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铁道科学与工程学报

JOURNAL OF RAILWAY SCIENCE AND ENGINEERING

Vol. 19    Special 3    December 2009

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Tempering microstructure and mechanical properties of pipeline steel X80
NIU Jing(牛 靖)1,2, QI Li-hua(齐丽华)1,2, LIU Ying-lai(刘迎来)1, MA Lei(马 蕾)2,
FENG Yao-rong(冯耀荣)1, ZHANG Jian-xun(张建勋)2

1. Xi’an Tubular Goods Research Center of China National Petroleum Corporation, Xi’an 710065,China;
2. School of Materials Science and Engineering, Xi’an Jiaotong University, Xi’an 710049,China

Abstract:The tempering microstructure and mechanical properties of X80 steel used for heating-bent pipe were analyzed. The results show that the microstructure of X80 steel tempered at 550 ℃ and 600 ℃ is bainitic ferrite (BF)+granular bainite (GB), and partial ferrite laths in BF merge and broaden. The interior sub-lath boundary of some GB begins to disappear due to merging, the M/A constituent (a mixture of martensite plus retained austenite) in GB is orbicular. At the two tempering temperatures the tested X80 steel shows a certain degree of tempering stability. After being tempered at 650 ℃, the microstructure of X80 steel is GB+quasi-polygonal ferrite(QF), and the original BF laths have merged to form smaller GB crystal grains. The reason is that the steel shows better match of strength and toughness. After being tempered at 700 ℃, the microstructure of X80 steel is composed mainly of QF, which can improve the plasticity but decline severely the yield strength of X80, and the M/A constituent assembles and grows up at the grain boundary of QF, resulting in excellent lower low-temperature toughness of X80.

 

Key words: X80 steel; microstructure; tempering temperature; mechanical property

ISSN 1672-7029
CN 43-1423/U

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