There are high demands placed on ensuring the integrity when building blocks of fossil power plants with USC steam parameters. Weld joints are critical parts of fossil power units. At present, the behaviour of the new austenitic steels such as HR3C (X6CrNiNbN 25-20) is not sufficiently studied. The aim of this paper is to study the microstructure and creep behaviour of the homogeneous HR3C weld joints in two states: in the as—welded state (AW) and after the post-weld heat treatment (PWHT). The PWHT was carried out at the temperature of 1230 °C for 15 min. Stress rupture tests were performed on the cross-weld joints of tubes ø 38 x 6.3 mm at 700 °C with times to rupture up to nearly 22,000 hours. The structural changes after long-term creep exposure were studied on longitudinal sections by various microscopic techniques.The stress rupture test results of welds after PWHT indicate slightly better long-term creep strength when compared to the AW state. The calculated creep rupture strengths at 700 °C/100,000 hours for the base material (BM) and the homogeneous weld joints after PWHT are almost the same. The AW specimens as opposed to the PWHT specimens did not show a noticeable growth of austenitic grains in the heat-affected zone (HAZ). In specimens after PWHT the average grain size in HAZ was more than twice that of the BM.Keywords: HR3C, PWHT, creep-resistant steel, austenitic stainless steel, homogeneous weld joint.
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