18Ni300马氏体时效钢表面离子氮化研究

Research on Surface Ion Nitriding of 18Ni300 Maraging Steel

通过对渗层硬度分布、金相组织形貌和物相组成,以及拉伸性能、缺口敏感性和延迟断裂抗力等的分析,研究了18Ni300马氏体时效钢离子氮化后的渗层及对力学性能的影响。结果表明:离子氮化表面形成了Fe_4N硬化相,硬度从表面820 HV逐步下降到基体的610HV。由于平缓的硬度分布和不存在Fe_(2-3)N脆性相,使渗层与基体具有较强的协调变形能力;离子氮化后缺口与光滑抗拉强度之比仍达到1.2,可保障氮化构件的安全性。极低的位移速度(0.0015mm/min)缺口拉伸证明了氮化并未增大延迟断裂倾向。

The nitride layer of 18Ni300 maraging steel after ion nitriding was studied, and its influences on the mechanical properties were studied by analyzing the hardness distribution of the nitrided layer, metallographic structure morphology, phase composition and tensile property, notch sensitivity and delayed fracture property resistance. The results show that the hardening phase Fe4N is formed on the ion nitriding surface layer. The hardness of the nitride steel gradually declines form 820 HV of the surface to 610 HV of the base material. The coordination deformation ability the between surface and the base is quite strong due to the gradual hardness distribution and inexistent brittle Fe2.3N phase. The ratio of notched tensile strength to smooth tensile strength after ion nitriding is 1.2, which can guarantee the safety of the nitridestructural parts. The delayed fracture tendency after ion nitriding does not increase ,which is proved by the notched tensile test under the very low displacement speed of 0.0015 mm/min.