The microstructures of additively manufactured (AM) precipitation-hardenable stainless steels 17-4 and 15-5 were investigated and compared to those of conventionally produced materials. The residual N found in N₂-atomized 17-4 powder feedstock is inherited by the additively produced material, and has dramatic effects on phase stability, microstructure, and microstructural evolution. Nitrogen is a known austenite stabilizing element, and the as-built microstructure of AM 17-4 can contain up to 90 pct or more retained austenite, compared to the nearly 100 pct martensite structure of wrought 17-4. Even after homogenization and solutionization heat treatments, AM 17-4 contains 5 to 20 pct retained austenite. In contrast, AM 15-5 and Ar-atomized AM 17-4 contain < 5 pct retained austenite in the as-built condition, and this level is further decreased following post-build thermal processing. Computational thermodynamics-based calculations qualitatively describe the observed depression in the martensite start temperature and martensite stability as a function of N-content, but require further refinements to become quantitative. A significant increase in the volume fraction of fine-scale carbide precipitates attributed to the high N-content of AM 17-4 is also hypothesized to give rise to additional activation barriers for the dislocation motion required for martensite nucleation and subsequent growth. An increase in the volume fraction of carbide/nitride precipitates is observed in AM 15-5, although they do not inhibit martensite formation to the extent observed in AM 17-4.

对增材制造 (AM) 沉淀硬化不锈钢 17-4 和 15-5 的微观结构进行了研究，并将其与传统生产材料的微观结构进行了比较。_{N 2}中发现的残留 N-雾化的 17-4 粉末原料由增材制造的材料继承，对相稳定性、微观结构和微观结构演变具有显着影响。氮是一种已知的奥氏体稳定元素，AM 17-4 的制造微观结构可包含高达 90% 或更多的残余奥氏体，而锻造 17-4 的马氏体结构接近 100%。即使经过均质化和固溶化热处理，AM 17-4 仍含有 5 至 20% 的残余奥氏体。相比之下，AM 15-5 和 Ar 雾化 AM 17-4 在制造状态下含有 < 5% 的残余奥氏体，并且这一水平在制造后热处理后进一步降低。基于计算热力学的计算定性描述了观察到的马氏体开始温度和马氏体稳定性随 N 含量的下降，但需要进一步改进才能定量。由于 AM 17-4 的高 N 含量，细小碳化物析出物体积分数的显着增加也被假设为马氏体成核和后续生长所需的位错运动产生了额外的活化势垒。在 AM 15-5 中观察到碳化物/氮化物析出物体积分数的增加，尽管它们不会像在 AM 17-4 中观察到的那样抑制马氏体形成。由于 AM 17-4 的高 N 含量，细小碳化物析出物体积分数的显着增加也被假设为马氏体成核和后续生长所需的位错运动产生了额外的活化势垒。在 AM 15-5 中观察到碳化物/氮化物析出物体积分数的增加，尽管它们不会像在 AM 17-4 中观察到的那样抑制马氏体形成。由于 AM 17-4 的高 N 含量，细小碳化物析出物体积分数的显着增加也被假设为马氏体成核和后续生长所需的位错运动产生了额外的活化势垒。在 AM 15-5 中观察到碳化物/氮化物析出物体积分数的增加，尽管它们不会像在 AM 17-4 中观察到的那样抑制马氏体形成。