*3.3. LBW Varestraint Weldability Test Results*

Figure 6 shows the hot cracking behaviour observed in the five casting heats that was determined by LBW Varestraint test. Moulds O (low Si), P (high Si), and E (standard Si), which were cast without ceramic blanket and therefore solidified at quicker cooling rates, were tested at augmented strain levels from 1 to 8%. Slowly cooled heats (moulds N and NP) were only tested up to 4% augmented strain. Results show that in all casting heats, FZ cracking was much more prominent than HAZ cracking. In fact, TCL measured in FZ was more than 5–6 times longer than in HAZ. At 8% augmented strains, TCL determined in the HAZ ranged between 2.5 and 5 mm, whereas for the same testing conditions, TCL in FZ was between 20 and 30 mm. Therefore, it was observed that LBW Varestraint test mainly enhanced FZ cracking.

(**a**) (**b**)

(**c**) (**d**)

**Figure 5.** Grain size of different moulds in the as-cast state: (**a**) O, (**b**) E, (**c**) P, and (**d**) NP.


**Figure 6.** (**a**) FZ and (**b**) HAZ cracking response of five alloy 718 casting heats in LBW Varestraint test.

Mould P (high Si content) showed a comparatively higher cracking susceptibility than the rest of the heat levels. Nevertheless, mould O (low Si) was ranked second in terms of trend towards FZ and HAZ cracking. Mould E with intermediate Si content and NP showed slightly lower TCL values, whereas behaviour of mould N was in between.
