Abstract: T91 steel pipe was joined by transient liquid phase bonding under low pressure at 1 230-1 260℃,and the influence of bonding temperature on the microstructure and composition of the joints was investigated by EPMA.The results show that with increasing of the bonding temperature,the diffusion of alloying elements across the joint is accelerated and the homogenization of the joint microstructure is promoted.However,some cavities are produced in the joint when the bonding temperature arrives at 1 260℃.The two step heating process,which is that the joint is firstly heated up to 1 260℃ and keep for 5s and then cool to 1 230℃ and keep for 180 s,can not only reduce the defects,but also dismiss the bonding interface,producing a seamless joint.The joint fails in base metal and no failure occurs when it is tensioned and bended to 180° respectively,indicating that the joint mechanical properties arrive to the base metal.In contrast to braze press welding,the axes of pipes are not shifted to each other and only little deformation can be observed.