The usage of an appropriate shield gas for laser beam powder bed fusion (LB-PBF) of the popular 17−4 precipitation hardened (PH) stainless steel (SS) has long been debated in the additive manufacturing (AM) community. While the inertness of Ar is often desirable as the shield gas from unwanted chemical reactions, its low solubility combined with the violent nature of the melt pool inevitably results in the formation of defects that are detrimental to the fatigue performance of the alloy. On the other hand, although N₂ is reactive with some alloys (e.g. titanium), it may have remarkable favorable effects on the mechanical properties and fatigue performance of 17−4 PH SS. In this article, the advantageous effects of N₂ as an in-process micro-/defect-structure refiner of LB-PBF 17−4 PH SS, and in turn, an enhancer of its mechanical/fatigue properties are demonstrated. It is shown that, compared to Ar, the use of N₂ shield gas induces more retained austenite, refines grains, makes the melt pools deeper, produces fewer and smaller pores, and as a result, slightly improves tensile properties, moderately improves crack growth resistance, and considerably improves axial fatigue properties in the high cycle regime.

在增材制造（AM）社区中，长期以来一直在争论使用适当的保护气体用于流行的17-4沉淀硬化（PH）不锈钢（SS）的激光束粉末床熔合（LB-PBF）。尽管通常需要Ar的惰性作为保护气体，以防止不必要的化学反应，但Ar的低溶解度与熔池的剧烈反应相结合，不可避免地导致形成有害于合金疲劳性能的缺陷。另一方面，尽管N ₂与某些合金（例如钛）具有反应性，但它​​可能对17-4 PH SS的机械性能和疲劳性能产生显着的有利影响。在本文中，N ₂的有利作用作为LB-PBF 17-4 PH SS的加工中微/缺陷结构细化剂，又证明了其机械/疲劳性能的增强剂。结果表明，与Ar相比，使用N ₂保护气会产生更多的残留奥氏体，细化晶粒，使熔池更深，产生更少和更小的孔，结果稍微改善了拉伸性能，适度改善了裂纹扩展阻力，并在高循环工况下显着改善轴向疲劳性能。