Research On Multi-technology Coupling Strengthening Process And Performance Of Gear Steel 18Cr2Ni4WA Surface

With the development of ship and marine industry,the performance requirements of transmission system for large-scale ships and other marine transportation platforms are becoming increasingly stringent.As the key part of marine transmission system,the performance and strengthening technology of its surface strengthening layer need to be further improved.The coupling of various surface strengthening technologies is a new trend in the development of surface technology.In this paper,many strengthening technologies such as supersonic particle bombardment,rare earth ion implantation,vacuum carburizing and Cr/Zr/Ti-N double ion implantation are combined.The multi technology coupling strengthening of 18Cr2Ni4 WA surface of gear steel was realized.The results show that:By using supersonic surface nano-modification and rare earth ion implantation composite pretreatment technology,a composite modified layer in which a La element doped layer with a depth of about 100 nm is distributed on a fine crystal layer having a thickness of about 75.1 ?m can be prepared on the sample surface.The grain size distribution of the composite modified layer is 10?80nm,the surface hardness increased to 45.3 HRC,and the residual stress increased to-598 MPa.La introduced by rare earth ion implantation exists in the form of oxides and hydroxides.The composite pretreatment modified carburizing layer was prepared by vacuum carburizing at 925? after modification.The phase composition of the modified carburized layer after composite pretreatment is still martensite,retained austenite and carbide,and some lath martensite is transformed into fine lamellar twin martensite.Although the phase structure and composition of the carburized layer were not changed,the quality and performance of the carburized layer were improved.The grains on the surface of the carburized layer are refined by 49.4%,the thickness of carburized layer is increased by 24.7%,the surface hardness is increased to 65.7 HRC,and the wear resistance is increased by 50%.A thin layer rich in nano-hard ceramics such as CrN,ZrN and TiN was formed on the surface of the modified carburized layer by Cr/Zr/Ti-N double ion implantation technology.Radiation damage and lattice distortion can be caused by the process of ion implantation,thus further improving the surface hardness,tribological properties,rolling contact fatigue and other properties of the carburized layer.The results show that the effect of Cr-N double ion implantation on the properties of carburized layer is the most remarkable.After Cr-N double ion implantation,the nano hardness of carburized layer increases by 38.9%,the wear resistance increases by 66.7% and the rolling contact fatigue life increases by more than 10% under dry friction at room temperature.