Investigations to the mechanisms of the layer formation using gas nitriding on remelted ledeburitic surfaces of unalloyed cast irons

非合金铸铁重熔莱氏体表面气体渗氮成膜机理研究

• 批准号: 286878415
• 负责人: Professor Dr.-Ing. Horst Biermann, since 5/2023
• 金额: --
• 依托单位: Institut für Werkstofftechnik
• 依托单位国家: 德国
• 项目类别: Research Grants
• 资助国家: 德国
• 项目状态: 未结题
• 来源: https://gepris.dfg.de/gepris/projekt/286878415?language=en
• 关键词: Investigations; mechanisms; layer; formation; using

Within the framework of the project (3+2 years), the layer formation mechanism during nitriding for graphitic and remelted (ledeburitic) high C and Si cast iron alloys was researched and clarified for the first time. The chosen approach of carrying out the investigations on model alloys as well as on technical alloys allowed a separation of cause and effect and thus simplified the definition of objective functions. As a result, a model was developed for the time-dependent phase and precipitation formation in the different areas of the nitriding layer (compound/diffusion layer) depending on the microstructural constituents (eutectic and eutectoid cementite, ferrite, silicocarbide) of the white solidified Fe-xC-ySi alloys. Nitriding experiments at 540 °C on Fe-Si and Fe-C-Si alloys gave new conclusions on the Fe-Si-C-N phase diagram (metastable considering the amorphous Si nitride phase X). It was shown that the Mn and Cu contents additionally present in the cast iron alloys have an influence on the phase formation in the compound layer. While Mn obviously promotes the formation of ε-nitride, Cu supports the formation of γ‘-nitride. In addition, in the presence of Mn and Cu, there is a coupled effect that accelerates the precipitation of the Si-containing nitride. Mn apparently prevents the diffusion of carbon and thus the transformation of the eutectic cementite into α-Fe.The wear and corrosion behaviour of the nitrided cast irons is mainly determined by the inhomogeneous, not fully formed compound layers due to the graphite. In contrast, the stress behaviour of the combined treated edge layers is significantly better and is mainly determined by the phase composition of the compound layers.The aim of the continuation period applied for here is to investigate and analyse the essential findings on the nitriding mechanism of combined treated cast iron edge layers with regard to their effects on the depth-dependent (in the removal process) tribological (ball-plate test) and corrosive (current density potential curve) stress behaviour (damage mechanisms). A target-oriented delimitation of the treatment variants for an in-depth analysis of the stress behaviour on the basis of ablation tests in 3 levels was therefore carried out on the basis of different nitride layer structures and includes the limit states (in addition to Si nitride): I. ε-rich; II. γ'-rich; III. ε/ γ' (≈ 50:50 %). With the extensive database thus determined, the developed model conception of the nitriding mechanism is to be extended by the phase- and depth-dependent stress behaviour on the one hand. On the other hand, practical specifications for the nitriding process and the development of a nitriding-suitable alloy design for cast iron materials are to be derived and particularly suitable layer structures identified.

在该项目（3+2年）的框架内，首次研究和阐明了石墨和重熔（莱氏体）高碳和高硅铸铁合金在氮化过程中的层形成机理。所选择的对模型合金和工业合金进行研究的方法允许分离因果关系，从而简化了目标函数的定义。因此，开发了一个模型的时间依赖性相和沉淀形成在不同的区域的氮化层（化合物/扩散层）取决于微观结构成分（共晶和共析铁素体，铁素体，碳化硅）的白色凝固的Fe-xC-ySi合金。在540 °C下对Fe-Si和Fe-C-Si合金的氮化实验给出了关于Fe-Si-C-N相图的新结论（考虑非晶Si氮化物相X的亚稳）。结果表明，额外存在于铸铁合金中的Mn和Cu含量对化合物层中的相形成有影响。Mn明显促进ε-氮化物的形成，Cu支持ε ′-氮化物的形成。此外，在Mn和Cu的存在下，存在加速含Si氮化物的沉淀的耦合效应。Mn明显地阻止了碳的扩散，从而阻止了共晶碳化物向α-Fe的转变。氮化铸铁的磨损和腐蚀行为主要取决于石墨形成的不均匀、不完全的化合物层。与此相反，复合处理的边缘层的应力行为明显更好，主要由化合物层的相组成决定。此处应用的延续期的目的是调查和分析关于复合处理铸铁边缘层的氮化机理的基本发现，以及它们对深度相关的（在去除过程中）摩擦学（球板试验）和腐蚀（电流密度电位曲线）应力行为（损坏机制）。因此，基于不同的氮化物层结构进行了针对目标的处理变体定界，以用于基于3个级别的烧蚀测试对应力行为进行深入分析，并且包括极限状态（除了Si氮化物之外）：ε-rich; II.富马酸; III.ε/ γ'（ε 50：50%）。随着广泛的数据库，从而确定，开发的模型概念的氮化机制是扩展相和深度依赖的应力行为一方面。另一方面，氮化工艺的实用规范和开发铸铁材料的氮化合适的合金设计是派生的，特别是合适的层结构确定。