This study investigates the diffusion-bonding behaviour of 316 L stainless steel joints with emphasis on their short-term tensile response at elevated temperature. An L9 Taguchi orthogonal array was employed to preliminarily screen the main effects of bonding temperature, applied pressure and holding time within the selected parameter range. Joint performance was evaluated by tensile testing at room temperature and 550 \(^\circ \)C, together with metallographic observation and X-ray diffraction analysis. Within the present dataset, bonding pressure exerted the most significant influence on joint performance, followed by holding time, whereas bonding temperature showed a comparatively smaller effect. The results indicate that elevated-temperature tensile behaviour is associated with both interfacial continuity and phase evolution. Prolonged holding time generally improves geometric continuity at the bonded interface, but it is also accompanied by the appearance of Fe–Cr-rich phases under some bonding conditions, whereas shorter or intermediate holding times favour Fe–Ni-type phases and reduce the likelihood of Fe–Cr-rich phase formation. Accordingly, the 120 min joint is treated in this work as an additional verification condition rather than a Taguchi-predicted optimum. This verification joint, prepared at 1100 \(^\circ \)C, 10 MPa and 2 h, exhibited ultimate tensile strengths of 525.7 MPa at room temperature and 381.9 MPa at 550 \(^\circ \)C. Overall, the present results support a recommended holding-time interval of 2–3 h at 1100 \(^\circ \)C and 10 MPa for direct diffusion bonding of 316 L stainless steel within the investigated process range. The 120 min joint provides a useful reference point within this interval, but it is not presented as a strict global optimum. The conclusions of this study are limited to short-term tensile loading at 550 \(^\circ \)C, and the applicability to long-term service should be validated by dedicated creep and durability testing.
