Optimization of gas tungsten arc welding parameters for welding of super duplex stainless steel using factorial design

Figures & data

Table 1. Mechanical properties of superduplex stainless steel (UNS S32750)

Mechanical Property	SDSS (UNS S32750)	Exaton 25.10.4.L
Tensile strength	116 ksi (800 MPa)	850 MPa
Yield strength	80 ksi (550 MPa)	650 MPa
Elongation in 2-inch or 4D	25%	25%
Hardness maximum	32 HRC (301 HBW or 330 HV10)	-
Reduction of cross-section area	25%	-

Table 2. Chemical composition of superduplex stainless steel (UNS S32750)

Elements	SDSS (UNS S32750)	Exaton 25.10.4.L
	Wt. Percentage (%)
Carbon	0.03	0.01
Manganese	1.20	0.4
Phosphorous	0.035	0.4
Sulfur	0.020	0.001
Silicon	0.80	-
Nitrogen	0.24–0.32	0.24
Nickel	6.0–8.0	9.5
Chromium	24.0–26.0	25
Molybdenum	3.0–5.0	3.9
Copper	0.50	-

Table 3. Values of welding input parameter

Parameters	Units	Symbols	Lower Limit (−1)	Upper Limit (+1)
Heat input	kJ/mm	Q	0.54	0.70
Welding speed	mm/sec	S	0.46	0.71
Voltage	Volts	V	9.3	11.60
Current	Amps	I	30	38

Figure 1. (a) Schematic of the welding setup (b) Photograph of gas tungsten arc welding of super-duplex stainless-steel pipe.

Table 4. Factorial points of welding input parameters

Factorial Point	Heat input	Welding Speed	Voltage	Current
1	0.54	0.46	9.3	30
2	0.70	0.46	9.3	30
3	0.54	0.71	9.3	30
4	0.70	0.71	9.3	30
5	0.54	0.46	11.6	30
6	0.70	0.46	11.6	30
7	0.54	0.71	11.6	30
8	0.70	0.71	11.6	30
8	0.54	0.46	9.3	38
10	0.70	0.46	9.3	38
11	0.54	0.71	9.3	38
12	0.70	0.71	9.3	38
13	0.54	0.46	11.6	38
14	0.70	0.46	11.6	38
15	0.54	0.71	11.6	38
16	0.70	0.71	11.6	38

Table 5. Other parameters of the welding process

Other Parameters of welding machine	Value
Diameter of electrode	0.5mm
Gas type	Argon
Gas flow type	Continuous gas flow

Figure 2. Photograph of setup for tensile testing.

Table 6. Average response for the ultimate tensile strength and yield strength

Run Order	Factorial Point	Ultimate Tensile Strength			Yield Strength
		Run 1	Run 2	Mean	Run 1	Run 2	Mean
3	1	791	785	788	490	475	482.5
10	2	705	703	704	462	458	460
1	3	750	740	745	450	452	451
5	4	780	776	778	530	515	522.5
8	5	730	728	729	421	425	423
7	6	785	780	782.5	485	490	487.5
11	7	742	737	739.5	415	420	417.5
9	8	764	759	761.5	452	450	451
4	9	727	725	726	325	333	329
16	10	735	731	733	400	410	405
6	11	776	767	771.5	348	356	352
14	12	755	752	753.5	421	417	419
12	13	758	750	754	491	482	486.5
2	14	710	705	707.5	500	495	497.5
15	15	729	721	725	520	511	515.5
13	16	740	733	736.5	404	413	408.5

Table 7. X-ray radiography tests

Exp	Weld Quality	X-ray Radiograph	Photograph of Welded Specimen
1	No defects along the weld lines
2	No defects along the weld lines
3	No defects along the weld lines
4	No defects along the weld lines
5	No defects along the weld lines
6	No defects along the weld lines
7	No defects along the weld lines
8	No defects along the weld lines
9	No defects along the weld lines
10	No defects along the weld lines
11	No defects along the weld lines
12	No defects along the weld lines
13	No defects along the weld lines
14	No defects along the weld lines
15	No defects along the weld lines
16	No defects along the weld lines

Table 8. Coded level with average UTS and YS response

Factorial points	Coded				Mean UTS	Mean YS
	a	b	c	d
1	−1	−1	−1	−1	788	482.5
2	1	−1	−1	−1	704	460
3	−1	1	−1	−1	745	451
4	1	1	−1	−1	778	522.5
5	−1	−1	1	−1	729	423
6	1	−1	1	−1	782.5	487.5
7	−1	1	1	−1	739.5	417.5
8	1	1	1	−1	761.5	451
9	−1	−1	−1	1	726	329
10	1	−1	−1	1	733	405
11	−1	1	−1	1	771.5	352
12	1	1	−1	1	753.5	419
13	−1	−1	1	1	754	486.5
14	1	−1	1	1	707.5	497.5
15	−1	1	1	1	725	515.5
16	1	1	1	1	736.5	408.5

Table 9. Coefficient of analysis for ultimate tensile strength and yield strength

Term	Ultimate Tensile Strength			Yield Strength
	Effect	Coefficient($\mathit{\beta }$)	Standard Error ($S_e$)	Effect	Coefficient($\mathit{\beta }$)	Standard Error ($S_e$)
Constant (mean)		745.906	0.731		444.25	1.01
Voltage	−2.687	−1.344	0.731	24.25	12.12	1.01
Current	10.813	5.406	0.731	−4.25	−2.13	1.01
Welding Speed	−7.937	−3.969	0.731	33.25	16.62	1.01
Heat Input	−15.063	−7.531	0.731	−35.25	−17.63	1.01
Voltage*Current	14.812	7.406	0.731	−8	−4	1.01
Voltage*Welding Speed	12.812	6.406	0.731	−23.75	−11.87	1.01
Voltage*Heat Input	−8.813	−4.406	0.731	−12.5	−6.25	.01
Current*Welding Speed	−13.437	−6.719	0.731	−21.25	−10.62	1.01
Current*Heat Input	5.688	2.844	0.731	−1.5	−0.75	1.01
Welding Speed*Heat Input	−7.313	−3.656	0.731	67.5	33.75	1.01
Voltage*Current*Welding Speed	−8.187	−4.094	0.731	−29.25	−14.62	1.01
Voltage*Current*Heat Input	−6.562	−3.281	0.731	−23.75	−11.87	1.01
Voltage*Welding Speed*Heat Input	−18.812	−9.406	0.731	−36	−18	1.01
Current*Welding Speed*Heat Input	−3.062	−1.531	0.731	−3	−1.5	1.01
Voltage*Current*Welding Speed*Heat Input	28.937	14.469	0.731	2	1	1.01

Figure 3. Main effects plot for ultimate Tensile strength.

Figure 4. Main effects plot for yield strength.

Figure 5. Interaction plot for ultimate tensile strength.

Figure 6. Interaction plot for yield strength.

Figure 7. Pareto chart of standardized effects for UTS.

Figure 8. Pareto chart of standardized effects for YS.

Table 10. Comparison of experimental values with predicted values of ultimate Tensile strength

Run1			Run2
Experimental UTS (MPa)	Predicted UTS (MPa)	Accuracy (Yes/No)	Experimental UTS (MPa)	Predicted UTS (MPa)	Accuracy (Yes/No)
791	788 $\pm$3.27	Yes	785	788 $\pm$3.27	Yes
705	704 $\pm$3.27	Yes	703	704 $\pm$3.27	Yes
750	749 $\pm$3.27	Yes	740	745 $\pm$3.27	No
780	778 $\pm$3.27	Yes	776	778 $\pm$3.27	Yes
730	729 $\pm$3.27	Yes	728	729 $\pm$3.27	Yes
785	782.5 $\pm$3.27	Yes	780	782.5 $\pm$3.27	Yes
742	739.5 $\pm$3.27	Yes	737	739.5 $\pm$3.27	Yes
764	761.5 $\pm$3.27	Yes	759	761.5 $\pm$3.27	Yes
727	726 $\pm$3.27	Yes	725	726 $\pm$3.27	Yes
735	733 $\pm$3.27	Yes	731	733 $\pm$3.27	Yes
776	773.5 $\pm$3.27	Yes	767	771.5 $\pm$3.27	No
755	753.5 $\pm$3.27	Yes	752	753.5 $\pm$3.27	Yes
758	754 $\pm$3.27	No	750	754 $\pm$3.27	No
710	707.5 $\pm$3.27	Yes	705	707.5 $\pm$3.27	Yes
729	725 $\pm$3.27	No	721	725 $\pm$3.27	No
740	738.5 $\pm$3.27	Yes	733	736.5 $\pm$3.27	No

Table 11. Comparison of experimental values with predicted values of Yield Strength

Run 1			Run 2
Experimental YS (MPa)	Predicted YS (MPa)	Accuracy (Yes/No)	Experimental YS (MPa)	Predicted YS (MPa)	Accuracy (Yes/No)
490	485.5 $\pm$ 4.55	Yes	475	482.5 $\pm$4.55	No
462	460 $\pm$ 4.55	Yes	458	460 $\pm$ 4.55	Yes
450	451 $\pm$ 4.55	Yes	452	451 $\pm$ 4.55	Yes
530	522.5 $\pm$ 4.55	No	515	522.5 $\pm$4.55	No
421	423 $\pm$ 4.55	Yes	425	423 $\pm$ 4.55	Yes
485	487.5 $\pm$ 4.55	Yes	490	487.5 $\pm$4.55	Yes
415	417.5 $\pm$ 4.55	Yes	420	417.5 $\pm$4.55	Yes
452	451 $\pm$ 4.55	Yes	450	451 $\pm$ 4.55	Yes
325	329 $\pm$ 4.55	Yes	333	329 $\pm$ 4.55	Yes
400	404 $\pm$ 4.55	Yes	410	405 $\pm$ 4.55	No
348	352 $\pm$ 4.55	Yes	356	352 $\pm$ 4.55	Yes
421	419 $\pm$ 4.55	Yes	417	419 $\pm$ 4.55	Yes
491	486.5 $\pm$ 4.55	Yes	482	486.5 $\pm$4.55	Yes
500	497.5 $\pm$ 4.55	Yes	495	497.5 $\pm$4.55	Yes
520	515.5 $\pm$ 4.55	Yes	511	515.5 $\pm$4.55	Yes
404	408.5 $\pm$ 4.55	Yes	413	408.5 $\pm$4.55	Yes

Figure 9. Optimization plot for ultimate tensile strength.

Figure 10. Optimization plot for yield strength.