| As an important part of industrial mold,hot working die has very strict service conditions.The instantaneous temperature of the surface can exceed 600?,and it will reach 700? in some areas.At the same time,the hot die also needs to bear the influence of the thermal shock stress caused by the circulation heating and cooling,which extremely prone to failure.Therefore,surface cladding technology can be used for surface modification or repair of hot working dies,so as to extend the service performance and service life of hot working dies,which has a great market value.In this paper,a multi-alloy reinforced ortho-experimental cladding layer with self-fluxing Fe65 as the iron-base component was prepared on the H13 steel substrate by plasma cladding,which suitably added Mo,V,W elements.The forming state,interface state,microstructure,alloying element distribution and phase composition of each sample were characterized and analyzed respectively.The hardness distribution,high temperature tempering resistance,high temperature wear resistance,high temperature oxidation resistance and so on were measured,characterized and analyzed.The study of process performance and structure shows that when the cladding current 110 A < I < 120 A and the addition of modified elements < 20%,the coating is well formed,the interface is firmly bonded,and the distribution of elements is smooth.Similar to the Fe65 coating,the modified coating contains more elements such as Cr,Mo,W and V.The matrix structure is lath martensite,which uniformly distributed black cluster pearlite and a small amount of retained austenite.The microhardness(600~690HV0.1)of the modified coating was significantly higher than H13 steel's(440 HV0.1)and Fe65 coating's(560HV0.1)before high temperature tempering.After tempering at 600 C,the hardness of the Fe65 coating decreased significantly(about 300 HV0.1)due to the recovery and recrystallization of the lath martensite.Due to the transformation of retained austenite and the precipitation of special carbides of MC type,the hardness of the modified coatings decrease slightly(about 150HV0.1),which reflects excellent high temperature temper resistance.The ball-disk wear test found that the 4 groups of modified coatings showed better wear resistance compared with the H13 steel and Fe65 coating.The high temperature friction coefficient of the No.3 modified coatings is minimum(0.25),which is only equivalent to 62.5% and 50.1% of the H13 steel and the Fe65 coating.The wear morphology observed that the H13 steel specimens showed serious oxidation wear,adhesive wear and shallow peeling.The Fe65 coating showed a certain degree of oxidation wear,abrasive wear and a small amount of fatigue wear.The No.3 modified coating showed mild oxidation wear and abrasive wear in different degrees.The strengthening effect of solid solution and MC carbides in the coating inhibited the strip exfoliation of the matrix,prevented the falling off of the hard particle phase,lightened the abrasive wear and improved the high temperature wear resistance of the material.The phenomenon of abrasive wear was aggravated by the aggregation and growth of carbides in the No.4 modified coating,which resulted the high temperature wear resistance was worse than the No.3 modified coating's.The oxidation of H13 steel is serious at 600 C,with the highest oxidation dynamic curve,the surface is black and exfoliate.The surface oxides of Fe65 samples are mostly Cr2O3,and pitting defects appear on the surface.The No.3 modified coating still has metallic luster.The surface oxide is Cr2O3,Si O2 and Mo5Si3.The oxide film is continuous and dense,the oxidation dynamic curve is the lowest,and the high temperature oxidation resistance is the best.The carbides in the No.4 modified coating appear to be aggregated and grown,and become weak oxidation areas,and the high temperature oxidation resistance is worse than the No.3 modified coating's.In summary,the high temperature comprehensive performance of the No.3 modified coating is obviously better than that of Fe65 base coating and H13 steel,which has an important reference value for the research of surface modification of hot die. |
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