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research-article

Effects of post-weld heat-treatment on girth weld tensile property and microstructure of high-frequency electric resistance welded pipe for API X80 grade casing pipe

[+] Author and Article Information
Sota Goto

Steel Research Laboratory, JFE Steel Corporation, 1-1, Minamiwatarida-cho, Kawasaki-ku, Kawasaki 210-0855, Japan
s-goto@jfe-steel.co.jp

Shunsuke Toyoda

Steel Research Laboratory, JFE Steel Corporation, 1-1, Minamiwatarida-cho, Kawasaki-ku, Kawasaki 210-0855, Japan
stoyoda@jrcm.jp

Shinsuke Ide

Steel Research Laboratory, JFE Steel Corporation, 1-1, Kawasaki-cho, Handa, Aichi 475-8611, Japan
s-ide@jfe-steel.co.jp

Yukihiko Okazaki

Products Service & Development Section, Chita Works, JFE Steel Corporation, 1-1, Kawasaki-cho, Handa, Aichi 475-8611, Japan
y-okazaki@jfe-steel.co.jp

Kota Nakashima

JFE Steel America, Inc., 10777 Westheimer, Suite 230, Houston, TX 77042
k-nakashima@jfe-steel.co.jp

1Corresponding author.

ASME doi:10.1115/1.4040289 History: Received November 02, 2016; Revised May 10, 2018

Abstract

The girth weld tensile properties of API X80 grade HFW steel pipe for surface casing with the chemical composition of 0.05C-1.6Mn-0.06Nb (mass%) and the diameter of 558.8 mm and wall thickness of 25.4 mm were investigated by simulated post-weld heat-treatment (PWHT). The tensile specimens taken from girth butt welded pipe were heat-treated under the conditions of 625?×2 h and 675?×2 h in an air furnace in order to simulate PWHT of casing products. The result of the girth weld tensile test of the heat-treated specimens showed that yield strength and tensile strength decreased very little and these properties sufficiently satisfied the API X80 specification. The change in strength due to heat treatment was discussed based on microscopic observation of the sub-microstructures of the base metal by the electron back-scattered diffraction technique, transmission electron microscopy, X-ray diffraction, and the extraction residue precipitate classification method. The authors concluded that the fine NbC with a diameter of 12-18 nm, which precipitated during the heat treatment, prevented the decrease of strength due to the slight grain growth and dislocation recovery associated with PWHT. Additionally, the effect of PWHT conditions was evaluated by using small-scale laboratory specimens obtained from the base metal. Tensile properties were summarized as a function of the tempering parameter. As a result, strength remained almost constant at the tempering parameter equivalent to the PWHT conditions of 625?×16 h.

Copyright (c) 2018 by ASME
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