Oxidation phenomena of medium-Mn steels

中锰钢，也被称为第三代先进高强度钢，具有通过形变处理以应用为导向调整其性能的非凡潜力。由于含锰量高，在空冷过程中形成的马氏体在临界区的退火过程中转变为奥氏体，通过元素再分布(分配)提高了奥氏体的稳定性。在最终冷却过程中，形成了一种显微组织，这种组织除了具有很高的延展性外，还表现出显著的应变硬化潜力。然而，相对较高的锰浓度是有益的，也是有害的。锰对氧有很高的亲和力，即使在低氧分压下，也会在热处理过程中形成氧化层，从而严重影响防腐涂层的附着力。对这些钢在热处理过程中的氧化行为的了解主要基于工业经验，而对这些钢的长期氧化行为，特别是电厂钢的长期氧化行为，已经进行了定量的研究和广泛的了解。在本项目范围内，将对中锰钢在400°C至900°C温度下的氧化早期阶段进行实验量化，并就相关的传输和相形成过程进行描述。为了阐明锰、硅和铝对氧化和相形成的重要性，实验室生产了成分精确控制的高纯熔体，并对微观结构进行了专门的调整。氧化动力学的分析，形成的氧化相及其形态的局部识别，以及氧化物和金属中浓度分布的局部和整体测定，构成了基于有限差分和CALPHAD方法的数值模型的基础，利用该模型可以预测这些钢的氧化行为。根据高纯度实验室熔体的结果，选择有限数量的工业熔体并使用通常的伴生元素来生产，以测试所确定的机制的可转移性。在工业熔体的基础上，采用适当的工艺控制，确定了中锰钢在适合热镀锌表面进行退火热处理的程度。预计该项目的结果将通过控制温度和环境气氛，通过中锰钢的组织结构，以成本效益的方式控制不同氧化相的形成。此外，优先形成合适的氧化物相在氧化的早期阶段，氧化物的形成是最小的，这减少了材料损失，改善了二氧化碳平衡。

Medium Mn-steels, also referred to as 3rd generation Advanced High Strength Steels, have an extraordinary potential for an application-oriented adjustment of their properties via thermomechanical treatment. Martensite, which form during air cooling due to the high content of manganese, is transformed into austenite during intercritical annealing, the stability of which is increased by elemental redistribution (partitioning). During the final cooling, a microstructure is formed which, in addition to high ductility, also exhibits a pronounced strain hardening potential. However, the comparatively high manganese concentration is both a beneficial and detrimental. Manganese has a high affinity for oxygen, which leads to the formation of an oxide layer during heat treatment, even at low oxygen partial pressures, which in turn severly impairs the adhesion of anti-corrosion coatings. Knowledge of the oxidation behavior of these steels during such thermomechanical treatment with comparably short annealing times of a few minutes is largely based on industrial experience, whereas the long-term oxidation behavior, especially of power plant steels, has already been quantitatively investigated and is widely understood. Within the scope of this project, the early stage of oxidation of medium manganese steels at temperatures between 400°C and 900°C is to be experimentally quantified and described with regard to the relevant transport and phase formation processes. To clarify the importance of Mn, Si and Al for oxidation and phase formation, high-purity laboratory melts with a precisely controlled composition are produced and the microstructure is specifically adjusted. The analysis of the oxidation kinetics, the local identification of formed oxide phases and their morphology as well as the local and integral determination of the concentration distribution in the oxide and metal form the basis for a numerical model based on finite differences and the CALPHAD method, with which the oxidation behavior of these Steels should become predictable. Based on the results of the high-purity laboratory melts, a limited number of industrial melts are selected and produced with the usual accompanying elements in order to test the transferability of identified mechanisms. On the basis of industrial melts, the extent to which medium-Mn steels can be annealed with a surface suitable for hot-dip galvanization is determined using suitable process control. The results of the project are expected provide access to cost-effectively controlling the formation of different oxide phases through the microstructure of a medium-Mn steel and by controlling the temperature and the ambient atmosphere. In addition, preferential formation of suitable oxide phases in the early stages of oxidation, the formation of oxide is to be minimized, which reduces material loss and improves the CO2 balance.