## 4 Conclusions
When subjected to equal pressure, the hardness increment in SS308L outstripped that of Inconel625, a phenomenon that can likely be ascribed to the inherent superior mechanical properties of Inconel625, leading to its lower susceptibility to pressure. The effect of pressure on the tensile strength and fracture were analyzed. Figure 9 displays the tensile properties, including the yield strength (YS) and ultimate tensile strength (UTS), for all the experimental cases. The average tensile values for Case 1(344 MPa and 539 MPa) and Case 2 (337 MPa and 541 MPa) were similar. However, both the YS and UTS improved in Case 3 (377 MPa and 564 MPa) and Case 4 (374 MPa and 585 MPa). The elongation averages for Cases 1 through 4 were 44%, 42%, 38%, and 37%, respectively. Applying 10,000 N pressure to Inconel625 in Cases 1 and 2 had a minimal effect on the tensile strength. The longitudinal tensile strength increased in Cases 2, 3, and 4 when pressure was applied to the SS308L region. However, compared to the tensile strength results of Cases 1 and 2, where pressure was only applied to the Inconel625 region, the effect of the applied pressure on the tensile strength of Inconel625 seemed to be insignificant. This was because the fracture of the longitudinal tensile strength occurred in the SS308L region. Accordingly, it can be confirmed that the pressure in Cases 2, 3, and 4, which pressured SS308L, affected the tensile strength, but not in Case 1, where only the Inconel625 region was pressured. In the comparison between Case 1 and 2, applying 10,000 N pressure to Inconel625 had a minor effect on the tensile strength. However, a significant rise in the bimetallic structure's longitudinal tensile strength was seen in Cases 2, 3, and 4, especially when pressure was applied to the mechanically weaker SS308L side. The SEM images of fracture surfaces in Figure 10 showed dimple-like features, with the equiaxed shape of these dimples in all cases pointing to the primary role of uniaxial tensile stress. This suggested that the WAAM-rolling SS308L had a good toughness, indicating a ductile fracture mechanism driven by microvoids merging. These microvoids started at the secondary phase and their combination led to the final fracture of the specimen. The presence of equiaxed dimples in Figure 10 suggested that SS308L displayed a good toughness due to the dominant effect of uniaxial tensile stress in this area. In this study, the effect of variable pressure on the mechanical attributes of an Inconel625-SS308L bimetallic structure, produced through wire arc additive manufacturing, was investigated. Bimetallic structures of SS308L and Inconel 625 find potential application in nuclear power plants, industrial gas turbines, shipbuilding, and oil refineries. Finally, understanding the metallurgical and thermal properties of the materials provided insight into a novel approach for fabricating a bimetallic structure of SS308L and Inconel 625, grounded in variable-pressure rolling WAAM. Future studies will consider real-time temperature variations and varying pressures. Furthermore, research will also be conducted on specific alloys such as aluminum and titanium, essential to the aerospace, defense, and automotive sectors. In addition, the rolling pressure system used in this study applies only to straight walls. However, future research will aim to modify this system for application on curved walls. Conceptualization, Y.-H.H. and D.-H.K. ; methodology, Y.-H.H.H. and D.-H.K. ; software, Y.-H.H. ; validation, Y.-H.H. ; formal analysis, Y.-H.H. ; investigation, Y.-H.H. ; resources, Y.-H.H. ; data curation, Y.-H.H. ; writing--original draft preparation, Y.-H.H. and D.-H.K. ; visualization, Y.-H.H. ; writing--review and editing, D.-H.K. ; supervision, D.-H.K. and C.-M.L. ; project administration, D.-H.K. and C.-M.L. ; funding acquisition, C.-M.L. All authors have read and agreed to the published version of the manuscript. This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (No.