連続鋳造鋳片中心偏析帯のリン化物の析出挙動
1986 年 50 巻 1 号 p. 89-97
詳細
1986 年 50 巻 1 号 p. 89-97
The precipitation behavior of phosphides which are the most important compounds in the centerline segregation zone of continuously cast (CC) steel slabs has been studied using the non-aqueous electrolyte-potentiostatic etching method (the SPEED method).
The results are summarized as follows.
(1) Iron phosphides were clearly observed in middle (0.16%C or more) and high carbon steel slabs as spheroidized eutectic compounds, but not observed in low carbon steels.
The spheroidized eutectic phosphides were identified as (Fe, Mn)3P, (Fe, Mn)2P and steadite (Fe3P-Fe3C-Fe).
(2) The precipitation zone of the eutectic phosphides depends on the C and P contents of CC slabs, and the phosphide precipitates in slabs of about 0.16%C or more. Thus it is considered that the precipitation of the spheroidized eutectic phosphides depends on the primary austenite (γ) at solidification of CC slabs, and an increase in the γ quantity causes the solubility of P in the γ to drop. Therefore, the P segregates along γ grain boundaries, and then concentrates spheroidized and precipitates as the eutectic phosphides.
(3) The morphology and composition of the spheroidized eutectic phosphide, (Fe, Mn)3P, change into those of (Fe, Mn)2P and FeP by heating at about 1173 K.
(4) The precipitation zone of the phosphides is in good agreement with both the weld cracking zone and the poor ductility zone concerning hot ductility in carbon steels.
Thus it is considered that the embrittlement owing to phosphorus is caused by the phosphides with low melting point.
