## 1 Introduction
The grain structure in the weld's recrystallization zone resulted from the competition between dynamic recrystallization (DRX) and grain boundary sliding (GBS), controlled by the local deformation condition. Decreasing the rotation rate resulted in a smaller grain size in the weld's nugget zone, necessitating a lower applied force to enable GBS. The tensile strength of the IN718 alloy weld joint could be enhanced by optimizing the friction welding parameters and post-weld heat treatment (PWHT) conditions. [PERSON] et al. [15] investigated the effect of various cooling methods on the performance of steel in the welding processes. Their study compared the use of water, air, and oil as cooling agents during the welding process and evaluated the resulting microstructure, hardness, and tensile strength of the welded metal. The results indicated that the cooling method significantly impacted the microstructure and mechanical properties of the welded steel, with the use of water showing the most favorable results, in terms of both microstructure and mechanical properties. The mechanical properties of the welded steel material depend on the methods used for cooling the material after welding [15]. [PERSON] et al. [16] reported that TMAZ exhibited serrated necklace-shaped, deformed grain boundaries, with fine grains surrounding the original deformed grains. A variation in microstructure was observed between the weld zone and the TMAZ, due to recrystallization. At the interface, fully recrystallized grains developed, but the recrystallization in the TMAZ was restricted to elongated grains. [PERSON] and [PERSON] et al. [17] investigated the microstructure evolution and process optimization of linear friction welded IN718 joints. They observed a decrease in hardness in the TMAZ on the hardness plot (334 HV to 250 HV), which was attributed to the dissolution of \(\gamma^{\prime}/\gamma^{\prime\prime}\) precipitates and grain coarsening during the rotary friction welding process, owing to high temperatures throughout the process. [PERSON] et al. [18] investigated the mechanical property evolution during dissimilar friction welding of IN600 to SS304L. They found that the welds displayed a higher ultimate tensile strength (UTS-500 MPa) and yield strength (YS-315 MPa) than the base materials. [PERSON] et al. [19] investigated the dissimilar metal friction welding of austenitic-ferritic stainless steel and observed that the dissimilar metal weld' notch tensile strength (NTS: 600-697 MPa) properties were superior to those of the ferritic stainless steel parent metal (NTS: 547-590 MPa). The joining of stainless steel (SS304L) with dissimilar materials such as titanium, ferritic stainless steels, Inconel600, and titanium with nickel interlayer has been widely investigated, in terms of strength and metallurgical characteristics, and a substantial amount of literature is available on friction welding methods [18; 19; 20; 21]. However, to the best of the author's knowledge, the literature on the joining of low carbon grade austenitic stainless steel (304L) to IN718 by rotary continuous friction welding is limited. The present study aimed to evaluate the effect of heat treatments on the microstructural and mechanical properties of rotary friction welded dissimilar joints of Inconel 718 to 304L austenitic stainless steel.