【摘要】 本文对稀土在铁铬铝合金中的作用机理从热力学和动力学两方面进行了研究,证实了稀土在合金中以稀土夹杂、金属间化合物和固溶稀土三种形式存在。稀土在不同工艺冶炼的铁铬铝合金中的物相分配不同。讨论了稀土的脱氧、脱硫、抑制晶粒长大、净化晶界和基体,以及对氧化铝夹杂的变质作用。通过动力学试验和氧化膜分析得到,稀土改变了氧化膜的组成和结构,增加了氧化膜的粘附性、提高了合金的抗氧化性和高温寿命。提出了几种主要的铁铬铝合金冶炼工艺的稀土最佳加入量。更多还原

【Abstract】 The mechanism of the influence of rare earth additions on the properties of Fe-Cr-Al alloys has been studied from thermodynamic and kinetic viewpoints. Rare earths in Fe-Cr-Al alloys exist in three forms: rare earth inclusions, Fe-RE metallic compounds and RE solid solution. The free energy of formation of rare earth compounds in Fe-Cr-Al alloys （standard stats are 1 wt％ for the elements in alloy） has been calculated, according to the data of standard free energy given by Vahed. The formation of（RE）₂O₃, （RE）₂O₂S, （RE）AlO₃, （RE）_xS_y and（RE）OF have been observed in our experiments. When cerium content was more than 0.15 wt％, the spindle and tongue shaped metallic compound Fe₅Ce phase had been easily observed. When yttrium content was more than 0.2 wt％, the metallic compound Fe₉Y made its appearance in OCr₂₅Al₅ alloy. The amount of rare earths in solid solution is very low, but it increases with the increase of the total amount of rare earth additions （within a certain content range）. The relation of the alloying rate （Q）with the total amount of rare earth additions [％RE] has been studied for OCr₂₅Al₅ alloy, which have been obtained by a combination of arc melting with electrical-slage refining or by vaccum induction melting. The result is given by the equation Q%=-0.0037+0.64[RE％]。Rare earths in Fe-Cr-Al alloys play the role of deoxidation, desulfuration, modifying of Al₂O₃ non-metallic inclusion, grain refinement, suppressing growth of grain and raising the adhesiveness of the oxide film of Fe-Cr-Al alloys. The ability of deoxidation is decreased in the order of Pr、Nd、La and Ce. Pr and Nd react upon oxygen first, forming Pr₂O₃ and Nd₂O₃ respectively. La and Ce concentrate on La₂O₂S and Ce_xS_y respectively.Non-metallic inclusion in Fe-Cr-Al alloys without addition of RE’s are mainly alumina and aluminate, which possess high hardness and pointed shape. Thermodynamical calculation shows that RE’s convert Al₂O₃ to （RE）AlO₃ or RE₂O₃. That is one of the reasons for increasing mechnical properties of alloys.Rare earths in Fe-Cr-Al alloys may change the structure of oxide film. After the addition of rare earths, the major phase （α-Al₂O₃） in oxide film remained unchanged, but the minor phase （FeO·Cr₂O₃） has been substituted by La₂O₃, CeO₂, Al₂Y₄O₉ etc.Experiments show that the optimum rare earth content is different and depends upon the method of alloy refining. The optimum rare earth content in the alloy melted by vaccum induction is 0.05～0.12 wt％.更多还原