Microscopic Observation of the Brittle-Striation Formation Mechanism in Low Carbon Steel Fatigued in Hydrogen Gas (TEM and EBSD Observation Corresponding to Fractography)

Abstract

Observations by Transmission Electron Microscopy and Electron Backscatter Diffraction corresponding to Fractography were conducted in order to investigate the brittle-striation formation mechanism of low carbon steel JIS S10C in a hydrogen gas environment. The main results are as follows: (1) The quasi-cleavage (QC) facets plane with brittle-striations does not coincide with the (100) cleavage plane. (2) Slip deformation distributions reflecting the brittle-striation formation processes are observed by TEM. One of the conceivable brittle-striation formation mechanisms which can explain these results is as follows. A striation line is formed during the loading part of the cycle as a trace of blunting by slips. A stable ductile crack then starts growing. These processes are similar to those in the normal ductile fracture from a crack; that is, a ductile tearing process in tension.