Measurement of fracture toughness transition behaviour of Cr–Ni–Mo–V pressure vessel steel using pre-cracked Charpy specimens

Abstract

The potential application of small pre-cracked Charpy specimens for the prediction of the fracture toughness of the 1T-thickness specimens and the reference temperature T 0 has been examined. Transition fracture behaviour of plane sided, side-grooved and 1T SENB specimens, respectively, was investigated over a wide temperature range. The fracture toughness regions with various fracture initiation mechanisms were defined and ductile to brittle transition temperatures denoted. The fracture toughness transition region of small pre-cracked specimens was shifted to lower temperatures as compared with that of 1T SENB specimens. The fracture toughness data of small pre-cracked specimens have been size corrected (weakest link) to 1T thickness and used to establish the reference temperature T 0 and K J c(mean) fracture toughness vs. temperature curve. The calculated temperature T 0 has been in consistence with that of the 1T SENB specimen. However, some corrected fracture toughness data lay outside the scatter band of 1T thickness specimens and the shape of the K J c(mean) curve has been quite different from the K J c(med)(1T) curve. It was found out that the original measured fracture toughness results of corrected data points lying outside the scatter band violated the validity condition b 0 R p0.2/ J c≥30. Bearing in mind the work of Koppenhoefer and Dodds Jr. (Engng Fract Mechanics (1997);58:249–270), and the most recent analysis of Ruggieri et al. (Engng Fract Mechanics (1998);60:19–36), the fracture data of small pre-cracked specimens having the validity parameter lower than 50 have been first constraint adjusted using the cleavage fracture toughness scaling model of Dodds and coworkers (J Testing Evaluation (1991);19:123–134; Int J Fracture (1995); 74:131–161; Engng Fract Mechanics (1997);58:249–270), and only then size corrected. The K J c(mean) curve of such treated data was identical with K J c(med)(1T) .