Research On Laser Cladding Repairing Cutter Pulverizer

D2 tool steel,as the base material of the cutter head of garbage crusher,belongs to the micro-deformation cold-working die steel.It has good wear resistance and is widely used in various cold stamping dies and cold cutting edges.Laser cladding technology is a new,non-contact,pollution-free and efficient method for repairing worn mechanical parts.In this paper,laser cladding technology is used to clad multi-layer Fe+WC gradient composite cladding layer on the surface of D2 tool steel.By designing gradient composite cladding layer,the problem of cracks caused by adding tungsten carbide into the cladding layer is effectively solved,and the hardness and wear resistance of gradient composite cladding layer are improved.The main research methods and conclusions are as follows:?1?The effects of laser power,scanning speed,defocusing amount and powder feeding speed on the surface morphology and the size of heat affected zone of single laser cladding layer were investigated by single factor experiment.The results show that the quality of single laser cladding layer is better with the laser power of 1350W,the scanning speed of1.5mm/s,the defocusing amount of-10mm and the powder feeding speed of 6g/min.Due to the influence of shape control factor?temperature gradient G/crystallization rate R?,the order of crystalline morphology of the single-channel Fe-based alloy cladding layer from the surface of the cladding layer to the direction of the matrix is equiaxed,dendrite,cellular and plane crystals.?2?The effect of lapping ratio on the surface quality of cladding layer was explored by single factor experiment.When the lapping ratio is 15%,the cladding layer with uniform thickness and smooth surface can be obtained.There are no micro-cracks,pore,slag inclusion and other defects at the interface between the cladding layer and the matrix by Scanning electron microscopy?SEM?.The element diffusion between the cladding layer and the matrix indicates that the cladding layer and the matrix are metallurgical bonding.?3?In order to further improve the hardness of the cladding layer,tungsten carbide hard particles were added to Fe-based alloy powder.The experimental results show that there is no crack in the cladding layer without adding tungsten carbide hard particles.When adding 5%tungsten carbide hard particles,cracks occur.The number of cracks increases with the increase of the proportion of tungsten carbide hard particles.The element content at grain and grain boundary is different by the analysis of EDS.When tungsten carbide hard particles are added,the content of iron and iron at grain boundary decreases rapidly,and the change of elements at grain boundary will affect the physical properties of the cladding layer.Then the cladding layers with different compositions were analyzed by XRD phase analysis.The results show that the peak diffraction intensity of phases of?-Fe,Fe₃N,MnNi and Cr-Fe decreases with the increase of tungsten carbide hard particles.The diffraction peaks of the formed CrFe₇C_0.45 and Cr_2.4W_0.6Si phases gradually increase,while the WN phases tend to be stable.The changes of these phases have a certain effect on the cracking of the cladding layer.?4?By using Fe50 alloy cladding layer as intermediate transition layer,the tendency of cracking in cladding layer with tungsten carbide hard particles is reduced.When the content of tungsten carbide hard particles reaches 15%,cracks begin to appear in the gradient composite cladding layer.Compared with the formation without intermediate transition layer,the intermediate transition layer has a certain toughness,and forms a buffer zone between the intermediate transition layer and the matrix,which effectively reduces the crack cracking trend.It can be seen that the microstructure and grain of the cladding layer are refined gradually after adding tungsten carbide hard particles by the observation of the metallographic structure.?5?The average hardness of cutter head of crusher is 302.73 HV.When there is no crack in the gradient composite cladding layer,the average hardness of the Fe-based gradient composite cladding layer containing 10%tungsten carbide hard particles is 771.85 HV,which is 2.55 times of the matrix hardness.In the friction and wear experiments,the friction coefficient of the matrix is 0.556 in the stable friction stage.When the mass fraction of tungsten carbide hard particles reaches 10%,the friction coefficient of the Fe-based composite cladding layer decreases to 0.449,which is 19.2%lower than that of the matrix.The wear rate of matrix is 45 mg,and the wear rate of composite cladding layer decreases with the increase of tungsten carbide hard particles.The wear rate of gradient composite cladding layer containing 10%tungsten carbide hard particles decreases to 12 mg.When the mass fraction of tungsten carbide hard particles reaches 15%,the wear resistance of gradient composite cladding layer decreases with the increase of unmelted tungsten carbide hard particles in the cladding layer.?6?The morphology of wear marks was observed by scanning electron microscopy.The main wear types between matrix and GCr15 steel balls,Fe-based alloy cladding layer and GCr15 steel balls were adhesion wear.With the increase of tungsten carbide hard particles,the wear type between gradient composite cladding layer and GCr15 steel ball is changed to abrasive wear,while adhesive wear is secondary.With the increase of tungsten carbide hard particles,the ploughing phenomenon on gradient composite cladding layer becomes more obvious.