The research aims to provide an alternative to austempering treatment of ductile cast iron with a simple and cost-effective heat-treatment process. This goal was accomplished by applying a simple one-step spheroidization heat treatment to the as-cast ductile iron, which would normally possess a coarse pearlitic microstructure to a significant extent. Spheroidization experiments involving isothermal holding below the lower critical temperature (A1) were conducted followed by standard mechanical testing and microstructural characterization for an experimental ductile iron. After improving the spheroidization holding time at a given temperature, the work shows that the ductility and toughness of an as-cast ductile iron can be improved by 90% and 40%, respectively, at the cost of reducing the tensile strength by 8%. Controlled discretization of the continuous cementite network in pearlitic matrix of the ductile iron is deemed responsible for the improved properties. The work also shows that prolonged holding time during spheroidization heat treatment leads to degradation of mechanical properties due to the inhomogenous microstructure formation caused by heterogeneous decomposition and cementite clustering in the material. The main outcome of this work is the demonstration of ductile cast iron’s necking behavior due to spheroidization heat treatment.

该研究旨在通过简单且经济高效的热处理工艺为球墨铸铁的奥氏体回火处理提供替代方案。通过对铸态球墨铸铁进行简单的一步球化热处理即可实现该目标，球墨铸铁通常在很大程度上具有粗糙的珠光体组织。进行了球化实验，包括等温保持在较低的临界温度（A1）以下，然后进行了标准机械测试和实验球墨铸铁的微观结构表征。在改善给定温度下的球化保持时间后，该工作表明，铸态球墨铸铁的延展性和韧性可以分别提高90％和40％，其代价是将拉伸强度降低8％。球墨铸铁珠光体基体中连续渗碳体网络的受控离散被认为是改善性能的原因。这项工作还表明，由于材料中的不均匀分解和渗碳体聚集而导致的不均匀的微观结构形成，在球化热处理过程中延长的保持时间会导致机械性能下降。这项工作的主要成果是通过球化热处理证明了球墨铸铁的颈缩行为。这项工作还表明，由于材料中的不均匀分解和渗碳体聚集而导致的不均匀的微观结构形成，在球化热处理过程中延长的保持时间会导致机械性能下降。这项工作的主要成果是通过球化热处理证明了球墨铸铁的颈缩行为。这项工作还表明，由于材料中的不均匀分解和渗碳体聚集而导致的不均匀的微观结构形成，在球化热处理过程中延长的保持时间会导致机械性能下降。这项工作的主要成果是通过球化热处理证明了球墨铸铁的颈缩行为。