Investigation of the Role of Second Phase Particles in the Design of Ultra High Strength Steels of Improved Toughness.

摘要

In this report summarized work carried out as part of a research program designed to improve the upper shelf fracture toughness of ultra high strength steels and to gain further understanding of the processes associated with the fracture of these materials and how these processes are related to microstructure. The results emphasized are: (a) blunting behavior and its effects on toughness, (b) the effects of inclusion spacing at constant inclusion volume fraction on toughness, (c) observations on the effects of carbides and nitrides on toughness, (d) grain size effects and (e) studies of void nucleation at inclusions and the effects on toughness of gettering sulfur as particles rich in Ti, C, and S rather than as manganese sulfide. Our blunting studies indicate that blunting to vertices, although it is associated with low work hardening, appears to result in higher levels of toughness than smooth blunting. The results show that increasing inclusion spacing at constant inclusion volume fraction results in improvements in toughness until the inclusion spacing approaches some critical value; once the inclusion spacing exceeds that value the toughness is independent of particle spacing. (js)