## 4 Conclusions  
The dissimilar SS304L/IN718 welds in this investigation were prepared utilizing the rotary continuous friction welding process. The influence of heat treatment on the microstructural and mechanical properties was evaluated under ST, STA, and PWHT conditions. The following conclusions were drawn:  
1. Defect-free dissimilar SS304L/IN718 welds with no solidification cracking, fissure cracks, or imperfect bonding could be attained using the rotary continuous friction welding process. 2. The macrostructure of dissimilar SS304L/IN718 welds revealed a higher flash on the SS304L side and less flash on the IN718 side, owing to a sharp reduction in flow stress in the SS304L at high temperatures. 3. The dissimilar friction welds of SS304L/IN718 in the ST and STA conditions underwent dynamic recrystallization, as shown by the finer equiaxed grains in the FDZ, with an average grain size of 6 \(\pm\) 2 \(\mu\)m. This encourages the creation of high-quality joints with superior mechanical properties. 4. The SS304L/IN718 weldment in the PWHTed condition showed the highest hardness (486 \(\pm\) 4 HV) in the FDZ of IN718; this was due to the creation of strengthening precipitates. The lowest microhardness of 193 \(\pm\) 2 HV was observed in the HAZ on the SS304L side of the SS304L/IN718 PWHT, due to grain coarsening. 5. Among all the weldments, the dissimilar SS304L/IN718 weldment in the PWHTed condition showed a higher strength and lower elongation (UTS-721 \(\pm\) 4 MPa, 7 \(\pm\) 1% elongation). This could be attributed to the formation of strengthening precipitates \(\gamma^{\prime}\) and \(\gamma^{\prime\prime}\) in IN718. Furthermore, the PWHTed weldment failed in the BM region of SS304L, while the other two welds (ST, STA) failed in the HAZ region of SS 304L. 6. To obtain the best combination of mechanical properties, while keeping the practical difficulties of welding large components in mind, a dissimilar SS304L/IN718 rotary friction welded joint should be welded in a solution-treated (ST) condition and subjected to post-weld heat treatment (PWHT). Figure 17: Fracture surfaces of the dissimilar SS304L/IN718 welded joints in the (**a**) as-welded ST, (**b**) STA, and (**c**) PWHT conditions. **Author Contributions:** Conceptualization, P.P., M.K.T. and N.K.B. ; Data curation, P.P., M.K.T. and N.K.B. ; Formal analysis, P.P., M.K.T., N.K.B., A.U.R. and P.S. ; Funding acquisition, A.U.R. and P.S. ; Investigation, P.P., M.K.T., N.K.B. and A.U.R. ; Methodology, P.P., M.K.T., N.K.B., A.U.R. and P.S. ; Resources, M.K.T., N.K.B., A.U.R. and P.S. ; Supervision, M.K.T., N.K.B. and A.U.R. ; Visualization, P.P., M.K.T., N.K.B., A.U.R. and P.S. ; Writing--original draft, P.P., M.K.T. and N.K.B. ; Writing--review and editing, M.K.T., N.K.B., A.U.R. and P.S. All authors have read and agreed to the published version of the manuscript. This research was funded by King Saud University through Researchers Supporting Project number (RSPD2023R701), King Saud University, Riyadh, Saudi Arabia. Not applicable. Data Availability Statement: Data are contained within this article. The authors are thankful to King Saud University for funding this work through Researchers Supporting Project number (RSPD2023R701), King Saud University, Riyadh, Saudi Arabia. The authors  
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