Modern blocks of fossil fuel power plants designed for steam temperatures above 600 °C require advanced stainless steels in superheater or reheater systems. Great attention is paid to the exploitation of new steel grades with higher material properties. In the area of austenitic steels, the perspective grade is undoubtedly HR3C steel (X6CrNiNbN 25-20). In terms of the use of similar weld joints made of HR3C steel in fossil fuel power plants, detailed knowledge on creep resistance and microstructural stability of these weld joints is necessary.Similar weld joints made of HR3C steel tubes were manufactured using a combination of GTAW and SMAW welding technologies. Weld joints were studied in both the as-welded state (PW), and after post-weld heat treatment (PWHT) at 1230 °C for 15 minutes. The paper presents the results of creep rupture tests on cross-weld samples tested at 650 and 700 °C. Metallographic analysis was performed on longitudinal sections of creep ruptured samples and microhardness HV 0.5 profiles over cross-weld samples were determined. The paper analyses the preferential rupture locations of the HR3C similar weld joints in dependence on the temperature of creep exposure and applied stress.Keywords: HR3C steel, similar weld joints, PWHT, creep resistance, cross-weld samples.
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