IN-SITU OBSERVATION OF NUCLEATION AND GROWTH OF HIGH-TEMPERATURE δ PHASE DURING AUSTENITE → FERRITE+LIQUID PHASE TRANSFORMATION IN AN AISI304 STAINLESS STEEL
Gaofei Liang;;
上海宝钢技术中心前沿技术研究所
Cite this article:
Gaofei Liang. IN-SITU OBSERVATION OF NUCLEATION AND GROWTH OF HIGH-TEMPERATURE δ PHASE DURING AUSTENITE → FERRITE+LIQUID PHASE TRANSFORMATION IN AN AISI304 STAINLESS STEEL. Acta Metall Sin, 2006, 42(8): 805-809 .
Abstract The nucleation and growth behaviors of high-temperature δ during austenite (γ) → ferrite (δ) + liquid (L) phase transformation in an AISI30 stainless steel have been observed in-situ by using a confocal laser scanning microscope. The results show that δ appears prior from the γ crystal boundary at the temperature range from 1300 to 1400 0C, and appears at full blast in the γ gains above 1410 0C. The γ→δ+L phase transformation is controlled mainly the diffusion of Ni atoms near the γ/δ/L phase interface. With the increment of temperature risen rate, the size of δ gain decreases, the δ/γ planer interface becomes unstable, and a certain secondary branch appears. The δ grows mainly in the non-faceted style at first. Twin-crystal is the key shape of the sidestep forming in the δ/γ interface. The faceted δ trends to passivate its edge and transfers to non-faceted style with the γ →δ+L phase transformation. The mechanisms of the growth interface instability for δ are discussed by using the critical wavelength to stabilize a planar interface theory. The transformation reason for growth style of δ is analyzed by using the crystal dynamics theory.
