Correlation Between Microstructure and Properties of New Heat-Resistant Alloy SP2215

With the improvement of the steam parameters of thermal power units, the requirements put forward for the stress rupture strength and structural stability of heat-resistant materials for boiler superheater/reheater pipes become higher. SP2215, as a new heat-resistant alloy, is an excellent candidate for 620-650 degrees C ultra-supercritical boiler superheater/reheater. In this study, the correlation between microstructure evolution and properties of the SP2215 heat-resistant alloy aging at different temperatures and time was studied via a series of creep and impact tests. The results show that the SP2215 alloy has excellent microstructure stability in high-temperature condition. Moreover, various nanoscale precipitations such as Cu-rich, MX, NbCrN, and M23C6 phases occur during aging. In the early period of aging, with the increase in aging temperature and aging time, the precipitations increase rapidly, improving the strength of the material; however, the impact toughness of the SP2215 alloy decreases considerably, with substantial intergranular fracture caused by the continuous precipitation and growth of M23C6 at the boundary, as shown with the quantitative calculation using the JMA model. In the late period of aging, the precipitations gradually stabilize, and the grain size remains in the range of 4.5-5 grade. As a result, the 1 x 10(5) h stress rupture strength of the SP2215 alloy at 650 and 700 degrees C still remain more than 120 and 70 MPa, respectively. Hence, the alloy can be used as a domestic replacement for foreign HR3C, Super304H, and other similar heat-resistant alloys.