Comparison of NiAl precipitation in a medium carbon secondary hardening steel and C-free PH13-8 maraging steel

The microstructural evolution of an experimental Fe-1.4C-2.6Cr-1.4Mo-6.0Ni-5.0Al (composition in at.%) secondary hardening steel has been studied during isothermal aging at 610 °C. Atom probe field ion microscopy and transmission electron microscopy have been used to characterise precipitate types and precipitation sequences as well as to examine changes in the solute distribution. The strengthening effects were identified as multiphase precipitation processes of secondary hardening carbides and an intermetallic β-NiAl phase, starting at aging times of less than 1 min. The results are discussed regarding the evolution of phase composition and precipitate morphology. Special emphasis is placed on the comparison of the NiAl precipitation behaviour in the investigated experimental steel and in C-free PH13-8 maraging steel.