Regularities of the phase transformations in low-activation 12 % chromium ferritic-martensitic steel EK-181

The regularities of structural-phase transformations during heating and cooling of low-activation 12 % chromium ferritic-martensitic steel EK-181 (Fe-12Cr-2W-V-Ta-B) in the temperature range from 30 to 1100 °C using in situ high-temperature X-ray diffraction analysis (XRD) were studied . The critical points of the (α → γ) transformation (A_c1 ≈ 850 °C, A_c3 ≈ 950 °C) during heating of steel and the temperature range (910-890 °C) of the «austenite → α-ferrite» diffusion transformation during steel cooling are determined. It has been shown that the position of these points varies depending on the method of their determination (XRD or differential scanning calorimetry), which is due to the difference in the heating-cooling rate. At heating in the temperature range of 830-875 °C a significant increase of the volume fraction of M₂₃C₆ carbides is observed. A further increase in temperature to 1000-1100 °C leads to their complete dissolution. During the cooling of samples from 1100 to 30 °С the discussed particles do not form.

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