Temperature Dependence of Cleavage Fracture Toughness for an Ultra High Strength Martensitic Steel

This work conducts an exploratory evaluation of the brittle fracture behavior for a high-strength martensitic steel using conventional three-point bend SE(B) and pre-cracked Charpy V-notch (PCVN) specimens. A primary purpose of this study is to verify the effectiveness of the Master Curve methodology in providing a reliable estimate of the reference temperature ( T 0 ) derived from fracture toughness data sets measured in the ductile-to-brittle transition region (DBT) of a ultra high strength, low alloy martensitic steel. Fracture toughness testing conducted on three-point bend SE(B) specimens and pre-cracked Charpy (PCVN) configurations at different test temperatures in the DBT region provides the cleavage fracture resistance data in terms of the J -integral at cleavage instability, J c , and its corresponding K J c -values for the tested material. While this class of ultra high strength steel having a martensitic microstructure is currently beyond the reach of ASTM E1921, the analyses described here show that the predicted normalized curves of median fracture toughness vs. temperature are in good agreement with the experimental measurements.