Untempered Ultra High Strength Steels of High Fracture Toughness.

摘要

The objective of the present investigation was to establish,in high yield strength steels,relationships between microstructure,fracture toughness and fatigue crack growth. Extensive microstructural examination and characterization were conducted on as-quenched,and quenched and tempered AISI 4340steel which was austenitized both at the conventional (870C) and the high (1200C) austenitizing temperatures. Changes in fracture toughness resulting from variations in austenitizing and tempering treatments were related to changes in the amount and distribution of retained austenite,the morphology and distribution of carbides,and the martensite substructure and morphology. The influence of microstructure on fatigue crack propagation was investigated in as-quenched,and quenched and tempered 5Mo-0.3C secondary hardening steel. (Modified author abstract)