P92钢焊接接头Ⅳ型蠕变断裂特性

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%.

TYPE IV CREEP RUPTURE CHARACTERISTICS OF P92 STEEL WELDMENT

Creep tests at 600—650℃with applied stresses in the range 100—240 MPa and microstructural observations by means of OM,SEM,TEM were conducted on welded joints of P92 steel prepared by submerged arc welding（SAW） process to investigated its characteristics of typeⅣcreep rupture.The results showed that type IV failure tack place at higher temperature and lower stress and tends to have a critical condition expressed by Larson-Miller parameter（LMP） and stress level which values are 35.5 and 120 MPa,respectively.Type IV failure showed a lack of ductility and located in the fine grained heat affected zone（FGHAZ）(heated to just above A_C3)close to intercritical heat affected zone（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 typeⅣfailure.The size of M₂₃C₆ carbide in the 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 was nucleated at coarse precipitates of Laves phase.The fraction of grain boundary facets cavitated and the area fraction of voids can be employed to quantify grain boundary damage and evaluate typeⅣfailure of P92 steel welded joints,and when their values were about 1.2%and 0.5%,type IV failure would occur.