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

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include: sufficiently high control accuracy, relative ease of implementation, physical clarity, versatility of use in laboratory conditions and at various stages of production, operation and repair of products, the possibility of automating the control process (Guz, 2000; Kowalczyk, 2023; Sheng, 2023). However, the issue of obtaining general patterns of changes in acoustic parameters and their comprehensive application for a wide range of tasks is relevant due to the separated studies in different areas of industrial activity. Another most relevant and urgent problem of this work is the physical substantiation of the observed patterns, that will help to generalize the measured quantities for different classes of materials and the development of uniform diagnostic criteria (Wang, 2021). It is known that in an operation process, various elements of metal structures interact with aggressive environments and experience corrosion destruction (Marcantonio, 2019). A hydrogen environment, diffusing into the volume of structural elements, leads to a significant degradation in the mechanical characteristics of the material (Belyaev, 2012). They cause a change in the stress-strain state and lead to a significant decrease in the loadability and a reduction in the durability of structures (Zhao, 2019; Nagumo, 2023). The problem of predicting the behavior of loaded metal structures under the influence of hydrogen embrittlement is very important, but is still far from being finally solved. Therefore, the study of the effect of hydrogen embrittlement on the acoustic characteristics of structural alloys is an important engineering task. The potential of using acoustic methods to control the physical and mechanical properties of metals and alloys in the research of metal-hydrogen systems has been demonstrated in number of papers (Dea, 1998; Chunjie, 2013). However, the known works on the development of modern non-destructive approaches to assessing the hydrogen-charged state of structural materials are non-systematic and are devoted to certain alloys (Dea, 1998; Gomes, 2006). The aim of this work is to find fundamental dependencies of changes of ultrasound propagation velocities and to estimate hydrogen embrittlement under load. The research material is AISI 420 martensitic stainless steel with the composition 0.44%C-0.4%Si-0.5%Mn 13.2%Cr-0.5%Ni. In this work, flat dog-bone specimens with working part dimensions of 50×10×2 mm were cut by electric spark cutting from a hot-rolled sheet in the as-delivered condition. Quenching of the samples was carried out after homogenization at T = 1050 ºС for 3 hours by rapid cooling in air. After high tempering with a temperature of 600 ºС and a waiting time of 3 hours and furnace cooling, a sorbite structure with a carbide size of Me 23 C 6 ~ 1 μm is formed in the material (Barannikova, 2016). Hydrogen charging of steel samples after heat treatment was carried out by electrolytic method in a thermostatic three-electrode electrochemical cell at a constant cathode potential U = -600 mV under the influence of a silver chloride electrode (Barannikova, 2016). The sample was placed in a 1N sulfuric acid solution with the addition of 20 mg/l thiourea at T = 323 K for up to 24 hours. For each hydrogen-charged state, 5 samples were obtained. To analyze the total hydrogen concentration in the samples (after mechanical testing until fracture), glow discharge atomic emission spectrometry was used on a Profiler 2 spectrometer. Mechanical tests of flat specimens were carried out according to the uniaxial tension scheme on a Walter+Bai testing machine (Switzerland) at room temperature and at a rate of 6.67×10 -5 s -1 . Simultaneously with the recording of the loading curves, the change in the velocity of ultrasonic waves was recorded in the alloy under study. The autocirculation method for measuring this value is described in (Murav'ev, 1996). The propagation velocity of Rayleigh waves was determined as the ratio of the wave path length in the sample to the delay time of the signal arrival at the receiving transducer relative to the transmitting one. The delay time was measured from an oscillogram recorded using a digital oscilloscope with a sampling frequency of 5 GHz. The details and capabilities of this technique are described in (Murav'ev, 1996; Lunev, 2018) and will not be discussed here. 2. Materials and methods

3. Results and discussions

An informative feature characterizing the deformability of metals and alloys is the propagation velocity of ultrasonic waves. Synchronous recording of tensile stress σ(ε) diagrams and measurements of the velocity of