Precipitation reactions during the early stages of aging in a Ni and Al alloyed martensitic medium carbon steel

Steels in hot‐work applications are exposed to a complex combination of mechanical, thermal and creep loading conditions. Advanced hot‐work tool steels combine precipitation of alloy carbides and intermetallic phases and, therefore, exhibit a higher thermal stability than conventional tool steels. The mechanical and thermophysical properties of a Fe‐0.32C‐6.5Ni‐2.5Al wt% martensitic tool steel are mainly determined by the combined precipitation of secondary hardening carbides and of intermetallic NiAl precipitates of B2‐type. This alloy shows a large and rapid hardening reaction upon aging for as short as 60 s at a temperature of 610 °C. Atom probe field ion microscopy has been used to investigate both the composition and morphology of the fine precipitates and the matrix present after aging for 0, 30 and 60 s at 610 °C. In particular, chemical composition, particle radii and number density of the precipitates have been determined as a function of the aging time. The data obtained from these initial stages of the precipitation processes were analysed by means of statistical calculations. Copyright © 2007 John Wiley & Sons, Ltd.