Influence of reversion austenite on fatigue property of 18% Ni maraging steel

The influence of reversion austenite on the fatigue behavior of a maraging steel has been investigated by using 18%Ni-8%Co-5%Mo steel. The behaviors of age hardening and reversion from martensite to austenite were examined first under various aging conditions in the temperature range of 750-850K. These aging conditions were chosen so that a selected volume fraction of austenite (γvol%=1, 2, 3 or 24%) was formed in the age hardened maraging steel. The specimens were subjected to fatigue test, crack growth test and fractography. The results obtained are as follows:(1) The formation of reversion austenite results in a great improvement of fatigue strength. Especially, a small amount of austenite (2-3vol%) markedly increases the fatigue limit of a maraging steel without reducing the hardness so much. Due to the existence of reversion austenite, crack growth tends to be suppressed and the maximum length of non-propagating crack becomes longer.(2) The existence of reversion austenite improves the fatigue fracture toughness.