PSI- Issue 9

Romanin Luca et al. / Procedia Structural Integrity 9 (2018) 55–63

58

Author name / Structural Integrity Procedia 00 (2018) 000 – 000

4

Fig. 1. CCT diagram used for FE analysis. The influence of the parameters is shown by the arrows.

Fig. 2. CCT diagrams derived by using empirical correlations

A time factor greater than 1 means that the same transformation occurs for a faster cooling rate (CCT diagram moved to the left) (Fig. 3). On the contrary, a time factor lower than 1 implies that martensite is formed even for slow cooling rates ( “ cA ” case ).

Fig. 3. Comparison between “ cA ” and “ cE ” cases (time factor of 1/5 and 5 respectively). For the blue diagram, martensite is formed only for very fast cooling rate

2.2. FE model

A butt-welded joint has been considered for the analyses (Fig. 4). The plate is 60 x 40 mm with a thickness of 3 mm. By taking advantage of the symmetry, only one half of the joint was modelled. The ends are left unclamped while the heat source is modelled using the Goldak ’s function (Goldak et al., 1984), which parameters have been chosen in order to simulate a one-pass welding (see Table 2).

Table 2. Goldak heat source function parameters

a r [mm] a f [mm] c [mm] b [mm]

f r

f f

v [mm/s]

3.5

2.2

6

2.2

1.4 0.6

10

The power input is 2.85 kW and a process efficiency of 64% has been assumed. The welding speed is supposed to be constant at 10 mm/s.