Effect of welding process, type of electrode and electrode core diameter on the tensile property of 304L austenitic stainless steel

 

Akinlabi OYETUNJI1, Nwafagu NWIGBOJI2

 

I Department of Metallurgical and Materials Engineering; Federal University of Technology, Akure, Ondo State, NIGERIA

2Industrial Skills Training Centre (ISTC) - Ikeja Lagos, Industrial Training Fund Nigeria

E-mails: 1akinlabioyetunji@yahoo.com, aoyetunji@futa.edu.ng;

 

 

Abstract

The effect of welding process, type of electrode and electrode core diameter on the tensile property of AISI 304L Austenitic Stainless Steel (ASS) was studied. The tensile strength property of ASS welded samples was evaluated. Prepared samples of the ASS were welded under these three various variables. Tensile test was then carried out on the welded samples. It was found that the reduction in ultimate tensile strength (UTS) of the butt joint samples increases with increase in core diameter of the electrode. Also, the best electrode for welding 304L ASS is 308L stainless steel-core electrode of 3.2 mm core diameter. It is recommended that the findings of this work can be applied in the chemical, food and oil industries where 304L ASS are predominantly used.

Keywords

Austenitic stainless steel; Tensile property; Industries; Welding process; Electrode type; Electrode size

 

 

Introduction

 

Welding is basically a fusion of two or more pieces of metals by the application of heat and sometimes pressure [1]. Among the popular grades of austenitic stainless steels (ASS) with excellent formability, corrosion resistance, and weld ability is the type 304L ASS [2].

Welding process which involves a wide range of scientific variables such as time, temperature, electrode, power input and welding speed has been successfully utilized for the fabrication of 304L ASS components, especially in almost all environments that require an optimization of these properties including low and high pressure boilers and vessels, fossil-fired power plant, evaporator tubing, steam headers and pipes [3, 4, 5].

In the independent research findings of Avery and Parijslaan, it was reported that improper techniques employed in welding ASS may lead to serious consequences of the structures [6, 7]. Failures as a result of poor mechanical and micro-structural properties have found their places, from household equipment to industrial structures such as road bridges, storage tanks and process lines. Many other failures have proved to be welding prone or propagated [8, 9, and 10].

This study is therefore aimed at examining the tensile response of  welded 304L austenitic stainless steel to these three welding variables (welding process, type of electrode and electrode core diameter) to achieve failure resistant weld. The results obtained from this study are expected to provide more information on effect of these three welding variables on the tensile behaviour of ASS components with a view to reducing future failures.

 

 

Material and method

 

Materials used for this study include a flat bar of austenitic stainless steel type 304L (8 mm thickness), rutile stainless steel core electrode fluxed with manganese and molybdenum (class AWS – American Welding Society) of type E308L with diameters 2.5 mm, 3.2 mm, 4.0 mm; stainless steel electrode AWS E312 and AWS E316 both with diameter 3.2 mm, AWS ER 308L MIG wire; and ER 308L filler rod.

 

Chemical analysis

The chemical analysis of the as-received austenitic stainless steel type 304L flat bar was done by the optical emission spectrometer using AR 430 meter analyser [11]. The chemical composition is depicted in Table 1.


Table 1. Chemical composition of the type 304L stainless steel flat bar

Element

C

Si

S

P

Mn

Ni

Cr

Mo

Bar Composition %

0.0327

0.6489

0.0153

0.0505

1.8599

8.0798

18.4032

0.3194

 

Table 1 cont. Chemical composition of the type 304L stainless steel flat bar

V

Cu

W

Co

Al

Pb

Ca

Zn

Fe

0.0756

0.8713

0.1036

0.1718

0.0265

0.0126

0.0046

0.0313

69.2398

 

Welding samples preparation

Samples of dimension 50 mm length, 50 mm breadth and 8 mm thickness were cut from the 304L ASS flat bar  into four geometries namely: square edge, double V edge, single V edge, and single bevel edge in accordance with work done by Agarwal [1]. This was necessary to allow for adequate penetration. Chamfering of the samples to the various geometries was done with hack saw to prevent thermal stresses that may be introduced by gas cutting. The preparation was followed by thorough cleaning. Depicted in Figure 1 are the various geometries.

Figure 1: Shapes of the ASS welding samples

 

Welding

Edges of the samples were firmly clamped together with a little root gap between them. Welding was carried out in the flat (1G) position [12], and at constant power input of 9.2KW and moderate welding speed [11].

Varied welding process

Shielded Metal Arc Welding (SMAW), Gas Tungsten Arc Welding (GTAW) and Gas Metal Arc Welding (GMAW) processes and 308L electrode with diameter 2.5 mm at constant power and welding were used to weld six single V samples in pairs to produce three butt joint samples [13, 14].

 

Varied electrode type

GTAW technique was used with electrodes types of American Welding Standard with specifications E308L, AWS E312 and AWS E316 with dimension 3.2 mm (internal core) to weld six single V samples in pairs. In all three butt samples were produced, the welding was carried out under constant power input and welding speed [11, 15].

 

Electrode core diameter

Stainless steel electrode type E308L with different diameters of 2.5 mm, 3.2 mm, and 4.0 mm (internal core) whose sizes were chosen in accordance with American Welding Standard (AWS) A5.4, was used with GTAW process to produce three butt samples by welding in pairs six single V sample while keeping constant the power input and welding speed [11].

 

Tensile test

A 3369 Instron Universal Tester was used to carry out the tensile tests. The test piece was gripped at the ends in the machine and a continually increasing uni-axial load was applied until failure occurred. The load ranged between 10,000N and 50,000N [13, 14, 15]. The reading was then taken. The tensile test results at varied welding processes were shown in Tables 2, 3, 4, and 5. The tensile test results at varied welding electrodes were shown in Tables 2, 6, 7 and 8 while the tensile test results for electrode core diameter were presented in Tables 2, 9, 10 and 11. Tables 2, 3, 4, 5, 6, 7, 8, 9, 10 and 11 were presented in graphical forms and are depicted in Figures 2, 3 and 4 respectively.

The True Stress and Strain at varied welding processes variables were calculated using the following equations 1, 2, 3, 4, 5, and 6 [17].

Stress and strain are commonly represented in 2-Dimensional by these equations 1 and 2:

Strain = L / L0

(1)

δ = F / A0

(2)

 Engineering stress and strain are commonly represented in 2D by these equations:

Є = ln (L / L0)

(3)

δ = F / Ao

(4)

For uniaxial stress-strain data, engineering stress and strain can be converted to true stress - log strain by:

ЄT = ln (1+Є)

(5)

δT = δ (1+Є)

(6)

where e = Extension (L); Engineering Stress = δ; Engineering Strain = Є; True Stress = δT; True Strain = ЄT Original Gauge length (Lo) = 0.02 m; Original Area of Gauge Length (Ao) = 1.2·10-5 m2.

 

 

Results and discussion

 

The procedure used for obtaining the data series of experimental results in Tables 2, 3, 4, 5, 6, 7, 8, 9, 10 and 11 which were finally presented in graphical forms was through the use of  equations 1 to 6. These equations were used to evaluate the experimental data and the true stress and strain values were gotten. These true stress and strain values in variation with varied welding processes variables were then presented in graphical forms as Figures 2, 3 and 4.


Table 2. True stress-true strain data for 304L ASS (as-received sample)

e·10-3 (m)

δ (MPa)

Є

δT  = δ(1+ Є) (MPa)

ЄT= ln(1+ Є)

0.00

0.00

0.00

0.00

0.00

0.50

100.00

0.03

103.00

0.03

1.00

230.00

0.05

241.50

0.05

2.00

400.00

0.10

440.00

0.10

3.00

550.00

0.15

632.50

0.14

3.50

600.00

0.18

708.00

0.17

4.00

640.00

0.20

768.00

0.18

5.00

570.00

0.25

712.50

0.22

6.00

590.00

0.30

767.00

0.26

7.00

705.00

0.35

951.75

0.30

8.00

720.00

0.40

1008.00

0.34

9.00

730.00

0.45

1058.50

0.37

10.00

735.00

0.50

1102.50

0.41

11.00

740.00

0.55

1147.00

0.44

12.00

745.00

0.60

1192.00

0.47

13.00

745.00

0.65

1229.25

0.50

14.00

740.00

0.70

1258.00

0.53

15.00

735.00

0.75

1286.25

0.56

16.00

720.00

0.80

1296.00

0.59

17.00

680.00

0.85

1258.00

0.62

18.00

600.00

0.90

1140.00

0.64

18.60

470.00

0.93

907.10

0.66

18.60

270.00

0.93

521.10

0.66

 

Table 3. Effect of manual metal arc welding process on mechanical properties of 304L ASS

e·10-3 (m)

δ (MPa)

Є

δT  = δ(1+ Є) (MPa)

ЄT= ln(1+ Є)

0.00

0.00

0.00

0.00

0.00

0.50

75.00

0.03

77.25

0.03

1.00

240.00

0.05

252.00

0.05

1.50

350.00

0.08

378.00

0.08

2.00

380.00

0.10

418.00

0.10

3.00

410.00

0.15

471.50

0.14

4.00

440.00

0.20

528.00

0.18

5.00

455.00

0.25

568.75

0.22

6.00

480.00

0.30

624.00

0.26

7.00

490.00

0.35

661.50

0.30

8.00

495.00

0.40

693.00

0.34

9.00

505.00

0.45

732.25

0.37

10.00

510.00

0.50

765.00

0.41

11.00

505.00

0.55

782.75

0.44

12.00

490.00

0.60

784.00

0.47

12.60

470.00

0.63

766.10

0.49

12.60

260.00

0.63

423.80

0.49

 


Table 4. Effect of Tungsten inert gas (TIG) welding process on mechanical properties of 304L ASS

e·10-3 (m)

δ (MPa)

Є

δT (MPa) = δ(1+ Є)

ЄT = ln(1+ Є)

0.00

0.00

0.00

0.00

0.00

0.50

100.00

0.03

103.00

0.03

1.00

230.00

0.05

241.50

0.05

1.50

300.00

0.08

324.00

0.08

2.00

390.00

0.10

429.00

0.10

3.00

450.00

0.15

517.50

0.14

4.00

480.00

0.20

576.00

0.18

5.00

500.00

0.25

625.00

0.22

6.00

510.00

0.30

663.00

0.26

7.00

520.00

0.35

702.00

0.30

8.00

530.00

0.40

742.00

0.34

9.00

540.00

0.45

783.00

0.37

10.00

540.00

0.50

810.00

0.41

11.00

530.00

0.55

821.50

0.44

12.00

500.00

0.60

800.00

0.47

13.00

420.00

0.65

693.00

0.50

13.40

350.00

0.67

584.50

0.51

13.40

190.00

0.67

317.30

0.51

 

Table 5. Effect of metal inert gas (MIG) welding process on mechanical properties of 304L ASS

e·10-3 (m)

δ (MPa)

Є

δT (MPa) = δ(1+ Є)

ЄT = ln(1+ Є)

0.00

0.00

0.00

0.00

0.00

0.50

110.00

0.03

113.30

0.03

1.00

280.00

0.05

294.00

0.05

1.50

360.00

0.08

388.80

0.08

2.00

420.00

0.10

462.00

0.10

3.00

470.00

0.15

540.50

0.14

4.00

495.00

0.20

594.00

0.18

5.00

530.00

0.25

662.50

0.22

6.00

540.00

0.30

702.00

0.26

7.00

560.00

0.35

756.00

0.30

8.00

570.00

0.40

798.00

0.34

9.00

570.00

0.45

826.50

0.37

10.00

560.00

0.50

840.00

0.41

10.50

550.00

0.53

841.50

0.43

11.00

450.00

0.55

687.50

0.44

11.10

390.00

0.56

608.40

0.44

11.30

250.00

0.57

392.50

0.45

11.30

150.00

0.57

235.50

0.45

 


Table 6. Effect of 308L ASS electrode on mechanical properties of 304L ASS

e·10-3 (m)

δ (MPa)

Є

δT (MPa) = δ(1+ Є)

ЄT = ln(1+ Є)

0.00

0.00

0.00

0.00

0.00

0.50

100.00

0.03

103.00

0.03

1.00

280.00

0.05

294.00

0.05

1.50

380.00

0.08

410.40

0.08

2.00

430.00

0.10

473.00

0.10

3.00

460.00

0.15

529.00

0.14

4.00

490.00

0.20

588.00

0.18

5.00

520.00

0.25

650.00

0.22

6.00

540.00

0.30

702.00

0.26

7.00

560.00

0.35

756.00

0.30

8.00

570.00

0.40

798.00

0.34

9.00

580.00

0.45

841.00

0.37

10.00

585.00

0.50

877.50

0.41

11.00

580.00

0.55

899.00

0.44

12.00

570.00

0.60

912.00

0.47

12.80

500.00

0.64

820.00

0.49

12.90

260.00

0.65

429.00

0.50

 

Table 7. Effect of 312 ASS electrode on mechanical properties of 304L ASS

e·10-3 (m)

δ (MPa)

Є

δT (MPa) = δ(1+ Є)

ЄT= ln(1+ Є)

0.00

0.00

0.00

0.00

0.00

0.50

200.00

0.03

206.00

0.03

1.00

320.00

0.05

336.00

0.05

1.50

400.00

0.08

432.00

0.08

2.00

450.00

0.10

495.00

0.10

3.00

500.00

0.15

575.00

0.14

4.00

550.00

0.20

660.00

0.18

5.00

580.00

0.25

725.00

0.22

6.00

590.00

0.30

767.00

0.26

6.15

580.00

0.31

759.80

0.27

6.40

450.00

0.32

594.00

0.28

6.50

370.00

0.33

492.10

0.29

6.50

220.00

0.33

292.60

0.29

 

Table 8. Effect of 316 ASS electrode on mechanical properties of 304L ASS

e·10-3 (m)

δ (MPa)

Є

δT (MPa) = δ(1+ Є)

ЄT= ln(1+ Є)

0.00

0.00

0.00

0.00

0.00

0.50

180.00

0.03

185.40

0.03

1.00

350.00

0.05

367.50

0.05

1.50

450.00

0.08

486.00

0.08

2.00

480.00

0.10

528.00

0.10

3.00

525.00

0.15

603.75

0.14

4.00

550.00

0.20

660.00

0.18

5.00

580.00

0.25

725.00

0.22

6.00

595.00

0.30

773.50

0.26

7.00

600.00

0.35

810.00

0.30

8.00

600.00

0.40

840.00

0.34

8.50

595.00

0.43

850.85

0.36

9.00

570.00

0.45

826.50

0.37

9.10

300.00

0.46

438.00

0.39

Table 9. Effect of electrode core diameter (2.5mm) on mechanical properties of 304L ASS

e·10-3 (m)

δ (MPa)

Є

δT (MPa) = δ(1+ Є)

ЄT= ln(1+ Є)

0.40

0.00

0.02

0.00

0.02

0.50

10.00

0.03

10.30

0.03

1.00

180.00

0.05

189.00

0.05

1.50

300.00

0.08

324.00

0.08

2.00

370.00

0.10

407.00

0.10

2.50

400.00

0.13

452.00

0.12

3.00

420.00

0.15

483.00

0.14

4.00

450.00

0.20

540.00

0.18

5.00

480.00

0.25

600.00

0.22

6.00

495.00

0.30

643.50

0.26

7.00

510.00

0.35

688.50

0.30

8.00

530.00

0.40

742.00

0.34

9.00

540.00

0.45

783.00

0.37

10.00

550.00

0.50

825.00

0.41

11.00

560.00

0.55

868.00

0.44

12.00

570.00

0.60

912.00

0.47

13.00

575.00

0.65

948.75

0.50

14.00

575.00

0.70

977.50

0.53

15.00

530.00

0.75

927.50

0.56

15.10

500.00

0.76

880.00

0.57

15.10

300.00

0.76

528.00

0.57

 

Table 10. Effect of electrode core diameter (3.2mm) on mechanical properties of 304L ASS

e·10-3 (m)

δ (MPa)

Є

δT (MPa) = δ(1+ Є)

ЄT= ln(1+ Є)

0.00

0.00

0.00

0.00

0.00

0.50

100.00

0.03

103.00

0.03

1.00

260.00

0.05

273.00

0.05

1.50

350.00

0.08

378.00

0.08

1.80

400.00

0.09

436.00

0.09

2.00

420.00

0.10

462.00

0.10

3.00

460.00

0.15

529.00

0.14

4.00

490.00

0.20

588.00

0.18

5.00

510.00

0.25

637.50

0.22

6.00

540.00

0.30

702.00

0.26

7.00

550.00

0.35

742.50

0.30

8.00

570.00

0.40

798.00

0.34

9.00

580.00

0.45

841.00

0.37

10.00

590.00

0.50

885.00

0.41

11.00

595.00

0.55

922.25

0.44

12.00

595.00

0.60

952.00

0.47

13.00

570.00

0.65

940.50

0.50

13.40

550.00

0.67

918.50

0.51

13.40

320.00

0.67

534.40

0.51

 


Table 11. Effect of electrode core diameter (4.0mm) on mechanical properties of 304L ASS

e·10-3 (m)

δ (MPa)

Є

δT (MPa) = δ(1+ Є)

ЄT= ln(1+ Є)

0.70

0.00

0.04

0.00

0.04

1.00

140.00

0.05

147.00

0.05

1.50

180.00

0.08

194.40

0.08

2.00

200.00

0.10

220.00

0.10

3.00

230.00

0.15

264.50

0.14

4.00

270.00

0.20

324.00

0.18

5.00

290.00

0.25

362.50

0.22

6.00

300.00

0.30

390.00

0.26

7.00

320.00

0.35

432.00

0.30

7.30

300.00

0.37

411.00

0.31

7.50

290.00

0.38

400.20

0.32

7.50

200.00

0.38

276.00

0.32

8.00

0.00

0.40

0.00

0.34

8.20

-250.00

0.41

-352.50

0.34

8.50

-250.00

0.43

-357.50

0.36

 

The tensile test results at varied welding processes, electrodes and core diameter are depicted in Figures 2, 3 and 4 respectively.

Figure 2. Variation of true stress with true strain for 304L austenitic stainless steel under various welding processes

 

The observed improved tensile strength of the sample in order of SMAW, GTAW and GMAW samples (Figure 2) may be due to the relative heat inputs of the processes which have effect on rate of solidification [2]. Oyetunji, et al. [11] reported that rapid rate of solidification could results in greater tendency for distortion and cracking [11] and the observed superior tensile strength of the as-received sample relative to the welded sample may be due to the present of cracks which are known to have debilitating effects on materials’ mechanical properties [1,4].

 

Figure 3. Variation of true stress with true strain for 304L austenitic stainless steel under various electrode types

 

Cunat reported that low carbon stainless steels should be welded with low carbon filler material [10]. Therefore, the observed decreasing values of UTS in the order 308L ASS, 316 ASS and 312 ASS welded samples (Figure 3) could have resulted from relative difference in compositions of the electrodes and the base plate. The better tensile strength of the 308L welded relative to 316 and 312 welded samples respectively sample may be an indicative of  greater homogeneity and compatibility with the 304L ASS.

Figure 4. Variation of true stress with true strain for 304L austenitic stainless steel under various electrode core diameters

 

The observed variations in tensile strength of the samples welded with 308L electrode of different electrode core diameters of 2.5 mm, 3.2 mm, and 4.0 mm (internal core) as seen in Figure 4 may have resulted from the relative effects of stresses introduced during welding which are due to difference in heat inputs [16].  Penetration rate has been revealed to be influenced by electrode size or core diameter [10]. Hence, the observed extremely low ultimate tensile strength (UTS) of the sample produced with 308L electrode of 4.0 mm diameter may have be accounted for by relative poor penetration.

 

 

Conclusions

 

From the results obtained, the following conclusions were drawn:

¸        GMAW process, 308L stainless steel and electrode core diameter of 3.2 mm are the most appropriate parameters for the production of  butt joint with better weld integrity in 304L ASS when used in conjunction with single V geometry, power input of 9.2KW and moderate welding speed.

¸        Reduction in UTS of the butt joint samples increases with increase in core diameter of the electrode.

 

 

References

 

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