PSI - Issue 65

S.A. Barannikova et al. / Procedia Structural Integrity 65 (2024) 11–16 S.A. Barannikova, A.M. Nikonova/ Structural Integrity Procedia 00 (2024) 000–000

15 5

0 V V   V V

,

(2)

R



i

p

0

where V i , V 0 , V p are values of the propagation velocity of Rayleigh waves at the time of measurements (diagnostics), in an initial state without hydrogen and at the time of fracture, respectively. At R > 0.7, the metal is in a state close to fracture and reaches the limit state. The values of V i are equal to the values of the Rayleigh wave velocities shown in Fig. 2a (curve 3) and correspond to the extremum of the derivatives dV R /dε (Fig. 2b, curve 2). We substituted the values of V i into formula (2) and obtained the value R = 0.65 ≈ 0.7, which is close to the limit state. Thus, the experimentally observed nature of the change in the propagation velocity V R with increasing strain (or stress) indicates a change in the state of stressed regions in the deformed sample under hydrogen embrittlement conditions. The change in the stages of the V R (ε) dependence is associated with the formation of structural fragments with different levels of internal stresses in the volume of the sample, caused by hydrogen embrittlement. The same changes concerned the character of the flow curve σ(ε). The heat treatment mode (tempering in the temperature range of excess phases precipitation) leads to a decrease in the resistance of steel to intercrystalline corrosion. This is caused to the formation of chromium-depleted zones around the carbides, which have reduced corrosion resistance. Hydrogen-induced fracture in loaded martensitic steels can be explained by the simultaneous action of hydrogen-enhanced local plasticity (HELP) and the decohesion (HEDE) mechanisms described in the literature (Nagumo, 2023). The problem of estimating the degree of hydrogen embrittlement of steel by the acoustic method under static loading was discussed. The results of our research of heat-treated samples of AISI 420 martensitic stainless steel showed the possibility of determining variations in the propagation velocities of Rayleigh waves depending on the time of electrolytic saturation with hydrogen during mechanical tensile. In the initial state, the Rayleigh wave propagation velocity in the sorbite structure obtained by quenching and tempering has a minimum value. At a constant cathode potential subsequent saturation with hydrogen for up to 24 hours in an electrolytic cell leads to an increase in the velocity of ultrasonic waves in both the undeformed and deformed states of the material. The dependences of the strength degradation coefficients and hydrogen embrittlement on the acoustic property’s degradation coefficient were found. They are approximated by the Boltzmann sigmoid function with high correlation coefficients. An estimate of the critical hydrogen concentration was derived, which 80% of the initial mechanical properties are preserved. The values of the Rayleigh wave propagation velocities characteristic of the limit state of a deformed material under hydrogen saturation conditions were determined. 4. Summary

Acknowledgements

This study was carried out within the framework of the Governmental Assignment for the ISPMS SB RAS (Project No. FWRW-2021-0011).

References

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