THE EFFECT OF MICROSTRUCTURE AND AGING CONDITION ON THE FATIGUE CHARACTERISTICS OF THE 18% NI MARAGING STEELS.

摘要

Smooth and notched rotating beam fatigue characteristics at various strength levels are presented over the range of 1000-100000cycles-to-failure for 250and 300grade 18% Ni maraging steels and a modified 4330alloy. Two different heats of each of the maraging steels having large differences in ductility and toughness due to microsegregation are examined. In addition,the effects of under-and over-aging on fatigue properties are also studied. The microstructural segregation in the maraging steel showed no detrimental effect on the smooth or notched fatigue properties even though the ductility and toughness values were greatly reduced. Underaging the maraging steels was found to drastically impair the notched fatigue behavior. No correlation was found between notched fatigue behavior,as expressed by notched strength reduction factor,and the standard engineering mechanical properties of ductility and toughness. (Author)