Table 1
Chemical structure of SDSS.
| Element | Cr | Mo | Si | N | Ni | O | C | Cu | Fe |
|---|---|---|---|---|---|---|---|---|---|
| Weight (%) | 25.7 | 3.01 | 0.32 | 0.23 | 7.3 | 0.9 | 0.1 | 0.21 | Balance |
Table 2
Mechanical properties of SDSS grade 2507 [37].
| Grade | UTS (MPa) | 0.2% proof yield strength (MPa) | Minimum elongation (%) | Hardness | |
|---|---|---|---|---|---|
| Rockwell hardness | Brinell hardness | ||||
| 2507 | 800–850 | 550–560 | 14–15 | 31–33 | 309–312 |
Table 3
TIG process settings.
| S. No | TIG parameters | Range |
|---|---|---|
| 1 | Welding current intensity (A) | 70–80 |
| 2 | Arc potential (V) | 12–16 |
| 3 | Feed rate (mm/min) | 80–120 |
| 4 | Argon gas flow rate (L/min) | 8–16 |
Figure 1
Layout of the research.
Figure 2
(a) TIG experimental setup. SDSS plate welded by the TIG process: (b) top bead and (c) bottom bead.
Figure 3
(a) UTM for tensile tests and (b) tensile test sample before fracture.
Table 4
Process parameters for the TIG bead on plate.
| TIG parameters | Unit | Level | ||||
|---|---|---|---|---|---|---|
| 1 | 2 | 3 | 4 | 5 | ||
| Welding current | A | 70 | 72 | 75 | 77 | 80 |
| Arc potential | V | 12 | 13 | 14 | 15 | 16 |
| Feed rate | mm/min | 80 | 90 | 100 | 110 | 120 |
| Argon gas flow rate | L/mm | 8 | 10 | 12 | 14 | 16 |
Table 5
L25 array for TIG parameters and their corresponding output. Italic and bold text shows optimized parameters of welded joint.
| Experiment | Factors | Outputs | ||||||
|---|---|---|---|---|---|---|---|---|
| Welding current (A) | Arc potential (V) | Feed rate (mm/min) | Argon gas flow rate (LPM) | UTS (MPa) | Elongation (%) | Hardness (HV) | Heat input (kJ/mm) | |
| 1 | 70 | 12 | 80 | 8 | 754 | 22.7 | 330 | 0.567 |
| 2 | 70 | 13 | 90 | 10 | 753 | 22.6 | 331 | 0.546 |
| 3 | 70 | 14 | 100 | 12 | 752 | 23.4 | 332 | 0.529 |
| 4 | 70 | 15 | 110 | 14 | 751 | 22.2 | 332 | 0.515 |
| 5 | 70 | 16 | 120 | 16 | 755 | 21.5 | 334 | 0.504 |
| 6 | 72 | 12 | 90 | 12 | 755 | 22.5 | 335 | 0.518 |
| 7 | 72 | 13 | 100 | 14 | 756 | 21.8 | 334 | 0.505 |
| 8 | 72 | 14 | 110 | 16 | 751 | 22.6 | 335 | 0.495 |
| 9 | 72 | 15 | 120 | 8 | 754 | 29.7 | 336 | 0.486 |
| 10 | 72 | 16 | 80 | 10 | 752 | 21.2 | 337 | 0.778 |
| 11 | 75 | 12 | 90 | 16 | 755 | 21.3 | 323 | 0.540 |
| 12 | 75 | 13 | 100 | 8 | 756 | 23.9 | 331 | 0.527 |
| 13 | 75 | 14 | 110 | 10 | 754 | 22.8 | 332 | 0.515 |
| 14 | 75 | 15 | 120 | 12 | 789 | 24.7 | 325 | 0.506 |
| 15 | 75 | 16 | 90 | 14 | 763 | 25.7 | 322 | 0.720 |
| 16 | 77 | 12 | 110 | 10 | 761 | 24.4 | 324 | 0.454 |
| 17 | 77 | 13 | 120 | 12 | 758 | 23.2 | 340 | 0.450 |
| 18 | 77 | 14 | 80 | 14 | 759 | 23.6 | 340 | 0.728 |
| 19 | 77 | 15 | 90 | 16 | 763 | 25.6 | 324 | 0.693 |
| 20 | 77 | 16 | 100 | 8 | 757 | 23.8 | 326 | 0.665 |
| 21 | 80 | 12 | 110 | 14 | 758 | 22.2 | 327 | 0.471 |
| 22 | 80 | 13 | 120 | 16 | 765 | 23.7 | 338 | 0.468 |
| 23 | 80 | 14 | 90 | 8 | 762 | 23.4 | 326 | 0.672 |
| 24 | 80 | 15 | 100 | 10 | 768 | 23.6 | 327 | 0.648 |
| 25 | 80 | 16 | 110 | 12 | 758 | 23.8 | 328 | 0.628 |
Table 6
Response table for S/N ratios for UTS (larger is better).
| Level | Welding current (A) | Arc potential (V) | Feed rate (mm/min) | Argon gas flow rate (L/min) |
|---|---|---|---|---|
| 1 | 57.51 | 57.57 | 57.56 | 57.57 |
| 2 | 57.54 | 57.57 | 57.59 | 57.57 |
| 3 | 57.60 | 57.56 | 57.56 | 57.59 |
| 4 | 57.60 | 57.59 | 57.56 | 57.57 |
| 5 | 57.61 | 57.58 | 57.59 | 57.57 |
| Delta | 0.10 | 0.04 | 0.03 | 0.02 |
| Rank | 1 | 2 | 3 | 4 |
Table 7
Response table for S/N ratios for elongation (%) (larger is better).
| Level | Welding current (A) | Arc potential (V) | Feed rate (mm/min) | Argon gas flow rate (L/min) |
|---|---|---|---|---|
| 1 | 26.60 | 27.00 | 26.91 | 26.97 |
| 2 | 26.80 | 27.04 | 27.21 | 27.03 |
| 3 | 27.32 | 26.91 | 26.95 | 27.25 |
| 4 | 27.28 | 27.26 | 26.96 | 27.07 |
| 5 | 27.35 | 27.14 | 27.25 | 27.03 |
| Delta | 0.75 | 0.35 | 0.34 | 0.29 |
| Rank | 1 | 2 | 3 | 4 |
Table 8
Response table for S/N ratios for micro-hardness (smaller is better).
| Level | Welding current (A) | Arc potential (V) | Feed rate (mm/min) | Argon gas flow rate (L/min) |
|---|---|---|---|---|
| 1 | −48.86 | −48.95 | −48.95 | −48.96 |
| 2 | −48.87 | −48.93 | −48.92 | −48.97 |
| 3 | −48.95 | −48.96 | −48.96 | −48.95 |
| 4 | −49.01 | −48.94 | −48.96 | −48.93 |
| 5 | −49.00 | −48.92 | −48.93 | −48.90 |
| Delta | 0.15 | 0.04 | 0.04 | 0.07 |
| Rank | 1 | 3 | 4 | 2 |
Table 9
Results of ANOVA.
| Source | DF | Adj SS | Adj MS | F-value | P-value | Contribution (%) |
|---|---|---|---|---|---|---|
| Welding current | 4 | 309.75 | 77.436 | 6.12 | 0.015 | 46.95 |
| Arc potential | 4 | 18.43 | 4.607 | 0.36 | 0.828 | 10.25 |
| Feed rate | 4 | 41.63 | 10.406 | 0.82 | 0.546 | 13.26 |
| Argon gas flow rate | 4 | 18.52 | 4.631 | 0.37 | 0.826 | 24.56 |
| Error | 8 | 101.15 | 12.644 | 4.98 | ||
| Total | 24 | 490.26 |
Figure 4
Contribution of each parameter: (a) UTS, (b) elongation, and (c) microhardness.
Figure 5
Macrostructure of the TIG welded joint of the SDSS sheet.
Figure 6
Microstructure of (a) base metal and HAZ, (b) FZ, and (c) enlarged view of FZ.
Table 10
Ferrite percentage of SDSS in the FZ and HAZ with varying heat input.
| Heat input (kJ/mm) | Top weld | Root weld | Top HAZ | Root HAZ |
|---|---|---|---|---|
| 0.546 | 66 | 33 | 62 | 58 |
| 0.486 | 57 | 30 | 59 | 57 |
| 0.506 | 50 | 27 | 58 | 55 |
| 0.495 | 48 | 26 | 55 | 52 |
Figure 7
SEM images of (a) base metal and of welded joint’s (b) HAZ and (c) FZ.
Figure 8
Elemental mapping of the base metal and welded joint.
Figure 9
Tensile test samples: (a) base metal, (b) broken base metal, (c) TIG welded, and (d) broken TIG welded joint.
Figure 10
Stress–strain diagram for the SDSS base metal and welded joint tensile test sample.
Figure 11
Bar graph of comparative study of base metal’s and welded joint’s (a) UTS, (b) elongation, (c) yield strength, and (d) weld efficiency.
Figure 12
Fracture surfaces for the tensile test specimens with the (a) base metal, (b) a close-up view of the base metal fracture surface, (c) welded joint, and (d) a close-up view of the welded joint fracture surface.
Figure 13
Micro-hardness values in the (a) base metal, HAZ, and FZ and (b) SEM image of indentation on the base metal.
Figure 14
Micro-hardness variation with heat input.