African Fusion March 2016

Welding parameters In order to establish appropriate parameters for the experi- ments and simulation, a series of tests were done. This section introduces some of these variations. Figure 3 a-g is a compila- tion of metallographic sections fromsamples welded at differ- ent speeds and currents, while Table 2 gives a list of all these different welding current, welding speed and processes used to produce the samples. Steel grade Outer diameter [mm] Wall thickness [mm] S355-TT 73.5 4 S355-TT 101 6 20MnV6-TT 168.3 8 20MnV6-TT 168.3 16 S890QL1 168.3 8 S890QL1 168.3 16 Table 1: A list of materials and dimensions used.

Sample number

Welding current [A]

Welding speed [cm/min]

Process

a b

320 320 320 320 320 320 270

70 90

standard standard standard standard

c

100 110

d e

70 70 50

pulse 3 [Hz] pulse 10 [Hz]

Figure 3 a-g: Metallographic sections of joints welded at different welding speeds and welding currents, as per Table 2.

f

Themetallographic sections are necessary to characterise theweldpenetrationandweld formation, (Figure 3a-g). At first, all micro-sections look similar, but looking into the detail a more homogeneousweld formation andweld penetration can be seen when using pulse GMAW (Figure 3e and 3f). However, the advantage of pulse welding cannot be modelled in common FE welding simulation software and is therefore only an option for welding experiments. In addition to weld penetration and weld formation, it is important to consider hardening. These investigations were done according to DIN EN ISO 9015-1:2011-05 [4]. Figure 4 and Figure 5 show the results of standardised testing, which is divided into a measurement close to the surface and another close to the root. standard Table 2: A list of parameter variations for the metallographic sections shown below. g

Considering the area close to the surface it is noticeable that all standard welds are very close to each other and have a similar curve. The pulsed welding is at the same level of hardness as standard base metal S355-TT. In contrast to standardwelding, thepulsedweldingdoes not tend to increase the hardness in the heat-affected zone. Vickers hardness values close to the root (see Figure 5), do not deviate from this trend. The pulsed welding is again at a lower level of hardness compared with standard welding at a welding speed of 70 cm/min. Welding simulation To save money and time during the development of a K- joint truss

Figure 4: Vickers hardness tests close to surface.

Figure 5: Vickers hardness values close to the root.

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March 2016

AFRICAN FUSION