Investigation of the Role of Second Phase Particles in the Design of Ultra HighStrength Steels of Improved Toughness

摘要

The influence of inclusion distributions and fine scale microstructure on thefracture toughness and fracture processes of ultra high strength steels have been investigated. The inclusion distributions vary in the sulfide type and the sulfide types considered were MnS, CrS, La2O2S and Ti2CS. The MnS and CrS particles are smaller and more closely spaced than particles of La2O2S. Resistance to void nucleation is the same if the sulfur is gettered as CrS, MnS or La2O2S. The particles of Ti2CS are smaller and much more resistant to void nucleation than the other sulfide types. The fine scale microstructures were those obtained for the as-quenched, tempered at 425 deg C and tempered at 510 deg C conditions for HY180 and AF1410 steels. The topics then addressed are (a) effect of fine scale microstructure and inclusion distributions on blunting behavior, (b) the role of inclusion spacing at constant inclusion volume fraction on fracture toughness of three fine scale microstructures for HY 180 steel, (c) effect of gettering sulfur as Ti2CS on the fracture toughness of three fine scale microstructures of HY180 steel, (d) morphology of Ti2CS particles, (e) effect of gettering sulfur as Ti2CS on the fracture toughness of AF1410 steel tempered at 510 deg C, and (f) conclusions regarding improving toughness by gettering sulfur as Ti2CS.... Steels, Fracture toughness, Inclusions, Void nucleation, Titanium carbosulfides.