All Issue

2025 Vol.35, Issue 7 Preview Page

Research Paper

Effect of Delayed Quenching on Mechanical Properties of High-Strength API X70 Linepipe Steels

고강도 API X70 라인파이프강의 기계적 특성에 미치는 지연 급랭의 영향

Min-Seop Jeong1
,
Dong-Kyu Oh1
,
Seung-Hyeok Shin1
,
Myeong-Gyu Seo2
,
Kyutae Kim2
,
Byoungchul Hwang1†
정 민섭1
,
오 동규1
,
신 승혁1
,
서 명규2
,
김 규태2
,
황 병철1†
1Department of Materials Science and Engineering, Seoul National University of Science and Technology, Seoul 01811, Republic of Korea
2Hyundai Steel Company, Dangjin 31719, Republic of Korea
1서울과학기술대학교 신소재공학과
2현대제철 연구개발본부
†Corresponding author E-Mail : bhwang@seoultech.ac.kr (B. Hwang, Seoul Nat’l Univ. Sci. and Technol.)
27 July 2025. pp. 328-334
PDF XML Citation
Abstract

This study examines the effect of delayed quenching (DQ) temperature on the microstructure and mechanical properties of API X70 linepipe steels. Three types of steels were fabricated by varying the DQ conditions: Base (without DQ), LDQ (low-temperature delayed quenching at 700 °C), and HDQ (high-temperature delayed quenching at 740 °C). The microstructures were characterized using optical microscopy, scanning electron microscope (SEM), and electron back-scattered diffraction (EBSD), and their mechanical properties were evaluated through tensile and Charpy impact tests. The Base specimen exhibited the finest effective grain size and the highest bainite fraction, resulting in superior yield strength and impact toughness. In contrast, the LDQ specimen showed increased pearlite content and coarser grains, leading to the highest tensile strength due to work hardening, but reduced impact properties due to crack initiation at the pearlite regions. The HDQ specimen, with the highest ferrite fraction, showed the best ductility and acceptable strength, as well as improved low-temperature toughness owing to increased resistance to cleavage propagation. EBSD analysis confirmed that finer grains and higher fractions of high-angle grain boundaries play a crucial role in enhancing impact energy and lowering the ductile-to-brittle transition temperature (DBTT). These findings highlight the importance of optimizing DQ parameters to achieve a balanced combination of strength–toughness in high-strength linepipe steels.

Keywords
API linepipe steel
delayed quenching
microstructure
tensile property
Charpy impact toughness
References
1

S. S. Sohn, S. Y. Han, J.-H. Bae, H. S. Kim and S. Lee, Mater. Sci. Eng. A., 573, 18 (2013).

10.1016/j.msea.2013.02.050
2

D.-K. Oh, S.-H. Shin and B. Hwang, Korean J. Mater. Res., 33, 251 (2023).

10.3740/MRSK.2023.33.6.251
3

Y. Tian, H. T. Wang, Z. D. Wang, R. D. K. Misra and G. D. Wang, J. Mater. Eng. Perform., 27, 1494 (2018).

10.1007/s11665-018-3197-x
4

S.-I. Lee, S.-Y. Lee, S. G. Lee, H. G. Jung and B. Hwang, Mat. Mater. Int., 24, 1221 (2018).

10.1007/s12540-018-0173-9
5

Y. Liu, F. Zhu, Y. Li and G. Wang, ISIJ Int., 45, 851 (2005).

10.2355/isijinternational.45.851
6

S.-I Lee, S.-W. Lee, S. G. Lee, S. Lee, H. G. Jung and B. Hwang, Korean J. Met. Mater., 56, 413 (2018).

10.3365/KJMM.2018.56.6.413
7

Y. Shao, C. Liu, Z. Yan, H. Li and Y. Liu, J. Mater. Sci. Technol., 34, 737 (2018).

10.1016/j.jmst.2017.11.020
8

X.-Q. Wang, G. Yuan, J.-H. Zhao and G.-D. Wang, Metals, 10, 1323 (2020).

10.3390/met10101323
9

H. Zhao, B. P. Wynne and E. J. Palmiere, J. Mater. Sci., 53, 3785 (2018).

10.1007/s10853-017-1781-3
10

S. S. Babu and H. K. D. H. Bhadeshia, Mater. Trans. JIM, 32, 679 (1991).

10.2320/matertrans1989.32.679
11

API Specifications 5L, Specifications for Line Pipe, 43rd ed., American Petroleum Institute, Washington, D.C., USA (2004), p.9.

12

S.-I. Lee, J. Lee and B. Hwang, Mater. Sci. Eng. A., 758, 56 (2019).

13

D.-K. Oh, S.-G. Kim, S.-H. Shin and B. Hwang, Materials, 17, 4887 (2024).

10.3390/ma1719488739410457PMC11477694
14

S.-W. Lee, S.-I. Lee and B. Hwang, Korean J. Meter. Res., 27, 524 (2017).

10.3740/MRSK.2017.27.10.524
15

S. Y. Han, S. Y. Shin, S. Lee, N. J. Kim, J.-H. Bae and K. Kim, Metall. Mater. Trans. A, 41, 329 (2010).

10.1007/s11661-009-0135-4
16

X. N. Xu, Y. Tian, Q. B. Ye, R. D. K. Misra and Z. D. Wang, J. Mater. Eng. Perform., 30, 7479 (2021).

10.1007/s11665-021-05887-x
17

S. Gao, M. Chen, M. Joshi, A. Shibata and N. Tsuji, J. Mater. Sci., 49, 6536 (2014).

10.1007/s10853-014-8233-0
18

B. G. Prusty and A. Banerjee, Materials, 13, 556 (2020).

10.3390/ma1303055631991545PMC7040721
19

Y. Yan, L. Li, H. Wang, N. He, Y. Sun, L. Xu, L. Li, H. Li, Z. Wang, C. Zhang, Y. Fang, D. Li, K. Bao, K. Hao and Y. Han, Int. J. Hydrogen Energy., 84, 118 (2024).

10.1016/j.ijhydene.2024.08.247
20

A. A. Johnson, Philos. Mag., 7, 177 (1962).

21

D.-K. Oh,M.-S. Jeong, S.-H. Shin and B. Hwang, Metals, 14, 1397 (2024).

10.3390/met14121397
22

Y. Niu, S. Jia, Q. Liu, S. Tong, B. Li, Y. Ren and B. Wang, Materials, 12, 3672 (2019).

10.3390/ma1222367231703383PMC6888431
23

W. Wang, W. Yan, L. Zhu, P. Hu, Y. Shan, K. Yang, Mater. Des., 30, 3436 (2009).

10.1016/j.matdes.2009.03.026
24

Y. M. Kim, S. Y. Shin, H. Lee, B. Hwang, B. G. Park, S. Lee and N. J. Kim, J. Kor. Inst. Met. & Mater., 44, 223 (2006).

Information
  • Publisher :Materials Research Society of Korea
  • Publisher(Ko) :한국재료학회
  • Journal Title :Korean Journal of Materials Research
  • Journal Title(Ko) :한국재료학회지
  • Volume : 35
  • No :7
  • Pages :328-334
  • Received Date : 2025-05-26
  • Revised Date : 2025-07-14
  • Accepted Date : 2025-07-17
  • DOI :https://doi.org/10.3740/MRSK.2025.35.7.328
Journal Informaiton Korean Journal of Materials Research Korean Journal of Materials Research
Online Submission
  • scopus
  • NRF
  • KOFST
  • crossref crossmark
  • crossref cited-by
  • crosscheck
  • open access
  • ccl
Journal Informaiton Journal Informaiton - close