Influence of stress triaxiality and temperature on void growth and ductile/brittle transition behavior of 40 Cr steel

Abstract

Examined experimentally are the influence of stress triaxiality and temperature on the growth of microvoids and the ductile/brittle transition (DBT) macrobehavior of 40 Cr steel subjected to two different heat treatments. This is accomplished by testing more than 300 smooth and notched specimens over a temperature range of 20°C to −196°C. Changes in the microstructure morphology are examined by scanning electron microscopy (SEM) and identified with fracture data on a surface constructed from the uniaxial strain ϵ c at fracture, the stress triaxiality R σ and the temperature T. While stress triaxiality has a significant influence on the DBT temperature T c, it does not affect the ratio of the average radius of voids R o to that of inclusions R i. The ratio R o R i is found to increase with temperature and remains constant in specimens with different notch radii regardless of the temperature. Empirical relations between T c and R σ − and R o R i and T are proposed to better understand how macrofracture parameters are influenced by microstructure entities.