时效温度对SLM 18Ni300马氏体时效钢显微组织和力学性能的影响

采用激光选区熔化(SLM)技术制备了18Ni300马氏体时效钢，结合拉伸试验、硬度测试和显微组织表征等手段，研究了时效温度(390, 490, 590℃)对SLM 18Ni300马氏体时效钢显微组织和力学性能的影响。结果表明，SLM成形试样主要由Fe-Ni马氏体基体和胞状亚结构组成，经时效处理后，试样微观组织发生显著变化。随着时效温度的升高，胞状亚结构逐渐分解，马氏体逆转变成为奥氏体，Σ3晶界占比下降。同时，Ni₃X(X=Ti, Al, Mo)纳米相弥散析出，并在590℃时粗化。随着时效温度的升高，SLM 18Ni300马氏体时效钢的强度和硬度均先增加后下降，伸长率先降低后增加。其中，490℃时效的SLM马氏体时效钢兼具超高强度和较好塑性，这与其基体中弥散分布的纳米析出相、适量的奥氏体含量和较低的Σ3晶界占比有关。

Effect of aging temperature on microstructure and mechanical properties of SLM 18Ni300 maraging steel

Effect of aging temperature (390, 490, 590 ℃) on microstructure and mechanical properties of selective laser melting (SLM) 18Ni300 maraging steel was investigated by means of tensile test, hardness test and microstructure characterization. The results show that the microstructure of the as-printed SLM 18Ni300 steel specimen is composed mainly of Fe-Ni martensite matrix and cellular substructure, which changes significantly after aging treatment. With the increase of aging temperature, the cellular substructure gradually decomposes, the martensite transforms into reversed austenite, and the fraction of Σ3 grain boundaries decreases. Meanwhile, dispersed nano-sized Ni₃X precipitates are formed and coarsen at 590 ℃. With the increase of aging temperature, the strength and hardness of the SLM 18Ni300 maraging steel increase first and then decrease, while the elongation decreases first and then increases. When aged at 490 ℃, the steel has both high strength and good plasticity, which is attributed to the dispersed nano-sized precipitates in the matrix, moderate content of austenite and low fraction of Σ3 grain boundaries.