Change of Mechanical Properties of High Strength Line Pipe by Thermal Coating Treatment

Shinohara, Yasuhiro; Hara, Takuya; Tsuru, Eiji; Asahi, Hitoshi; Terada, Yoshio; Doi, Naoki

doi:10.1115/omae2005-67055

Cited by 13 publications

(12 citation statements)

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“…Unfortunately, the steel pipes reveal discontinuous yielding behavior after anti-corrosion coating process, so-called occurrence of strain aging. Then deformability of the linepipes significantly degraded [4][5][6]. Thus, we investigated the exact mechanism of strain aging in linepipe steels and based on it we tried to fabricate SBD X80 and X100 linepipe steels.…”

Section: Linepipe Steels For Strain-based Designmentioning

confidence: 99%

Development of High Strength and High Performance Linepipe and Shipbuilding Steels

Kang

Yoo

et al. 2011

Advanced Steels

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Advanced TMCP products, such as X80/X100 linepipe steels and YS 460MPa grade shipbuilding steel, have been developed by POSCO. In order to apply X80/X100 linepipe to strain-based design (SBD) concept, the main issue is to prevent strain aging after thermal coating. In case of YS 460MPa shipbuilding steel, challenging study is necessary to increase plate thickness up to 80 mm without deterioration of strength and toughness. It was found that solute carbon started to segregate at dislocation tangles in coarse ferrite during and after UOE pipe forming, resulting in strain aging. And it was shown that the optimum microstructure of X80 and X100 steels was the mixture of acicular ferrite, bainitic ferrite and fine ferrite. Those X80 and X100 steels revealed good strain hardening resistance as well as reasonable compressive strain capacity. The developed YS 460MPa grade steel plate for shipbuilding showed a good mechanical property at quarter and mid-thickness and also an excellent weldability. It was confirmed that the developed steel had a high CTOD value both HAZ and base metal to prevent an initiation of brittle crack and a good crack arrestablity to suppress long distance propagation of brittle crack.

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Section: Linepipe Steels For Strain-based Designmentioning

confidence: 99%

Development of High Strength and High Performance Linepipe and Shipbuilding Steels

Kang

Yoo

et al. 2011

Advanced Steels

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“…[1][2][3] Pipeline steels are used after the piping and corrosion-resistant coating processes, in which uniform elongation and the deformability decrease because of the strain aging phenomenon. [4][5][6] To restrain the strain aging phenomenon during the piping and corrosion-resistant coating processes, many studies have been conducted to reduce the number of carbon atoms in ferrite and to form more cementite. [7][8][9] Shigesato et al [7] reported that cementites were distributed uniformly when Cr was added in American Petroleum Institute (API) X80 pipeline steels.…”

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“…[4][5][6] To restrain the strain aging phenomenon during the piping and corrosion-resistant coating processes, many studies have been conducted to reduce the number of carbon atoms in ferrite and to form more cementite. [7][8][9] Shigesato et al [7] reported that cementites were distributed uniformly when Cr was added in American Petroleum Institute (API) X80 pipeline steels. When Mo was added to the API X80 pipeline steels, however, the cementites were not distributed uniformly but were almost formed in the narrow space of the bainite lath; hence, the uniform elongation and deformability of the API X80 pipeline steels decreased.…”

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“…[7] Hara et al [8] reported that continuous yielding behaviors occurred without a rapid decrease in uniform elongation when Cr, a strong carbide-forming element, was added to the API X80 pipeline steels. Shinohara et al [9] reported that the uniform elongation of the bainitic API X80 and X100 pipeline steels increased with increasing the volume fraction of polygonal ferrite (PF) formed by the mild accelerated cooling processes. The recently developed strain-based pipeline steels exhibited discontinuous yielding behavior because the main microstructure was polygonal ferrite and the volume fraction of hard secondary phases was low.…”

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Correlation Between Microstructures and Tensile Properties of Strain-Based API X60 Pipeline Steels

Sung

Lee

et al. 2016

Metall Mater Trans A

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The correlation between the microstructures and tensile properties of strain-based American Petroleum Institute (API) X60 pipeline steels was investigated. Eight types of strain-based API X60 pipeline steels were fabricated by varying the chemical compositions, such as C, Ni, Cr, and Mo, and the finish cooling temperatures, such as single-phase and dual-phase regions. In the 4N and 5C steels, the volume fractions of bainitic ferrite (BF) and the secondary phases increased with the increasing C and adding Cr instead of Ni. In the 5C and 6NC steels, the volume fractions of acicular ferrite (AF) and BF decreased with increasing C and adding Ni, whereas the volume fractions of polygonal ferrite (PF) and the secondary phases increased. In the 6NC and 6NM steels, the volume fraction of BF was increased by adding Mo instead of Cr, whereas the volume fractions of PF and the secondary phases decreased. In the steels rolled in the single-phase region, the volume fraction of polygonal ferrite ranged from 40 to 60 pct and the volume fraction of AF ranged from 20 to 40 pct. In the steels rolled in the dual-phase region, however, the volume fraction of PF was more than 70 pct and the volume fraction of AF was below 20 pct. The strength of the steels with a high volume fraction of AF was higher than those of the steels with a high volume fraction of PF, whereas the yield point elongation and the strain hardening exponent were opposite. The uniform elongation after the thermal aging process decreased with increasing volume fraction of PF, whereas the uniform elongation increased with increasing volume fraction of AF. The strain hardening exponent increased with increasing volume fraction of PF, but decreased with increasing volume fraction of AF and effective grain size.

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“…[5] In the Cottrell atmosphere, the decrease in uniform elongation is caused by the interactions between the carbon atoms in ferrite and dislocations, which results in yield point phenomena during the tensile tests. [5,6] Many studies have been conducted to form large amounts of cementite in linepipe steels and to reduce the number of carbon atoms in ferrite because carbon atoms are the main factors for the strain aging phenomena. [7][8][9][10][11][12] The finish cooling temperatures strongly affect the formation of secondary phases, such as cementite and martensite-austenite constituents (MA).…”

Section: Introductionmentioning

confidence: 99%

Effects of Finish Cooling Temperature on Tensile Properties After Thermal Aging of Strain-Based API X60 Linepipe Steels

Sung

Lee

Shin

et al. 2015

Metall Mater Trans A

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Two types of strain-based American Petroleum Institute (API) X60 linepipe steels were fabricated at two finish cooling temperatures, 673 K and 723 K (400°C and 450°C), and the effects of the finish cooling temperatures on the tensile properties after thermal aging were investigated. The strain-based API X60 linepipe steels consisted mainly of polygonal ferrite (PF) or quasipolygonal ferrite and the volume fraction of acicular ferrite increased with the increasing finish cooling temperature. In contrast, the volume fractions of bainitic ferrite (BF) and secondary phases decreased. The tensile properties before and after thermal aging at 473 K and 523 K (200°C and 250°C) were measured. The yield strength, ultimate tensile strength, and yield ratio increased with the increasing thermal aging temperature. The strain hardening rate in the steel fabricated at the higher finish cooling temperature decreased rapidly after thermal aging, probably due to the Cottrell atmosphere, whereas the strain hardening rate in the steel fabricated at the lower finish cooling temperature changed slightly after thermal aging. The uniform elongation and total elongation decreased with increasing thermal aging temperature, probably due to the interactions between carbon atoms and dislocations. The uniform elongation decreased rapidly with the decreasing volume fractions of BF and martensite and secondary phases. The yield ratio increased with the increasing thermal aging temperature, whereas the strain hardening exponent decreased. The strain hardening exponent of PL steel decreased rapidly after thermal aging because of the large number of mobile dislocations between PF and BF or martensite or secondary phases.

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Change of Mechanical Properties of High Strength Line Pipe by Thermal Coating Treatment

Cited by 13 publications

References 0 publications

Development of High Strength and High Performance Linepipe and Shipbuilding Steels

Development of High Strength and High Performance Linepipe and Shipbuilding Steels

Correlation Between Microstructures and Tensile Properties of Strain-Based API X60 Pipeline Steels

Effects of Finish Cooling Temperature on Tensile Properties After Thermal Aging of Strain-Based API X60 Linepipe Steels

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