| Marine high-load gears as the core components of the marine gear transmission device,whose performance make a direct influence on the service life of the transmission system and the safety coefficient in the operation.With the trend of increasing power density of Large Marine gear transmission device,the requirements for gear bearing capacity are also increasing such as harder tooth surface,deeper thickness of hardening layer,and higher control accuracy of thickness of hardening layer.The traditional carburizing and quenching strengthening process on the one hand is difficult to accommodate today’s trend of development,on the other hand,various defects in the production make processing difficult and high production costs,therefore,it is demanded that gear tooth surface modification technology be researched.Laser alloying technology is a new surface modification technology that holds significant advantages over traditional processes,which is a new option for gear tooth surface modification.This thesis mainly study the application of this technology to the modification of tooth surface of Marine high-load gears,and combine with experiments to verify the feasibility of this technology in the modification of tooth surface of Marine high-load gears.The main study are as follows:(1)Carry out structural analysis of the surface strengthening layer,design the hardness and depth of the alloying layer and hardened layer in a reasonable manner,increase depth of the strengthening layer and make it have proper hardness transition,so as to increase the fatigue resistance of gear teeth.The microstructure design of the alloying layer was also carried out in conjunction with the working conditions of Marine gears,and the size and density of distribution of hard ceramic particles precipitated in situ were designed and optimized in comparative experiments,complete with the microstructure design within the laser-reinforced layer.(2)The output power,scanning speed,defocusing amount of the laser,thickness and composition of the alloyed prefabricated powder layer,as well as the protective atmosphere were studied,a large number of parameter optimization experiments were carried out by single-pass scanning,and the combination of optimized process parameters on the 42 CrMoA gear steel flat sample obtains the hardening layer whose indicators meet technical requirements.(3)Lap scanning experiments at different overlapping rates were conducted with the parameters selected from laser single-pass scanning,the influence of heat accumulation caused by continuous scanning on the hardness of strengthened layer during the experiment;The microstructure,hardness,layer depth and surface formation of the lapped zone were observed and analyzed;Finally,the laser scanning method of large area strengthening was designed and selected by combining with the force analysis of the tooth meshing area.(4)Experimental gears were designed,machined and strengthened,whose tooth surface hardness and core hardness and depth of effective hardening layer as well as microstructure were given a test.Finally,the mechnical property experiment would be conducted on the gear fatigue tester.The results of the experiment show the contact fatigue limit was 1786 MPa and the bending fatigue limit was 1010 MPa for the 42 CrMoA steel quenched and tempered gear after the laser alloying tooth surface modification.The 42 CrMoA gears through the tooth surface modification by laser alloying that average contact fatigue limit and bending fatigue limit are respectively 16.5% and 35.1% higher than those of the 17 Cr Ni Mo6 carburizing and quenching gears.According to the comparative experiment of mechanical properties of gears,it has been verified that it is feasible to apply laser alloying tooth surface modofication technology to Marine high-load gears,which has certain engineering application value. |
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