Quantification of Structural Transformations during Heat Treatment in Ultra-high Carbon Steels

钢是一种以铁和碳为主要成分的金属材料。根据含碳量和加工工艺的不同，钢的性能会有很大的不同。超高碳含量的钢表现得更像陶瓷，而不是金属；它们非常硬，非常脆。这些钢主要用于工具部件，以塑造较软的钢和其他金属，但如果它们的脆性可以降低，则可以看到更大的用途。迄今为止，通过加热和成型循环来降低脆性，但在大规模生产中实施这些方法具有挑战性。可以通过简单的单独加热来降低这些材料的脆性；然而，现有的热处理是能源密集型的，远非优化。该奖项支持对超高碳钢在加热过程中组织转变行为的基础研究。该研究利用新颖的实验方法实时观察钢结构在加热过程中的变化，并开发出可用于优化加工和性能的新指标。这些基础研究将改进热处理策略，使超高碳钢的生产具有更好的性能组合，同时减少能源消耗。本研究的结果还将向材料科学专业的本科生介绍现代炼钢的基本主题，并将向初高中学生介绍数字图像分析和用于表征材料的方法。与其他低碳含量的钢相比，超高碳钢具有更高的硬度和强度。然而，这些钢中碳化物的高含量使它们对许多结构应用来说太脆了。该项目旨在研究含有超高碳含量（1.7-2.3重量%）的钢在高温下的微观组织转变，以及这些转变对机械性能的影响：韧性、硬度、强度和延展性。本研究将采用原位共聚焦扫描激光显微镜和非原位电子显微镜来研究和量化显微组织演变，特别是研究时间、温度和合金化学对碳化物溶解动力学及其在热处理钢中的最终分布的影响。重要力学性能的综合评估将与最终的微观组织状态相关。这些追求将产生一个分析模型，可以准确地描述超高碳钢热处理温度范围内碳化物的溶解和沉淀行为。

Steel is a metallic material with iron and carbon as the primary components. The properties of steel can vary greatly depending on carbon level and processing. Steels with ultra-high carbon levels behave more like ceramics than metals; they are extremely hard and very brittle. These steels are primarily utilized in tool components to shape softer steels and other metals, but could see greater usage if their brittleness can be reduced. To date, brittleness has been reduced by cycles of heating and forming, methods that are challenging to implement on a large production scale. It is possible to decrease brittleness in these materials by simply heating alone; however existing heat treatments are energy intensive and far from optimized. This award supports fundamental research on the structural transformation behavior of ultra-high carbon steels during heating. The research utilizes novel experimental methods to observe changes to the steel structure in real time during heating and to develop new metrics that can be used to optimize processing and properties. These fundamental studies will lead to improved heat treatment strategies that will enable production of ultra-high carbon steels with improved combinations of properties while also reducing energy usage. Results from this research will also introduce materials science undergraduate students to fundamental topics of modern steelmaking and an outreach component will expose middle and high school students to digital image analysis and methods used to characterize materials. Ultra-high carbon steels can exhibit superior hardness and strength compared to other steels of lower carbon contents. However, the high fraction of carbides in these steels render them too brittle for many structural applications. This project seeks to investigate microstructural transformations at elevated temperatures in steels containing ultrahigh carbon contents (1.7-2.3 weight percent) and the impact of these transformations on mechanical properties: toughness, hardness, strength and ductility. This study will apply in-situ confocal scanning laser microscopy and ex-situ electron microscopy to study and quantify microstructural evolution, specifically examining the effects of time, temperature and alloy chemistry on carbide dissolution kinetics and their final distribution in heat treated steels. A comprehensive assessment of important mechanical properties will be correlated to the final microstructural state. These pursuits will result in an analytical model that can accurately describe carbide dissolution and precipitation behavior at temperature ranges employed for heat treatments of ultra-high carbon steels.