Abstract
In order to ascertain the time at which thermal damage arises from over-heating the heat-resistant steel alloy 15Mo3 for a short time, simulation experiments were carried out with subsequent metallographic evaluation. It could be demonstrated from the micrographs how the pearlitic microstructures in the bands behaved after increasing to above the operating temperature for a short time. At temperatures up to 730°C, bainite was formed after cooling in parts of the pearlite bands that had been austenised during the over-heating. From 740°C and a thermal stress duration of 15 minutes, small grains identifiable by their darker colour could be discovered between the pearlite grains with coalesced carbides, which was the newly formed ferrite. After an annealing time of 20 minutes new ferrite grains built up to complete rows at some points within the former pearlite bands. As this new ferrite is considerably finer than that in the initial material, the microstructure became much finer. The percentage of new ferrite increases with increasing temperature and over-heating time, so the effect of the grain refinement is greater, and changes in the microstructure and consequently in the mechanical properties occur.
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