Metal Temperature Estimation in High-Strength Austenitic Stainless Steels through Precipitation Analysis
Metal Temperature Estimation in High-Strength Austenitic Stainless Steels through Precipitation Analysis
Tuesday, February 25, 2025: 10:55 AM
Indian Wells K (Grand Hyatt Indian Wells Resort)
This paper focuses on the development of metal temperature estimation techniques for high-strength stainless steels, such as 18Cr-9Ni-3Cu-Nb-N stainless steel. These stainless steels exhibit excellent creep rupture strength and corrosion resistance, making them widely used as heat exchanger tubes, such as super-heaters and re-heaters, in ultra-super critical (USC) power generation boilers. However, concerns have been raised about the long-term creep rupture strength of these materials, potentially lower than expected at the time of standardization. Moreover, the number of USC boilers with operating times exceeding 100,000 hours is increasing, leading to reports of leakage. Creep life evaluation is essential to prevent such leaks. However, evaluating creep life is challenging because the metal temperature of heat exchanger tubes depends on the specific site conditions.
In this study, we developed a technique for estimating metal temperature by focusing on precipitations that form and grow during heating of high-strength stainless steels. Microstructural observations of creep-ruptured specimens and aged materials for up to 120,000 hours, revealed a significant change in the size of σ phases depend on heating temperature and time. The Hollomon-Jaffe parameter (HJP), a temperature and time parameter, could be used to organize the average grain size of σ phases. Furthermore, in order to focus on σ phases precipitated in the early stage of heating, we developed a technique to estimate metal temperature with high accuracy (within ±10°C) by extracting only a certain number of coarse precipitates with an upper grain size and organizing their average grain size using the HJP.
During the oral presentation, we will also discuss a technique for the automatic segmentation of precipitates from replication microstructures observed using a movable optical microscope, facilitating rapid estimation of metal temperature in thermal power plants.
In this study, we developed a technique for estimating metal temperature by focusing on precipitations that form and grow during heating of high-strength stainless steels. Microstructural observations of creep-ruptured specimens and aged materials for up to 120,000 hours, revealed a significant change in the size of σ phases depend on heating temperature and time. The Hollomon-Jaffe parameter (HJP), a temperature and time parameter, could be used to organize the average grain size of σ phases. Furthermore, in order to focus on σ phases precipitated in the early stage of heating, we developed a technique to estimate metal temperature with high accuracy (within ±10°C) by extracting only a certain number of coarse precipitates with an upper grain size and organizing their average grain size using the HJP.
During the oral presentation, we will also discuss a technique for the automatic segmentation of precipitates from replication microstructures observed using a movable optical microscope, facilitating rapid estimation of metal temperature in thermal power plants.