Influence of Work Hardening Coefficient on Crack Propagation in High-Strength Steels.

摘要

Ths influence of work hardening exponent on the fracture toughness of 4340, 18% nickel maraging, and AM-355 stainless steel was studied. In most cases the effects produced by variations in work hardening were difficult to analyze due to accompanying changes in yield strength and microstructure. In this investigation the transition in fracture mode induced by varying section size was used as a basic evaluation method since complicating effects due to yield strength changes were not introduced. The results indicated that the transition from flat to shear failures occurred in larger section sizes in the material with the lower work hardening exponent. Once full shear failures were obtained, however, materials with higher work hardening coefficients required greater energy to produce failure. The influence of work hardening on the transition behavior could be rationalized on the basis of the larger plastic zone present in the steel with the lower strain hardening coefficient. Although useful correlations between the strain hardening index and the fracture mode transition could be obtained no quantitative relationship between work hardening exponent, as defined by strain to maximum load, and plane strain fracture toughness was evident. (Author)