Laser Cladding Process Research Of Fe-base Alloy Based On H13k Tool Repair

H13k which is one kind of hot die steel with high hardness and good toughness is usually used to make mechanical shearing blades.In the process of using mechanical shearing blades,wear and breakage often occur.In order to prolong the actual service life of the blades and reduce the cost of consumable materials in the enterprise,laser cladding as an additive manufacturing technology is induced into the repair process.Fe-based cladding layer has high hardness but poor toughness.The study on the process parameters,which can make the Fe-based cladding layer have comprehensive performance of good hardness and toughness,is of great significance for the industrial application of shear blade repair.In this paper,the main technological parameters which affected the hardness and impact toughness of the cladding layer were determined by theoretical analysis,and the main technological parameters obtained from the theoretical analysis were further optimized through multiple experiments.Finally,the process conditions to meet the industrial repair requirements were obtained.The main contents of the study include:?1?The relationship between hardness and impact toughness was analyzed by dimensional analysis.There was a relationship between dimensionless hardness and irreversible deformation work,and they were all functions ofYE,v,n,?.The stress required for crack growth during impact fracture was the function of E,?,v,a.Both of dimensionless hardness and crack-growth stress were related to the material properties of E and v.The change of element content and the heat treatment process had significant effects on E and v.?2?The effect of element content on the microstructure of multilayer cladding and its bonding zone was studied.From the bottom to the top of the multilayer cladding,the microstructure of X431 cladding coating was mainly composed of columnar dendrite,equiaxed dendrite and steering dendrite;The“white bright”band known as the bonding zone between layers were mainly composed of mixed equiaxed dendrites;There were irregular pore defects in dendrite.In addition of 8wt.%Ni45,the dendritic growth of X431 cladding layer was limited,the grain was smaller,the dendritic distribution was more uniform;The width of bonding zone was narrower,the grain size was smaller than that of the interior region;The pore defect in dendrite was disappeared.After adding 1.5wt.%Mo,the dendrite distribution in X431 cladding layer was more uniform and the grains were smaller,but the internal pore defects in the dendrites were not reduced.When F901 with higher C content was added for 8wt.%Ni45,the grain size was smaller but the internal pore defects in dendrites became larger and more.?3?The effect of the content of elements on the cooling mode and the phase composition of the cladding layer at room temperature and the distribution of elements in the dendrite and interdendrite were studied.XRD diffraction results showed that:The phase composition of X431 at room temperature was?-Fe,?-Fe,M₂B,M₂₃C₆ and M₇C₃,in which M represented metal elements such as Fe,Ni,Cr and Mo.The phase composition of X431+8wt.%Ni45 was?-Fe,M₂B,M₂₃C₆ and M₇C₃.The phase composition of F901+8wt.%Ni45 and X431+1.5wt.%Mo was?-Fe,M₂B,M₂₃C₆,M₇C₃ and little?-Fe.EDS mapping,line scanning and point analysis showed that the cladding layer mainly consisted of dendrite matrix and interdendrite netlike eutectic structure.Fe mainly distributed in the dendrite,the interdendrite netlike eutectic structure was relatively rich in the elements of C,B,Mo,Cr and Ni.When adding1.5wt.%Mo to X431 powder,Mo element only existed in interdendrite netlike eutectic structure.?4?Full annealing and high temperature tempering could promote dendrite growth and change phases in the cladding layer.The full annealing led to the diffusion phase transition after complete austenitization of cladding material and the mixed structure similar to pearlite formed.The high temperature tempering promoted the decomposition of martensite to form ferrite and fine cementite.There was no obvious decomposition of M₂B,M₂₃C₆ and M₇C₃ in the interdendrite region after heat treatment.?5?The effect of element content and heat treatment on the hardness and impact toughness was studied.The average hardness of X431 cladding layer was 55 HRC,When Ni45 addition content was less than 8wt.%,the hardness decreased slowly and not less than 50 HRC;When Ni45 content reached 10wt.%,the hardness decreased rapidly and to less than 40 HRC.3wt.%Mo addition led to the hardness decreasing to48 HRC.The hardness of the cladding layer was reduced after heat treatment.Research also showed that the impact toughness of X431+8wt.%Ni45 without heat treatment was the best in this paper,and the impact energy was 8.5 J,which was higher than that of quenched H13k?3.9 J?;The average hardness of H13k?52 HRC?was higher than H13k tool hardness requirement?50 HRC?;Thus this parameter could meet the basic requirement of industrial H13k tool repair.