Evaluation of microstructural and mechanical qualities in optimised TIG-welded SDSS 2507 joints

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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

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

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

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

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

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

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

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

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

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