Brinell and Rockwell Hardness Report - Louisiana State University

CE 3410 Mechanics of Materials Lab Louisiana State University

Laboratory Report No. 1 Hardness Test by Joshua Board

Table of Contents Purpose:............................................................................................................................... 3 Introduction: ........................................................................................................................ 3 Apparatus and Test Procedures:.......................................................................................... 7 Results:.............................................................................................................................. 11 Discussion: ........................................................................................................................ 13 Sample Calculations: ........................................................................................................ 17 Brinell Hardness Test .................................................................................................... 17 Rockwell Hardness Test ............................................................................................... 18 Conclusion: ....................................................................................................................... 19 References ......................................................................................................................... 20 Appendix ........................................................................................................................... 21 Appendices A1 – Original Test Data Sheet .................................................................. 21 Appendix A2 – Material Properties of Steel ................................................................. 22 Appendix A3 – Material Properties of Aluminum ....................................................... 23

TABLE OF FIGURES FIGURE 1 - BRINELL HARDNESS TESTER MODEL HB3000B ......................................................................................... 7 FIGURE 2 - ROCKWELL HARDNESS TESTER MODEL C504 ............................................................................................ 7 FIGURE 3 - RELATIONSHIP BETWEEN BRINELL EXPERIMENTAL HARDNESS AND REFERENCE HARDNESS ................................ 13 FIGURE 4 - RELATIONSHIP BETWEEN ROCKWELL EXPERIMENTAL HARDNESS AND REFERENCE HARDNESS ............................ 14 FIGURE 5 - COMPARISON OF TENSILE STRENGTH BASED ON BRINELL, ROCKWELL, AND REFERENCE DATA ............................ 15

TABLE 1- BRINELL STANDARDS FOR LOAD, TIME, AND HARDNESS ................................................................................. 4 TABLE 2 - RELATIONSHIP BETWEEN HARDNESS NUMBERS AND TENSILE STRENGTH........................................................... 6 TABLE 3 - BRINELL HARDNESS TEST DATA AND RESULTS ............................................................................................ 11 TABLE 4 - ROCKWELL HARDNESS TEST DATA AND RESULTS ......................................................................................... 12

Purpose: The purpose of this laboratory is to determine the hardness and the tensile strength of three metal samples: 1020 Steel, 6061 Aluminum and 2024 Aluminum. The Brinell and Rockwell Hardness Tests are used to determine this. With the results obtained from each sample, the engineer will be able to determine how the samples relate to each other. Both the Brinell and Rockwell Hardness Test are considered to be non-destructive.

Introduction: Hardness is the resistance of a material to penetration or abrasion under a locally applied load (Ref. 1). We use the concept of hardness almost every day. Any time we file our nails with a nail file or scratch a CD with our finger nails, hardness is involved. Hardness is used to measure a variety of resistances including: scratching, cutting, and indenting (Ref. 2). Also, Hardness may be used for grading similar materials, checking or controlling quality level and controlling uniformity of tensile strength (Ref. 2). As engineers, we find hardness tests useful for estimating the tensile strength of materials. The Brinell and Rockwell Tests are the most common experiments to determine the hardness of metals. Both Tests measure the resistance to indentation of a metal under a static load. However, as the technology has increased the usage of very hard steels, very thin materials, very small sized parts, etc, a number of other hardness tests have developed, and not just for metals but for wood, rubber, plastic, and paving materials (Ref. 2).

The Brinell Test procedures and specifications can be found in ASTM E10. The test consists of applying a load through a steel ball with a 10-millimeter diameter for a specific period of time. The standard for load amount, time period and hardness is shown below in Table I. Table 1- Brinell Standards for Load, Time, and Hardness

If the sample is expected to have a Brinell Hardness Number (BHN) greater than 450, an indenter made of a harder material should be used (Ref. 2). After removing the load, an indentation is left on the metal sample. By measuring the diameter of the indentation and using the known diameter of the steel ball that applies the load, the spherical area is calculated. The Brinell Hardness Number (BHN) is the ratio of the applied load in kilograms to the spherical area of the indentation in mm2 (Ref. 1). In order to find the BHN, the following equation is used: Equation (1)

Where: D = diameter of the steel ball, mm d = diameter of the indentation P = load, kg

The Brinell Hardness Number is used to give an estimation of the tensile strength of the metal using the following equation: T.S. = 500 x BHN

Equation (2)

Where: T.S. = tensile strength, psi BHN = Brinell Hardness Number The Rockwell Test procedures and specifications can be found in ASTM E18. This test uses the depth of indentation to determine the hardness number (Ref. 1). A minor load is applied to hold the sample in place then a major load is applied to indent the sample. The Rockwell Test is similar to the Brinell Test because both use indentation of a samples surface to determine hardness; however, the Rockwell Test measures depth of indentation not diameter as in the Brinell Test. The Rockwell Test uses smaller loads and creates smaller indentations on the sample as well (Ref.2). Also the Rockwell Hardness Tester has a gauge on the machine that will display the Rockwell Hardness Number, RHN, after the load is removed. For this test, a variety of indenters are used including: steel balls ranging from 1

/16-inch to ½-inch and spheroconical diamond tips (Ref.1). There are three standard

loads of 60, 100, and 150 kilograms that can be applied to a sample. Diamond tips along with a load of 150 kg are used for hard steel, while steel balls and a load of 100 kg is used for softer steel and aluminum. The gauge on the machine has two sets of numbers, a red and a black. 30 hardness numbers offset the scales with the black scale being the lower of the two (Ref.2). Each scale also provides a different pre-fix to be recorded with the hardness number, B for red and C for black. The combination of indenter and applied

load leads to what set of numbers, red or black, are used to measure the Rockwell Hardness Number. A diamond tip with applied load of 150 kg corresponds to the black scale and a steel ball with 100 kg corresponds to the red scale. The Rockwell Test is used for materials that are beyond the capabilities of the Brinell Test and because the Rockwell Hardness Number is shown on the machine if returns faster and more accurate hardness numbers (Ref. 2). However, the Rockwell test does not have such an easy way to calculated tensile strength as was afforded to us by the Brinell Test. In order to determine tensile strength, a standardized table showing the relationship between Rockwell Hardness Numbers, tensile strength and other properties has been developed and is provided below in Table II.

Table 2 - Relationship between Hardness Numbers and Tensile Strength

Picture taken by Joshua Board

Apparatus and Test Procedures:

Picture taken by Joshua Board

Figure 1 - Brinell Hardness Tester Model HB3000B

Figure 2 - Rockwell Hardness Tester Model C504

The Apparatus used for the Brinell Hardness Test is Model HB-3000B, shown in Figure 1. The apparatus used for the Rockwell Hardness Test is Model C504, shown in Figure 2. The Brinell Hardness Test requires the use of the following: 1- Brinell Hardness Tester Model HB-3000B (shown in Figure 1) 1- Testing Block with known BHN 3- Metal test samples 1- Microscope of low power 1- Ten millimeter diameter steel ball The Rockwell Hardness Test required the use of the following: 1- Rockwell Hardness Tester Model C504 (shown in Figure 2) 1- Testing Block with known RHN 3- Metal test samples 1- 1/16 inch diameter steel ball Both the Brinell and Rockwell Hardness Tests require three metal cubes with 1-inch sides to be the test samples. The samples to be tested are 1020 Steel, 6061 Aluminum and 2024 Aluminum. Before the test, each sample is inspected for any defects to the surface that could affect the results. All three samples were clean and passed inspection. The Brinell Test consists of pressing a steel ball of 10-millimeter diameter into the test sample for a standard amount of time, which will be 12 seconds for our laboratory. The 10-mm steel ball will impose a load of 3000 kg for steel samples and 1500 kg for aluminum samples. This load will cause a depression to remain on the surface of the sample after the load is removed. The spherical area of the indentation can

be calculated from the diameter of the indenter and the diameter of the depression on the surface of the sample. For the Brinell Test, the steel ball must not deviate in diameter more than 0.01 mm and balls of harder material are to be used if the sample has a known BHN greater than 450 (Ref. 1). Before starting either test, a test block was used on both the Brinell and Rockwell testers in order to verify accurate results. Tests should not be made too close together or too close to the edge of the sample. Procedure for Brinell Hardness Test: 1. Verify using the test block that the machine is accurate. 2. Determine the proper load to apply to the sample: 3000 kg for steel and 1500 kg for aluminum. 3. Set the amount of time for the test. In this lab we will use 12 seconds as our test time. 4. Select a test area on the sample, being sure to stay away for the edges and other indentions made on the sample. 5. Turn the screw until the sample and the steel ball contact each other and continue to turn the screw until the screw slips. 6. Push “Start” to begin the test and create an indentation on the sample. 7. Repeat step (4)-(6) two times so that a total of 3 indentations are on the sample. 8. Measure the diameter of each indentation with a low power microscope. 9. Determine the Brinell Hardness Number using Equation (1).

The Rockwell Hardness Test uses a steel ball 1/16-inch in diameter to indent the surface of a sample. This test uses a smaller load and indenter therefore the indentation is smaller and shallower. Similar to the Brinell test, the hardness number found by the Rockwell Test is a function of the indentation on the surface of the sample caused by the indenter under a static load (Ref. 2). However, the Rockwell Test is faster because the Rockwell Hardness Number is read straight from the machine. The Rockwell Hardness Number, RHN, is inversely related to the depth of indentation. Procedure for Rockwell Hardness Test: 1. Verify using the test block that the machine is accurate. 2. Determine the indenter to use. In this lab we will use a steel ball 1/16inch in diameter. 3. Select a test area on the sample, being sure to stay away for the edges and other indentions made on the sample. 4. Raise the sample against the indenter by turning the large screw until the center gauge is vertical. 5. Use the small screw to set the dial reading to zero. 6. Press the lever down to start the test. 7. Read the RHN from the red scale on the dial and include the prefix “B”. 8. Repeat steps (3)-(7) four times so that a total of five indentations are on the sample.

Results: The Table III below shows the data from the Brinell Hardness Test. Three diameter readings were recorded for each sample. The mean of the results for each individual sample is calculated and used as the diameter of the indentation. Knowing the applied load, the diameter of the indenter and the diameter of the indentation, equation (1) is used to find the Brinell Hardness Number for each sample. Using Equation (2), the tensile strength is determined. Table 3 - Brinell Hardness Test data and results

Brinell Hardness Test Data and Results Type of Material 1020 Steel 2024 Aluminum 6061 Aluminum Test No. Diameter (mm) 1 4.30 3.90 4.30 2 4.40 3.80 4.30 3 4.40 3.80 4.25 Mean 4.37 3.83 4.28 BHN 190 125 99.2 Tensile Strength (psi) 95000 62500 49600 Reference BHN* 179 120 95 Reference Tensile Strength (psi)* 87000 70000 45000

Table IV below shows the results of the Rockwell Hardness Test. Five tests were completed on each sample and the mean of each sample is calculated. The mean is recorded and used as the Rockwell Hardness Number, RHN, for each sample. Using Table II, the tensile strength of each sample is interpolated.

Table 4 - Rockwell Hardness Test data and results

Rockwell Hardness Test Data and Results Type of Material 1020 Steel 2024 Aluminum 6061 Aluminum Test No. Diameter (mm) 1 91.7 77.7 58.9 2 93.0 78.2 58.6 3 93.0 79.0 58.1 4 93.2 78.9 59.1 5 93.0 78.0 59.0 Mean 92.8 78.4 58.7 Tensile Strength (psi) 96071 71750 51360 Reference RHN** 88 75 60 Reference Tensile Strength (psi)** 87000 70000 45000

Discussion: Figure 3 below shows a graph of the relationship between the experimental BHN and the reference BHN obtained from MatWeb (Ref. 3), for both the steel and aluminum samples. The results show only a small deviation from the reference data and it should be noted that 1020 steel showed the most deviation at 5%. Also, each sample out preformed the reference hardness number recording higher values for hardness. 200

180

160

Brinell Hardness Number

140

120

100

BHN Ref. BHN

80

60

40

20

0

1020 Steel

2024 Aluminum

6061 Aluminum

Figure 3 - Relationship between Brinell Experimental Hardness and Reference Hardness

Figure 4, shown below, contains a graph of the experimental RHN and the reference hardness numbers given on MatWeb (Ref. 3). Both steel and aluminum samples remained close to the reference hardness with steel once again being 5% off of reference, but it is interesting to point out that 6061 Aluminum has fallen below the reference data provided by MatWeb (Ref. 3). In all other cases the hardness of the samples has exceeded that of the reference hardness. After comparing the data, both the Brinell and Rockwell test are producing accurate numbers and a maximum deviation of 5% over all further backs up both tests accuracy. 100.0

90.0

80.0

Rockwell Hardness Number

70.0

60.0

50.0

RHN Ref. RHN

40.0

30.0

20.0

10.0

0.0

1020 Steel

2024 Aluminum

6061 Aluminum

Figure 4 - Relationship between Rockwell Experimental Hardness and Reference Hardness

120000

100000

Tensile Strength (psi)

80000

60000

Brinell Tensile Strength (psi) Rockwell Tensile Strength (psi)

40000

20000

0 1020 Steel

2024 Aluminum

6061 Aluminum

Figure 5 - Comparison of Tensile Strength based on Brinell, Rockwell, and Reference data

Figure 5 above shows a comparison of the tensile strength recorded for each sample based on the Brinell and Rockwell tests. The graphs show that the Rockwell test recorded higher tensile strength for each of the samples but both 1020 steel and 6061 aluminum were determined to have values that were similar. The sample of 2024 Aluminum recorded interesting results as the greatest difference between the Brinell strength and Rockwell strength was found here. The Brinell test is more accurate for finding tensile strength, based on Equation (2)’s simplicity, where the Rockwell test has more room for error when interpolating Table II. For both tests, steel was determined to be the sample that exceeded the reference values for tensile strength by the most. 6061 Aluminum was found by both tests to be harder than the reference values. For 2024

Aluminum, the Rockwell test showed expected results, however the Brinell test determined that the 2024 Aluminum was not as strong as the reference tensile strength. Looking through the formulas, it seems that the Brinell Hardness Tests was able to create too large of an indentation in the surface of the 2024 Aluminum, recording a diameter of 3.83 mm. An indentation closer to 3.63 mm would have given the correct tensile strength according to the reference data. From the results shown it Figures 4, 5 and 6, it is clear that some errors have occurred. The Brinell Test required the reading of the diameter through a scope which could have lead to inaccuracies due to human error. Also it is possible that the load was prematurely removed from the sample before the 12 seconds had expired. For the Rockwell test it is possible that the numbers on the gauge were incorrectly read. However, there are other sources of error that can be pointed to in this lab. During the set up of the experiment it was noticed that the last inspection of the equipment was in 1999 and the label stated that both machines need to be inspected yearly.

Sample Calculations: Brinell Hardness Test (1020 Steel) Brinell Hardness Number, BHN D = 10-mm P = 3000 kg d = 4.37-mm

BHN = 190 Tensile Strength = BHN x 500 = 190 x 500 = 95000 psi

Rockwell Hardness Test (1020 Steel) Rockwell Hardness Number, RHN RHN = 92.8 (Read for gauge on Rockwell Tester) Tensile Strength = 96071 (Found using Table II)

Conclusion: The Brinell and Rockwell experiments are two tests that are both 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 and the Rockwell test measures the depth of penetration and returns a hardness number. Both tests are similar in this way but each offered its own individual advantages: Brinell with its ease of calculating tensile strength and Rockwell with its direct readings of hardness number for the machine. Both experiments are also considered non-destructive. Looking at the results it seems that both tests found our samples for the most part to be harder than the reference numbers indicated. The most likely source of error however seems to be the decade between inspections for both machines leading to uncertainty in the numbers they are providing. In future tests, more experience with the machine and metal samples along with better maintenance of the equipment would help to reduce errors. The recorded error for the hardness numbers was less than 5% for both the Brinell and Rockwell Hardness Tests and therefore each test can be considered reasonably accurate in terms of the tensile strength of a sample.

References 1. Mechanics of Materials Laboratory Manual CE 3410, Department of Civil and Environmental Engineering, Spring 2007, pT1-1 – T1-10. 2. Jacobs, C., CE 3410 Notes – “Hardness Testing”, received in class on January 13, 2009. 3. www.MatWeb.com 4. ASTM E 10 Standard Test Method for Brinell Hardness of Metallic Materials, ASTM International, April 2001. 5. ASTM E 18 Standard Test Method for Rockwell Hardness and Rockwell Superficial Hardness of Metallic Materials, ASTM International, April 2001.

Appendix Appendices A1 – Original Test Data Sheet Brinell Hardness Test Rockwell Hardness Test (Diameter, mm) (RHN) 1020 Steel 4.37 91.7 93.0 93.0 93.2 93.0 6061 Aluminum 4.28 58.9 58.6 58.1 59.1 59.0 2024 Aluminum 3.88 77.7 78.2 79.0 78.9 78.0

Appendix A2 – Material Properties of Steel Mechanical Properties

Metric

English

Hardness, Brinell

179

179

Hardness, Knoop

200

200 Converted from Brinell hardness.

88


Hardness, Rockwell B Hardness, Vickers Tensile Strength, Ultimate

188


600 MPa 370 MPa

87000 psi 53700 psi

Elongation at Break

23.00%

23.00%

Reduction of Area

64.20%

64.20%

200 GPa 140 GPa

29000 ksi 20300 ksi

0.29

0.29

Tensile Strength, Yield

Modulus of Elasticity Bulk Modulus Poissons Ratio

Comments

in 50 mm Typical for steel Typical for steel

Appendix A3 – Material Properties of Aluminum Mechanical Properties Hardness, Brinell Hardness, Knoop

Metric

English

Comments

120

120

AA; Typical; 500 g load; 10 mm ball

150

150

Converted from Brinell Hardness Value

Hardness, Rockwell A

46.8

46.8


Hardness, Rockwell B

75

75


137

137


483 MPa 345 MPa

70.0 ksi 50.0 ksi

AA; Typical

18.00%

18.00%

AA; Typical; 1/16 in. (1.6 mm) Thickness

Hardness, Vickers Ultimate Tensile Strength Tensile Yield Strength Elongation at Break

AA; Typical

Modulus AA;ofTypical; Elasticity Average of tension and compression. 73.1 GPa 10600 ksi Compression modulus is about 2% greater than tensile modulus. Notched Tensile Strength Ultimate Bearing Strength Bearing Yield Strength Poissons Ratio Fatigue Strength

379 MPa 855 MPa 524 MPa

55000 psi 124000 psi 76000 psi

0.33

0.33

138 MPa

20000 psi

2.5 cm width x 0.16 cm thick side-notched specimen, K t = 17. Edge distance/pin diameter = 2.0 Edge distance/pin diameter = 2.0 completely reversed stress; RR Moore machine/specimen

@# of Cycles 5.00e+8 @# of Cycles 5.00e+8

Machinability Shear Modulus Shear Strength

70.00%

70.00%

0-100 Scale of Aluminum Alloys

28.0 GPa 283 MPa

4060 ksi 41000 psi

AA; Typical