Experimental Study On Surface Laser Strengthening Of The Roller Spindle Of Hot Rolling Coiler

The reel main shaft of the hot-rolling coiler is an important part of metallurgical equipment.During its use,it is subjected to the effects of plate heat,coiling tension and sliding friction,which can easily cause failures such as cracks,corrosion,and excessive deformation phenomenon.This test was commissioned by the local metallurgical equipment company.According to the actual production needs of the enterprise,the RFL-C3300 fiber laser was used to perform the laser strengthening treatment process test on the surface of the base material of the 40CrNiMoA steel spindle.Two test plans were designed.Option 1:Use iron-based alloy powder to perform laser cladding on the surface of40CrNiMoA steel substrate;Option 2:Laser hardening the surface of the40CrNiMoA steel substrate.Use stereo microscope,metallographic microscope,scanning electron microscope（SEM）,X-ray diffractometer（XRD）,micro hardness tester,vertical universal friction and wear testing machine,universal testing machine,electrochemical workstation and other testing equipment for testing Such organization and performance are tested and analyzed.1.Based on the original process parameters of the enterprise,the laser power,scanning speed,and powder feeder speed are taken as the three changing factors of the test.Each factor takes three levels,and the L₉（3⁴）orthogonal table is formulated,using positive The optimized parameters were obtained by the cross test method:laser power 2000 W,spot size 4mm×2mm,scanning speed 10 mm/s,overlap rate 50%,powder feeder speed 0.8 r/min;Using optimized process parameters,two iron-based alloy cladding layers A and B were prepared on the surface of40CrNiMoA steel.The surfaces of the two were smooth and smooth without obvious defects such as cracks and pores.The microstructure of cladding layer A mainly consists of martensite and ferrite,and the cladding layer B mainly consists of austenite structure.Both cladding layers form a good metallurgical bond with the substrate.The microhardness value of the cladding layer showed a gradual downward trend from the inside and the inside.The highest hardness of the cladding layer A and the cladding layer B reached 348 HV_0.2 and 310 HV_0.2respectively,both higher than the base body,and the tensile strength was960¹000 Mpa and 830⁸70 Mpa,yield strength is 780⁸20 Mpa and490⁵20 Mpa respectively,elongation after fracture is 10%¹2%and24%²6%respectively,tensile fractures are brittle fracture and ductile fracture respectively.It can be seen that the plasticity of the cladding layer A is low,but the hardness is high and the strength is high;the hardness of the cladding layer B is low and the strength is poor,but the plasticity is excellent.2.According to the requirements of the enterprise,and considering the size of the spindle,the working conditions and the actual situation of the laser,the single variable control method is used to make the spot size constant is 12 mm×2 mm,the scanning speed constant is 20 mm/s,and the power is 1000 W 1300 W and 1600 W.After 40CrNiMoA steel samples were quenched with different laser powers,the surface showed a white bright layer with continuous distribution and uniform thickness,indicating that its microstructure was refined to varying degrees and the quenching effect was ideal.When the laser power is 1600W,the macrostructure of the sample cross section is divided into three parts:phase change hardening zone,transition zone and matrix.At this time,the structure of the surface hardened layer is the finest and densest,showing fine needle-shaped martensite,a small amount of retained austenite,and finely dispersed fine carbides.The microhardness of the surface of the three kinds of laser quenched samples prepared with different powers is higher than that of the matrix.Among them,when the laser power is 1600W,the hardness value of the phase change hardening zone is the largest,reaching 640.3⁷06.8 HV_0.2,which is about 2.5².8 times of the matrix.At this time,the friction factor and wear of the sample are the lowest.The friction factor is between 0.40 and 0.60,which is about 50%lower than that of the substrate;the amount of wear is 1.3 mg,which is only 36.1%of the substrate.The main wear mechanism is abrasive wear;at this time,the corrosion voltage of the sample is-0.497 V,self-corrosion current density is 2.16789×10^-99 A/cm²,corrosion resistance has been greatly improved.3.Both test schemes have strengthened the surface of 40CrNiMoA steel.Among them,the powder A is used to perform laser cladding on the surface of the main shaft of the reel of the hot-rolling coiler,and a process document has been formed and used to guide the actual production.At the same time,the test results of scheme two provide references for some large-scale metallurgical parts of the same material that need localized strengthening treatment.Laser quenching treatment can be considered to meet the performance.This article provides experimental methods and basis for enterprises to reduce production costs,repair metallurgical equipment parts and extend service life.