*3.1. Initial Mold Design*

The initial mold design is modeled in SOLIDWORKS as shown in Figure 4. It is a multi-cavity mold with sprue-runner configuration, where, instead of choking each casting separately, a single choke is used in the runner area. Casting simulations are done using MAGMASoft. The casting layout is divided into 1,975,320 volume elements using a cubical mesh. MAGMASoft offers a full range of material properties and heat transfer settings as an input to simulations [12]. The pouring temperature is set to be 1630 ◦C whereas the mold is assumed to be at room temperature, i.e., 20 ◦C. Pouring time is defined as 15 s. With these simulation settings, the feeding effectivity calculated by the software is ~30%. From a results perspective, it is decided to run simulations for filling and solidification sequence, residual stress distribution, and magnitude and locations of porosities.

**Figure 4.** Initial mold design for casting fatigue specimens.

Figure 5a depicts the temperature profile of the mold after pouring. As expected, solidification continues with a drop in temperature of the melt. It can be observed that solidification began with the test section of the specimens and all specimens are solidified at 50% solidification as shown in Figure 5b. The solidification time is recorded to be 8 min with risers being the last region to solidify in the mold. The distribution of residual stresses is presented in Figure 5c where stresses are concentrated in the test section of the specimens. The maximum residual stress at ejection is about 50 MPa, which is a typical magnitude of residual stress in steel castings [13].

**Figure 5.** (**a**) Temperature profile within the mold at 50% solidification, (**b**) Percentage fraction solid at 50% solidification, and (**c**) Residual stresses distribution.

In terms of porosity, the X-ray view shown in Figure 6a revealed only one specimen to be pore-free. However, significant porosity is observed in specimens 4, 6, 7 and 8 as shown in Figure 6. Despite the porosity being observed in the grips of test specimens, it had to be minimized for the reason that these specimens are simple cast products. Microporosity is distributed throughout the casting layout with a maximum microporosity to be ~4% as shown in Figure 6b. Figure 6c shows the total porosity in the specimens which is found to be nearly the same in all specimens and could be minimized with a better mold design.

**Figure 6.** X-ray views of (**a**) porosity, (**b**) microporosity and (**c**) total porosity in simulated cast specimens using initial mold design.
