During laser-based powder bed fusion, the non-equilibrium solidification conditions promote local elemental segregation, leading to a characteristic microstructure composed of cellular walls. These walls can display either low carbon BCC martensite or FCC retained austenite crystal structures, thus affecting the subsequent isochronal or isothermal martensite to austenite phase transformation mechanisms. In the present study, the effect of the non-homogeneous as-built microstructure on the martensite-to-austenite reversion phenomena was studied for a 18Ni maraging steel fabricated by laser-based powder bed fusion. In-situ synchrotron X-ray diffraction was used to retrieve the austenite volume fraction and lattice parameter evolution during the physical simulation of continuous heating cycles to the austenitic field; and during isothermal tempering cycles throughout the inter-critical tempered martensite + austenite (α’ + γ) field. The as-built microstructure resulted in the expansion of the inter-critical α’ + γ field during very slow heating rates. This was associated to the synergic effects of compositional segregations (anticipating reversion) and pre-existing retained austenite (delaying solubilization). During conventional inter-critical tempering, the as-built microstructure did not fundamentally alter the austenite reversion kinetics, resulting in similar high temperature microstructures at the end of the isothermal stage relative to the solution treated state.

在基于激光的粉末床熔合过程中，非平衡凝固条件促进了局部元素偏析，导致形成由细胞壁组成的特征微观结构。这些壁可以显示低碳 BCC 马氏体或 FCC 残留奥氏体晶体结构，从而影响随后的等时或等温马氏体到奥氏体的相变机制。在本研究中，针对激光粉末床熔融制造的 18Ni 马氏体时效钢，研究了非均匀的竣工组织对马氏体向奥氏体转变现象的影响。在对奥氏体场的连续加热循环的物理模拟过程中，原位同步加速器 X 射线衍射用于检索奥氏体体积分数和晶格参数演化；以及在整个临界间回火马氏体 + 奥氏体 (α' + γ) 场的等温回火循环期间。在非常缓慢的加热速率期间，竣工的微观结构导致临界间 α' + γ 场的扩展。这与成分偏析（预期回复）和预先存在的残余奥氏体（延迟溶解）的协同效应有关。在传统的临界间回火过程中，建成后的微观结构并没有从根本上改变奥氏体回复动力学，导致在等温阶段结束时与固溶处理状态类似的高温微观结构。在非常缓慢的加热速率期间，竣工的微观结构导致临界间 α' + γ 场的扩展。这与成分偏析（预期回复）和预先存在的残余奥氏体（延迟溶解）的协同效应有关。在传统的临界间回火过程中，建成后的微观结构并没有从根本上改变奥氏体回复动力学，导致在等温阶段结束时与固溶处理状态类似的高温微观结构。在非常缓慢的加热速率期间，竣工的微观结构导致临界间 α' + γ 场的扩展。这与成分偏析（预期回复）和预先存在的残余奥氏体（延迟溶解）的协同效应有关。在传统的临界间回火过程中，建成后的微观结构并没有从根本上改变奥氏体回复动力学，导致在等温阶段结束时与固溶处理状态类似的高温微观结构。