Abstract Current strategies for the 3rd generation of advanced high strength steels focus on the creation of a multiphase microstructure containing substantial amounts of retained austenite to enhance the mechanical properties. In the case of quenching and partitioning (Q&P) steels, the stabilization of austenite is achieved by carbon diffusion from the supersaturated martensite into the austenite, but carbon partitioning is often jeopardized by competing reactions such as carbide formation. In the present study, in-situ high-energy X-ray diffraction (HEXRD) was used to study the transformation kinetics during Q&P processing, and especially carbide formation at higher partitioning temperatures. It was found that this carbide precipitation resulted mainly from martensite tempering and partially also from a decomposition of the austenite. The detection of minor diffraction peaks that appeared during the partitioning step was assigned to θ- and χ-carbide formation, which was supported by correlative atom probe tomography (APT) and transmission electron microscopy (TEM). Additionally, NbC was detected by APT, but the amount was obviously too low to be detected by HEXRD. The applied methods are finally compared with regard to their applicability for carbide identification in Q&P steels.

中文翻译：

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使用高分辨率方法组合表征 Q&P 钢中的碳化物

摘要 第三代先进高强度钢的当前策略侧重于创建包含大量残余奥氏体的多相微观结构，以提高机械性能。在淬火和分配 (Q&P) 钢的情况下，奥氏体的稳定是通过碳从过饱和马氏体扩散到奥氏体来实现的，但碳分配通常会受到竞争反应（如碳化物形成）的影响。在本研究中，原位高能 X 射线衍射 (HEXRD) 用于研究 Q&P 加工过程中的转变动力学，尤其是在较高分配温度下的碳化物形成。发现这种碳化物析出主要是由于马氏体回火，部分是由于奥氏体的分解。在分配步骤中出现的次要衍射峰的检测被指定为 θ- 和 χ- 碳化物形成，这得到相关原子探针断层扫描 (APT) 和透射电子显微镜 (TEM) 的支持。此外，APT 检测到 NbC，但数量明显太少，HEXRD 检测不到。最后比较了所应用的方法在 Q&P 钢中碳化物识别的适用性。