Study On The Heattreatment And Ervin Life Of High Carbon Cast Steel Shot

The high carbon cast steel shot is the most widely used metal abrasive for blast cleaning and shot peening at present,and applicable for blast cleaning and shot peening of the metallic surface in the fields about autoindustry,shipbuilding,rolling stock,aerocraft,bridge,container,mechanical manufacturing,steel structure,pressure reservoir,stone etc.In this paper,the high carbon cast steel shot was studied mainly about the solidfication process in the centrifugal atomization,the heat treatments including first queching+100～700℃tempering,760～900℃secondary quenching and 840℃secondary quenching+150～650℃tempering,the influence of the size and heat treatment on the Ervin life and the wear faliure mode and wear process, whereas the C-S analyser and Si-Mn-P analyser,metallographic microscope, microhardness tester,Ervin test machine and test sieve were applied to test the chemical composition,metallurgical structure,hardness,Ervin life and size distribution respectively,and X-ray diffractometer,differential thermal analyzer and scanning electronic microscope were applied to analyse phase transformation and thermal analysis and observe the wear failure mode;afterwards the performance of the high carbon cast steel shot sample was characterized by the above parameters.The results show that the metallurgical structure of the as-cast(first quenching) high carbon cast steel shot is plate martensite and retained austenite with serious dendritic composition segregation.When tempering the as-cast high carbon cast steel shot,as the temperatrue increases from 100℃to 700℃,the metallurgical structure transforms from the tempering martensite to troosite and sorbite,the hardness decreases from HRC65 to HRC25 and at 350～650℃,the net carbide is precipitated at the original dendritic austenite boundary.When the as-cast high carbon cast steel shot is secondary quenched at 840℃,the structure is fine cryptocrystalline martensite and dispersed undissolved carbide,with the hardness is about HRC60;when the temperature increases to 880℃,the quenching temperature is too high and the structure is coarsened martensite and remaining austenite.After 840℃secondary quenching+150～650℃tempering,the structure gradually transforms to tempering martensite,troosite and sorbite,the hardness decreases and the toughness and shock resistance is improved,the Ervin life expressed by the breakdown curve increases gradually;based on the hardness-temperature curve can regulate the tempering tempature so as to get the user's hardness requirement.The Ervin life is also influenced by the particle size,the smaller the particle size is,the higher the Ervin life is.The wear failure mode of high carbon cast steel shot includes the brittle fracture, surface peeling,core spall and massive split;the weight ratio Gf/Gt is defined to represent the wear failure mode ratio.Gf/Gt can reflect the wear property of the abrasive,and Gf/Gt as well as the Ervin life is suggested to be added in the relevant standards,which can provide convenience for the end users to choose the suitable abrasive and encourage the manufacturers to improve their manufacturing process and the abrasive quality.The wear process of the high carbon cast steel shot can be concluded that at the lower Ervin cycle,the sample occurs surface peeling lead to a small weight loss;at the higher Ervin cycle,surface peeling gradually develops into core spall lead to a large weight loss,so for the high carbon cast steel shot,the surface peeling is the ideal wear failure mode.But the wear fairlure modes of the high carbon cast steel shot are affected by many factors,such as the heat treatment,Ervin cycle, metallurgical structure and flaws,particle size,target hardness,impact velocity and impact angle.