The aim of this study was to investigate phase formation under steam oxidation conditions and steam oxidation behaviours of two solid-solution-strengthened alloys—HAYNES^® 230^® and 617 alloy—two gamma-prime (γ′)-strengthened alloys—263 and HAYNES^® 282^®—and finally three austenitic steels rich in Cr—309S, 310S and HR3C. The samples were tested under 1 bar pressure in 100 % water–steam–water system at 800 °C for 1000 h. It was found that Ni-based solid-solution-strengthened alloys, HAYNES^® 230^® and 617 alloy, developed mainly Cr₂O₃ and MnCr₂O₄ phases on their surfaces, whereas the γ′-strengthened alloys, 263 and HAYNES^® 282^®, formed Cr₂O₃, TiO₂ and MnTiO₃ phases, indicating slightly higher corrosion degradation rate. The austenitic steels exposed for 1000 h formed Cr₂O₃, Fe₃O₄ and MnCr₂O₄ with traces of Fe,Mn(SiO)₄. Some sites on the austenitic steel surfaces were enriched with Fe₃O₄ with little amount of Cr. During the test, no spallation of the external oxide scale was observed. The kinetic data showed that only the 263 alloy oxidized according to parabolic behaviour, whereas the other alloys deviated from the parabolic rate law, with time exponents of 0.4–0.6 or 0.3. Finally, cross-sectioned investigations of the exposed samples revealed that Ni-based alloys underwent extended internal oxidation, with the highest extent in HAYNES^® 282^® reaching 25 μm and the lowest in HAYNES^® 230^® alloy reaching 7 μm. The austenitic steels showed no internal oxidation phenomena.

Inconel 740H is a nickel-based alloy for pressure components of ultra-supercritical boilers. Its chemical composition and strengthened matrix, as well as corrosion resistance, provide the highest creep resistance among the materials recommended for use in high-performance pressure components of power units. This paper investigates the changes in the microstructure and mechanical properties after ageing at 700 and 750 °C for 1000, 10,000, 20,000, and 30,000 h. Observation of the microstructure was performed using scanning and transmission electron microscopy. The identification of existing precipitates was conducted by X-ray phase analysis. The effects of time and ageing at elevated temperatures on the mechanical properties and precipitation process in the test alloy are discussed. The presented results are part of the material characteristics of the new-generation alloys to be used in the design of pressure equipment for steam boilers, as well as in diagnostic work during operation.

The present work compares the behaviour of four steels: (T23, T92, T347HFG, Super304H) in the temperature range 600–750 °C. This study focuses on the analysis of the oxidation kinetics in terms of mass change, metal loss and thickness change of the selected materials. In order to understand the differences in oxidation rates between the selected steels, the impact of chromium and the alloying elements were considered in this work. The obtained results show that the impact of alloying elements differs with exposure conditions and importance of the synergy effect.

Samples based on 316L stainless steel were prepared by conventional manufacturing process (CM) and laser powder bed fusion (L-PBF). Surface morphology changes under air oxidation in the temperature range 600-900 °C were carried out. Tensile tests were carried out in the temperature range of 700-900 °C for strain rates between 0.001 and 0.1 s⁻¹. The materials showed good oxidation resistance up to 700 °C. The CM and L-PBF material had a high mass gain instability and similar microstructures developed under high temperatures were found in both alloys. Increased temperature increases Cr concertation in the L-PBF material up to 40 at.% at 800 °C and a rich Fe based oxide is formed at 900 °C. Slightly thicker oxide scales were formed in the CM than in the L-PBF material.The hot tensile tests reveal that a fast work hardening occurs for all hot tensile tested samples up to a strain of approximately 0.025. Low temperatures and high strain rates within the investigated range promote a second work hardening regime, while a plateau in the flow stress is observed at high temperatures and low strain rates. The highest yield stress and peak stress values are reached at 700 °C. The yield stress is nearly independent of the strain rate at 700 °C. It decreases with a decrease in strain rate for 800 and 900 °C, and it decreases with an increase in temperature. The elongation till fracture varies from 10 to 22%, and it is strongly influenced by defects inherent of the L-PBF process.