405 / 2018-12-26 15:18:44

Effect of Aging Treatment on Toughness of 22Cr-15Ni-4Cu Austenitic Heat Resistant Steel

22Cr-15Ni-4Cu austenitic heat resistant steel; aging treatment; toughness; M23C6 precipitates

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China had built the first 600℃ ultra-supercritical (USC) power plant in order to improve the thermal efficiency and reduce the CO2 emission. Until now, over a hundred 600℃/1000MW USC power units have been already put into service, especially the 630℃ USC power units have been rapidly developed in the recent years. For the 600℃ USC boiler, the austenitic steels such as the HR3C and Super304H are commonly employed, which are not suitable for the boiler with higher level of temperature and pressure. For instance, the Super304H steel has been proved to have high strength but poor steam oxidation resistance, on the other side, the HR3C steel shows the opposite characteristics, which is characterized by good steam oxidation resistance but low strength. As a result, the boiler in the project of 630℃ USC power units is desperately in need of a new steel that has both excellent high temperature strength and steam oxidation resistance. A new austenitic heat resistant steel 22Cr-15Ni-4Cu has been designed according to the strengthening mechanism of multiphase precipitation, which has been considered to be the strong candidate material for 630℃ USC boiler. In the present work, the 22Cr-15Ni-4Cu heat resistance steels were aged for different times under 650℃, the effect of aging time on the toughness was studied. The results showed that the Charpy impact energy sharply decreased from 176J to 25.5J with increasing aging time after the first 500h and then nearly maintained steady with further extending aging time to 5000h during the heat treatment process. It was determined that the change of toughness was attributed to the M23C6 phase precipitation.