Study On Multi-round Deformation Behavior Of Casing Material For Steam Huff Thermal Recovery Well

As we all know,petroleum is a valuable resource in the world.In the process of petroleum exploitation,casing has an important role.Compared with service conditions,thermal cycling will cause the mechanical properties of the material to decrease.Therefore,in order to explore the law of the casing performance of thermal recovery wells with the number of thermal cycles,this paper takes 80 SH steel as the research object,combined with the service environment of the thermal recovery pipe,has conducted different rounds of thermal cycle tests on the material,and uses laser confocal Microscopy,mechanical performance testing and scanning electron microscopy methods were used to study the change of mechanical properties of the samples with microstructure after different thermal cycles.On this basis,the creep performance and low cycle fatigue behavior of 80 SH steel after different heat cycles were studied,and the low cycle fatigue fracture was analyzed.The results show that the microstructure of 80 SH steel is tempered sorbite,gray-black is acicular ferrite,white is granular bainite and the content is small,and a small amount of black spots are precipitates.At the same experimental temperature,when the material is increased from no thermal cycle(0 times)to 8 thermal cycles,the yield strength and tensile strength decrease,and the elongation and shrinkage rate increase;from 8 thermal cycles to At 30 heat cycles,the yield strength and tensile strength of the material increase,and the elongation and shrinkage of the area decrease.Under the same thermal cycle,as the temperature of the experiment increases,the yield strength and tensile strength of the material decrease,and the elongation and shrinkage increase.There is obvious plastic deformation in the tensile macro-fracture of 80 SH steel.The micro-morphology of the tensile fracture is shown as tough dimples.The fibrous area and the radiating area have increased pit size.When the experiment temperature is 350?,the creep rate of 30 thermal cycles is the highest,the creep rate of 15 thermal cycles is the second,and the creep rate without thermal cycles(0 times)is the smallest.When the test temperature is room temperature,the strain life without thermal cycle(0 times)is shorter than 15 and 30 thermal cycles in the short-life region,and the strain life without thermal cycle(0 times)is high in the long-life region.At 15 and 30 thermal cycles.In the long-life area and short-life area,the fatigue performance of the material with 15 thermal cycles and 30 thermal cycles is not much different.After different heat cycles,80 SH steel showed cyclic softening under cyclic load.Observation of its fatigue fracture revealed that fatigue cracks all originated on or near the surface of the specimen,and had multi-source characteristics.Nearby is cleavage fracture,and fatigue bands appear in the crack propagation area.