J. Mater. Sci. Technol. ›› 2019, Vol. 35 ›› Issue (6): 1081-1087.DOI: 10.1016/j.jmst.2018.12.019

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Hydrogen-assisted fracture features of a high strength ferrite-pearlite steel

Yuefeng Jiangab, Bo Zhanga*(), Dongying Wangc, Yu Zhoua, Jianqiu Wanga, En-Hou Hana, Wei Keaa   

  1. a CAS Key Laboratory of Nuclear Materials and Safety Assessment, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China
    b School of Materials Science and Engineering, University of Science and Technology of China, Shenyang 110016, China
    c Shenyang Blower Works Group Corporation, Shenyang 110869, China
  • Received:2018-08-30 Revised:2018-11-14 Accepted:2018-11-30 Online:2019-06-20 Published:2019-06-19
  • Contact: Zhang Bo
  • About author:

    1 These authors contributed equally to this work.

Abstract:

Up to now, the exact reason of hydrogen-induced fracture for ferrite-pearlite (FP) steel is still not fully understood. This study presents detail observations of the feature beneath the fracture surface with the aim to reveal the hydrogen-induced cracking initiation and propagation processes. Slow strain rate tensile (SSRT) testing shows that the FP steel is sensitive to hydrogen embrittlement (HE). Focused ion beam (FIB) was used to prepare samples for TEM observations after HE fracture. The corresponding fractographic morphologies of hydrogen charged specimen exhibit intergranular (IG) and quasi-cleavage (QC) fracture feature. Pearlite colony, ferrite/pearlite (F/P) boundary and the adjacent ferrite matrix are found to be responsible for the initial HE fracture and the subsequent propagation. With increasing of the stress intensity factor, fracture mode is found to change from mixed IG and QC to entire QC feature which only occurs at the ferrite matrix. No crack is observed at the ferrite/cementite (F/C) interface. This may be mainly due to the limited pearlite lamella size and relatively low interface energy.

Key words: Ferrite-pearlite steel, TEM, Fracture, Hydrogen embrittlement