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γ Grain Memory in X12CrMoWVNbN10-1-1 Steel
Xingang Tao, Lizhan Han, and Jianfeng Gu
Abstract: γ grain memory of X12CrMoWVNbN10-1-1 steel is investigated in order to clarify its
mechanism from the viewpoint of the roles of retained γ. “isothermal transformation” is
proposed to suppress the γ grain memory. The microstructure characterization during the
isothermal transformation is carried out. By in situ optical microscopy observation, the
acicular γ grains and globular γ grains nucleated in the interior of prior γ grains and along the prior γ grain boundaries or packet boundaries, respectively, when the sample with martensite matrix is reheated. The coarse γ grains are formed by the growth, impingement and coalescence of acicular γ grains with retained γ between martensite lath. The mechanism of suppressing γ grain memory by isothermal transformation is also discussed. It is demonstrated that the γ grain memory could be suppressed by decreasing the volume fraction (fγ) of retained γ before reheating. The critical upper limit fγ to suppress γ grain memory effectively is approximately 3.2%.
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