Effect of long term high temperature aging on CGHAZ mi-crostructure of T23 water wall welded joint
The micro-mechanism of reheat crack formation in coarse grain heat affected zone(CGHAZ)of welded joint of T23 water wall tube without heat treatment after welding was analyzed by high temperature aging method.It reveals the in-ternal reason that T23 water wall joint without heat treatment is easy to crack and leak in short-term operation after unit star-tup.The hardness,microstructure and precipitates of welded joints of water wall after unaged and high temperature aging treatment were systematically analyzed by means of material characterization.The results show that after aging at 530℃for 100 h,the hardness of CGHAZ appears secondary hardening caused by intragranular dispersion strengthening.With the in-crease of aging(running)time,the hardness of CGHAZ gradu-ally decreases,but after aging for 1 000 h,the hardness of CGHAZ is still 319 HV,which is higher than the standard re-quirement.After aging at 600℃,the hardness of CGHAZ de-creases with the increase of aging time.The hardness of CGHAZ decreased due to the recovery of microstructure,re-crystallization,broadening of martensite lath,reduction of dis-location density,and precipitation of C and alloy elements from the matrix,which is higher than the hardness increased due to dispersion and precipitation of MX carbide in the grain.M23C6 carbide gradually precipitates and grows at grain boundaries and subgrain boundaries.
high temperature agingT23 steelwater cool-ing wallCGHAZreheat crack
NETL
NSTL
万方数据
维普
