Microstructure and precipitates of 15NiCuMoNb5 steel after isothermal treatment at different temperatures below the Ms point were analyzed by using scanning electron microscope(SEM)and transmission electron microscope(TEM).The results show that when isothermally treated at 370 ℃,M-A islands mainly exhibit a micro-sized long-striped morphology,and the precipitated phases are mainly M3C and Cu-rich phases.After isothermal treatment at 310 ℃,the M-A island is dominated by traditional bulk morphology,and the precipitated phases are mainly spherical Nb-rich carbides.The difference of M-A island morphology and precipitated phase mainly depends on the difference of carbon diffusion rate and driving force of precipitated phase at different temperatures.
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