This paper won the Excellence Award of the "China Installation Association Welding Professional Committee 2012 Annual Meeting and Welding Standards and Advanced Welding Technology Seminar" paper contest.

1. Analysis of two steels

(1) T91 steel T91 steel belongs to martensite heat-resistant steel. It is a super 9Cr steel formed by adding a small amount of V and Nb to the 9Cr-1Mo steel and adjusting the addition amount of Si and Al. The steel has excellent high temperature strength. Above 550 °C, its design allowable stress is twice that of T9 steel and 2.25Cr-1Mo steel. Compared with 1Cr19Ni9 steel, its equivalent temperature is 625 °C, anti-oxidation and anti-steam corrosion. The performance is comparable to that of 9Cr-1Mo steel. Commonly used in subcritical, supercritical boiler wall temperature of 650 ° C superheater pipe and reheater pipe. Its chemical composition and mechanical properties at room temperature are shown in Table 1 and Table 2.

(2) T22 steel T22 steel belongs to bainite heat-resistant steel. Its chemical composition, mechanical properties and carbon equivalent are similar to those of 10CrMo910 steel, and it belongs to 2.25Cr-1Mo steel. The microstructure of the steel after normalizing is bainite + a small amount of martensite, and sometimes a small amount of ferrite. When it is operated at a high temperature for a long time, carbides are precipitated from the ferrite matrix and aggregated and grown. The steel has good process performance, is less sensitive to heat treatment temperature, has good weldability, and has good long-lasting plasticity, but its strength is low. It is often used as a superheater pipe with a wall temperature of ≤580 °C, a reheater pipe and a steam pipe with a wall temperature of ≤570 °C. Its chemical composition and room temperature mechanical properties are shown in Table 3.

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