Hardness Report

Title: The hardness tests and the Charpy test

Objective: 1. To analysis the hardness number of the material 2. To test the resistance of the material towards an impact load

Apparatus: I. Vickers Hardness Test instrument, a rod of mild steel and a rod of carbonate steel. II. Rockwell Hardness Test instrument, a rod of round shaped ASSAB steel with a center hole and a rod of carbonate steel without a center hole.

III. Brinell Hardness Test instrument, a rod of mild steel and a rod of carbonate steel. IV. Charpy Test instrument, a rod of mild steel and a rod of carbonate steel.

Introduction: The Hardness Test is a measurement of the resistance of the material to indentation, which indicates its strength. The indenter can be either rounded or pointed and is made of a material much harder than the test piece, for example hardened steel and diamond. There are 3 methods to test the hardness of the materials: PART A Vickers Hardness Test • Two techniques to test the hardness of a material are Knoop Test (called nup) and Vickers Test (also known as diamond pyramid). For each test, small diamond with pyramid geometry is used to indent the material surface. •

The force used is much lighter than the force used in Rockwell and Brinell test.

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The preparation of the specimen must be correct, to insure the measurement of the indent is exact.

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Knoop and Vickers Hardness Number are fixed which is HK and HV and the scale of both techniques are almost alike.

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Both techniques refer to the micro hardness methods based on the force and the measurement of the indent.

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Both are suitable to measure small value hardness of the selected specimen, especially Knoop, which is used to measure brittle materials such as ceramic.

Brinell Hardness Test •

Brinell test uses the force of a sphere shaped indenter on the specimen surface, just like the Rockwell Test.

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To test the hardness of a steel (or carbide tungsten), the diameter of the indentation used is 10.00mm(0.394 in.).

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Harder material requires more force.

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Brinell Hardness Number, HB serves as both function, as the diameter and the magnitude, which is the final result of an indentation.

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The force for each magnitude produced with the standard force between 500 and 3000 kg where the incensement of 500 kg in the test, follows a specified time (between 10 and 30 seconds).

Rockwell Hardness Test •

The most routinely used technique to measure the hardness of a material because of its simplicity and doesn’t require specific skills.

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A few scales can be used from few possibility different techniques that are used widely for many types of steel and alloy, from the soft materials to a more hard material.

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The Rockwell scale is known as HR, and its followed by a suitable identity. Example, 80HRB refers to the B scale of the Rockwell Hardness with the value of 80 and 60HR30W refers to the Rockwell Hardness of the value of 60 in the 30W scale.

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The table below shows the values of the steel sphere used : Steel sphere center point (mm) 1 2 5 10

Cast irons and steel P/D2 =30 30 120 750 3000

Load (kgf) Copper and Cu-Al alloys D/D2 = 10 10 40 250 1000

Aluminum P/D2 = 5 5 20 125 500

Titanium and other alloys P/D2 = 1 1 4 25 100

PART B Charpy Test

Figure 1 •

One of the impact energy tests used to determine the resistance towards load impulse, which directly changes the plastic shape that is known to be brittle.

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The elasticity state refers to the difficulty of the impact to change the plastic shape of the materials. 3

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Brittle fracture leads to a clear, shinny and surfaces results while elastically fracture results with a typical cleavage texture.

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Charpy test is a test to measure the resistance of the material towards the load impulse.

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The impacted specimen with small fracture or no even change in the plastic shape of the material is known as brittle.

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Fracture of plastic deformation mechanisms involved, is said to be in elasticity. The elasticity fracture results with the typical cleavage texture while the brittle fracture leads to a clear, shinny and surfaces.

Method: PART A a) Vickers Hardness Test (BS 427:1961) 1) The specimen (carbonate steel) is correctly place on anvil of the Vickers Hardness instrument. 2) The specimen is being focused and changed it below the indenter exactly. 3) The ‘START’ button is pressed and the machine will shine with the sound showed that the machine is readily operated. 4) When the ‘START’ light goes off, the indenter is assured that it doesn’t touches the specimen’s surface. 5) Change the indenter with the lens. 6) The width of the corner is measured and noted. 7) Step 1-6 is repeated for the other area of the steel and for the mild steel. b) Rockwell Hardness Test 1) The specimen is correctly placed on the anvil of the Rockwell Hardness instrument. 2) The base of the instrument is slowly rotated the LED will started to move until it reaches ‘SET’. 3) The test is automatically started.

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4) The reading is taken after ‘TI’ 5) Step 1-4 is repeated for the other area of the steel c) Brinell Hardness Test 1) The mild steel was placed correctly on the anvil of the instrument. 2) The base of the instrument is slowly rotated until the specimen touches the indenter. 3) The right holder of the machine is adjusted until it reaches the 1000kgf load and wait until 15 minutes. 4) The holder is moved forward again. 5) The base is anti-clockwise rotated. 6) The specimen is removed, and the reading is taken by using the microscope. 7) Step 1-4 is repeated for carbonate steel. PART B Charpy Test 1) The indenter specimen is positioned at the maximum heights and at the stress-concentrating notch. 2) The pendulum is swing from the initial height to the final heights towards the piece. 3) The necessary to fracture the test piece is directly calculated from difference heights.

RESULTS: PART A a) Vickers Hardness Test Carbonate steel Readings 1 2 3

d1(μm) 332.7 306.5 305.5

d2(μm) 304.4 301.7 315.3

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VHN 183 200 192.0

Average

191.7

d2 (μm) 363.3 361.3 361.8 Average

VHN 138.0 137.0 138.0 137.7

Mild steel Readings 1 2 3

d1(μm) 370.0 373.5 370.2

b) Rockwell Hardness Test ASSAB steel Readings 1 2 3 Average

Rockwell Hardness Number 26.6 26.7 27.0 26.8

Carbonate Steel Readings 1 2 3 Average

Rockwell Hardness Number 24.1 24.9 25.0 24.7

c) Brinell Hardness Test Load (1000kgf) Mild steel Readings 1 2 3

Center line for the notch part d (mm) 3.25 3.20 3.20 Average

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Brinnel Hardness Test number (BHN) 117 121 121 119.7

Carbonate Steel Readings 1 2 3

Center line for the notch part d (mm) 2.80 2.85 2.80 Average

Brinell Hardness Test Number (BHN) 159 154 159 157.3

Charpy Test Steel Mild steel Carbonate steel

Absorb Energy (Joule) 299.0 21.5

Mild steel Carbonate steel

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CALCULATIONS: a) Vickers Hardness Test Vickers Hardness Number (VHN) is defined as: VHN= Load impacted Surfaces area

where: P= load impacted d= dı + d2 2

= 2P sin 136/2 d² = 1.854 F/d² (less then) b) Rockwell Hardness Test Rockwell Hardness Test (RHT) is defined as: HRC= 100- d 0.002

where: the depth of the indent

c) Brinell Hardness Test Brinell Hardness Number is defined as: BHN= =

Load impacted Surface area of sphere indenter P D/2 (D- √D² - d² )

=

P πDh Where: P = Load impacted (kgf) D = Sphere center point (mm) d = Indenter center line (mm) H = Indenter depth (mm)

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DISCUSSION: PART A 1) Knowing that the Vickers Hardness test and the Brinell Hardness test were using both mild steel and carbonate steel while the Rockwell Hardness test used both ASSAB steel and high quality of carbonate steel. 2) The values of the BHN and VHN are much higher for carbonate steel compared to the values of mild steel. 3) The value of Rockwell Hardness Number is higher for the ASSAB steel than the value of the high quality of carbonate steel. 4) However, the value of the center line of the indenter for mild steel are much higher compared to the carbonate steel in the Vickers and Brinell hardness test. PART B 1) From the results, based on the shape of the test piece after the pendulum swing was; a) The mild steel was not fully break that is the end of the specimen is still connected with each other. b) The carbonate steel is fully broken. 2) All this happened is because of (a) has higher plasticity properties compared to the (b) The carbonate steel has high carbon that caused it more ductile. 3) The carbonate steel is much harder and brittle while the mild steel is ductile and elastic. This caused the carbonate steel cannot absorb the impact energy. Thus, it made the test piece break into two. While, for the mild steel, which is softer and more elastic can absorb the energy. 4) The high carbon carbonate steel reduced the ability to absorb the impact energy. 5) As the assumption, the carbonate steel can change the shape easily when there is impacted energy put on it. The surface of this steel is shinny and smooth. While the surface of the mild steel is results with typical cleavage on it. 6) There is 0.2% carbon in the mild steel. The carbonate steel has almost 85% carbon. The amount of carbon affected the mechanical properties of the materials.

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ERRATUM: PART A 1) The imperfect surfaces of each steel such as rusty surface. 2) Steel’s surfaces have lots of small indentation that result in only small area left for new indentation. 3) Position of the specimen not exactly localize as wanted.

CONCLUSION: PART A The ASSAB steel is the hardest steel, followed by carbonate steel and lastly the mild steel. PART B From the aspect of strength ness of steels, the mild steel have the most strength followed by the carbonate steel. Where as, the ASSAB steel is the hardest, followed by carbonate steel and lastly the mild steel. REFFENCES 1) Cliffe “Technical Metallurgy” page 150 – 154 2) Sergal “Material, Their Nature, Fabrication and Properties” page 143 – 145, 71 – 72 3) Rollesan “Metallurgy for Engineers” page 15 4) British Standard, 131 Part 2 (1959) 5) British Standard, 427: 1961 6) British Standard, 420: 1962 7) British Standard, 131, Part 2 : 1959

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