| The dual characteristics of hot forging die’s service environment,such as rapid cooling and heating and torsion-compression load,lead to many kinds of failure,such as wear,plastic deformation,fatigue and so on.Abrasion and thermal fatigue account for more than 70%of the failure.At present,the common performance testing devices on the market,such as thermal fatigue testing machine,pin-on-disc friction and wear testing machine,often only have a single testing function,which does not meet the complex scene under the actual working conditions of hot forging dies.It is necessary to simulate the actual working conditions of hot forging dies in service environment by using appropriate performance testing devices and to study the changes of surface properties and structure of different materials.Based on torsion-compression test,combined with the characteristics of friction,wear and thermal fatigue,a torsion-compression test device for hot forging die was prepared,in which the cyclic action of high temperature,torsion and high load could be realized.At the same time,plasma surfacing cladding was prepared to improve the matrix performance.The performance of Ni60 cladding and WC reinforced nickel cladding were tested and phase structure was analyzed.The samples were processed into die samples which could be placed in the device,torsion-compression test and cyclic torsion-compression test.The main research results are as follows:(1)The experimental device for torsional compression of hot forging die consists of control system,heating system,torsional compression system and cooling system.According to the actual service environment of hot forging die and the requirement of torsional compression experiment,the overall structure of the compression and torsion experimental device and the functions of each system are analyzed and explained.The specific parameters of the experimental equipment include:applying pressure of 0-18KN,connecting rod speed of 0-161r/min,heating furnace temperature of 0-900℃,grinding area of 98.17mm~2 for grinding samples,and grinding time of the shortest one minute.(2)Nickel-based cladding and WC-reinforced nickel-based cladding were prepared.The morphology,phase and microhardness of the cladding were analyzed by metallographic microscope,electron probe analyzer,X-ray electron spectroscopy and microhardness tester.The addition of nickel-based cladding makes the iron-nickel solid solution and chromium carbide formed in the cladding layer,which improves the hardness and strength.The addition of WC phase makes the bottom sink near the fusion line,and the tungsten-rich phase enhances its wear resistance.The hardness of WC reinforced cladding is about 300HV higher than that of Ni60 cladding.The hardness of the matrix near the fusion line will be increased for a short time due to hardening.The hardness of the cladding near the fusion line decreases due to the high temperature and the large grain size.(3)H13 steel sample,nickel-based cladding sample and WC reinforced nickel-based sample were processed into die sample size,and experiments were carried out in the testing machine.In the process test,45 MPa and 60s of counter-grinding pressure were determined.In the compression and torsion load experiment,grinding was carried out at 550℃,650℃and 750℃respectively.In high temperature friction and wear tests,50 cycles were carried out at 500℃and 45 Mpa.The results are as follows:With the increase of temperature,the surface wear and defects of the three kinds of specimens become more and more obvious.The adhesion wear and abrasive wear of H13specimens are more obvious.The adhesion wear of Ni60 and WC reinforced nickel-based specimens is the main form at 550℃and 650℃,and the abrasive wear range increases at 750℃.During 50 cycles of twist-compression test,the oxidation area of H13 surface increased,wear and spalling were obvious,the surface of Ni60 sample collapsed in a small range,and the surface material of WC reinforced nickel-based sample shifted a small part. |
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