SB-07-4(084) Mechanical Properties and Microstructure of 0.1C-18Cr-9Ni-3Cu-Nb, N Steel Tube after Long Term Exposure in a Power Boiler(Changes in Microstructure 2)

概要

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An economical austenitic stainless steel, 0.1C-18Cr-9Ni-3Cu-Nb, N (KA-SUS304J1HTB) has been developed for superheater and/or reheater tubes in fossil fired boilers. The allowable tensile stress at 600〜700℃ of this steel is more than 20% higher compared with ASME SA-213 TP347H. This excellent creep rupture strength of this steel is based on the finely precipitated particles such as Cu-rich phase, NbCrN, Nb (C, N) and M_<23>C_6 carbide. The tubes have been installed in superheater and reheater section of a Japanese utility boiler. After 1-year, 2.5-year, 6.5-year and 10-year service exposure, the tubes have been removed in order to investigate the change in mechanical properties and microstructures. These investigations confirmed that there was little change in creep rupture strength between virgin tubes and removed ones. It was demonstrated that 10〜20nm diameter Cu-rich phase which precipitated during exposure showed little growth and kept the coherent relationship with matrix even after 10-year service. This coherent strain was considered to increase the creep resistance by obstructing the dislocation climb. The tensile ductility at room temperature and Charpy impact values at 0℃ of this steel deteriorated after 1 year service, but they tended to saturate and kept enough values even after 10-year exposure.
一般社団法人日本機械学会の論文
2001-06-03