PSI - Issue 14

P D Gosavi et al. / Procedia Structural Integrity 14 (2019) 304–313 P D Gosavi et al./ Structural Integrity Procedia 00 (2018) 000 – 000

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(a)

(b)

(c)

(d)

Fig.9. Microstructural phase Analysis at 200X (a) W1 (SMAW process); (b) W2 (GTAW process); (c)W3 (SAW process); (d) W4 (GMAW process)

3.3. Tensile properties

The tensile properties of base metal and weld are presented in table 6. The yield strength and tensile strength of different welds are higher than those of base metal. The weld metal ductility is lower than that of base metal but higher than specified. All the weld joints met the property requirements. The tensile property of weld joints W2 made with GTAW process (moderate heat input – 1.85 kJ/mm) was observed to be highest whilst those of welds (W3) made by SAW process (high heat input – 2.4 kJ/mm) was on the lower side. The tensile property of center of SAW welds was higher than those of top and bottom as root was made by SMAW process (Heat input- 1.3 kJ/mm). As considering microstructural analysis and chemistry, tensile properties of weld joint of particular process is high for higher percentage of acicular ferrite and highest P cm value; as GTAW has highest tensile properties and higher percentage of acicular ferrite, while SAW process has lowest tensile properties and lower percentage of acicular ferrite.

Table 6. Tensile result data for base and all weld specimens tested on UTS

Properties

W1

W2

W3

W4

Top

Bottom 863±10 898±20

Top

Bottom 901±10 949±20

Top

Centre 794±10 833±20

Bottom 691±10 735±20

Top

Bottom 789±10 851±20

YS(MPa)

876±10

912±10 948±20

663±10 712±20

872±10 907±20

UTS(MPa) 901±20

El(%)

15

17

17.2

19

25

22

23

14

21

3.4. Impact toughness

The impact toughness was determined at different temperatures from 20 ° C to sub-zero temperatures as low as -80 ° C in some cases. For W1 weld joint, the average impact toughness was high at 82 J at 20 ° C and while at -40 ° C the average value was 39J. The W2 weld joint has high toughness at 157 J at 20 ° C and the average minimum value was 191 J at -40 ° C for GTAW. Variation of weld metal impact toughness with test temperature is graphically shown in fig.12. For W3 and W4 joint impact toughness at 20 ° C was found within 60-70 J. For W3 joint the impact toughness dropped to about 15-25 J at -40 ° C . The toughness drop was steeper at weld center (root weld) than at surface. The root was made by SMAW process at relatively lower heat input and was tempered by subsequent passes from either side of root which might have contributed to lower impact toughness as given in fig.12(c)&(d). For W4 weld joint the impact toughness at -20 ° C was similar to that of W3 at 60-70J. But the drop was gradual to an average impact toughness of 52 J at -40 ° C as given in fig. 10(e). The W3 joint made by GTAW process showed highest tensile properties in combination with maximum -40 ° C impact toughness compared to those of other