在600-650℃, 100-240 MPa对用埋弧自动焊工艺制备的P92钢焊接接头进行高温蠕变实验, 采用OM, SEM和TEM等研究焊接接头的IV型蠕变断裂特性. 结果表明, P92钢焊接接头的IV型断裂发生在高温和低应力条件下, 存在一个临界Larson--Miller参数LMP和临界应力, 它们的值分别约为35.5和120 MPa; IV型断裂部位的变形很小, 位于靠近临界热影响区的细晶区, 即加热峰值温度在AC3附近, 该部位显微结构退化为铁素体等轴晶及蠕变过程中Laves相在晶界析出和长大是影响IV型断裂的主要因素, M23C6粗化的影响较小; 焊接接头IV型断裂是一种晶界孔洞聚集型蠕变断裂, 孔洞在粗大Laves相附近形核, 可用损伤晶界上孔洞面积分数f或孔洞面积分数a作为发生IV型断裂的微观判据, 它们在650℃时的临界值分别约为0.5%和1.2%.
Creep tests at 600～650℃ with applied stresses in the range 100～240MPa and microstructural observations by means of OM, SEM, TEM were conducted on weld joints of P92 steel prepared by SAW process to investigated its characteristics of Type Ⅳ creep rupture. The results showed that Type Ⅳ failure took place at higher temperature and lower stress and tend to have a critical condition expressed by Larson-Miller parameter（L.M.P.）or stress level which values are 35.5 and 120MPa respectively. Type Ⅳ failure showed a lack of ductility and located in the fine grained HAZ（heated to just above AC3）close to intercritical HAZ, where microstructural changes are obviously different from those in the base metal, including formation of equiaxed sub-grain structure, mass precipitation and rapid growth of Laves phases on the grain boundaries during creep exposure, which lead to the Type Ⅳ failure. The size of M23C6 carbide in the AC3 FGHAZ was almost the same as that in the base metal, which has little effect on the failure. Type Ⅳ rupture is a brittle intergranular fracture due to cavity coalescence, which were nucleated at coarse precipitates of Laves phase. The void area ratio of f or AA is employed to quantify grain boundary damage and evaluate Type Ⅳ failure of P92 steel weld joints, and when their values were above 1～1.2% or 0.5%, Type Ⅳ failure would occur.
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