Study On Deformation-induced Phase Transforma Tion In Iron-graphite Metals And Its Effects On Fricti On And Wear Properties

In this paper,the deformation-induced phase transformation behavior of the retained austenite in the iron-graphite series metal and its effects on tribological properties are systematically studied.Firstly,the different austenite contents(sample-230,sample-300,and sample-380)of iron-graphite metals were obtained by adjusting the austempering temperature during the austempering process.The deformation induced transformation of iron-graphite metal was studied by compression test at room temperature with different strain rate(0.1mm/min,0.5mm/min,1mm/min,5mm/min,10mm/min)and strain variables(10.54%,18.17%,25.96%,40.58%)on samplewith about 44%volume fraction of retained austenite.Then,the effect of deformation-induced phase transformation on friction and wear behavior was studied by dry sliding friction and wear test of iron-graphite metals with different amounts of retained austenite.The results show that the iron-graphite metal matrix is composed of acicular nano-ferrite(?-phase)and high-carbon austenite(y-phase)after austempering treatment,and the high-carbon austenite content increases with the increase of austempering temperature.High-carbon austenite exists in the matrix of iron-graphite metal in the shape of coarse block or fine needle.The strength of the iron-graphite metal decreases and the plasticit y increases with the increase of retained austenite.With the increase of strain,the defor mation induced transformation ofhigh carbon austenite increases,and high strain rate in hibits the formation ofdeformation induced transformation.This is mainly because the increase of strain rate reduces the driving force of martensitic transformation,which leads to the difficulty of deformation-induced phase transformation.The results of friction and wear tests show that the friction behavior and wear resistance of iron graphite metals are closely related to the content of retained austenite.First the graphite in iron-graphite metals can be dragged to the worn surface in the process of friction and wear to act as lubricant,which is the reason for the low friction coefficient of iron-graphite metal,the friction coefficient decreases with the increase of retained austenite content.High-carbon austenite in iron-graphite metals will undergo defor mation-induced phase transformation under the action of friction,thereby forming a hardened layer on the subsurface.Under the same wear conditions,the thickness of the hardened layer increases with the increase of the retained austenite content.The formation of such a hardened layer will effectively reduce the wear rate,which is very beneficial to improve the wear resistance of iron-graphite metals.In addition,the wear mechanism of iron-graphite metals is mainly manifested by micro-cutting wear and furrow wear at the initial stage of wear,and micro-fatigue wear and adhesive wear after a long time.