渗氮工艺对18Ni马氏体时效钢性能的影响  

Effect of nitriding process on mechanical properties of 18Ni maraging steel

作　　者：胡乃悦 高齐[2] 杨卓越[2] 刘荣佩[1] 

机构地区：[1]昆明理工大学材料科学与工程学院,云南昆明650093 [2]钢铁研究总院特殊钢研究所,北京100081

出　　处：《金属热处理》2017年第12期111-116,共6页Heat Treatment of Metals

摘　　要：通过对渗氮层硬度分布、显微组织形貌和X射线衍射分析,以及力学性能、缺口敏感性和延迟断裂抗力等性能的分析,研究了18Ni300马氏体时效钢在不同渗氮温度和时间后的渗氮层及对力学性能的影响。当480℃渗氮时间为24 h时,渗氮层厚度为0.14 mm;渗氮时间为48 h时,厚度为0.17 mm;当500℃渗氮时间为24 h时,渗氮层厚度为0.17 mm;渗氮时间为48 h时厚度为0.19 mm。渗氮层厚度增加会降低了材料的韧性,但是渗氮层与基体之间仍有非常高的结合强度。提高渗氮温度和延长渗氮时间对渗氮层硬度影响不大,但都会增加基体残留奥氏体含量,从而降低了基体的硬度。渗氮后使得试样表面的压应力增加,对裂纹扩展有阻碍作用,使得带渗氮层试样的断裂韧度K_(IC)值更高;但随着渗氮温度和时间的增加,脆性的渗氮层厚度增加,抵消了畸变的Fe_4N相对裂纹扩展的阻碍作用,会使得K_(IC)值降低。缺口根部高硬度的渗氮层提高了缺口敏感性,渗氮温度和时间的增加使得缺口敏感指数由480℃×24 h的1.18,降低到500℃×48 h的0.917,缺口敏感性指数小于1时,不足以保障渗氮构件的安全性和可靠性。极低的拉伸速度(0.0015 mm/min)使得拉伸时缺口的抗拉强度不下降,证明渗氮并未增大延迟断裂倾向。Effects of different nitriding time and temperature on nitrided layer and mechanical properties of 18Ni300 maraging steel was studied by analyzing nitrided layer hardness distribution, microstructure, phase structure, mechanical properties, notch sensitivity and delayed fracture resistance. The thickness of nitrided layer is 0.14 mm when nitrided at 480 ℃ for 24 h and 0.17 mm when nitrided at 480 ℃ for 48 h. The thickness of nitrided layer is 0.17 mm when nitrided at 500 ℃ for 24 h and 0.19 mm when nitrided at 500 ℃ for 48 h. The increase of nitrided layer can lower the toughness, but the bond between nitrided layer and matrix is still strong. The increase of nitriding temperature and time have little effect on nitrided layer hardness, but it increases retained austenite content in the matrix, and lowers matrix hardness. The increase of compressive stress on the surface after nitriding can impede crack propagation and increase the fracture toughness value （Klc） of the nitrided samples. But the increase of the brittle nitride layer thickness can counteract the effect of the distorted Fe4N phase on inhibition of crack propagation, which can remarkably lower the Kic value. The hard nitrided layer on the notch root can increase the notch sensitivity. The increase of nitriding time and temperature lower the notch sensitivity value from 1.18, when nitrided at 480 ℃ for 24 h, to 0.917, when nitrided at 500 ℃ for 48 h. It is harmful to the safety and reliability of nitrided layer when notch sensitivity value lower than 1. The notched tensile test with 0. 0015 mm/min tensile speed can not lower the tensile strength, so gas nitriding can not increase the delayed fracture tendency.

关 键 词：渗氮时间 渗氮温度 渗氮层 硬度 缺口敏感性 

分 类 号：TG142.1[一般工业技术—材料科学与工程]