Titanium Carbosulfides and the Fracture Toughness of Ultra High Strength Steels
CARNEGIE-MELLON UNIV PITTSBURGH PA
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The objectives of this work were to calculate from first principles the work of adhesion associated with the steel-MnS and steel-Ti2CS interfaces and to examine with transmission electron microscopy void nucleation at particles of MnS and particles of Ti2CS in steel. The motivation for this work was the observation that gettering sulfur as Ti2CS rather than as MnS leads to doubling and even tripling of the fracture toughness of some ultra-high strength steels and that these improvements in toughness were believed to be due to particles of Ti2CS being much more resistant to void nucleation than particles of MnS. The results are as follows. Using the LKKR approach the bulk properties and surface energies of MnS and F.C.C. iron were calculated as was the interface energy of a MnS-steel interface. With these the results the work of adhesion for this interface was determined. The bulk properties of Ti2CS were determined but we were unable to obtain reasonable results for a Ti2CS-steel interface. The investigations of void nucleation at particles of MnS and Ti2CS in two different heats of an austenitic 0.0730Ni steel were surprising. In this material it was found that voids were first nucleated at both inclusion types at strains as low as 0.20. It had been expected that voids would be first nucleated at the particles of MnS at these low strains but that voids would not be observed at the particles of Ti2CS until the strains had exceeded at least one.
- Properties of Metals and Alloys