Original paper(Vol.49 No.6 pp.631)

Influence of Aging Condition and Reversion Austenite on Fatigue Property of the 300 Grade 18Ni Maraging Steel

Michihiko Moriyama, Setsuo Takaki and Norio Kawagoishi

Abstract: Influence of aging condition and reversion austenite on fatigue property was investigated for the 300 grade 18%Ni maraging steel with various aging treatment. Since a small amount of reversion austenite greatly influences the fatigue behavior of the material, the magnetic method by direct current magnetic flux measurement was applied to the measurement of volume fraction of austenite, because it is convenient for the accurate detection in compalison with the X-ray method. The results obtained are as follows:
　1) The fatigue strength of under-aged materials is very low as that of unaged material. The highest fatigue strength can be achieved by the aging treatment which gives about twice larger harness than that in unaged material.
　2) With the formation of reversion austenite, endurance ratio is increased.
　3) The materials containing about 2vol% of reversion austenite has the highest fatigue limit.

Key Words:Fatigue, 300 grade maraging steel, Age- hardening , Reversion austenite, Rotating bending test， Fractography