SGER: A Novel Thermomagnetic Austempering Process

这是材料研究部授予韦恩州立大学的探索性研究（SGER）的一笔小额赠款，用于探索一种名为“热磁等温淬火”的新工艺。“据推测，在磁场中进行两步等温淬火处理将导致铁碳合金具有高屈服强度，疲劳强度，断裂韧性和冲击强度，这些特性的组合通常不会在结构合金中获得。凭借这一奖项，Putatunda教授将把这一创新工艺应用于奥贝球铁（ADI），奥贝球铁是一种因其在运输、国防和制造业中的众多应用而被选中的材料。作为该工艺发展的一个组成部分，奥氏体向铁素体和高碳奥氏体相变的自由能变化的热力学分析已经发展。该分析表明，在外部施加的磁场下，铁素体成核的驱动力应该增加，从而在材料中产生非常细晶粒的显微组织。这一分析模型的适用性和有效性的假设在推导它将被检查。该研究将确定ADI的热磁等温淬火是否在奥氏体相中产生具有非常高的碳含量的超细晶显微组织。研究了碳在奥贝球铁显微组织发展中的作用以及细化铁素体和奥氏体对奥贝球铁断裂韧性和高周疲劳强度的影响。该研究将有助于提高铁基物理冶金学的现有知识水平。该项目将确定在磁场中两步等温淬火工艺的可行性和工艺参数的正确组合，以创建由（a）非常大体积分数的细铁素体和奥氏体，（B）奥氏体中非常高的碳含量和（c）稳定的奥氏体组成的独特显微组织。这种独特的微观结构将在ADI合金中提供高屈服强度、疲劳强度、冲击强度和断裂韧性。热磁等温淬火工艺可以提供高可靠性、低成本、高耐久性的工程合金，从而对材料加工行业产生重大影响。此外，将这种新方法应用于其他金属合金，如碳钢、铁镍合金和镍基超合金，以生产具有独特机械性能组合的合金。 学生培训和教学将是这一过程发展的组成部分。

This small grant for exploratory research (SGER) award by the Division of Materials Research to Wayne State University is to explore a new process termed "thermomagnetic austempering." It is hypothesized that applying a two-step austempering treatment within a magnetic field will result in iron-carbon alloys with high yield strength, fatigue strength, fracture toughness and impact strength, a combination of properties not normally obtained in structural alloys. With this award, Professor Putatunda will apply this innovative process to austempered ductile cast iron (ADI), a material chosen because of its numerous applications in the transportation, defense and manufacturing industries. As an integral part of the development of this process, a thermodynamic analysis of free energy change for the phase transformation of austenite to ferrite and high carbon austenite has been developed. This analysis indicates that the driving force for ferrite nucleation should increase under an externally applied magnetic field, resulting in a very fine-grained microstructure in the material. The applicability of this analytical model and the validity of the assumptions made in deriving it will be examined. The research will establish if thermomagnetic austempering of ADI creates an ultra-fine grained microstructure with very high carbon content in the austenite phase. The role of carbon in the development of the microstructures of ADI and the influence of refined ferrite and austenite on the fracture toughness and high cycle fatigue strength of ADI will be established. The research will contribute to advancing the present state of knowledge in ferrous physical metallurgy.The project will establish the feasibility of the two-step austempering process in a magnetic field and the right combination of processing parameters that creates a unique microstructure consisting of (a) a very large volume fraction of fine ferrite and austenite, (b) a very high carbon content in austenite, and (c) a stable austenite. This unique microstructure will provide high yield strength, fatigue strength, impact strength and fracture toughness in ADI alloys. The thermomagnetic austempering process could have a significant impact in materials processing industries by providing high-reliability, low-cost engineering alloys with great durability. Furthermore, it may be possible to apply this new approach to other metal alloys such as carbon steels, iron-nickel alloys, and nickel-based superalloys to produce alloys with unique combinations of mechanical properties. Student training and teaching will be integral part of this process development.