Abstract

In high-temperature applications, like exhaust manifolds, cast irons with a ferritic matrix are mostly used. However, the increasing demand for higher-temperature applications has led manufacturers to use additional expensive materials such as stainless steels and Ni-resist austenitic ductile cast irons. Thus, in order to meet the demand while using low-cost materials, new alloys with improved high-temperature strength and oxidation resistance must be developed. In this study, thermodynamic calculations with Thermo-Calc software were applied to study a novel ductile cast iron with a composition of 3.5wt% C, 4wt% Si, 1wt% Nb, 0–4wt% Al. The designed compositions were cast, and thermal analysis and microstructural characterization were performed to validate the calculations. The lowest critical temperature of austenite to pearlite eutectoid transformation, i.e., A₁, was calculated, and the solidification sequence was determined. Both calculations and experimental data revealed the importance of aluminum addition, as the A₁ increased by increasing the aluminum content in the alloys, indicating the possibility of utilizing the alloys at higher temperature. The experimental data validated the transformation temperature during solidification and at the solid state and confirmed the equilibrium phases at room temperature as ferrite, graphite, and MC-type carbides.

中文翻译：

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铝添加改性的新型球墨铸铁的热和微观结构表征

摘要

在高温应用中，例如排气歧管，通常使用具有铁素体基体的铸铁。但是，对高​​温应用的需求不断增加，导致制造商使用其他昂贵的材料，例如不锈钢和耐镍奥氏体球墨铸铁。因此，为了在使用低成本材料的同时满足需求，必须开发具有改善的高温强度和抗氧化性的新合金。在这项研究中，使用Thermo-Calc软件进行的热力学计算研究了一种新型球墨铸铁，其成分为3.5wt％C，4wt％Si，1wt％Nb，0–4wt％Al。设计的成分进行了铸造，并进行了热分析和微观结构表征以验证计算结果。计算A ₁，并确定固化顺序。计算和实验数据均显示出铝添加的重要性，因为通过增加合金中铝的含量来增加A ₁，这表明在更高温度下利用合金的可能性。实验数据验证了凝固过程中和固态时的相变温度，并确认了室温下的平衡相为铁素体，石墨和MC型碳化物。