Fe-C-Cr合金定向凝固组织

对经定向凝固的共晶 Fe—2.94％C—29.1％Cr 合金及过共晶 Fe—3.12％C—35.9％Cr、Fe—2.80％C—33.1％Cr 合金的凝固组织作了研究。上述三种合金中的初晶及共晶碳化物均为(Fe,Cr)_7C_3它们都以小面状析出,其中初晶在与凝固方向垂直的截面上为六角形块。初晶碳化物在定向凝固时以六角形状进行包抄式的凝固,然后再从六角形壳向内凝固,最终生成完整六角形。随着凝固速度变小,初晶(Fe,Cr)_7C_3的截面尺寸及间距增大,且从实心的六角形棒变成空心的六角形棒。过共晶合金的液固两相区长度约为1.5mm。共晶合金凝固时,碳化物的形貌为不规则多边形棒,且在凝固速度大时,组织细小。上述三种合金,当凝固速度 R>2m/sec 时,液固界面将变得凹凸不平。

Microstructures of Directionally Solidified Fe-C-Cr Alloys

The solidified microstructures of hydpereutectic (Fe-3.12%C-35.9%Cr, Fe-2.80%C-33.1%Cr) and eutectie (Fe-2.94%C-29.1%Cr) alloys which solidify directionally have been studied.The primary and eutectic carbides in the above three alloys are of the pattern (Fe,Cr)_7C_3,and they segregate in facets.The form of primary crystals in the cross-section perpendicular to the solidification direction is hexagon.During directional solidification,the primary crystal carbides solidify around the hexagon Shell,then they extend from the shell to its centre,and finally they become complete hexagon rods. The crosssection size and the space between the primary crystals,(Fe,Cr)_7C_3, increase as the rate of solidification decreases and the solid hexagon rods transform to the hollow hexagon rods.The length of the solidification region of the hypereutectic alloy is about 1.5mm.When the eutectic solidifies,the shape of the carbides becomes an irregular polygon.When the solidifying rate is large,its microstructure is rather fine.If the solidifying rate R of the above three alloys is greater than 2 um/sec,the solidified interface will become very reugh.