The Effect of Long-Term Impact of Elevated Temperature on Changes in Microstructure and Mechanical Properties of HR3C Steel

Abstract

The HR3C is a new steel for pressure components used in the construction of boilers with supercritical working parameters. In the HR3C steel, due to adding Nb and N, the compounds such as MX, CrNbN and M23C6 precipitate during service at elevated temperature, resulting in changes in mechanical properties. This paper presents the results of microstructure investigations after ageing at 650, 700 and 750 °C for 5,000 h. The microstructure investigations were carried out using scanning and transmission electron microscopy. The qualitative and quantitative identification of the existing precipitates was carried out using X-ray analysis of phase composition. The effect elevated temperature on microstructure and mechanical properties of the examined steel was described.

Effects of Long‐Term Ageing at High Temperatures on Oxide Scale Development and Evolution of Austenitic Steels Microstructure

“…The current study showed that precipitation of the σ phase at 650 °C during the aging process was not observed due to lack of Si‐rich phase (Figure A). The achieved results in this work are in good agreement with the study performed by Zielinski et al, where σ phase in the aging process was observed in HR3C steel at 700 °C after 5000 h; however, at 650 °C, σ phase was found after 30 000 h. In the case of HR6W and Sanicro 25 stainless steel, numerous precipitates were observed with different morphologies, inside and at the grain boundaries. Precipitates were also observed at the twin boundaries (Figure and ).…”

The Effect of Service on Microstructure and Mechanical Properties of HR3C Heat-Resistant Austenitic Stainless Steel

“…The laboratory tests of HR3C steel made so far confirmed the assumed high corrosion resistance, but at the same time showed its susceptibility to very fast decrease in impact strength, with the cracking mechanism changed from ductile to brittle-intercrystalline [3][4][5][6][7]. The performed tests showed what was responsible for the low impact strength of HR3C steel after ageing at above 600 • C. It was the unfavourable morphology of the secondary phases-M 23 C 6 carbides-precipitated at the grain boundaries, as well as the coarse-grained structure of the steel.…”

“…As residual particles, these precipitates were formed during solidification and are undissolved by the solution treatment [9,10]. The Z-phase in the as-received HR3C steel was also observed by Zieliński [3], while Bai [6] and Peng [11] reported the presence of primary Nb-rich MX particles in the as-received samples. The presence of primary precipitates in austenitic steels stabilised by microadditions of niobium or/and titanium is a typical feature of these materials.…”

Analysis of Phase Precipitation in Sanicro 25 Austenitic Steel after Ageing

“…The increase in the performance of newly built power units results at the same time in the increase in their efficiency. It is inseparably connected with the need to use materials with increased functional properties [4][5][6][7].…”