Correlation of crack-tip opening angle for stable crack propagation with charpy and drop-weight tear test properties in high-toughness API X70 pipeline steels

Abstract

Correlation between Charpy V-notch (CVN) impact properties, drop-weight tear test (DWTT) properties, and crack-tip opening angles for stable crack propagation (CTOA(SC)) in high-toughness API X70 pipeline steels was investigated in this study. Two-specimen CTOA test (TSCT) was conducted on the rolled steel materials to measure the CTOA, and the test results were compared to the CVN and DWTT data to find correlations between them. The CVN total energy density showed an almost 1:1 linear correlation with the DWTT initiation energy density. The TSCT results indicated that the materials rolled in the single-phase region had the larger CTOA,c as well as the higher CVN and DWTT energy density than those rolled in the two-phase region because their microstructures were composed of acicular ferrites and fine polygonal ferrites. The CTOA(SC) had a better correlation with the DWTT propagation energy density or the CVN total energy density than the DWTT total energy density. In particular, the value of sin (2CTOA(SC)) reliably represented a linear proportional relation to the DWTT propagation energy density.