模拟瞬时液相扩散焊三温工艺对T91钢进行焊接，并进行了780℃×2 h回火处理，研究了热影响区的组织和力学性能以及回火处理对热影响区力学性能的影响。结果表明：热影响区可分为距焊缝0~7.5 mm处的过热粗大板条马氏体区、距焊缝7.5~22.5 mm处的细小板条马氏体区、距焊缝22.5~37.5 mm处的铁素体+马氏体区以及距焊缝37.5~42.5 mm处的回火马氏体区等4个区域；随着距焊缝距离的增大，热影响区的脆硬倾向降低，断裂机制由脆性断裂向韧性断裂转变；回火处理后热影响区的抗拉强度和硬度相比回火处理前的有所降低，但韧性提高。

T91 steel was welded by simulated three-temperature process of transient liquid phase diffusion welding, and then tempered at 780℃ for 2 h. The microstructure and mechanical properties of the heat-affected zone and the effect of tempering treatment on the mechanical properties of the heat-affected zone were studied. The results show that the heat-affected zone was divided into four zones:overheated coarse lath martensite zone at 0-7.5 mm distance from the weld, fine lath martensite zone at 7.5-22.5 mm distance from the weld, ferrite+martensite zone at 22.5-37.5 mm distance from the weld and tempered martensite zone at 37.5-42.5 mm distance from the weld. With increasing distance from the weld, the hard and brittle tendency of the heat-affected zone decreased and the fracture mechanism changed from brittle fracture to ductile fracture. Compared with those before tempering, the tensile strength and hardness of the heat-affected zone after tempering decreased but the toughness increased.