The Microstructure And Corrosion Performance Study Of Fe_?58-X?Ti_XSi₁₄B₁₀Nb₁₈ Coating On 45 Steel By Laser Cladding

45 steel is a kind of medium carbon steel with low price,which has good mechanical properties by proper heat treatment.As modern machinery develop into high speed and intellectualization orientation,machinery have high demands on material properties.Traditional heat treatment processing could not meet strict requirements of machinery on parts.To get high hardness and good corrosion resistance of modified surface layer and maintain excellent mechanical properties of 45 steel,45 steel was usually treated by laser cladding surface treatment.Laser cladding is a processing method that make use of high-energy heat source for rapid heating and melting,and the rapid cooling after the spot removed.The Fe_?58-X?Ti _XSi₁₄B₁₀Nb₁₈ alloy coating and Fe-Si-B coating were prepared by laser cladding on 45 steel surface,to study coating morphology and solidification mechanism by testing method:OM/SEM/XRD/BSD,for example,also with the help of microhardness tester and electrochemical workstation respectively to test the hardness of alloy coating and polarization curve.And S1 specimen is Fe₄₂Ti₁₆Si₁₄B₁₀Nb₁₈?X=16?,S2 specimen is Fe₄₈Ti₁₀Si₁₄B₁₀Nb₁₈?X=10?,S3 specimen is Fe₅₄Ti₄Si₁₄B₁₀Nb₁₈?X=4?,S4 specimen is e₅₈Si₁₄B₁₀Nb₁₈?X=0?,S5 specimen is Fe₇₆Si₁₄B₁₀.The following conclusions are summarized:Matrix wettability is better with the sample S3/S4/S5,and the coating surface is smooth,but the whole sample of macro morphology showed that slag is much,in relation to the proportion of Si,B content.In the latter stages of development,Si and B should be replaced with Fe element.Compared with the cross section morphology of the specimens with different compositions,the cracks in the specimens?S4 and S2?were slightly distinct and more than those in S3 specimen,which indicated that the addition of Ti content was helpful to reduce the formation of cracks,which is related to the coefficient of thermal expansion of Ti.The coefficient of thermal expansion of Ti is in between Fe and Nb,which plays a gradient role to reduce the crack sensitivity.In this paper,the formation mechanism of equiaxed crystals of S5/S4/S3/S2 cladding coatings has been analyzed in detail by OM/XRD/SEM.The phase compositions of Sl are mainly:FeSi,TiB₂,Si,Nb₃B₂,a?Fe,Si?,Fe₃Si,Fe₅Si₃.The phase compositions of S2 are mainly:solid solution a?Fe,Si?,NbTB₄,Fe3Si,NbB₂,TiB₂.The phase compositions of S3 are mainly:solid solution a?Fe,Si?,NbTiB₄,Fe₃Si,NbB₂.The phase compositions of S4 are mainly:solid solution a?Fe,Si?,solid solution y?Fe,Si?,Fe₃Si,Fe_0.42Si_2.76,FeB,NbB₂.And y?Fe?,FeSi and FeB were formed because it only contains Fe,Si and B elements.There are two reasons for the formation of equiaxed crystals in S5 samples.Firstly,the structure of molten pool flow crushing can provide nucleation particles for the formation of equiaxed crystals,reducing the amount of nuclear energy needed for equiaxed crystal formation.In addition,the formation of equiaxed crystals in which tips break with the reason that solute enrichment occurs in the growth of the dendrite.The formation of equiaxed crystals in the S2/S3/S4 cladding layer,mainly,where the high melting point material is brought into the molten pool.This will inhibit the formation and growth of dendrites.In addition,the formation of high melting point substances will cause the underflow of elements around them,that is,the enrichment of solute elements,which will increase the solute concentration in the front end of the dendrites,to promote the breaking down of the dendrites.This will also facilitate the transformation of equiaxed grains.According to the properties of the material,the better powder ratio is obtained.The average microhardness of the alloy coating S3 is 1359.4HV_0.2,which is 5.91 times than the matrix.The corrosion electrochemistry corrosion ratev of S3 is 7.422×10-5A cm^-2 and the weight loss of chemical static immersion test is the smallest,which is about 8.16%of the matrix.The hardness and corrosion resistance of Fe₅₄Ti₄Si₁₄B₁₀Nb₁₈ are better than other coatings.