| The purpose of this paper is to study the addition of proper amount of boron to iron-based alloy powder,to replace expensive alloy elements with cheap boron,and then to prevent the cladding from cracking based on the principle of fast cooling induced martensite transformation in laser melting pool.Promote the formation of boron carbon supersaturated martensite cladding with certain high temperature stability during cladding.The micro-structure of the high-hardness boron-carbon martensite cladding layer was studied by XRD,SEM,OM and other methods.The results show that the high-hardness boron-carbon martensite cladding layer has good high-temperature stability performance.After the cladding layer is tempered at different temperatures for two hours,through the observation of the microscopic metallographic structure,the phase composition is not carried out.It is a high-hard boron-carbon martensite phase during heat treatment without any precipitates;When the tempering temperature rises to 300°C,the high-hard boron-carbon martensite phase is also maintained without any precipitates;but when the tempering temperature reaches 500°C,a phase peak of low energy intensity appears,which is calibrated by jade.The substance is a boron-carbon compound,but the peak intensity is very low,indicating that the content is small.Observe the microstructure and confirm that the substance is a white boron-carbon compound.At this time,the phase composition changes.With the precipitation of boron-carbon elements,a small amount of decomposition of the martensite structure occurs,and a ferrite phase appears;when the tempering temperature rises to 600 ℃,a large amount of decomposition of the martensite structure occurs,and the XRD peak of the boron-carbon compound rises at the same time.A small amount of carbide phase appears.After observation,a large amount of white borides and black network carbides appear in the cladding layer;when the tempering temperature rises to 700 ℃,Martensite has been basically decomposed into ferrite,and the phase composition is ferrite and part of boron-carbon alloy compounds.The mechanical properties of the cladding layer after tempering at different temperatures were characterized by Rockwell hardness tester,normal temperature friction and wear tester,and high temperature friction and wear tester.The corrosion resistance of the cladding layer was characterized by electrochemical corrosion workstation.The results show that the hardness of the cladding layer in the original state,after tempering at 300°C for 2 hours,remains basically unchanged,and the average value only changes from HRC58 to HRC56.3.At this time,the resistance to friction and wear is strong;when the tempering temperature rises to 500°C,the average Rockwell hardness becomes HRC57.6.At this time,a small amount of boron-carbon compound appears around the grain boundary,which is around the dislocation and grain boundary.A "Cottrell air mass" is formed.At this time,the boron and carbon atoms play a pinning role to increase the surface hardness and form a secondary hardening.However,due to the increase of the surface hard phase,The dynamic friction factor decreases slightly,but the amount of wear still increases;but when the temperature rises to 600°C,the boron and carbon elements inside the atoms precipitate out and form compounds with alloying elements around the grain boundaries.The strengthening elements and alloying elements in the crystal are reduced,and the hardness is reduced.It begins to decrease.When the temperature rises to700°C,the inside of the crystal basically becomes ferrite.The hardness is greatly reduced,and its wear resistance also drops sharply.High temperature friction and wear is to test the working condition of the cladding layer in a continuous high temperature environment.The wear amount of the cladding layer is small before 500 ℃.When the temperature rises above 600℃,the amount of wear doubles.From the perspective of corrosion resistance performance,the structure of the cladding layer has not changed due to the low temperature tempering treatment.The alloying elements are evenly distributed,and the corrosion resistance is very strong.When the temperature rises above 500℃,the precipitation of boron-carbon compounds causes the chromium element to segregate near the grain boundary,resulting in a chromium-depleted zone,and the corrosion resistance is reduced.Therefore,from the characterization of the metallographic structure,mechanical properties and corrosion resistance,the high-hardness boron-carbon martensite cladding layer has a certain high temperature stability. |
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