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S. Primig, G. Stechauner, E. Kozeschnik:
"Early Stages of Cu Precipitation in 15 - 5 PH Maraging Steel Revisited - Part I: Experimental Analysis";
Steel Research International, 88 (2017), 1; 1 - 10.

Even though Cu precipitation during isothermal aging of binary Fe-Cu alloys and of
Cu-alloyed maraging steel has been carefully studied in the past, no detailed
investigations of the early stages of Cu clustering upon continuous aging have been
carried out so far. During continuous aging with a heating rate around 15 Kmin 1 of
as-quenched 15-5 PH maraging steel in a differential scanning calorimeter (DSC), two
exothermal reactions are observed, one at approximately 300 8C and the other one around
500 8C. These DSC signals are attributed to the nucleation and growth of Fe-rich Cu
clusters in the lower temperature range, followed by Cu-enrichment of these clusters and
seamless transformation into bcc-Cu precipitates at higher temperatures. Part I of this
investigation focuses on the experimental characterization of the mechanisms governing
these reactions in a comprehensive manner, where the authors first present the results of
this analysis based on dilatometry, differential scanning calorimetry, hardness testing,
and 3D atom probe tomography. The latter method is capable of detecting early clusters,
which are not yet accessible by transmission electron microscopy. In the companion
paper, part II, thermo-kinetic simulations are presented, which support the interpretation
of the observed reactions and substantially aid in understanding the underlying
mechanisms.

Cu Precipitation

http://dx.doi.org/10.1002/srin.201600084