Investigation On The Strength And Toughness And High-cycle Fatigue Behavior Of Maraging Steel

In order to meet the needs of high speeding and light weighting development in the transportation industry,maraging steel with high strength and toughness has been widely used in the manufacturing of aircraft landing gear and other key components.However,these key components are often subjected to the cyclic loading during service,which would cause the fatigue damage and final fatigue fracture.Therefore,in addition to the strength and toughness of maraging steel,its fatigue performance has also made an important indicator in the scientific and industrial circles.In this paper,18Ni maraging steel(T250)was used as the research object and two typical aging treatment conditions were selected.Then its microstructure,tensile properties,impact toughness and high cycle fatigue properties were studied,and the effect of aging treatment on its performance was analyzed.The microstructures of maraging steel under different aging treatments were investigated.It is found that when the aging temperature is low,the size and spacing of precipitates are small and the austenite content is low.The size and distance of precipitates,together with austenite content all affect the strength and impact toughness of maraging steel.The tensile properties and impact toughness of maraging steel under different aging treatments were investigated.It is found that the strength is higher but the elongation after fracture is lower when the aging temperature is lower.The tensile fracture morphologies of maraging steel under two aging treatments both show the characteristics of transgranular fracture.When the aging temperature is higher,the impact toughness of maraging steel is larger,and the resistance of the material to impact fracture is higher.The impact fracture morphologies of maraging steel under two aging treatments also show the characteristics of transgranular fracture.The high-cycle fatigue behavior of maraging steel under different aging treatments was investigated.It is found that the fatigue cracks mainly occur on the surface of samples,but some of them originate from the inclusions.The cycle is very high when cracks are generated from the inside,which can reach 106 cycles.The inclusion size has little influence on the area and cycles of "fisheye area".If the distance between the inclusions and the sample surface is larger,the area of "fisheye area" of the fracture surface and the cycles will be larger.The effect of inclusions on fatigue sensitivity increases with the increase of material strength.Because of the inclusions,the increase strength of maraging steel is not beneficial to its fatigue strength.The fatigue strength of maraging steel under different aging treatment is the results of a combination of inclusions,yield strength,microstructural homogeneity and deformation uniformity.It is proved that the optimum position of tension-tension high cycle fatigue is offset from tension-compression high cycle fatigue of previous studies.In this investigation,the optimal fatigue strength will point to the tensile strength of the lower position offset and appear at between 550? and 600?,and tensile strength is also in between.