NOMENCLATURE
CHAPTER 5 Results and discussions
B. Results of experimental investigation
5.11 Effect of surface active elements on weld bead geometry
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.
5.11.1 Influence of surface active elements on penetration
Weld penetration is defined as the total distance between the top surface of the base plate to the tip of fusion depth. Among the all cases, the mixture of three surface active elements produced most noticeable effect. It increased the penetration more than twice as compared with conventional submerged arc welding. The measured values of weld penetration using different active elements are shown in the Tables 5.23. Total four repetitions were carried out for each measurement.
Table 5.24 Average depth of penetration
PC1 (300A, 30V, 6 mm/s)
PC2 (325A, 32V, 6 mm/s)
PC3 (350A, 34V, 6 mm/s)
SiO2 3.632 3.702 4.225
TiO2 3.635 3.945 4.112
Cr2O3 3.852 4.127 4.665
SiO2+ TiO2+ Cr2O3
4.867 5.032 5.42
No SA Elements 2.197 2.76 2.842
PC=Parameter combination
Figure 5.93 depicts the variation of the weld penetration for different surface-active elements at different parameter combinations as per Table 5.24.
2 3 4 5 6 7
PC3 PC2
PC1
SiO2 TiO2 Cr2O3 Mixture No SA elements
Penetration (mm)
Parameter combination
Figure 5.93 Effect of surface-active elements on weld penetration
Welding current has a linear relationship with the penetration i.e. if current is increased then the penetration in all cases increases. SiO2 flux has shown least amount of penetration. The activating elements increases the transfer of molten metal droplets, this increases the striking and gets more penetration as compare to the welding without activating flux.
5.11.2 Influence of activating flux on bead width
Surface active elements have significant variations in weld bead width. The weld bead widths with surface active elements becomes narrower than those without it. When SiO2, TiO2 and Cr2O3 flux are used, the surface tension at the center of the weld pool becomes higher than that near the edges. Four repetitions were carried out for each experiments and the average vales of the weld bead width with and without surface active elements are shown in Table 5.25.
Table 5.25 Average weld bead width
Flux type PC1 (300A,
30V, 6 mm/s)
PC2 (325 A, 32V, 6 mm/s)
PC3 (350A, 34V, 6 mm/s)
SiO2 15.01 18.05 18.08
TiO2 18.33 18.42 18.82
Cr2O3 12.26 13.48 13.91
SiO2+ TiO2+ Cr2O3 12.81 16.06 18.18
No Activated elements 16.05 17.25 19.31
PC=Parameter combination
Figure 5.94 illustrates the variation of the weld bead width for different surface active elements at different parameter combinations as per Table 5.25. Least bead width and highest bead width can be seen for Cr2O3 andTiO2 elements respectively.
.
10 12 14 16 18 20 22 24
PC3 PC2
SiO2 TiO2 Cr2O3 Mixture No SA elements
Bead width (mm)
Parameter combination PC1
Figure 5.94 Effect of surface-active elements on weld bead width
In conventional SAW, the flow of molten metal takes place from center of the weld to the edges because surface tension at the center is less than that at the welding edges. This results in less penetration and more width of the weld pool. But when surface activating fluxes are used, the reversal of Marangoni effect occurs and due to arc constriction, improvement in depth of penetration and significantly less decrease in bead width are obtained.
5.11.3 Influence of activating flux on weld reinforcement
Reinforcement is the amount of molten metal deposition above the flat surface of the weld base plate. The average values of weld reinforcements are shown in Table 5.26.
Table 5.26 Average weld bead reinforcement
Flux Type PC1 (300A,
30V, 6 mm/s)
PC2 (320 A, 32V, 6 mm/s)
PC3 (350A, 34v, 6 mm/s)
SiO2 2.72 2.72 2.63
TiO2 2.76 2.51 2.53
Cr2O3 3.32 3.21 3.13
SiO2+TiO2+ Cr2O3 3.13 2.73 2.72
No Activated Elements 2.47 2.4 2.48
PC=Parameter combination
Figure 5.95 describes the effect of different surface-active element & its mixtures on weld reinforcement at different weld parameter setting as per Table 5.26. From Figure 5.95, it is evident that reinforcement decrease with the increase in voltage & current while keeping other parameters constant. Cr2O3 elements shows highest weld reinforcement.
1.6 2.4 3.2 4.0
4.8 SiO2
TiO2 Cr2O
3
Mixture
No SA elements
Reinforcement (mm)
Parameter combination
PC1 PC2 PC3
Figure 5.95 Effect of surface-active elements on reinforcement
Without surface activating elements the reinforcement is less than the weld metal using the surface activating elements. Cr2O3 has the highest reinforcement and TiO2 has the lowest reinforcement among all the activating flux. The reinforcement decreases sharply in the weld where the mixture of surface active elements was used.
5.11.4 Summary
The summary from the above investigation of effect surface active elements on weld bead geometry can be summarized as below:
The mixture of three surface active elements produced most noticeable effect, it was observed that by using surface active elements the penetration can be increased more than twice as compared with conventional submerged arc welding.
Maximum bead width can be seen in case of TiO2 flux and maximum penetration was achieved in case of Cr2O3 flux.