Effects of Grain Size on Hydrogen Environment Embrittlement of High Strength Low Alloy Steel in 45 MPa Gaseous Hydrogen

Abstract

The effect of grain size on the susceptibility of high-strength low alloy steels to hydrogen environment embrittlement in a 45 MPa gaseous hydrogen atmosphere was examined in term of the hydrogen content penetrating the specimen during the deformation. Notch tensile tests were performed in a 45 MPa hydrogen environment using specimens with different prior austenite grain size numbers varying from 2.5 to 5.4. The hydrogen content was measured by thermal desorption analysis with a quadrupole mass spectrometer before and after the tensile test. The fracture stress of the notch tensile test increased with increasing grain size number; this showed that grain refinement was effective in reducing the susceptibility of the specimens to hydrogen environment embrittlement in a high-pressure hydrogen atmosphere. The addition of nickel did not affect the fracture stress. A remarkable increase in the content of diffusive hydrogen was observed after the notch tensile test. Assuming that part of the diffusive hydrogen desorbed from grain boundaries, it can be inferred that grain refinement can reduce the mass of hydrogen in the unit grain boundary area, and the susceptibility to high-pressure hydrogen environment embrittlement.

Alloy Optimization for Reducing Delayed Fracture Sensitivity of 2000 MPa Press Hardening Steel

“…An initiated crack propagates along the grain boundary if its cohesion is substantially compromised, leading to grain boundary (intergranular) fracture (Figure 1a). This fracture appearance can indeed be observed, particularly after the severe hydrogen charging of martensite with a coarse prior austenite grain structure [14]. Impurities as well as certain alloying elements, e.g., phosphorous and manganese [15][16][17], additionally reduce coherency when segregated to the prior austenite grain boundary, thereby enhancing the deleterious effect of hydrogen.…”

Effect of Nickel on the Hydrogen Stress Cracking Resistance of Ferritic/Pearlitic Low Alloy Steels

“…Takasawa et al 67 reported improved HSC resistance with decreasing prior austenite grain size (PAGS), while Asahi et al 68 and Asahi and Ueno 69 reported improved SSC resistance with refined PAGS, all for QT LAS. A few attempts have been done to investigate the effect of ferrite grain size on HE resistance.…”

Characterization of hydrogen embrittlement sensitivity of 18CrNiMo7-6 alloy steel surface-modified layer based on scratch method

“…Molecular hydrogen is adsorbed onto metal surfaces through physical and chemical adsorption. The molecules then dissociate into atomic hydrogen, which diffuses into the metal body through dislocations at grain boundaries and grains (Takasawa et al, 2010), leading to stress corrosion cracking, hydrogen-induced cracking, hydride cracking and other adverse effects (Okonkwo et al, 2023). These phenomena result in destructive cracks and catastrophic brittle failure of materials sensitive to hydrogen embrittlement (HE).…”