Description of the module: Steels rang among the most important materials – more than 1200 base alloys were developed to match a large field of application. Beyond the chemical analysis following materials parameter are of spezial importance:
Grain size: With decreasing size of grains, the strength of a material increases at the same chemical analysis without a loss in ductility. (Hall-Petch relation)
Tiniest precipitates of second phase because they pin the microstructural boundaries. This pinning preserves the high strength of fine grained materials up to high temperatures. In common, fine grained materials are characterized by increased creep rates in high temperature applications which can lead to serious problems. The pinning of grain boundaries by tiny precipitates of second phase can lower this negative effect of this class of materials.
Thermomechanical processing – the plastic deformation
within defined ranges of temperature - provides both, control about the grain size and the precipitation of second phase particles during deformation. This method is used since several decays whereby grain sizes of about 2 microns are nowadays are realized in industrial dimensions.
The endeavor of the last years in this scientific field is mainly focused in the research how smaller grain sizes can be realized. Consequently, mainly powder metallurgical processes has been developed to obtain nanometer of even submicron-grained microstructures. A serious disadvantage of these processing routes is the complicated and often dangerous handling of nano-powders and the lack in quantity that can be produced.
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