In Situ Observation of Phase Transformation Process of P91 Heat Resistant Steel
A laser confocal microscope was used to study the microstructure variation of P91 heat-resistant steel.The results show that the microstructure starts to transform to austenite(γ)when the temperature rises to 780℃.when the temperature reaches 965℃,a trace amount of δ-ferrite is emergent.The surface grain boundary of P91 is obvious when the temperature comes up to 1093℃,and there is lumphy δ-ferrite generated during heating.A mass of δ-ferrite appear around 1187℃,and irregular polygonal grains are present at 1200℃.In the cooling rate of 300℃/min,the microstructure is δ-ferrite with a spot of precipitates at 1164℃.The δ-ferrite to austenitic(α)phase transformation is observed around 909℃.This phase transition determines the amount and morphology of the residual δ-ferrite and austenite(γ)phases.
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