Effects of particle spacing and void nucleation characteristics on the toughness of high strength steels

In this work we have examined the effects of inclusion spacing and inclusion void nucleation resistance on toughness for several fine scale microstructures for the case of ductile fracture. It was found for high-strength fine-scale microstructures that the crack tip opening displacement at fracture can increase almost linearly with increasing inclusion spacing. However, as the strength of the fine-scale microstructure decreases to about 850 MPa the toughness of the fine scale microstructure become essentially independent of inclusion spacing, at least over the range of inclusion spacings which be obtained experimentally. It has also been found that exceptional increases in toughness can be achieved by gettering sulfur as titanium carbosulfide rather than as manganese sulfide. These improvements of toughness have been observed in steels having strengths ranging from 850 to 1500 MPa. The improvement in toughness associated with gettering sulfur as titanium carbosulfide has been attributed to particles of titanium carbosulfide being more resistant to void nucleation than particles of manganese sulfide or lanthanum oxy-sulfides. (author)