LAB 4 Technical Report: Hardness Testing PDF

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Hardness Testing...

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Hardness Testing

By

Quang Nguyen

School of Engineering Grand Valley State University

Laboratory Module 4 EGR 250 – Material Science & Engineering Section 902

Instructor: Professor Lindsay Corneal

October 27, 2016

Abstract The purpose of this experiment were to utilize the hardness as an index of mechanical properties to relate the mechanical properties of ferrous and non-ferrous metal to their areas of application, and to determine the effect of chemical composition on the hardness of these metals. In the laboratory, the hardness of 10 different metals including 5 ferrous metals and 5 non-ferrous metals were measured using digital Rockwell hardness LECO R-600, analyzed, and compared to published values to identify which of these metal specimens would be the most suitable for wear resistance application. The comparison between experimental value and published value would suggest the condition of tested material. Finally, the ductility of 10 metal materials was ranked to select the metal that was the most suitable for wear resistance application. Gray cast iron, which had the highest hardness, was selected for wear resistance application.

1. Introduction The most important decision in engineering is proper choice of materials. The selection of material and process is always a difficult task because there are more than 100000 materials from which to choose, and there is a complex interdependence of designs, materials properties, and manufacturing processes. Hardness is the ability of material to resist plastic deformation, normally achieved by indentation with a substance more resistance than itself [1]. This is an important consideration in the selection of a material for application. Hardness helps compare different materials, indicate the strength, ductility, and strength of material, control quality, and specify the manufacturing process and heat treatment [1]. Hardness, especially Rockwell hardness test, is convenient technique because it is quick, simple and requires practically no specimen preparation. As a consequence, hardness test is ideal for laboratories, production lines, and other situation where the time and expense of conducting a tensile test are not appropriate [1]. Moreover, hardness test have wide range of application especially in application on metal materials. Metal material that has high hardness would be the most proper selection for wear resistance application. The learning objective of this laboratory was to introduce the hands-on experience on the hardness measurement of engineering materials, and to present the different type 1

of materials and their distinguishing characteristic. The experiment also introduced the differences in the mechanical properties of the different types of engineering materials, the effects of alloy composition on the mechanical properties of metal alloy as well as the effects of metal product form and condition on mechanical properties. During the lab period, the hardness of 5 ferrous metals, which were C1018 steel, tool steel, stainless steel, ductile cast iron, and gray cast iron, and 5 non-ferrous metals, which were aluminum alloy 2024, aluminum alloy 6061, copper, brass, and phospher Bronze, were measured, analyzed, and compared to published value to identify which of the metal specimen had the best wear resistance property.

2. Experimental Procedure In the laboratory, 10 metals samples, which is shown in Table 1, were obtained from the stock of engineering materials. After that, 5 ferrous metal samples and 5 nonferrous metal samples’ hardness was measured, three times for each sample, using digital Rockwell Hardness tester LECO R-600. LECO R-600 Rockwell Hardness tester should be examined to see if it was in good operating condition. The standard calibration scale of this hardness test was 90.8 RB

± 1.00 RB, and the measurement value was 91.5 RB.

The measured calibration scale was consistent with the manufacturer’s calibration scale, which meant that the Rockwell Hardness tester was in good operating condition. Each metal sample was placed squarely on the anvil, and the test load was applied by levering the surface of specimen in contact with penetrator. The next steps were waiting for the tester taking measurement, and recorded the value of hardness.

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Table 1: List of material used in laboratory

Ferrous Metal

C1018 Steel Tool Steel Stainless Steel Ductile Cast Iron Gray Cast Iron Aluminum Alloy 2024 Aluminum Alloy 6061 Cooper Brass Phospher Bronze

Non-ferrous Metal

3. Results The experimental measurement was recorded in Table 2. The average, range, and standard deviation value of each specimen’s hardness were also calculated. The metal that has highest hardness is gray cast iron which has experimental hardness value of 100.5 RB. The standard deviation, which has the largest value of 2.676, shows a small variation among values in measurement. The ranges, which is the difference between the minimum and the maximum measured hardness, are also insignificant, which supports the fact of small variation among values in measurements.

Table 2: Measurement Hardness for 10 metal samples 3

Hardness (RB) Trial

Trial

Unit: RB C1018 Steel Tool Steel Stainless Steel Ductile Cast

Trial 1 90.9 92.6 90.6

2 91.2 90.5 88.6

3 93 89.6 93.9

Average Range 91.7 2.1 90.9 3 91.0 5.3

Std. Dev 1.136 1.539 2.676

Iron Gray Cast Iron) Al alloy 2024 Al alloy 6061 Copper Brass Phosphor

95.8 100.8 80.4 67.2 63 73.5

94.1 100.3 82.8 65 62.8 71.5

95.8 100.5 81 68.7 62.5 72.3

95.2 100.5 81.4 67.0 62.8 72.4

1.7 0.5 2.4 3.7 0.5 2

0.981 0.252 1.249 1.861 0.252 1.007

Bronze

78.6

79.8

81.2

79.9

2.6

1.301

Furthermore, published value of each metal sample provides information about chemical composition of each sample. The chemical composition of each sample is displayed in Table 3. These compositions not only give the acceptable range of primary alloying elements but also exclude impurities in the alloys.

Table 3: Chemical composition of 10 metal samples Metal C1018 steel

Chemical composition Mn C 4

Weight percentage (wt. %) 0.6 – 0.9 [2] 0.15 – 0.2 [2]

A7 Tool Steel

A303 Stainless Steel

Ductile Cast Iron ASTM A536

Gray Cast Iron ASTM A48 Class 40

Al 2024 T-81

Al 6061 T91

S P Mn C Cr Si Ni Mo W V Cu P S C Mn Si P S Cr Ni C Mn Si S P C Cr Cu Fe Mn Mo Ni P Si S Al Cr Cu Fe Mg Mn Si Ti Zn Al Cr Cu Fe Mg Mn Si Ti

0.05 [2] 0.04 [2] 0.8 [2] 2.00 - 2.85 [2] 5.00 - 5.75 [2] 0.5 [2] 0.3 [2] 0.9 - 1.4 [2] 0.5 – 1.5 [2] 3.9 – 5.15 [2] 0.25 [2] 0.03 [2] 0.03 [2] 0 – 0.1 [2] 0 – 2.0 [2] 0 – 1.0 [2] 0 – 0.4 [2] 0 – 0.15 [2] 17 – 19 [2] 8 – 10 [2] 3.5 – 3.9 [4] 0.15 – 0.35 [4] 2.25 – 2.75 [4] 0.01 – 0.025 [4] 0.05 [4] 3.25 – 3.5 [3] 0.050 - 0.45 [3] 0.15 - 0.40[3] 91.9 - 94.2 [3] 0.50 - 0.90 [3] 0.050 - 0.10 [3] 0.050 - 0.20 [3] 0.12 [3] 1.8 - 2.3 [3] 0.15 [3] 90.7 – 94.7 [3] 0.1 [3] 3.8 - 4.9 [3] 0.5 [3] 1.2 - 1.8 [3] 0.30 - 0.90 [3] 0.50 [3] 0.15 [3] 0.25 [3] 95.8 - 98.6 [3] 0.04 – 0.35 [3] 0.15 – 0.4 [3] 0.5 [3] 1.2 – 1.8 [3] 0.3 – 0.9 [3] 0.5 [3] 0.15 [3] 5

Copper Brass

Phosphor Bronze

Zn Cu Fe Pb Cu Sn P Fe Pb Zn Cu

0.25 [3] 99.9 [5] 0.05 [5] 0.07 [5] 68.5 – 71.5 [5] 4.2 – 5.8 [5] 0.03 – 0.35 [5] 0.1 [5] 0.05 [5] 0.3 [5] 93.7 - 95.3 [5]

4. Discussion The differences between the hardness values obtained for the different metal samples are statistically significant. The metal that has highest hardness is gray cast iron which has the hardness of 100.5 RB, and the metal that has lowest hardness is copper which has the hardness of 62.8 RB. The experimental hardness values closely match with published value in which the smallest percent difference is 0.25% for ductile cast iron, and the largest percent difference is 7.14% for brass. The comparison between average experimental value and published value was showed in Table 4. Figure 1 also expresses more clearly the similarity between experimental hardness and published hardness of 10 metals. Moreover, the published values that are closest to experimental values indicate processing condition of each metals in 10 tested materials. The appropriate condition of each specimen is also recorded in Table 4. In addition, Table 4 showed that the hardness value for metals and alloys in the same subgroups and alloy families are different. The reason for these differences is that each alloy have its own chemical composition and treatment condition. These difference indicate that the material is not homogenous in nature. The chemical composition of each sample of metals and alloy in the laboratory was showed in Table 3. The condition of each sample was also displayed in Table 4.

Table 4: Comparison between Average experimental hardness value and published hardness value, and condition of 10 metal specimen

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Published

Percent

Condition

Average

Value

Difference

(RB)

(RB)

(%) Cold Drawn ,

C1018 Steel Tool Steel Stainless Steel Ductile Cast

91.7

92 [3]

0.33

Quenched, and T [3]

90.9

85 [3]

6.94

A7 Tool Steel [3]

91.0

96 [3]

5.17

Type 303 [3]

95.2

95 [3]

0.25

Grade 65-45-12 [3]

Iron

ASTM A48 Class 40 Gray Cast Iron Al alloy 2024 Al alloy 6061 Copper Brass Phospher

100.5

97 [3]

3.64

[3]

81.4

79 [3]

3.04

T-81 [3]

67.0

69 [3]

2.95

T-91 [3]

62.8

60 [5]

4.61

C11000 [5]

72.4

78 [3]

7.14

C26000 [3]

79.9

78 [3]

2.39

C51000 CDA 510 [3]

Bronze

120.0 100.0

Hardness, (RB)

80.0 60.0 40.0 20.0 0.0 8 01 C1

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Metal Average Value

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Published Values

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Br

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p os Ph

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Figure 1: Comparison between Average experimental hardness value and published hardness value

The similarities between experimental values and published values of hardness of 10 metal specimens provides the condition as well as the treatment of each metals. According to Table 4, C1018 steel sample’s hardness was closed to the C1018 steel’s hardness that was cold drawn, and water quenched [3]. Tool steel sample had hardness which was similar to that of A7 tool steel, which indicated that this type of tool steel was air quenched from 955 ℃ and tempered for 3 hours [3]. Stainless steel sample had a hardness which is closely matched with type 303 stainless steel. This suggested that this stainless steel sample could be fabricated by forging after uniform heating to 1149 – 1260 ℃ , and then be rapidly cooled to ensure maximum corrosion resistant [6]. The ductile cast iron sample’s hardness matched the hardness of ductile cast iron ASTM A536, which could be oil quenched harden from 885

℃

to Rockwell C 50 minimum on the outside

of the bar [7]. The gray cast iron sample had hardness close to that of gray cast iron A48 Class 40 [3]. On the other hand, with non-ferrous metals, aluminum alloy 2024 specimen’s experimental hardness was similar to the hardness of aluminum alloy 2024 T81, which was heat treated, cold worked and then artificial aged. Aluminum alloy 6061 specimen had hardness closely matched with that of aluminum alloy 6061 T-91, the material that was used a lot in manufacturing aircraft [3]. Copper had a hardness relatively close to that of C11000 copper, which could be hot worked in the range of temperature from 1400 ℉ between 700 ℉

to 1600 ℉ , and annealed in the range of temperature

and 1200 ℉ . [8]. Brass had hardness close to that of C26000

brass, which has excellent corrosion resistance and cold workability as well as good hot formability [3]. Finally, phosphor bronze sample had hardness value close to that of C51000 CDA 510, which has excellent corrosion resistance and cold workability, and was fabricated by blanking, drawing, bending, heading, and upsetting, shearing, roll threading, knurling and stamping [3]. Table 5 show the ranking of 10 metals’ hardness value obtained from the experiment. The hardness indicates the best choice of metal material would be most suitable for wear resistance application. Metal sample that has the highest hardness will be chosen as the most suitable material for wear resistance application. According to 8

Table 5, gray cast iron had the highest hardness, which was 100.5 RB. As a consequence, gray cast iron would be the most suitable for wear resistance application.

Table 5: Ranking 10 metal samples’ hardness Metal sample Copper Al alloy 6061 Brass Phosphor Bronze Al alloy 2024 Tool Steel Stainless Steel C1018 Steel Ductile Cast Iron Gray Cast Iron

Hardness (RB) 62.8 67.0 72.4 79.9 81.4 90.9 91.0 91.7 95.2 100.5

The hardness test results was valid because the hardness measured values in 3 trials of each sample closely matched with each other. Moreover, the experimental hardness values closely match with published value in which the smallest percent difference is 0.25% for ductile cast iron, and the largest percent difference is 7.14% for brass. The main source of error in the laboratory could be the location of the sample when it was placed between anvil and indenter of the LECO R-600 digital Rockwell hardness tester. When each sample was hardness tested, the process would become more difficult due to the deformation. Moreover, the result tend to be slightly off if the location of intender was close to the test side of previous sample. Another source of error could be the uncertainty of calibration scale of LECO R-600 digital Rockwell hardness tester which was

± 1.0 RB. This uncertainty possibly made the hardness measurement

slightly different from the published hardness values.

5. Conclusion 1. The measurement results of hardness values of 10 metal samples was valid. 2. The variability in 10 metal samples was closely related to that of the calibration scale.

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3. Chemical composition and treatment condition have significant effect on the hardness of metals and alloys. 4. The experimental hardness values of 10 metals closely matched with their published hardness value. 5. Gray cast iron has the highest hardness, which is 100.5 RB, and appears to be the most suitable material in a wear resistance application.

6. Reference

1. Dr. P.N. Anyalebechi: “Materials Science and Engineering Laboratory Manual,” School of Engineering, Padnos College of Engineering and Computing, Grand Valley State University, August 2016, pp. 78-80. 2. "Materials Science and Engineering | Materials Engineering | News." AZoM.com. AZO Materials, n.d. Web. 28 Oct. 2016. 3. Matweb – Material Property Data, www.matweb.com, June 27, 2005. 4. "Materials Engineering." Ductile Cast Iron ASTM A536 [SubsTech]. SubsTech, n.d. Web. 28 Oct. 2016. 5. "Copper Physical and Chemical Specifications - Mead Metals." Copper Physical and Chemical Specifications - Mead Metals. Mead Metal, Inc, n.d. Web. 28 Oct. 2016. 6. "Stainless Steel." AZOM.com. AZO Materials, n.d. Web. 28 Oct. 2016. 7. "65-45-12 Ductile Iron - Morgan Bronze." N.p., n.d. Web. 28 Oct. 2016. 8. "Copper Shim for Gas Checks. [Archive] - Cast Boolits." Copper Shim for Gas Checks. [Archive] - Cast Boolits. N.p., n.d. Web. 28 Oct. 2016.

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