We have investigated the multiple influences of Cu addition into the NiAl-strengthened medium Mn steels (MMS) on the precipitation and austenitic reversion during the different ageing processes and the resultant mechanical properties, and conclude that such an alloying is the exceptional approach of simultaneously improving yield strength, work hardening sustainability and plasticity all together due to the following reasons. First, it promotes the precipitation and growth of NiAl for greater precipitation hardening because the prior Cu-rich precipitation provides the dispersed nucleation sites for NiAl in company with Ni/Mn enrichment at the interface of Cu and martensite. Next, such an enrichment also accelerates the nucleation and growth of austenite on the Cu-NiAl co-precipitates during the ageing, leading to larger fraction of austenite grains retained with coarser size than those in the non-Cu-alloyed counterpart. Particularly, the presence of Cu nanoparticles in the reverted austenite may result in not only strengtheneing but also the increase of Mn content in the interiof of austenite by retarding the migrating phase interface, both improving mechanical stability of retained austenite (RA). Consequently, the Cu alloying significantly increases yield strength, work hardening sustainability and ductility simutaeously due to greater precipitation strengthening and more durable austenite-to-martensite transformation during deformation.

中文翻译：

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Cu合金化对NiAl强化中Mn钢析出、奥氏体回归和力学性能的影响


我们研究了在 NiAl强化中锰钢 （MMS） 中添加铜对不同时效过程中沉淀和奥氏体回归以及由此产生的机械性能的多重影响，并得出结论，由于以下原因，这种合金化是同时提高屈服强度、加工硬化可持续性和塑性的特殊方法。首先，它促进了 NiAl 的沉淀和生长，以实现更大的沉淀硬化，因为先前的富铜沉淀为 NiAl 提供了分散的成核位点，同时在 Cu 和马氏体界面处富集了 Ni/Mn。接下来，这种富集还加速了奥氏体在时效过程中 Cu-NiAl 共沉淀物上的成核和生长，导致奥氏体晶粒比非铜合金晶粒中的奥氏体晶粒保留得更大比例，但尺寸更粗。特别是，还原奥氏体中 Cu 纳米颗粒的存在不仅可能导致增强，而且通过延迟迁移相界面，奥氏体内部的 Mn 含量增加，两者都提高了残余奥氏体 （RA） 的机械稳定性。因此，由于变形过程中更大的沉淀强度和更持久的奥氏体到马氏体转变，Cu合金化显著提高了屈服强度、加工硬化可持续性和延展性。