PSI - Issue 28

Fedor S. Belyaev et al. / Procedia Structural Integrity 28 (2020) 2110–2117 Author name / Structural Integrity Procedia 00 (2019) 000–000

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for the TiNi SMA. Progress in materials science, allowing to improve shape recovery and corrosion resistance of FeMnSi-based alloys, has made them very attractive for use as working elements of thermomechanical couplings, reinforcing parts, and vibration protection devices for large-size structures due to their good machinability and low price compared to TiNi (Sawaguchi et al. (2006), Nikulin et al. (2015)). Alloying gives opportunity to control mechanical characteristics of these steels. For example, it was shown (Sagaradze and Afanas’ev (2015)) that hardening due to the intense precipitation of the vanadium monocarbide VC nanoparticles both enhances the strength characteristics of the alloy and increases the recoverable strain. Since the FeMnSi-based alloys are of great interest in connection with their possible applications in various seismic vibration control and seismic isolation devices (Sawaguchi et al. (2006), Sawaguchi et al. (2015), Nikulin et al. (2015), Nikulin et al. (2016), Ghafoori et al. (2017)), the present work is focused on the experimental study and simulation of the fatigue fracture of the high-strength steel Fe – 0.40 С – 18 Mn – 2 Si – 2 V (mass percent). The microstructural model (Evard et al. (2016), Evard et al.(2018), Belyaev et al. (2018)) accounting for the specific features of the fcc hcp martensitic transformation in these SMA was used for simulation of the material mechanical behavior. It was supposed that at the temperature under investigation (293 K), at which the alloy is in the martensitic state, the prevailing deformation mechanism is the reorientation of martensitic domains. This process is accompanied by irreversible micro plastic deformation and the accumulation of the deformation defects, which results in the material failure. 2. Experimental procedure and results A bunch of flat specimens with the working part 20.0 х 2.85 х 2.0 mm were cut from the FeMnSi plate containing 18% Mn, 2% Si, 2%V and 0.4% С (mass percent). The specimens were investigated either as received (after rolling, quenching from 1150°C and aging 12 hours at 650°C) or were subjected to additional aging for 3 hours at 720°C. The stress-strain diagrams were obtained with the Instron ElectroPuls E3000 testing machine. The latent heat of the martensitic transformation and the characteristic temperatures were obtained by the differential scanning calorimetry on the NETZSCH DSC 204F1 Phoenix equipment. The cyclic fatigue tests were carried out on the servohydraulic testing machine Si-Plan SH-B. (Sagaradze and Afanas’ev (2015)) have shown that precipitation of the VC particles in the steels under consideration increases the yield stress up to σ 0.2 = 728 MPa, which is much higher than 257 MPa for the Fe – 0.20 С – 18 Mn – 2 Si – 1 V steel and 496 MPa for the Fe – 28 Mn – 6 Si steel. Besides, this steel demonstrates substantial plasticity (maximum homogenous strain before failure δ = 14%) and the shape memory effect: after preliminary tension it can recover from 1.4 % (after quenching) to 2.1 % (after additional aging for 3 hours at 720°C).

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Fig.1. Stress-strain diagrams of steel 0.40 С – 18 Mn – 2 Si – 2 V at room temperature: curve 1 - as-received specimens (after quenching from 1150°С and annealing 12 hours at 650  С); curve 2 – specimens after additional annealing for 3 hours at 720°С.