Abstract: The high-temperature aging tests of T23 water-cooled pipe joint were carried out with 6 parameters, namely 530 ℃×100 h, 530 ℃×500 h, 530 ℃×1 000 h, 600 ℃×100 h, 600 ℃×500 h, 600 ℃×1 000 h. A systematic study on the weld zone of the joint shows that：firstly, the reheat crack in the weld zone is mainly caused by the precipitation and growth of M₂₃C₆precipitates at the grain boundary, which leads to the formation of a softening zone at the grain boundary, and the pores associated with M₂₃C₆ further weaken the intergranular bonding force, and the strain is mainly concentrated at the grain boundary during the stress relaxation process; Secondly, after the welded joint without heat treatment was put into service, secondary hardening occurred in the weld zone in a short period of time, the difference between intragranular strength and grain boundary strength increased, and the sensitivity of reheat crack increased, which led to the leakage of T23 water wall joint in a short period of time. Thirdly, the post-weld heat treatment makes the unstable weld zone structure pre-transform, a large number of carbides precipitate, the matrix recovers and recrystallizes, which reduces the intragranular strength. At the same time, the dilution of alloy elements near the grain boundary is eliminated, the difference between intragranular and grain boundary strength is reduced, the plastic deformation ability is obviously improved, and the sensitivity of reheat cracking is reduced.

Key words: high temperature aging, T23 steel, water wall, weld zone, reheat crack