Effects of alloy composition on the mechanical properties of 18Ni-Co-Mo-Ti-Al maraging steels have been studied by means of tensile tests, optical and electron microscopy, and fractography, in order to examine the possibility of saving Co and Mo contents without sacrifice of the mechanical properties.
It was found that Co does not play an important role in precipitation hardening when the addition of Mo is less than 2%, while an addition of above 2% Mo is indispensable to prevent the formation of coarse precipitates of Ni₃Ti along prior austenite grain boundaries, and to obtain a uniform distribution of the fine precipitates. Increase in Mo contents beyond 5% is detrimental for reduction of area and notch tensile strength because of the presence of undissolved coarse particles of Fe₂Mo.
Ti is the most important element for precipitation hardening the Co free maraging steel.
As a result the 18Ni-2Mo-2Ti-0.1Al maraging steel showed mechanical properties equivalent to the conventional 18Ni maraging steel.