PRECIPITATES IN HR3C STEEL AGED AT HIGH TEMPERATURE
FANG Yuanyuan1), ZHAO Jie1), LI Xiaona1, 2)
1) School of Material Science and Engineering, Dalian University of Technology, Dalian 116085
2) Key Laboratory of Materials Modification by Laser, Ion and Electron Beams of Ministry of Education Dalian University of Technology, Dalian 116085
Cite this article:
FANG Yuanyuan ZHAO Jie LI Xiaona. PRECIPITATES IN HR3C STEEL AGED AT HIGH TEMPERATURE. Acta Metall Sin, 2010, 46(7): 844-849.
HR3C steel (Fe-25Cr-20Ni-Nb-N) is a new type of austenitic heat-resistant steel which has been widely used for super-heater and re-heater tubes in the ultra supercritical pressure (USC) boiler. The mechanical properties of HR3C steel were dependent on the stability of the microstructure, particularly the large amount of precipitates formed during service. This work was focused on the change of microstructure and the precipitations of HR3C steel after thermal aging for 500 h at 750℃. The results indicated that the major precipitates were variform M23C6 carbides and NbCrN nitrides. M23C6 carbides precipitated on grain boundaries and in intragranular. Fine and dispersed NbCrN nitrides were found to precipitate in intragranular. The hardness of HR3C steel had been improved through dispersed M23C6 and fine NbCrN precipitates after thermal aging for 500 h at\linebreak 750℃. All the M23C6 carbides, with lattice parameter of three times of the austenite matrix, grown in a cube to cube orientation relationship with the matrix. Some of the M23C6 carbides which precipitated on grain boundaries were transformed into σ phase.
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