Technical Highlight Vol.21

Vol.21: TRUSTARC™ DW-A62LSR(A5.29 E91T1-GM) improves notch toughness of HSLA weld metal after PWHT

Vol.20: Recent developments of AWS specifications

In the construction of structures such as spherical tanks and pressure vessels, weldments are subjected to postweld heat treatment (PWHT) in order to reduce the residual stresses induced by welding and for improving the fracture toughness and fatigue properties of the welds. As these structures have grown larger in size and are being operated at even-higher pressures, in tandem with recent growth in energy demand, the steel materials used have been increasingly strengthened. To company with such a trend, TRUSTARC™ DW-A62LSR, a rutile type flux cored wire (FCW) for HT610 or higher class steel materials, has been developed and confirmed to satisfy the following requirements:

As welded:TS≧621MPa (90ksi), vE≧27J at-60℃
PWHT: TS≧586MPa (85ksi), vE≧27J at-40℃

Table 1 shows the typical chemical compositions of deposited metal with TRUSTARC™ DW-A62LSR.

Table 1: chemical compositions of deposited metal (mass%)
C Si Mn P S Ni Others
0.05 1.14 1.29 0.007 0.008 2.59 Mo, Ti, B

Figures 1 and 2 show the relationship between PWHT conditions and mechanical properties of the deposited metal.


Figure 1

Figure1: Relationship between tensile strength and the Larson Miller's Temper Parameter (LMTP)
LMTP=T (20+log t).
(T: Temperature [K]; t:holding time [hour])

Figure 2

Figure2: Relationship between absorbed
energy and LMTP


The effect of heat input (cooling rate at 540℃ [℃/sec], calculated by Rosenthal's equation) on the tensile strength and absorbed energy of deposited metal in as welded and PWHT conditions was studied and the results are shown in Figures 3 and 4, respectively.

Figure 3

Figure3: Relationship between tensile strength and cooling rate at 540℃ in as welded and PWHT (620℃×8hours; LMTP=18.7×103)conditions Solid line: as-welded; Dotted line:PWHT

Figure 4

Figure4: Relationship between absorbed energy and cooling rate at 540℃ in as welded and PWHT (620℃×8hours; LMTP=18.7×103)conditions Solid line: as-welded; Dotted line:PWHT


A butt joint weld test was conducted under the conditions shown in Table2.

Table 2: Welding conditions
Welding wire DW-A62LSR (1.2mmΦ)
Base metal TS610MPa class steel (60mm thick)
Dimension of groove

Figure 4

After welding the face side, the groove of reverse side was machined to a shape of 50° angle and 35 mm depth.
Welding position & parameters(heat input) (1) Flat (1G): 270A-28V (1.2 kJ/mm)
(2) Horizontal (2G): 260A-28V (0.8 kJ/mm)
(3) Vertical-up (3G): 220A-24V (2.4 kJ/mm)
PWHT As welded & 620℃x 8 hours (LMTP18.7x10³)
Preheating & interpass temperature 90-110℃ and 140-160℃
Shielding gas 80%Ar-20%CO2; 25 liter/min

Figure 5 shows the macrostructures of the welded joints in 1G, 2G and 3G positions. The test results of mechanical properties in as welded and PWHT conditions are shown in Tables 3.

Figure 5

Figure5: Macrostructure of welded joints (1G,2G and 3G positions from the left to the right)



Table 3: Mechanical properties of welded joint (Location: center)
Position PWHT
condition
Tensile properties Notch toughness
0.2%PS
[MPa]
TS
[MPa]
El
[%]
Absorbed energy [J]
-60℃ -40℃
1G AW *1 713 748 22 67 81
PWHT *2 627 692 22 41 61
2G AW *1 722 752 22 81 91
PWHT *2 678 721 27 47 62
3G AW *1 640 706 24 61 90
PWHT *2 619 686 28 31 64

*1 AW: as welded *2 PWHT: 620℃ x 8 hours


Page Top

Products

Welding Robot/Software
japanese_scenery