Influence of microstructure on fatigue small crack growth behaviour of 18NI maraging steel weldment

icaf2023 Tracking Number 27

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Experiments were carried out to study the influence of microstructure on fatigue small crack growth behavior of 18Ni(250) maraging steel and weld. Microstructure characteristics of base metal and weld metal were analyzed by optical microscope and scaning electron microscope. Results show that the segregation of elements such as Mo, Ti and Ni leads to the formation of massive reversed austenite phases in the weld interdendrites, and correspondingly reduces the content of these elements in martensite matrix of weld metal, thereby reducing the amount of N3(Mo, Ti) in the weld matrix, leading to decrease of microhardness and tensile strength of weld metal compared to that of base metal.. Fatigue tests show that the behaviour of fatigue small crack growth in weld metal is obviously faster than that in base metal. The distribution characteristics of test data of fatigue crack growth rate are similar to that of large crack for base metal. Clearly, there is coalescence of microcracks in small crack growth path of base metal. And this phenomenon rearly occurred in the small crack growth path of weld metal.