| Laser cladding is an advanced surface treatment technology to improve the wear resistance of parts and prolong their service life.We should give full play to the significant advantages of semiconductor lasers in the field of advanced lasers,thus escorting for remanufacturing laser cladding.In addition,the impact of coal particles will also cause damage to the surface of the coating,causing a large reduction in life span.The hydraulic props lose efficacy hundreds of thousands per year according to the statistics,which provides a large market for laser cladding remanufacture.The representative materials are the steel of 20#,45# used in the production of coal mine hydraulic support.In this paper,45# steel and 20# steel are selected as the substrate material and on which the Ni/Cr,self-made stainless steel powder and 316 L coatings were prepared respectively,using a high-power fiber coupled semiconductor laser processing system(LDF 4000-100)equipped with a powder delivery device.The influence of different process parameters on the cladding effect was analyzed,and optimum technology parameter were selected to provide references for the practical application of laser cladding to repair coal machine.With the appropriate laser power and scanning speed,Ni/Cr cladding layer,self-made stainless steel cladding layer and 316 L cladding layer can be prepared on 45 steel and low carbon steel surface with smooth and no crack while realized metallurgical bonding with substrate.The coating can be divided into 3 zones in the section which are the clad zone,the bonding zone and the thermo-affected zone.The crystal structure also changed regularly from the cladding surface to the substrate perpendicular to the cladding.The optimum process parameters of the test for cladding Ni/Cr on 45# steel substrate,the content of 30%Cr powder,2600 W laser power,scanning speed is 7mm/s;While on the 45 steel substrate cladding stainless steel coating,the laser power is 2100 W and the scanning speed is 12mm/s;Then using this parameter with 50% lap rate of laser cladding coating onthe 20 steel pipe cladded with 316 L stainless steel,we get good effect of cladding and the industrial reference value.The hardness of cladding layer was greatly improved compared to the substrate in general,and the hardness can be 3-4 times than the substrate attainability after cladding in different material systems.The hardness was affected by the parameters such as scanning speed,laser power and different content of Cr.The enhancement of the hardness of the cladding was mainly due to the grain structure,as well as the solid solution strengthening and dispersion strengthening.The corrosion resistance of the cladding was closely related to the grain structure and strengthening phase.Because of the dense grain structure and the strengthening phase,the corrosion resistance of the cladding layer is much higher than that of the substrate.The existence of oxides of Cr and hardening phase can significantly improve the corrosion resistance of the cladding layer,Using the weight loss method calculated the wear resistance of the cladding layer and matrix,we find that the weight loss rate of cladding layer was significantly lower than that of the matrix,this is due to the comprehensive influence of the 316 L cladding layer with high hardness,fine grain composition and Mo elements with good wear resistance..The optimum technology parameter and 50% overlap rate were chose to have a multicladding 316 L stainless steel on the hydraulic support 20# steel.According to the microstructure observation of different overlap and non overlap region,we can find that microstructure of bonding area shows different direction of the dendrite and fine cellular crystal,which is different with the regular changes of the organizational structure in the single cladding;The hardness of the laser cladding is also improved compared to the matrix steel tube,so as to provide a reference value and significance for laser cladding repairing hydraulic equipment. |
PDF Full Text Request