Surface transformation treatments like laser surface melting and laser surface hardening have been mostly developed in austempered ductile iron and gray cast iron. In this work, we explore the effects of the linear laser energy of the treatment on the microstructure, chemical composition, and hardness of ferritic nodular cast iron, using a fiber delivery diode laser. We found changes in the microstructure above 120 J/mm, characterized by the presence of graphite nodules surrounded by martensitic/dendritic shells. Above 316 J/mm, Fe3C and γ-Fe2O3 phases arise, together with a saturation of the microhardness around 1000 HV0.3 within the first 200 μm of depth, and of the surface hardness around 90 HR15N. Changes in microstructure and composition due to the laser treatment directly affect the thermal diffusion between the surface-modified zones and the nodular cast iron bulk. Our work highlights the importance of the linear energy in the design and planning of laser treatments.

中文翻译：

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铁素体球墨铸铁表面激光处理：线性能量对显微组织、化学成分和硬度的影响

激光表面熔化和激光表面硬化等表面转变处理主要用于奥氏体球墨铸铁和灰口铸铁。在这项工作中，我们使用光纤传输二极管激光器探索了处理的线性激光能量对铁素体球墨铸铁的微观结构、化学成分和硬度的影响。我们发现 120 J/mm 以上的微观结构发生了变化，其特征是存在被马氏体/枝晶壳包围的石墨结节。超过 316 J/mm 时，出现 Fe3C 和 γ-Fe2O3 相，同时在前 200 μm 深度内显微硬度达到 1000 HV0.3 左右，表面硬度达到 90 HR15N 左右。由于激光处理引起的微观结构和成分的变化直接影响表面改性区域和球墨铸铁块体之间的热扩散。我们的工作强调了线性能量在激光治疗设计和规划中的重要性。