Abstract

The microstructural evolution and fire-resistant properties in the weld heat-affected zone (HAZ) of Mo and Mo + Nb-added fire-resistant steels were investigated. For this purpose, three Fe-0.1 wt%C-1.5 wt%Mn-0.1 wt%Si steels containing various Mo and Nb contents were prepared. HAZ samples were experimentally simulated using a Gleeble simulator at a welding heat input of 30 and 300 kJ/cm. The yield strength of the HAZ samples was higher than those of base steels at both room temperature and 600 ℃, whereas a greater decrease in the yield strength at 600 ℃ compared to that at room temperature occurred in the HAZ samples than in the base steels, indicating that the fire-resistance deteriorated in the HAZs as compared to the base steels. This is due to the formation of hard phases such as bainite and martensite in the HAZs, i.e., bainite and martensite phase have very high yield strength with high dislocation density at room temperature, while their strengths decrease rapidly at high temperature due to a great annihilation and recovery of dislocations at high temperature. In addition, the fire-resistance of the HAZ improved as the heat input was increased. The alloying of Mo and Nb improved the fire-resistance of both the base steels and the HAZs. Finally, the changes in the microstructures of the base steels and the HAZs upon alloying and the heat input and corresponding effects on the fire-resistance were carefully explored and discussed through transmission electron microscopy analyses, atom probe tomography analyses, and calculations of continuous cooling transformation diagrams.

Graphical abstract

中文翻译：

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耐火钢焊接粗粒热影响区的组织和高温强度及Mo和Nb添加的影响

摘要

研究了Mo和添加了Mo + Nb的耐火钢在焊接热影响区（HAZ）的组织演变和耐火性能。为此目的，制备了三种含有各种Mo和Nb含量的Fe-0.1wt％C-1.5wt％Mn-0.1wt％Si钢。使用Gleeble仿真器以30和300 kJ / cm的焊接热输入对HAZ样品进行了实验仿真。在室温和600℃下，热影响区样品的屈服强度均高于基础钢，而在室温下，与室温下相比，热影响区样品在600℃时的屈服强度下降幅度要大于室温，表明与基础钢相比，热影响区的耐火性下降。这是由于在热影响区中形成了硬质相，如贝氏体和马氏体，即 贝氏体和马氏体相在室温下具有很高的屈服强度和高的位错密度，而由于高温下的大量an没和位错的恢复，它们的强度在高温下迅速降低。另外，随着热量输入的增加，HAZ的耐火性也得到了提高。Mo和Nb的合金化改善了基础钢和HAZ的耐火性。最后，通过透射电子显微镜分析，原子探针层析成像分析和连续冷却转变计算，仔细探讨和讨论了合金化时基体钢和热影响区组织的变化以及热量输入以及对耐火性的相应影响。图。而其强度由于高温下的大量an灭和位错的恢复而在高温下迅速降低。另外，随着热量输入的增加，HAZ的耐火性也得到了提高。Mo和Nb的合金化改善了基础钢和HAZ的耐火性。最后，通过透射电子显微镜分析，原子探针层析成像分析和连续冷却转变计算，仔细探讨和讨论了合金化时基体钢和热影响区组织的变化以及热量输入以及对耐火性的相应影响。图。而其强度由于高温下的大量an灭和位错的恢复而在高温下迅速降低。另外，随着热量输入的增加，HAZ的耐火性也得到了提高。Mo和Nb的合金化改善了基础钢和HAZ的耐火性。最后，通过透射电子显微镜分析，原子探针层析成像分析和连续冷却转变计算，仔细探讨和讨论了合金化时基体钢和热影响区组织的变化以及热量输入以及对耐火性的相应影响。图。随着热量输入的增加，热影响区的耐火性提高。Mo和Nb的合金化改善了基础钢和HAZ的耐火性。最后，通过透射电子显微镜分析，原子探针层析成像分析和连续冷却转变计算，仔细探讨和讨论了合金化时基体钢和热影响区组织的变化以及热量输入以及对耐火性的相应影响。图。随着热量输入的增加，热影响区的耐火性提高。Mo和Nb的合金化改善了基础钢和HAZ的耐火性。最后，通过透射电子显微镜分析，原子探针层析成像分析和连续冷却转变计算，仔细探讨和讨论了合金化时基体钢和热影响区组织的变化以及热量输入以及对耐火性的相应影响。图。

图形概要