Improved process understanding of case hardening with low pressure carburizing based on in-situ X-ray diffraction experiments

在本研究项目中，将基于高时间分辨的原位x射线衍射数据，对低压渗碳硬化过程有一个基本的了解。在项目的继续，在第一个资助期获得的理解将扩展到包括碳化物形成的深入研究，现在补充到包括通常的后处理，即回火和沉淀过程中发生的过程。虽然第一个资助期的重点是表面硬化钢20MnCr5，但在项目的继续中，计划转移到其他典型的表面硬化钢，即Ni和Cr含量增加的钢14NiCrMo13-4和18CrNiMo7-6。由于化学成分的显著差异，预计在渗碳过程中，根据不同的成分，碳化物的形成/溶解将发生不同的行为。由于在助推和扩散阶段碳化物的形成和溶解，预计过程动力学和碳吸收将发生重大变化。在项目的继续，两个工艺室设置（透射和反射几何）将用于获取其他材料的微观结构和应力发展的基本时间和空间分辨信息。通过分析的扩展，从根本上分析了围绕合金初始成分影响发生的机制，从而获得了对该过程的扩展理解。此外，在项目继续进行期间，不仅要对渗碳和淬火工艺步骤进行调查，而且要将调查扩展到对后续回火步骤的考虑，以便更接近工业案例。结合原位WAXS（广角x射线散射）和SAXS（小角x射线散射）实验，将利用现有的工艺室研究碳化物前驱体和渗碳体的形成，以及进一步的微观结构和应力变化。在回火过程中结合原位实验，可以同时记录时间分辨衍射数据和小角度散射信号，不仅可以进行结构分析，还可以同时分析纳米范围内碳化物前驱体的尺寸和分布。此外，在项目的继续进行中，该过程将转移到具有局部复杂几何形状的样品。除其他外，采用适应的测量策略对具有不同纵横比的盲孔进行原位调查。借助对最终状态的综合分析，伴随的高分辨率非原位调查也将评估残余应力和微观结构如何受到局部影响。

In the research project, a fundamental understanding of the process of case hardening with low pressure carburization to be obtained on the basis of highly time-resolved in situ X-ray diffraction data. In the continuation of the project, the understanding gained in the first funding period will be extended to include in-depth investigations of carbide formation and now supplemented to include the usual post-treatment by tempering and the precipitation processes that take place in the process. While the focus in the first funding period was on the case-hardening steel 20MnCr5, in the continuation of the project the transfer to other typical case-hardening steels, the steels 14NiCrMo13-4 and 18CrNiMo7-6 with increasing Ni and Cr contents, is planned. Due to the significantly different chemical composition, it is expected that, depending on the composition, a different behavior will occur in the carbide formation/dissolution during carburizing. It is expected that the process kinetics and carbon uptake will change significantly due to the formation and dissolution of carbides during the boost and diffusion phases. In the continuation of the project, both process chamber setups (transmission and reflection geometry) will be used to obtain fundamental time- and spatially-resolved information on the development of the microstructure and stresses for the other materials. Through the extension of the analyses, the mechanisms occurring around the influence of the initial alloy composition are fundamentally analyzed and thus an extended comprehension of the process is gained.Furthermore, during the continuation of the project, not only the carburizing and quenching process steps are to be investigated, but the investigations are to be extended to the consideration of the subsequent tempering step in order to come closer to the industrial case. In combined in situ WAXS (wide angle X-ray scattering) and SAXS experiments (small angle X-ray scattering), the formation of carbide precursors and cementite, together with further microstructure and stress changes, will be investigated using the existing process chamber. In this combined in situ experiment during tempering, time-resolved diffraction data can be recorded simultaneously with small-angle scattering signals, which allows not only structural analysis but also simultaneous analysis of the size and distribution of the carbide precursors in the nanometer range. Furthermore, the process will be transferred to samples with locally complex geometries in the continuation of the project. Among other things, blind holes with different aspect ratios are to be investigated in situ by using adapted measurement strategies. With the help of comprehensive analyses of the final state, accompanying high-resolution ex situ investigations will also assess how the residual stresses and the microstructure are influenced locally.