Analysis of fracture toughness in the transition-temperature region of an Mn-Mo-Ni low-alloy steel

Abstract

This study is concerned with the analysis of fracture toughness in the transition region of an Mn-Mo-Ni low-alloy steel, in accordance with the ASTM E1921 standard test method. Elastic-plastic cleavage fracture toughness (K-Jc) was determined by three-point bend tests, using precracked Charpy V-notch (PCVN) specimens, and relationships between K-Jc, the critical component of J (J(c)), critical distance (X-c), stretch-zone width (SZW), local fracture stress, and plane-strain fracture toughness K-Ic were discussed on the basis of the cleavage fracture behavior in the transition region. The master curve and the 95 pct confidence curves well explained the variation in the measured K-Jc, and the Weibull slope measured on the Weibull plots was consistent with the theoretical slope of 4. Fractographic observation indicated that X-c linearly increased with increasing J(c), and that the SZW had a good correlation with K-Jc, irrespective of the test temperature. In addition, the local fracture stress was independent of the test temperature, because the tempered bainitic steel used in this study showed a propagation-controlled cleavage fracture behavior.