含硅过共析钢晶界铁素体形成的热力学分析

Thermodynamic Analysis of Grain Boundary Ferrite Formation in Si containing Hypereutectoid Steels

将合金元素在珠光体相变时无分配状态下形成的含Ｓｉ合金渗碳体做为一种介稳相处理，利用规则溶液亚点阵模型和有关文献中的数据，计算了含Ｓｉ合金渗碳体相对于无Ｓｉ渗碳体的自由能增量δＧＦｅ３ＣＳｉ，得到了渗碳体中含Ｓｉ量和δＧＦｅ３ＣＳｉ的对应关系；并利用Ｓｉ在不同温度下的分配系数，计算了Ｓｉ对ＦｅＣ合金介稳态γ／［γ＋Ｆｅ３Ｃ］相界碳浓度（Ａ′ｃｍ）的影响。所得结果认为，含Ｓｉ过共析钢珠光体转变时在原奥氏体晶界出现连续网状铁素体，是Ｓｉ增加含Ｓｉ渗碳体自由能，从而提高了介稳态γ／［γ＋Ｆｅ３Ｃ］相界碳浓度（Ａ′ｃｍ）的结果。

Alloyed cementite containing silicon formed under no partition conditions is treated as a metastable phase in this article, and the regular solution sub lattice model along with thermodynamic data published in literature is utilized to estimate δ G Fe 3C Si , the Gibbs energy increment of silicon containing cementite above that of cementite free of silicon. The relation between the content of silicon and δ G Fe 3C Si has been established. Calculation of the metastable A′ cm line ( SE ′′) modified by silicon is based on the data of the partition coefficient of silicon between ferrite and cementite under a series of temperatures. The results show that the necessary carbon content in austenite for Si containing cementite to precipitate has been greatly increased. The formation mechanism of grain boundary ferrite in silicon containing hypereutectoid steels can be explained explicitly with this metastable diagram.