Carbon partitioning is the core design of quenching and partitioning (Q&P) process, which significantly improves the stability of retained austenite (RA). However, the inevitable precipitation of transition carbides leads to a substantial consumption of carbon atoms. Conversely, in the present study, we have realized the full inhibition of transition carbides in martensitic lath and, in turn, improved the carbon utilization efficiency to stabilize austenite. During fast austenitization from Mn-partitioned pearlite, Mn-heterogeneous high-temperature austenite is produced and more carbon atoms are trapped in the Mn-enriched region. Following Q&P, the alternative film RA and lath martensite in nanoscale is obtained, in which RA is enriched with Mn and C while the lath martensite is depleted with Mn and C. On one hand, the depletion of Mn and C in lath martensite strongly reduces the driving force and nucleation rate for carbide precipitation. On the other hand, the nanoscale microstructure and heterogeneous Mn distribution effectively accelerate carbon diffusion from lath martensite into austenite. Therefore, carbide precipitation is substantially inhibited in lath martensite due to the kinetic mismatch between fast carbon diffusion and sluggish carbide precipitation. This study demonstrates that chemical heterogeneity provides a novel pathway to enhance carbon partitioning efficiency and tensile properties in Q&P steels.

中文翻译：

---

淬火和分配过程中化学不均匀性在碳扩散中的作用

碳分配是淬火分配（Q&P）工艺的核心设计，可显着提高残余奥氏体（RA）的稳定性。然而，过渡碳化物不可避免的沉淀导致碳原子的大量消耗。相反，在本研究中，我们实现了马氏体板条中过渡碳化物的充分抑制，进而提高了碳利用效率以稳定奥氏体。在Mn配分珠光体快速奥氏体化过程中，产生Mn异质高温奥氏体，并且更多的碳原子被捕获在富Mn区域。经过Q&P后，得到了纳米级的替代膜RA和板条马氏体，其中RA富Mn和C，而板条马氏体贫Mn和C。一方面，板条马氏体中Mn和C的贫化强烈降低了板条马氏体的强度。碳化物析出的驱动力和成核速率。另一方面，纳米级的微观结构和不均匀的Mn分布有效地加速了碳从板条马氏体到奥氏体的扩散。因此，由于快速的碳扩散和缓慢的碳化物析出之间的动力学不匹配，板条马氏体中的碳化物析出被显着抑制。这项研究表明，化学异质性为提高 Q&P 钢的碳分配效率和拉伸性能提供了一条新途径。