The Study Of Cr Layer Preparation Process And Organization Properties Of 40Cr Steel Surface

When gear work,tend to appear surface damage failure.It continues to work and results in high costs.It must improve hardness,wear resistance and other properties of the gear surface to prolong working life.It can effectively prolong the service life of gear to use the coating as a layer of the gear.Brush plating is more traditional gear strengthening technology and Cr coating has high hardness,excellent wear resistance,Cr coatings have been widely applied in industry.However,because of its low adhesion strength,its development is quite limited.This paper combines the brush plating and heat treatment to solve this problem.Not only get a different size of grain,but also make the Cr element diffused to the substrate.At the same time,use induction heating chromizing and box-type furnace heating chromizing to carry out the corresponding organization and performance research,providing strong support for the gear surface coating preparation technology.The main tasks are as follows:(1)Explore process parameter of brush-plating technology were explored,and the formation mechanism of the Cr plating layer were analyzed.The microstructure and properties of the Cr coating were studied.Combined brush-plating and heat treatment,analyzed the reasons of the changes in grain size and element diffusion.(2)The X-ray diffraction(XRD)of sample treated by brush-plating was carried out.Observed the fracture morphology and tested binding force,friction and wear properties and corrosion resistance.(3)The differences and similarities between induction heating and box-type furnace heating were compared.The layer of microstructure and element distribution were observed.The coating of microstructure evolution and formation mechanism in heating and cooling process were explained.(4)The change in microstructure and element of chromized layer after quenching were observed.And the hardness of samples were tested.(5)The properties of chromized layers were tested.Compare the surface roughness,hardness,adhesion,corrosion resistance and so on and summary the advantages and disadvantages of two methods.Through the above analysis,the main conclusions are as follows:(1)Cr surface of electric brush plating sample is composed of uniformly distributed small nodule units because of cluster with an average size of 15-25?m.Nodules are composed of fine Cr particles smaller than 100 nm.40Cr steel has a uniform Cr layer with the deposit thickness of about 40?m by electric brush plating process,and unconspicuous wave-structured multilayer is observed.After the annealing treatment,at 300? and 500?,the Cr particles have no difference.But at 700?,the Cr particles grow up to grain and the grain size is about 840 nm.There exist abnormal phenomena in the process.At 900?the original coating is divided into double layers,and the new emergence of coating shows the columnar dendrite.At 1100?,the coating is divided into three layers.The second layer is still present columnar dendrite and the third layer is the element diffusion layer.(2)The surface hardness of sample treated by brush-plating is 877.41 HV.With the increasing of distance,the hardness decrease.After annealing,the surface hardness is the lowest at 700 ?.The critical load of Brush-plating sample is about 46.3N.And the wear loss decreases 12.5% comparing to the matrix.(3)Under the chromizing parameters,the induction heating chromizing samples have thicker Cr coating layer and stronger interface bond between the Cr coating and the 40 Cr substrate.However the box-type furnace heating chromizing samples have thin and discontinuous Cr coating.The Cr-diffusion depth is about 82?m in thickness and composed by(Cr,Fe)23C6and(Cr,Fe)7C3alloyed cementite lamellae.At the far end of the Cr-diffusion depth the small amount Cr has great effect on refining of the pearlite,which results in a fine pearlite band in the frontier of the 40 Cr substrate.It indicates that the relative content of Cr and C varies the pearlite phase and morphology.As one of the strong carbide forming elements,Cr can drag out carbon from the surface layer,and cause the formation of decarbonized zone forms in the subsurface stratum of the 40 Cr substrate.The pearlite piece of the induction heating chromized sample after quenching become smaller,and the coating thickness become thickening;The coating thickness of the box-type furnace heating Chromized sample after quenching,but the interface bond between the Cr coating and the 40 Cr substrate is more stronger.(4)The wear loss of induction heating chromizing sample and box-type furnace heating chromizing sample decreases 21.98% and 34.48% comparing to the matrix,respectively.The corrosion resistance performance of induction heating chromizing sample is better than the box-type furnace heating chromizing sample.