Prediction of the laves phase morphology in Fe-Cr-W-C quaternary steels with the aid of system free energy concept
Prediction of the laves phase morphology in Fe-Cr-W-C quaternary steels with the aid of system free energy concept
复制标题
借助系统自由能概念预测 Fe-Cr-W-C 四元钢中的 Laves 相形貌
DOI：
10.2355/isijinternational.42.1423
复制
发表时间：
2002
影响因子：
1.8
通讯作者：
T. Miyazaki
中科院分区：
文献类型：
--
作者：
Y. Murata;T. Koyama;M. Morinaga;T. Miyazaki
为了阐明先进高Cr耐热铁素体钢的显微组织演变，基于Koyama和Miyazaki提出的系统自由能理论，计算了Fe-10mass%Cr-W-C四元钢的时间-成分-温度图。使用这样的自由能系统可以预测钢的微观结构，该自由能由钢中基体和析出物之间的化学自由能、界面能和应变能组成。在这项研究中，我们的注意力集中在作为析出物的Laves相上，因为该相是在最近开发的耐热铁素体钢中形成的，并且很大程度上影响其蠕变强度。对 Fe-Cr-W-C 四元钢进行的计算得出以下结论： (i) 在 W 含量低于 0.4 mol%（约 1.4 质量% W）的钢中，即使在 923K 下长期时效后也不会形成 Laves 相； (ii)在含有0.4mol％W～1.05mol％W(约3.5质量％W)的钢中，即使在923K时效初期也仅析出粒状的Laves相。 (iii) 如果钢中 W 含量超过 1.05 mol%，则 Laves 相的形态变化会从细小的连贯析出物转变为粒状析出物，并在钢中按规则的时效顺序发生； (iv) 在准二元相图中确定 Laves 相的相干沉淀线作为 W 含量的函数。理论上获得的这些发现与实验结果是一致的。
In order to elucidate the microstructure evolution in advanced high Cr heat resisting ferritic steels, a time-composition-temperature diagram of Fe-10mass%Cr-W-C quaternary steels is calculated on the basis of the system free energy theory proposed by Koyama and Miyazaki. Microstructures of the steels are predictable using such a system free energy consisting of chemical free energy, interface energy and strain energy between the matrix and precipitates in the steels. In this study, our attention is focused on the Laves phase as the precipitate, because this phase is formed in recently developed heat resisting ferritic steels and affects their creep strength largely. The calculations conducted in the Fe-Cr-W-C quaternary steels lead to the following findings: (i) The Laves phase is not formed in those steels containing less than 0.4 mol% W (about 1.4 mass% W) even after a long term aging at 923K; (ii) Only granular Laves phase precipitates in the steel containing 0.4 mol% W to 1.05 mol% W (about 3.5 mass% W) even in the early stage of aging at 923 K; (iii) The morphological change of the Laves phase from the fine coherent precipitate to the granular one occurs in a regular aging sequence in the steel if it contains more than 1.05 mol% W; (iv) Coherent precipitation line for the Laves phase is determined in the quasi-binary phase diagram as a function of the W content. These findings obtained theoretically are consistent with experimental results.