Effect Of Nitriding Process On Mechanical Properties Of 18Ni Maraging Steel

18Ni300 maraging steel which has excellent strength and toughness is widely used in aviation,aerospace and nuclear power territory.Existing researches show that the fatigue resistance and wear resistance of 18Ni martensitic steel with the treatment of the surface nitride were significantly increased,which enlarged its application.However,the influence of high hardness nitride layer on the materials'strength is not systematic.Through the study of the heat treatment process of 18Ni300 martensitic steel,,a reasonable nitrification process was developed.A suitable nitriding process stee was developed on the study of 18 Ni300 maraging steel heat treatment process,and the gas nitriding and ion nitriding for the influence of mechanical properties.The results show that 900 ? ×1 h of pretreatment before the 820 ? × 1 h solid solution treatment can significantly refine 18 Ni300 maraging steel grain.In 480 ?aging 6-12 hours,strength and toughness to match the best.Increasing the aging temperature will shorten the time of limitation for optimal toughness.At the same time,the aging temperature and time will affect the sensitivity of the gap sensitivity of 18Ni300 martensitic steel.The study of four different nitriding system(480?×24h?480?×48h,500?×24h,500?×48h)have different system of nitriding surface hardness of nitrided layer,nitriding layer deep effect on the properties of the material and hardness distribution.Extended nitriding temperature and nitriding time impact on the nitride layer hardness is tiny,but will improve with notch sensitivity of the nitride layer components,notch sensitivity index by 1.18 of 480 ?× 24 h,down to0.917 of 500 ? x 48 h.The tensile strength of low displacement velocity(0.0015mm/min)is not reduced,and the gas nitride does not increase the tendency of delayed fracture.The specimen of 480?×9 hours ion nitriding after 480?×6 hours aging was tested and it formed 102?m nitride layer.The hardness gently decline from HV810 of nitride layer to HV610 of matrix.The nitride layer formed Fe4N hardening phase,and no appearance of Fe2-3N brittle phase.Compared with the gas nitride,ionic nitride technology is complex and not suitable for large components.The best suitable for 18Ni300 maraging steel nitriding process is 480 ? gas nitriding 48 hours.