Effect of carburizing nitriding compound treatment on microstructure evolution and properties of low carbon gear steel

Abstract

17CrNiMo6 steel is a low-carbon alloy exhibiting excellent comprehensive mechanical properties. It has often been employed as a vital component of machinery. In this study, a composite heat treatment technology based on vacuum carburizing and ion nitriding was developed. The effects of rare earth supersonic fine particle bombardment (SFPB) pretreatment on the microstructure and properties of the composite strengthening layer of 17CrNiMo6 steel after composite heat treatment were systematically studied. The results indicated that the surfaces of carbonitriding layers of vacuum carburizing + ion nitriding sample, supersonic fine particle bombardment + vacuum carburizing + ion nitriding sample, and supersonic fine particle bombardment + vacuum carburizing + rare earth lanthanum ion nitriding sample primarily comprised the ε-Fe_2∼3N phase and γ ' -Fe₄N phase. The surface hardness was nearly 940 HV₁, and the thickness of the strengthening layer reached 1.71 mm, 1.85 mm, and 2.11 mm, respectively. Compared with the vacuum carburizing treatment, the composite heat treatment had a deeper strengthening layer while significantly enhancing the wear and corrosion resistance of the surface. Specifically, the carbonitride layer of the sample with supersonic fine particle bombardment + vacuum carburizing + rare earth lanthanum ion nitriding achieved the smallest friction coefficient, wear scar width, and wear weight loss (0.61, 824 μm, and 0.7 mg), and it exhibited −0.23V and 8.97 × 10⁻⁸ A·cm⁻² minimum corrosion potential and current. Accordingly, supersonic fine particle bombardment + vacuum carburizing + rare earth lanthanum + ion nitriding sample exhibits optimal corrosion and wear resistance.