Microstructure and Corrosion Resistance of Nitrided Layer on 2Cr13 Stainless Steel by Active Screen Plasma Source Nitriding

This paper aims to explore the feasibility of the active screen plasma source nitriding technology to improved the hardness and corrosion resistance of martensite stainless steel. The 2Cr13 martensitic stainless steel was nitrided by the active screen plasma source nitriding at 350~550 ℃ for 6 h. The microstructure, phase structure and microhardness of the nitrided layer were characterized by means of optical microscopy (OM), electron probe microanalyzer (EPMA), X-ray diffraction (XRD) and microhardness tester. The corrosion resistance of the nitrided layer were evaluated by electrochemical corrosion test. The results show that after nitriding treatment with active screen plasma source nitriding, the nitrided layer with a thickness range of 2~45 μm and N concentration of 20at.%~25at.% (atomic fraction) can be obtained on the surface of martensitic stainless steel, and its surface microhardness was measured to be 1 050~1 350HV0.25, which is about 4~5 times of the untreated substrate. The nitrided layer was mainly consisted of ε-Fe2-3N phases and a few αN phase at 350 ℃. The nitrided layer consisted of αN, ε-Fe2-3N and γʹ-Fe4N phase at 450 ℃. When the nitriding temperature increases to 550 ℃, the nitrided layer mainly consists of α-Fe, CrN and γʹ-Fe4N phases, as well as αN and ε-Fe2-3N phases disappeared nearly. The anodic polarization curves of the nitrided layer at nitriding temperature of 350 ℃ and 450 ℃ in 3.5% NaCl solution showed an obvious passivation region, but no passivation region is found in the unnitrided 2Cr13 stainless steel. The self-corrosion potential Ecorr increases from –308 mV (vs. SCE) without nitriding to –151 mV and –104 mV, respectively, and the corrosion current density remain in the lower range of 0.03~0.2 µA/cm2. However, the corrosion resistance is relatively deteriorated due to the CrN phase precipitation on the surface of the nitrided layer at 550 ℃. The EIS results show that the interfacial charge transfer resistance Rct of the nitrided layer passive film at 350 ℃ and 450 ℃ increases from 5.25×104 Ω·cm2 to 2.76×105 Ω·cm2 and 3.18×105 Ω·cm2, respectively. The double layer capacitance Cdl decreases from 473 µF/cm2 to 74 µF/cm2 and 103 µF/cm2, respectively, indicating that the passivation film on the surface of the nitrided layer is thicker and denser, which can effectively hinder the permeation and migration of reactive ions and significantly improve the corrosion resistance. It can be concluded that the 2Cr13 martensite stainless steel treated by active screen plasma source nitriding technology to obtain high surface hardness and excellent corrosion resistance. © 2022, Chongqing Wujiu Periodicals Press. All rights reserved.