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 toot 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 degrees 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 degrees 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 (C) 2007 John Wiley & Sons, Ltd.