NOMENCLATURE
CHAPTER 5 Results and discussions
B. Results of experimental investigation
5.10 Effect of welding parameters on weld bead geometry & mechanical properties
failure. During tensile testing of the welded samples, failure occurred in between base metal and heat affected zone, which was away from the weld line, which indicates a superior weld quality.
5.9.4 Summary
The summary of the preceding study can be stated as below:
Maximum hardness was observed in the weld zone and which decreases gradually away from the weld line towards base material. The hardness in the weld zone was more due to the greater carbon content in the filler wire.
None of the tensile samples failed in the weld zone, therefore the strength of the welding was more than the base metal, which confirms a sound welding joint.Based on UTS the maximum joint efficiency was 96%.
Figure 5.79 Bead on plate weld bead cross section
Table 5.22 Input parameters and corresponding output
Exp.
no.
Welding current
(A)
Welding voltage
(V)
Welding speed (mm/s)
Length of stick out
(mm)
Bead width (mm)
Top bead reinforcement
(mm)
1 330 28 5.5 23 15.31 2.37
2 340 28 5.5 23 15.8 2.78
3 350 28 5.5 23 16.09 2.94
4 360 28 5.5 23 17.16 3.13
5 330 28 5.5 23 15.31 2.37
6 330 30 5.5 23 16.03 2.45
7 330 32 5.5 23 17.45 3.26
8 330 34 5.5 23 18.25 3.74
9 330 28 5.5 23 15.31 2.37
10 330 28 6 23 15.1 2.22
11 330 28 6.5 23 14.15 1.88
12 330 28 7 23 13.69 1.79
13 330 28 5.5 23 15.31 2.37
14 360 28 5.5 25 15.43 2.46
15 360 28 5.5 27 15.88 3.07
16 360 28 5.5 29 16.28 3.10
5.10.1 Effect of input parameters on bead width
It was observed from Table 5.22 that the welding input parameters have considerable effect on weld bead geometry. It can be observed that current effects on overall weld bead geometry i.e.
with increase of current the weld bead width, bead height and penetration increases. However, with the increase of voltage the weld bead becomes wider and flatter but weld penetration remains almost constant. With the increase in welding speed, the overall size of weld geometry decreases but with the increase in length of stick-out, overall size of weld geometry increases.
28 29 30 31 32 33 34 35
15 16 17 18 19
Bead width (mm)
Voltage (V) Bead width
Figure 5.80 Effect of voltage on bead width
Figures 5.80 & 5.81 show the effect of welding voltage, current, speed and length of stick out on weld bead width. From the Table 5.22 & Figure 5.80, it can be understood that with increase in voltage, bead width generally increases. Welding voltage increases arc length i.e. the total area under the welding arc increases thus the bead width increases.
330 340 350 360 370
15 16 17 18
Bead width (mm)
Current (A)
Bead width
Figure 5.81 Effect of current on bead width
It is observed from Figure 5.81 that current affects the weld bead width significantly. As current level increases bead width increases. Figure 5.82 shows the effect of welding speed on weld bead width.
5.1 5.4 5.7 6.0 6.3 6.6
13.0 13.5 14.0 14.5 15.0 15.5 16.0
Bead width (mm)
Welding speed (mm/s)
Bead width
Figure 5.82 Effect of welding speed on bead width
It can be seen from Figure 5.82 that increase of welding speed has a tendency to decrease weld bead width. As heat input per unit length decreases with increase of welding speed, so bead width become narrower. Therefore, it is observed from Figures 5.80 to 5.82 that with increase welding speed the bead width decreases but it almost linearly increases with welding voltage and current. Figure 5.83 shows the effect of electrode stick out on weld bead width.
23 24 25 26 27 28 29 30
14.0 14.5 15.0 15.5 16.0 16.5 17.0
Bead width (mm)
Length of stick-out (mm) Bead width
Figure 5.83 Effect of length of stick-out on bead width
It can be seen from the Figure 5.83 that, with the increase in electrode stick out, bead width also increases. For the constant voltage, power source, with increase in stick out length electrode-melting rate increases, due to the resistive heating of the electrode, which in turn results in an increase in weld bead width.
5.10.2 Effect of input parameters on reinforcement
Figures 5.84 to 5.87 show the effect of welding process parameters (welding voltage, current
& speed) on weld bead reinforcement. Measured values of weld bead reinforcements of the bead on plate experiments are shown in Table 5.22. Results indicate that the process variables influence weld bead geometry to a significant extent. Welding reinforcement is significantly influenced by welding current and arc voltage.
330 340 350 360 370
1.8 2.1 2.4 2.7 3.0 3.3 3.6
Reinforcement (mm)
Current (A) Reinforcement
Figure 5.84 Effect of current on weld reinforcement
Figure 5.84 shows the effect of welding current on weld reinforcement. It can be observed from the Figure 5.84 that weld reinforcement increases with the increase of welding current due to the extra melt down of the electrode. Figure 5.86 shows the effect of welding voltage on weld reinforcement.
28 29 30 31 32 33 34 35 1.8
2.0 2.2 2.4 2.6 2.8 3.0
Reinforcement (mm)
Voltage (V)
Reinforcement
Figure 5.85 Effect of voltage on weld reinforcement
From Figure 5.85, it can be seen that with the increase in voltage reinforcement decreases. With the increase in voltage, flatten upper surface can be seen which reduces the weld reinforcement.
5.0 5.5 6.0 6.5 7.0
1.2 1.5 1.8 2.1 2.4 2.7 3.0
Reinforcement (mm)
Welding speed (mm/s) Reinforcement
Figure 5.86 Effect of welding speed on weld reinforcement
From Figure 5.86, it is seen that trend of reinforcement with welding speed is decreasing in nature because with higher value of speed, metal deposition rate decreases as well as less amount of heat available per unit time at a particular location, that’s why weld bead size decreases.
23 24 25 26 27 28 29 30 2.2
2.4 2.6 2.8 3.0 3.2 3.4
Reinforcement (mm)
Length of stick-out (mm) Reinforcement
Figure 5.87 Effect of electrode stick-out on weld reinforcement
Figure 5.87 shows the effect of electrode stick out on weld reinforcement. It can be observed from the Figure 5.87 that with the increase in electrode stick out weld reinforcement also increases due to the extra melting of the electrode.
5.10.3 Effect of input parameters on hardness
Hardness test was carried out at different weld zones of all samples as shown in Table 5.23.
Hardness ranges are observed from 156-160 HV at base metal, 161-178 HV at HAZ and 162- 190 HV at weld region. Results of hardness test are shown graphically in Figures 5.88- 5.91.
Hardness values in both HAZ and weld metal are found to be higher than base metal, in all the samples due to the grain refinement above recrystallization temperature.
28 29 30 31 32 33 34 35
140 150 160 170 180 190 200 210
Micro-hardness (HV)
Welding voltage (V) FZ HAZ
Figure 5.88 Effect of voltage on hardness of weld zone
Table 5.23 Welding input parameters and measured average hardness values
Weld Runs
Current (A)
Voltage (V)
Welding speed (mm/s)
Electrode stick out
(mm)
Hardness (HV) Weld Zone HAZ
1. 330 28 5.5 23 176.9 162.81
2. 340 28 5.5 23 183.55 168.93
3. 350 28 5.5 23 186.89 172.08
4. 360 28 5.5 23 187.18 178.53
5. 330 28 5.5 23 176.9 162.81
6. 330 30 5.5 23 172.56 162.9
7. 330 32 5.5 23 179.48 175.74
8. 330 34 5.5 23 183.55 177.64
9. 330 28 5.5 23 176.9 162.81
10. 330 28 6 23 183.72 165.05
11. 330 28 6.5 23 190.34 171.52
12. 330 28 7 23 182.12 168.17
13. 330 28 5.5 23 176.9 162.81
14. 360 28 5.5 25 172.09 165.04
15. 360 28 5.5 27 170.33 161.01
16. 360 28 5.5 29 179.89 165.89
330 335 340 345 350 355 360 365
150 160 170 180 190
200 FZ
HAZ
Micro-hardness (HV)
Welding current (A)
Figure 5.89 Effect of current on micro-hardness
4.8 5.1 5.4 5.7 6.0 6.3 6.6 140
150 160 170 180 190 200
210 FZ
HAZ
Micro-hardness (HV)
Welding speed (mm/s)
Figure 5.90 Effect of welding speed on micro-hardness
23 24 25 26 27 28 29 30
130 140 150 160 170 180 190 200
FZ HAZ
Micro-hardness (HV)
Length of stickout (mm)
Figure 5.91 Effect of electrode stickout length on hardness
It can be observed from Figure 5.88 & 5.89 that an increase of arc voltage and current produce an increase of amount of carbon precipitation in the weld zone, which results in increase of hardness. From the Figure 5.90, it can be seen that hardness first increases with the increase of welding speed but follows a downward trend at higher welding speed. Length of stick-out have less influence than voltage and current as the increases in hardness is less with compared to other parameters.
5.10.4 Summary
From the above investigation of effect of welding parameters on weld bead geometry & and mechanical properties, it can be summarized as below:
The submerged arc welding process parameters have significant effect on determination of the bead geometry as well as the mechanical property of the final weldment.
It can be seen from the results that with the increase in weld voltage, the bead width becomes flatter but top reinforcement decreases. However, with the increase in current both top reinforcement and bead width increases. Hardness shows an increasing trend with current and voltage, as the carbon content increases in the weld zone due to the melting of the electrode.
Welding speed has negative effect on weld bead dimensions; the overall bead geometry reduces with the reduction in welding speed. Hardness shows less variation with speed.
Length of stick out has minor effect on bead as well as micro-hardness.