Abstract Fire resistance of structural steels used in buildings is typically evaluated based on the ratio of the yield strength at 600 °C to that at room temperature. Fire-resistant steel shows a yield strength ratio of more than 2:3 between 600 °C and room temperature and achieves an excellent high-temperature strength. Alloying elements such as Mo and Nb are used to improve the strength at elevated temperatures. In this study, the effects of the addition of Mo and Nb on the fire resistance of steel were carefully investigated using SEM, TEM, in-situ TEM, EPMA, 3D-APT, positron annihilation lifetime spectroscopy, and first principles calculations. The fire resistance in Mo and Nb added steel (Mo + Nb) was shown to be drastically improved compared to plain carbon steel (C Mn). The improvement in the high-temperature strength in Mo + Nb was attributed to the precipitation of fine Nb-rich MX particles and a solid solution of Mo and Nb hindering the dislocation movement, and thereby minimizing the dislocation annihilation at elevated temperature. The solid solution of Mo and Nb lowers the vacancy formation energy and allows a vacancy to form more easily, leading to a large lattice distortion which results in a slower dislocation mobility in Mo + Nb.

中文翻译：

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提高含钼和铌耐火钢高温拉伸性能的机制

摘要 建筑用结构钢的耐火性通常根据 600 °C 下的屈服强度与室温下的屈服强度之比来评估。耐火钢在600°C和室温之间的屈服强度比超过2:3，并具有优异的高温强度。合金元素如 Mo 和 Nb 用于提高高温强度。在这项研究中，使用 SEM、TEM、原位 TEM、EPMA、3D-APT、正电子湮没寿命光谱和第一性原理计算仔细研究了添加 Mo 和 Nb 对钢的耐火性的影响。与普通碳钢 (C Mn) 相比，添加 Mo 和 Nb 的钢 (Mo + Nb) 的耐火性显着提高。Mo + Nb 高温强度的提高归因于细小的富含 Nb 的 MX 颗粒的析出以及 Mo 和 Nb 的固溶体阻碍了位错运动，从而最大限度地减少了高温下的位错湮灭。Mo和Nb的固溶降低了空位形成能，使空位更容易形成，导致大的晶格畸变，导致Mo+Nb中位错迁移率变慢。