Study On The Effect Of Working Temperature On The Wear Resistance And Characteristics Of Typical Cold-working Die Steel

As one of the most mature development of forming technology,the cold forming process,which forces the metal beyond its elastic limit into various shapes,is widely used and occupies a very important position in modern industry.Due to the mechanical forces,cold die failures in various forms,such as wear,fracture,deformation and so on,and wear accounts for the largest proportion,in the actual production process.Cold-working die steel is the main material for cold forming die because of its excellent abrasion resistance and high toughness.The surface friction and wear performance of cold-working die steel is very important for the bearing ability and service life of the mold,the quality and output of the products.What’s more,the maximum wear of the die surface directly decides its service life.Therefore,reducing the die wear has become an urgent need to reduce cost and improve the service life of the die,the quality and efficiency of production.In this paper,spur gear in camion reducer was studied.Firstly,the three-dimensional model of the spur gear cold extrusion is established and a finite element simulation of the cold extrusion was carried out.By analyzing the simulation results,the friction and wear properties of the cold-working die steel Cr12 MoV was obtained at different working temperatures.Then comparison tests of dry sliding wear under different working temperature were carried out by using a friction and wear tester.Four kinds of cold-working die steel were evaluated and ranked in term of wear weight.With the aid of SEM and EDS,wear mechanism was determined by observing and analyzing the morphology of the worn surface.Finally,the following conclusion was obtained by summarizing the results of simulation and experiment:With the increase of working temperature,the temperature of the die surface gradually increased.Under different working temperatures,the temperature distribution was same to the wear depth distribution of the die surface,and the higher temperature area corresponds to the serious wear and tear,the wear depth of the lower temperature zones was also slightly smaller.Working temperature has a great influence on the abrasion loss of cold-working die steel: With the increase of the working temperature,the abrasion loss of cold-working die steel 012 Al and ASSAB88 gradually decreased;the abrasion loss of cold-working die steel 9CrSi decreased after increased;the abrasion loss of cold-working die steel Cr12 MoV increased first,when the temperature exceeding 180℃ slightly decreased.The friction coefficients of four kinds of cold-working die steel reduced gradually with the increase of the temperature.At different temperature,friction coefficient rapidly increase then slightly decreased and maintained a stable fluctuations.Working temperature had different effects on the friction coefficient of different degree of cold-working die steel,since different cold-working die steel had different content and types of carbide at different temperature.The abrasion loss of 012 Al and Cr12 MoV were positively correlated with total carbide on the surface of the wear.This was mainly because the content of total carbide changed with the increase of working temperature.Especially the M23C6,M2 C,M6C and M7C3 of carbide,which distributed at the grain boundary,changed the wear mechanism.With the increase of temperature,the content of M7C3 in 9CrSi increases first then decreases,the positive relationship between total wear rate of weight and M7C3 eutectic carbide content was revealed;the content of M7C3 in ASSAB88 reduces gradually,wear rate was positively correlated with M7C3 eutectic carbide content and flatten out.Working temperature had a great influence on the wear mechanisms of four kinds cold-working die steel: The wear mechanism of four kinds cold-working die steel were mainly abrasive wear at the temperature of 40℃.When the temperature reaches 75℃ to 110℃,the main wear mechanism were adhesive wear and abrasive wear.At the temperature of 145℃,the main wear mechanism were the adhesive wear and slight abrasive wear.At the temperature of 180℃,the main wear mechanism was slight oxidative wear,accompanied by a small amount of adhesive wear.The main wear mechanism was the reoxidation mechanism of oxidation wear at the temperature of 215℃.