Analysis of fracture toughness in the transition temperature region of API X70 pipeline steels rolled in two-phase region

Sang Yong Shin, Guiliang Gong, Sangho Kim, Sunghak Lee

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13 Scopus citations

Abstract

In this study, fracture toughness in the transition temperature region of three API X70 line pipe steels rolled in the two-phase (α + γ) region was analyzed in accordance with the ASTME1921- 05 standard test method. Elastic-plastic cleavage fracture toughness (KJc) was determined by three-point bend tests, using precracked Charpy V-notch specimens, and then the measured KJc values were interpreted by the three-parameter Weibull distribution. The fracture toughness test results indicated that the master curve and the 98 pct con.dence curves explained the variation in the measured fracture toughness values well. Reference temperatures obtained from the fracture toughness tests as well as index temperatures obtained from the Charpy impact tests were lowest in the steel cooled at 500 °C, which did not contain brittle martensite and had a small e.ective grain size. In this steel, the absence of martensite led to the higher resistance to cleavage crack initiation, and the smaller e.ective grain size led to the higher possibility of crack arrest, thereby resulting in the best overall fracture properties.

Original languageEnglish
Pages (from-to)1012-1021
Number of pages10
JournalMetallurgical and Materials Transactions A: Physical Metallurgy and Materials Science
Volume38
Issue number5
DOIs
StatePublished - May 2007
Externally publishedYes

Funding

This work was financially supported by the National Research Laboratory Program of the Ministry of Science and Technology of Korea. The authors thank Professor Nack J. Kim, Dr. Byoungchul Hwang, and Dr. Young Min Kim, POSTECH, for their help with the fracture toughness testing.

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