Interface Migration between Martensite and Austenite during Quenching and Partitioning (Q&P) Process

An Fe-0.2C-1.5Si-1.67Mn steel was subjected to quenching and partitioning （Q＆P） process, and the interface migration between martensite and austenite at an elevated partitioning temperature was observed. The interface migration is excluded in constrained paraequilibrium （CPE） model. Based on ＂endpoint＂ predicted by CPE model the thermodynamic condition of interface migration is analyzed, that is, the difference in the chemical potential of iron in both ferrite （martenisite） and austenite produces the driving force of the iron atoms to migrate from one phase to the other phase. In addition, the interface migration can change the austenite fraction; as a result, the austenite fraction at partitioning temperature may be higher than that at quenching temperature through the interface migration, but this phenomenon cannot be explained by CPE model.

CO浓度对316L不锈钢准平衡气体渗碳的影响

采用准平衡气体渗碳工艺,在不同CO浓度的CO/H2/N2混合气体条件下制备了表面强化层,研究CO浓度对316L奥氏体不锈钢渗碳层的微观结构、碳浓度分布、表面纳米硬度和残余应力的影响。结果表明,准平衡气体渗碳层为单一的扩张奥氏体相;当CO浓度小于30%时,渗碳层厚度、表面纳米硬度和压缩残余应力均随CO浓度的提高而提高,当CO浓度高于35%时,渗碳气体碳活度降低,渗碳表面强化效果降低;经470℃条件下准平衡渗碳20 h后,316L不锈钢渗碳层厚度最高可达30μm,表面碳浓度增加至2.6 mass%,导致表面纳米硬度从3 GPa增加至9 GPa,并产生1300 MPa以上的压缩残余应力。

316L不锈钢准平衡气体渗碳层残余应力研究

利用X线衍射仪(XRD)、电子探针(EPMA)、扫描电子显微镜(SEM)、光学显微镜(OM)研究了316L奥氏体不锈钢准平衡气体渗碳层的残余应力、碳质量分数分布以及微观结构。结果表明:准平衡气体渗碳层内为单一的扩张奥氏体相(S相)结构;C原子的渗入及碳质量分数梯度分布,导致渗碳层表面产生极高的压缩残余应力,局部发生塑性变形。

计算Fe-C-X_i合金系在正平衡和准平衡模式下γ→α相变驱动力的简便方法

根据 Fe-C-Xi 合金系的正平衡和准平衡热力学模型,推导了简便的奥氏体-铁素体相变驱动力计算解析式．根据公式,代入合金原始成分和 A_(e3)温度,即可准确计算正平衡和准平衡模式下的奥氏体一铁素体相变驱动力．采用这一方法计算了 Fe-C-Mn-Si-Ni-Cr-Mo-Cu 八元系的正平衡和准平衡奥氏体-铁素体相变驱动力．