Quenching and partitioning (Q&P) is an effective way for retaining austenite at room temperature. The actual mechanisms responsible for austenite stabilization are still under debate, since it is impossible to track carbon diffusion with the conventional metallographic tools. The present work depicts several Q&P heat treatments performed on a 0.2 C commercial grade steel by in-situ High Energy X-Ray Diffraction (HEXRD). More specifically, the effect of three different initial quenching temperatures on the microstructural evolution occurring during Q&P was scrutinized in details.

It was shown that about 50% of the initial carbon partitions effectively to austenite. A carbon enrichment up to 0.8 wt% is sufficient to retain austenite at room temperature as grain size refinement contributes to further stabilize austenite. The origin of carbon enrichment in retained austenite depends on the initial quench temperature (Q_T). For low Q_T, corresponding to an initial martensite fraction larger than 0.75, austenite carbon enrichment is ensured by carbon partitioning from supersaturated martensite. For higher Q_T, austenite carbon enrichment results from both carbon partitioning from martensite and carbon rejected during the bainite transformation. The former mechanism proceeds rapidly and already starts during the reheating stage to the partitioning temperature. The latter is slower as the carbon enrichment is coupled to bainite formation.

淬火和分配（Q＆P）是在室温下保持奥氏体的有效方法。奥氏体稳定的实际机制仍在争论中，因为用传统的金相学工具无法追踪碳的扩散。本工作描述了通过原位高能X射线衍射（HEXRD）对0.2 C商业级钢进行的Q＆P热处理。更具体地说，详细研究了三种不同的初始淬火温度对在Q＆P过程中发生的微观结构演变的影响。

结果表明，约有50％的初始碳能有效地分配给奥氏体。高达0.8 wt％的碳富集足以在室温下保留奥氏体，因为晶粒细化有助于进一步稳定奥氏体。残余奥氏体中碳富集的来源取决于初始淬火温度（Q _T）。对于低Q _T，对应于大于0.75的初始马氏体分数，通过从过饱和马氏体中分配碳来确保奥氏体碳富集。对于更高的Q _T，奥氏体碳富集是由于马氏体中的碳分配和贝氏体相变过程中排出的碳所致。前一种机制进展迅速，并且已经在重新加热阶段达到分配温度期间开始。后者较慢，因为碳富集与贝氏体形成有关。