Heat Treatment of Metals ›› 2023, Vol. 48 ›› Issue (7): 277-282.DOI: 10.13251/j.issn.0254-6051.2023.07.046

• TEST AND ANALYSIS • Previous Articles     Next Articles

Cause analysis and control of surface cracking of 37Mn5 steel thick-walled oil casing

Ren Zhilan1, Tang Minghua1,2, Bi Hongxia1, Wu Yuanzhi1,2, Zhou Yong3   

  1. 1. School of Intelligent Manufacturing and Mechanical Engineering, Hunan Institute of Technology, Hengyang Hunan 421002, China;
    2. School of Materials Science and Engineering, Hunan Institute of Technology, Hengyang Hunan 421002, China;
    3. Technology Center, Hengyang Valin Steel Tube Group Co., Ltd., Hengyang Hunan 421001, China
  • Received:2022-03-18 Revised:2023-02-10 Online:2023-07-25 Published:2023-09-04

Abstract: Surface cracks were found on 37Mn5 steel thick-walled oil casing after quenching and high-temperature treatment, the analysis of cracking causes and research of process improvement were carried out by means of SEM, EDS and TEM. The results show that the cracks on the surface of the 37Mn5 steel oil casing are because of multiple factors coupling such as non-metallic inclusions in the steel, quenching stress concentration and high-temperature tempering brittleness, inclusions induce micro-cracking during the rolling process, the micro-crack is further expansion and extension under the action of quenching internal stress, coupled with the high temperature tempering brittleness reduces the toughness of the material, eventually a certain depth of macro cracks are formed on the surface of the pipe. By using improved sub-temperature quenching process treatment, the impact toughness of the 37Mn5 steel oil casing is significantly improved and the resistance to fracture failure on the premise basically not reduce the strength of material, inhibits high-temperature temper brittleness, basically eliminating the surface cracking phenomenon, and achieving good production application results.

Key words: 37Mn5V steel, surface cracks, sub-temperature quenching, microstructure and properties

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