Effects of oxides on tensile and charpy impact properties and fracture toughness in heat affected zones of oxide-containing API X80 linepipe steels

Hyo Kyung Sung, Seok S Sohn, Sang Yong Shin, Kyung Shik Oh, Sunghak Lee

Research output: Contribution to journalArticle

13 Citations (Scopus)

Abstract

This study is concerned with effects of complex oxides on acicular ferrite (AF) formation, tensile and Charpy impact properties, and fracture toughness in heat affected zones (HAZs) of oxide-containing API X80 linepipe steels. Three steels were fabricated by adding Mg and O2 to form oxides, and various HAZ microstructures were obtained by conducting HAZ simulation tests under different heat inputs. The no. of oxides increased with increasing amount of Mg and O2, while the volume fraction of AF present in the steel HAZs increased with increasing the no. of oxides. The strengths of the HAZ specimens were generally higher than those of the base metals because of the formation of hard microstructures of bainitic ferrite and granular bainite. When the total Charpy absorbed energy was divided into the fracture initiation and propagation energies, the fracture initiation energy was maintained constant at about 75 J at room temperature, irrespective of volume fraction of AF. The fracture propagation energy rapidly increased from 75 to 150 J and saturated when the volume fraction of AF exceeded 30 pct. At 253 K (-20 °C), the total absorbed energy increased with increasing volume fraction of AF, as the cleavage fracture was changed to the ductile fracture when the volume fraction of AF exceeded 45 pct. Thus, 45 vol pct of AF at least was needed to improve the Charpy impact energy, which could be achieved by forming a no. of oxides. The fracture toughness increased with increasing the no. of oxides because of the increased volume fraction of AF formed around oxides. The fracture toughness did not show a visible correlation with the Charpy absorbed energy at room temperature, because toughness properties obtained from these two toughness testing methods had different significations in view of fracture mechanics.

Original languageEnglish
Pages (from-to)3036-3050
Number of pages15
JournalMetallurgical and Materials Transactions A: Physical Metallurgy and Materials Science
Volume45
Issue number7
DOIs
Publication statusPublished - 2014 Jan 1
Externally publishedYes

Fingerprint

application programming interface
heat affected zone
Steel
Heat affected zone
toughness
fracture strength
Application programming interfaces (API)
Oxides
Ferrite
Fracture toughness
ferrites
steels
oxides
Volume fraction
energy
Toughness
bainite
microstructure
Microstructure
propagation

ASJC Scopus subject areas

  • Condensed Matter Physics
  • Mechanics of Materials
  • Metals and Alloys

Cite this

Effects of oxides on tensile and charpy impact properties and fracture toughness in heat affected zones of oxide-containing API X80 linepipe steels. / Sung, Hyo Kyung; Sohn, Seok S; Shin, Sang Yong; Oh, Kyung Shik; Lee, Sunghak.

In: Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science, Vol. 45, No. 7, 01.01.2014, p. 3036-3050.

Research output: Contribution to journalArticle

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