Effect of Nb Content and Second Heat Cycle Peak Temperatures on Toughness of X80 Pipeline Steel

Yuefeng Chen; Yaobin Yang; Xiaodong He; Qiang Chi; Lihua Qi; Weiwei Li; Xin Li

doi:10.3390/ma16247632

Effect of Nb Content and Second Heat Cycle Peak Temperatures on Toughness of X80 Pipeline Steel

Materials (Basel). 2023 Dec 13;16(24):7632. doi: 10.3390/ma16247632.

Authors

Yuefeng Chen^{1

2}, Yaobin Yang^{1

2}, Xiaodong He^{1

2}, Qiang Chi^{1

2}, Lihua Qi^{1

2}, Weiwei Li^{1

2}, Xin Li^{1

2}

Affiliations

¹ National Key Laboratory of Oil and Gas Drilling and Production Transportation Equipment, Tubular Goods Research Institute CNPC, Xi'an 710077, China.
² International Welding Technology Center, Xi'an 710077, China.

Abstract

The microstructure evolution and variation of impact toughness in the heat-affected zone (HAZ) of X80 pipeline steel with different Nb content under different peak temperatures in the secondary thermal cycle were studied through welding thermal simulation, the Charpy impact test, EBSD analysis, SEM observation, and TEM observation in this study. The results indicate that when the peak temperatures of the second pass were lower than A_c1, both X80 pipeline steels had high impact toughness. For secondary peak temperatures in the range of A_c1 to A_c3, both X80 pipeline steels had the worst impact toughness, mainly due to the formation of massive blocky M-A constituents in chain form on grain boundaries. When the secondary peak temperatures were higher than A_c3, both X80 pipeline steels had excellent impact toughness. Smaller grain size and higher proportions of HAGBs can effectively improve the impact toughness. Meanwhile, high Nb X80 pipeline steel had higher impact absorption energy and smaller dispersion. Adding an appropriate amount of Nb to X80 pipeline steel can ensure the impact toughness of SCCGHAZ and SCGHAZ in welded joints.

Keywords: HAZ; Nb; X80 pipeline steel; thermal simulation; toughness.

Grants and funding

The authors are grateful for the financial supports from the China National Petroleum Corporation for the research project (2023ZZ11-04, 2023-N/G-40528), Pipechina (PNPCM-CCCL-CSGG-FWJF-2022-191), Companhia Brasileira de Metalurgia e Mineração (CBMM), and CITIC Metal.