Session: MF-02-02 Materials for hydrogen service II (Joint with C&S)

Paper Number: 61877

Start Time: Tuesday, July 13, 2021, 05:00 PM

61877 - The Resistance of Pearlitic Lamellar Structure to Hydrogen-Induced Fatigue Crack Growth Acceleration in Carbon Steels 

In order to reduce the cost of structural materials in hydrogen storage/transportation systems, there is a strong demand from industry for substituting lower-cost materials such as carbon steels for austenite stainless steels. Microstructure of annealed carbon steels is normally composed of ferrite and pearlite, the volume fractions of which depend solely on the carbon content. In the past, a number of studies have investigated the effect of hydrogen on various strength properties of steels with the ferrite/pearlite structure. For example, it has been revealed that increasing fraction of pearlite makes ductility loss more susceptible to hydrogen. However, the effect of pearlite on hydrogen-enhanced FCG (fatigue crack growth), which is critical in practical fatigue design, has not yet been clarified in detail.

In this study, to elaborate the role of pearlite on FCG resistance in gaseous hydrogen, FCG tests of two carbon steels with deferent pearlite fractions (30 and 70%) were conducted in air and gaseous hydrogen, followed by microscopic observations of fracture surface and crack path. The results manifested that increasing fraction of pearlite mitigates the hydrogen-induced FCG acceleration, namely pearlite exerts a positive effect on the FCG resistance of materials in gaseous hydrogen. The microscale crack propagation in pearlite grains was classified into two types; the propagations (i) traversing the pearlite lamellar and (ii) delaminating the ferrite/cementite interfaces. Considering the results of experiments and observations together, it was concluded that the crack blocking effect stemming from the confronting cementite plate in the fracture mode (i) is the primary rationale of the superior resistance to hydrogen-induced FCG in a material with greater pearlite fraction.

Presenting Author: Haruki Nishida Kyushu University

Authors:

Haruki Nishida Kyushu University
Hisao Matsunaga Kyushu University
Yuhei Ogawa Kyushu Unversity