Effect of Metallurgical Factors on Fatigue Properties in 5.5Ni-Cr-Mo-V Steel

Abstract

Martensitic structures or mixed structures of martensite and bainite with various prior austenitic grain sizes and volumes or sizes of precipitates were obtained by various heat treatments, using HT140 steel. HY180 and 12%Ni-maraging steels were also used. The effect of metallurgical factors on cycles to failure, crack growth rate, and cyclic stress-strain curves was examined and discussed.
The results are as follows:
(1) Fatigue strength at 10⁵ cycles increases with increase of cyclic yield strength and decrease of prior austenite grain size.
(2) The difference of fatigue strength between various materials mainly depends on the difference of cycles required to initiate crack and behaviour of the very early crack growth.
(3) The stage of intermediate crack growth is hardly influenced by metallurgical factors of steels.
(4) The ratio of cyclic yield strength to monotonic one for steels peak-aged is lower than that for steels otherwise treated.