. The machine's dial gauge is provided with a long mouse with red and black scales. The red scale is used for the hardness measurements obtained with ball indentation and the black scale is used for the diamond indenter. The hardened steel is tested at C level with a diamond indenter and a large load of 150 kg. Soft materials are tested on a B scale steel ball with a diameter of 1.5875 mm and with a large load of 100 kg. The application of large load is preceded by 10 kg of small load. Conventional Rockwell hardness testing machines are shown in Figure below. Also known as the Black Diamond Indenter, the interlayers are made of hardened steel and cast iron with a brale indenter, a cone-shaped diamond with a peak angle of 120 degrees and a radius of 0.2 mm. For non-ferrous metals a hardened steel ball with a diameter of 1.5875 mm is used.

The Rockwell hardness test machine exerts a constant load on the steel ball or braille (diamond) inductor. The depth of indentation is recorded on the dial gauge based on Rockwell hardness numbers. The machine's dial gauge is provided with a long mouse with red and black scales. The red scale is used for hardness measurements obtained with ball indentation and the black scale is used for diamond indentation. The hardened steel is tested at C level with a diamond indentation and a large load of 150 kg. Soft materials are tested on a B-size steel ball with a diameter of 1.5875 mm and a large load of 100 kg. Large load application precedes 10 kg small load. Conventional Rockwell hardness testing machines are shown in the image below. Also known as the Black Diamond Indenter, the interlayers are made of hardened steel and cast iron with a braille indentation, a cone-shaped diamond with a maximum angle of 120 degrees and a radius of 0.2 mm. For non-ferrous metals, a hardened steel ball with a diameter of 1.5875 mm is used.

Typical Rockwell hardness testing machines

 

ROCKWELL HARDNESS TEST PROCEDURE

Step 1: Select a standard load of 100 kg or 150 kg to be used in the sample depending on the nature of the material being tested.

 

Step 2: Select the penetrator to be used corresponding to the load selected in Step 1.

 

Step 3: Remove any oxide scale and foreign materials from the surface of the specimen by rubbing with Emery paper.

 

Step 4: Place the specimen on the hardened anvil of the machine and turn the handwheel to move the anvil upwards till the surface of the specimen just touches the indentor.

 

Step 5: Apply the datum or minor load of 10 kg to the specimen by rotating the handwheel slowly until the smaller needle (pointer) on the dial reaches the red mark (dot); in some machines, at this point, the pilot lamp goes off.

 

Step 6: Actuate the lever or handle to apply a major load of 100 kg for scale B and 150 kg for scale C to the specimen by rotating the handwheel in about 5 to 8 seconds.

 

Step 7: On completion of penetration, remove the major load by pulling backwards the loading handle to the original position; the initial load 10 kg will still be on the specimen.

 

Step 8: Read the position of the pointer on the C or B scale dial which gives the Rockwell Hardness Number (RHN) of the specimen; record the hardness number read from the dial of the machine.

 

Step 9: Release the minor load of 10 kg by rotating the handwheel anticlockwise and lowering the screw.

 

Step 10: Repeat Steps 4 to 9 for five times on the same specimen selecting different points for indentation.

 

Step 11: Take average five values of indentation of each specimen to obtain the hardness number of the material sample. Plot the bar charts separately for B and C Scales.

 

Step 12: Compare the results obtained from other hardness tests and draw conclusions.

 

Observations and Calculations

For the various material guidelines for selecting the indentor, the main load and hardness levels are listed in the observation table below.

Material of the specimen is __________

Result

Rockwell hardness number for material is _________

 

PRECAUTIONS TO BE TAKEN

1. The surface of the specimen should be well polished, free of oxide levels and any foreign matter.

2. The thickness of the specimen should not be less than eight times the depth of the indentation, which should avoid deformation that should extend to the opposite surface of the specimen.

3. Do not push near the edge of a sample to avoid unnecessary concentration of pressures. In such a case, the distance from the edge to the center of the indentation should be 2.5 times the diameter of the indentation.

4. Rapid use of loads should be avoided. Sudden application of loads on the ball may increase the effective induction force. A more rapidly applied load will restrict the plastic flow of an object, which affects the amount of indentation.

5. Give the lever at least 10 seconds after resting before recording the reading.

 

Conclusion

The Rockwell hardness test uses the depth of penetration of a test indentation as a measure of hardness under a constant load. Indentation is selected depending on the nature and position of the object. A constant load of 100 kg is applied in about 5 to 6 seconds, while a 50 kg load is applied in about 6 to 8 seconds.

Rockwell hardness test is commonly used to detect the hardness of plastics such as ceramic materials, nylon, polycarbonate, polystyrene and acetyl. Dial gauge refers to the hardness based on the difference in depth of indentation generated by the datum and static loads.

For general reference, the key load and inductance combinations for some items are given in the table below.

Selection of combination of major load and indentor for some materials

NATIONAL STANDARDS

1. IS: 2-1960 (revised): Rules for Rounding off Numerical Values.

2. IS 432 (Parts 1 and 2)–1982: Specification for Mild Steel and Medium Tensile Steel Bars and Hard-Drawn Steel Wire for Concrete Reinforcement, Part I: Mild Steel and Medium Tensile Steel Bars; Part 2: Hard-Drawn Steel Wire

3. IS 961–1975: Structural Steel (High Tensile).

4. IS 1499:1977 (RA-2009) (1st revision): Method for Charpy impact test (U-notch) for metals

5. IS 1500:2005 (3rd revision)/ ISO 6506-1:1999; Metallic materials—Brinell hardness test—Test method

6. IS 1501:2002 (3rd revision) / ISO 6507-1:1997: Method for Vickers Hardness Test for Metallic Materials.

7. IS 1586:2000 (3rd revision): Method for Rockwell Hardness Test for Metallic Material.

8. IS 1598:1977 (RA-2009) (1st revision): Method for Izod Impact Test of Metals.

9. IS 1599:1985 (RA-2011)/ ISO 7438:2005 (2nd revision): Method for Bend Test for Steel Products Other.

10. IS 1608-2005 (RA-2011)/ ISO 6892:1998 (3rd revision): Metallic Materials—Tensile Testing at Ambient Temperature.

11. IS 1716:1985 (RA-2001) (2nd revision): Method for Reverse Bend Test for Metallic Wire

12. IS:1730-1989 (2nd revision): Steel Plates Sheets, Strips and Flats for Structural and General Engineering Purposes.

13. IS: 1732-1989 (1st revision): Dimensions for Round and Square Steel Bbars for Structural and General Engineering Purposes.

14. IS 1754:2002 (3rd revision) / ISO 6507-2:1997; Method for verification of Vickers hardness testing machines

15. IS 1757:1988 (RA-2009) (2nd revision): Method for Charpy Impact Test (V- notch) for Metallic Material.

16. IS 2281:2005 (RA-2011) (3rd revision)/ISO 6506-2:1999: Method for Verification of Brinell Hardness Testing Machines.

17. IS 2854:1990 (RA-2001) (1st revision): Determination of Young’s Modulus, Tangent Modulus and Chord Modulus—Test Method.

18. IS 4258:1982(RA-2003) (1st revision): Hardness Conversion Tables for Metallic Materials

19. IS 5069:1982 (RA-2003) (1st revision): Glossary of Terms Relating to Methods of Mechanical Testing of Metals.

20. IS 5074:1969 (RA-2001): Method for Axial Load Fatigue Testing of Steel.

21. IS 5075:1985 (RA-2001) (1st revision):  Method of Rotating Bar Bending Fatigue Testing of Metals.

22. IS 5242:1979 (RA-2006) (1st revision): Method of Test for Determining Shear Strength of Metals

23. IS 10588:1983 (RA-2001); Tables of Brinell Hardness Values for Use in Test Made on Flat Surfaces

24. IS 12514:1988 (RA-2003): Method for Torsional Stress Fatigue Testing.

25. IS 13780:1993 /ISO 4506:1979: Hard Metals—Compression Test

26. IS 13838:1993 (RA-2001): Mechanical Testing of Metals—Determination of Poisson’s Ratios.

27. ISO 178: Plastics—Determination of Flexural Properties

 

REFERENCES

1. AASHTO M31M/M 31-02: Specifications for Deformed and Plain Billet-Steel Bars for Concrete Reinforcement

2. ASTM E8 -Vol. 3.01: Test Methods for Tension Testing of Metallic Materials

3. ASTM E606 Standard Practice for Strain-Controlled Fatigue Testing

4. ASTM E855—08: Standard Test Methods for Bend Testing of Metallic Flat Materials for Spring Applications Involving Static Loading.

5. Gambhir, M. L., Fundamentals of Solid Mechanics, PHI Learning Private Limited, 2010.

6. Gambhir, M. L. and Neha Jamwal, Building Materials: Products, Properties and Systems, McGraw-Hill Education (India), 2011.