Dynamic Strain Aging and the Charpy Specimen Behavior of Annealed 4340 Steel

Abstract

V-notch Charpy bars were ruptured at seven deflection rates at test temperatures from the ambient through the blue-brittle range, while unnotched tensile specimens were equivalently tested at four strain rates. Objectives were to interpret and relate dynamic strain aging manifestations of annealed 4340 shown by the two types of tests. Comparisons are made with elastic-plastic formulations and experimental results for initial yielding and fracture of notched bars at or near room temperature. Quasi-cleavage fracture was observed in excess of 500 deg F. Dynamic strain aging effects are compared with those found with less alloyed lower carbon steels. Arrhenius type relations are developed and discussed, and from these other interrelations are derived, and mechanisms are discussed.