This paper was awarded the Excellence Prize at the "China Installation Association Welding Professional Committee 2012 Annual Meeting and Welding Standards and Advanced Welding Technology Seminar." The recognition highlights the significance of the research in welding technology and standards, particularly in the context of high-temperature materials used in power generation systems.
**1. Analysis of Two Steels**
**(1) T91 Steel**
T91 steel is a type of martensitic heat-resistant steel. It is a super 9Cr steel that is developed by adding small amounts of vanadium (V) and niobium (Nb) to 9Cr-1Mo steel, while adjusting the levels of silicon (Si) and aluminum (Al). This composition gives it excellent high-temperature strength. At temperatures above 550°C, its design allowable stress is twice that of T9 steel and 2.25Cr-1Mo steel. Compared to 1Cr19Ni9 stainless steel, T91 exhibits superior oxidation and steam corrosion resistance at an equivalent temperature of 625°C. It is commonly used in subcritical and supercritical boilers for superheater and reheater tubes operating at wall temperatures up to 650°C. Its chemical composition and mechanical properties at room temperature are detailed in Table 1 and Table 2.
**(2) T22 Steel**
T22 steel is classified as a bainitic heat-resistant steel. Its chemical composition, mechanical properties, and carbon equivalent are similar to those of 10CrMo910 steel, making it part of the 2.25Cr-1Mo family. After normalization, the microstructure consists mainly of bainite with a small amount of martensite, and sometimes a trace of ferrite. When exposed to high temperatures over extended periods, carbides can precipitate from the ferrite matrix and grow, affecting long-term performance. T22 steel offers good workability, is less sensitive to heat treatment, and has excellent weldability. However, its strength is relatively lower compared to other heat-resistant steels. It is typically used for superheater pipes with wall temperatures up to 580°C, reheater pipes, and steam lines operating at temperatures below 570°C. Its chemical composition and mechanical properties at room temperature are presented in Table 3.
For more detailed information, please refer to the attached document or read *Metal Processing (Hot Processing)*, Issue No. 18.
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