PSI - Issue 2_B

Balázs Fekete et al. / Procedia Structural Integrity 2 (2016) 2164–2172 Author name / Structural Integrity Procedia 00 (2016) 000–000

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2. Experimental 2.1. Materials and specimens

The test specimens were machined from the base metal (15Ch2MFA) and the anticorrosive cladding metal (08Ch18N10T) used for manufacturing of VVER-440 model 213 RPVs. After final heat treatment the 15Ch2MFA steel has a fine homogeneous bainitic structure and contains small particles of Cr-Mo-V carbides, while the 08Ch18N10T steel has an austenitic structure, consisting of austenitic grains about 100 µm in size containing many twins. Particles of δ-ferrite of the order of several tens of micrometers in size are relatively common. Their boundaries are occupied by coarser particles of M 23 C 6 carbides, which are also present inside austenitic grains as well as on grain boundaries. Furthermore, particles of coarser primary titanium carbonitrides are precipitated in the structure. The boundaries of sub-grains as well as individual dislocation substructures are stabilized with fine precipitates of titanium carbonitrides. The average Vickers hardness (HV0.5) was measured to be 230 and 165 for 15Ch2MFA and 08Ch18N10T, respectively. Further details regarding the properties and manufacturing process of these materials are given by Timofeev [Timofeev and Karzov (2006)]. Cylindrical specimens of 8 mm gauge diameter and 7 mm length were manufactured from the test materials. The specimen dimensions were chosen to avoid buckling phenomena under the highest compressive forces anticipated in the test program. The gauge surface of the test bars were finely polished before testing to ensure a consistent surface finish. 2.2. Fatigue parameters and conditions The fatigue experiments were performed using a servo valve-controlled GLEEBLE thermomechanical physical simulator. The tests were run under uniaxial tension-compression loading with total strain control. The test set-up and the chamber of the GLEEBLE-3800 are shown in Fig. 1.

Fig. 1. Experimental layout of the fatigue tests.

All fatigue tests were carried out at a frequency of 0.083 Hz and a triangular waveform with a fully reversed strain amplitudes. The longitudinal total strain was controlled by a HZT060 linear displacement transducer at various total strain amplitudes (TSA) of 0.3% to 1.5% for 15Ch2MFA and 0.9% to 2.0% for 08Ch18N10T. Each fatigue test was automatically stopped on reaching the failure criterion, which was chosen to be the 25% decrease from the maximum cyclic load in the tension phase. All tests were carried out in ambient laboratory air. A K-type thermocouple was welded in the middle of the gauge length to control and measure the temperature of the test specimen. For ISO tests, the specimens were heated up to a temperature of 260°C, which was kept constant during the entire test. The TMF tests were carried out within the VVER-relevant temperature range between 150 and 260°C, with a