Lab: Hardness Testing Report.Name: KAVENESH A/L GUNASEGARAN (015619)

QHT1Charpy Test samples: Effect of carbon content and heat treatment.Material & TreatmentHV20

Normalised 0.1% carbon steel175

Normalised 0.4% carbon steel126

Quenched 0.4% carbon steel224

Quenched and tempered 0.4% carbon steel182

Table 1Jominy Test bars: Effect of cooling rates.Vickers Hardness results

Jominy end quench test pieceHV20 as a function of distance from the quenched end

5mm20mm40mm 60mm80mm

Fe- 0.4C(No.3)476541502415563

Fe- 0.4C- 1.0Cr- 1.5Ni- 0.3Mo(No.14)345357310353325

Table 2

Rolled Al samples: Effects of cold working and heat treatement.Material & TreatmentHV5

As received aluminium alloy49

10% Cold rolled aluminium alloy50.5

20% Cold rolled aluminium alloy52.5

40% Cold rolled aluminium alloy53.5

60% Cold rolled aluminium alloy63.5

75% Cold rolled aluminium alloy61.0

Annealed aluminium alloy132.5

Table 3

QHT2By referring to Table 1, it can be said that hardness of carbon steel decreases as the percentage of carbon content increases. From Table 1, the harness number for Normalised 0.1% carbon steel is 175, while the hardness number of Normalised 0.4% carbon steel is only 126. Thus, this shows that the hardness of carbon steel is inversely proportional to percentage of carbon content. However, for Quenched 0.4% carbon steel, it poses a much greater hardness number, that is 224, compare to Normalised 0.4% carbon steel. Therefore, it can be said that quenching increases the hardness of carbon steel. Lastly, for Quenched and Tempered 0.4% carbon steel, the hardness number is only 182 which is slightly lower than Quenched 0.4% carbon steel. This proves that tempering the quenched material will cause decrease in hardness.

QHT3

Figure 1Based on figure 1, for Fe-0.4C, it can be observed that there is an increase in Vickers hardness value. As the distance increases, there is a decrease in the hardness and it followed by an increase at the end. On the other hand, for the Fe-0.4C -1.0Cr -1.5Ni -0.3Mo, the occurrence is quite similar to Fe-0.4C, except there is slight decrease in hardness as the distance passes 80mm. From the graph plotted, it may seem that Fe-0.4C has a higher Vickers hardness value than Fe-0.4C -1.0Cr -1.5Ni -0.3Mo and the hardness increases as distance increases. However, based on the data collected, it can be said that the result is invalid due to various types of error. In actual fact, the hardness of both materials should decrease gradually as distance from the quenched end gets further. This is mainly because the part of the bar that is quenched is forced to undergo fast cooling. In other words, as the bars undergo fast cooling, the carbon compound within the bar cannot diffuse fast enough. As a result, the carbon compound gets trapped in structure and this causes the structure within the bar to be distorted. This makes it very difficult for dislocation to occur and indirectly increases the hardness of the bar. Thus, as distance from the quenched end increases, the rate of cooling decreases. Therefore, a slower rate of cooling will enable the proper crystallization to occur. This makes the opposite to be softer and have lower hardness. So, the graph supposed to consist decreasing hardness with increasing distance from the quenched end.Besides that, Fe-0.4C -1.0Cr -1.5Ni -0.3Mo is supposed to have a higher hardness compare to Fe-0.4C. This is mainly because the Fe-0.4C -1.0Cr -1.5Ni -0.3Mo consist of different composition of material compare to Fe-0.4C. The Fe-0.4C -1.0Cr -1.5Ni -0.3Mo consist of Iron, 0.4% Carbon, 1.5% Nickle, 1% Chromium, 0.3% Molybdenum while Fe-0.4C only consist of 0.4% Carbon and Iron. The higher the composition of foreign element in a mixture, the harder the misalignment of atomic layer, which results in higher value of hardness.

QHT4By referring to Table 3, it can be clearly seen that as the percentage cold work increases, the hardness number of alumunium alloy also increases. This occurs because cold work is a process of strengthening of metal by plastic deformation at room temperature. Thus, as the percentage of cold work increases, this causes dislocation of atoms to occur within the crystal structure of the material, causing the hardness number to increase. However, annealing is a process used to reduce the effects of cold work by heating at very high temperature. As aluminium is undergoing annealing, the percentage cold work decreases. Thus, the hardness also supposed to decrease. However, due to various error, the experimental result for Annealed aluminium alloy may vary.

QHT5Material & TreatmentHV5(kgf/m)HV(kg/m)ln ln

As received aluminium alloy492403.51.00801.2undefined6.69

10% Cold rolled aluminium alloy50.52477.00.900.1054825.7-2.256.72

20% Cold rolled aluminium alloy52.52575.20.800.2231858.4-1.506.76

40% Cold rolled aluminium alloy53.52624.20.600.5108874.7-0.6726.77

60% Cold rolled aluminium alloy63.53114.70.400.91631038.2-0.0876.95

75% Cold rolled aluminium alloy61.02992.10.251.3863997.40.3276.91

Table 4

Equation 1: Where; = True flow stress = True strain

Equation 2: Where; = Vickers Hardness Value = Flow stress

Equation 8: Where; = True rolling strain

Figure 2

From Equation 1,

Can be rearranged into,Log = log + n log which is very similar to Y= mX + cTherefore, it can be said that gradient = n

Based on the equation of straight line obtained in figure 2, the gradient of the line is 0.0856. The gradient of the equation is n. Therefore, it can be concluded that the value of n is 0.0856.