Research On High-temperature Enduring Properties And Fatigue Performance Of 00Cr18Ni10N Steels

OOCr18NilON steel is the new kind of steel which has been developed on 18-8 nickelless stainless steel. Because of the good property of high strength, high toughness and corrosion resistance, it has been widely used in the aircraft industry for the airplane parts, such as the hydraulic system catheters, clamps, shells, nuts, angle boxes and etc. For suffering from high temperatures and alternating load in the flight, these components will unpredictably break after long term service and seriously threaten the aircraft's safety. Therefore, it is very necessary to study its high-temperature enduring properties and fatigue performance.In this paper, the enduring properties and fatigue performance of 00Cr18Ni10N steel have been studied by high-temperature tensile test, high-temperature enduring test and fatigue crack growth rate test and the fracture morphology of the samples has been observed by scanning electron microscope. The main results are as follows.Based on the Larson-miller parameter equation, the mathematical model in the given temperature of 00Cr18Ni10N steel is established with the relationship between the enduring strength and the high temperature tensile strength. The enduring strength can be accurately predicted by the high-temperature tensile strength, and the maximum relative error between the predicted value and the measured value is less than 4.3%.Theσ100,σ200, andσ500 enduring strength at 550℃,600℃and 700℃of 00Cr18Ni10N steel was measured and the results indicated that under the same temperature, the enduring strength decreases with the increasing of the enduring time and for a given enduring time there is the same variation tendency for the enduring strength with the test temperature.The results of fatigue crack propagation rate test show that the fatigue crack growth rate decreases with the decreasing of the stress ratio.SEM fracture analysis shows that the macro-fracture surface of the high temperature tensile has the obvious fibrous zone, radical zone and shears lips. Micro-fracture observation reveals that thers are a large number of dimples, holes and the second phase particles in the fracture and its fracture mechanism belongs to ductile fracture with microvoid aggregation. The macro-fracture surface of enduring samples looks very rough and appears the rock candy shape. The typical wedge-shaped cracks and the grain boundary voids have been observed in the micro-fracture and it reveals that the the grain boundary void is the main reason for the enduring fracture of 00Cr18Ni10N steel. Fatigue fracture morphology showed the characteristics of quasi-cleavage fracture. Fatigue mode in crack propagation region was mainly strip propagation mechanism and the width of the fatigue stripe increases with the increasing of the stress ratio. Moreover, secondary cracks, a number of shallow dimples and some lacerate ribs are observed in the instantaneous breaking zone.