## 2 Materials and Methods  
The managing steel samples examined in this study were fabricated by using a powder bed-type metal 3D printer (OPM 250L, Sodick Co., Ltd., Yokohama, Japan), equipped with single-mode 500 W ytterbium fiber laser with a wavelength of 1070 nm (YLR-500-WC, IPG Laser GmbH, Burbach, Germany). Gas-atomized maraging 18 Ni-300 steel powder (OPM Maraging, OPM Laboratory Co., Ltd., Kyoto, Japan) was used as the feedstock material. The chemical composition of the maraging steel powder used for the LPBF is given in Table 1. The LPBF of the maraging steel was carried out using the LPBF parameters recommended by the manufacturer, e.g., a laser power of 420 W, a laser scanning speed of 1000 mm/s, a hatch spacing of 0.1 mm, a layer thickness of 0.04 mm, and a substrate preheating temperature of 80 \({}^{\circ}\)C. According to the manufacturer's information, these LPBF parameters lead to almost fully dense maraging components with porosities of less than 0.2% and dimensional errors of less than 0.01 mm. A so-called 90\({}^{\circ}\) rotate scanning strategy was used. Therefore, the laser scanning lines were 90\({}^{\circ}\) tilted between each LPBF layer. More detailed information regarding the maraging steel produced by these LPBF process parameters, including the microstructure and the mechanical properties, can be found in the authors' previous work [9]. Table 2 summarizes the LPBF process parameters for the 18 Ni-300 used in this study. Cantilever-shaped specimens were designed and produced to quantitatively evaluate the residual stress in the maraging steel produced by the LPBF. Figure 1 shows the schematic design of the cantilever, the deformation measurement method, and the appearance of the LPBF processed maraging steel cantilever specimens used in this study. The cantilever design consists of a 10 mm thick artificial supporter, supporter legs, and a cantilever, as shown in Figure 1a. The supporter and the supporter legs were designed to restrain the vertical deformation of the cantilever during the LPBF and the post heat treatment processes. The cantilevers produced in this study had a horizontal length of 25 mm and had various thicknesses (\(t\)) in the range of 0.5-5 mm. Through this design, the residual stress induced by the LPBF process can be isolated in the cantilever and is released when the cantilever is detached from the supporter by cutting the supporter legs, as schematically shown in Figure 1a. With this method, the residual stress in the cantilever can be evaluated by measuring the deformation, \(\delta\), occurring when cutting the legs. This method had been successfully applied to evaluate the residual stress of AISI 316L stainless steel made by LPBF, with and without post heat treatment [24]. Detailed information about the cantilever design, as well as the finite element simulation results of the residual stress state, can be found in the authors' previous work [24]. The cutting of the supporter legs was performed gently and slowly by an electric abrasive hand grinder. The deformations of the cantilever while cutting the legs were measured using a height gauge (ABSOLUTE digimatic height gauge serial 570-322, Mitutoyo, Japan), with a resolution of 10 \(\mu\)m. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Element** & **Fe** & **Ni** & **Co** & **Mo** & **Ti** & **Mn** & **Al** \\ \hline wt.\% & Bal. & 17–19 & 8.5 & 4.0 & 0.7 & \(\leq\)0.1 & \(\leq\)0.1 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Chemical composition of maraging 18 Ni-300 steel powder. \begin{table}
\begin{tabular}{c c} \hline \hline
**Parameter** & **Value** \\ \hline Laser power (W) & 420 \\ Laser scanning speed (mm/s) & 1000 \\ Hatch spacing (mm) & 0.1 \\ Layer thickness (mm) & 0.04 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: LPBF process parameters used for 18 Ni-300 used in this study. Aging heat treatments of the cantilever specimens were performed in a box-type electric furnace.