| With the improvement of the boiler steam parameters, the requirements for the tube of the heated surface are becoming more and more severe. New austenitic heat-resistant steels gradually replace martensitic heat-resistant steels for high-parameter unit superheaters and reheaters due to their high creep strength, excellent corrosion resistance and oxidation resistance. However, the problems of poor thermal conductivity, large expansion coefficient and high content of alloy elements are easy to cause welding defects. In addition, the austenitic heat-resistant steel may precipitate the harmful phase such as sigma and Cr2N during the long term service, reducing the high temperature properties of the material. Therefore, the content of Cr and Ni in the austenitic heat-resistant steel is increased, and through multi-alloying, the Z-phase, MX-phase, and M23C6-phase are jointly compounded. The suitable grain size and surface quality are obtained with the help of a reasonable cold and heat forming process. Further the stability of the tissue and the high temperature performance is improved to meet the requirements of the superheater and reheater for the ultra supercritical boiler with higher steam parameters. |