Study Of Low Temperature Impact Property On Low Temperature Ductile Iron 400-18LT

As a fine engineering material,400-18 LT low temperature ductile iron has ver y good performance of fracture and impact toughness.This kind of material has already been globally widely applied in the industry of transportation,wind power and special equipment industry.Especially within transportation railway rolling stock industry,the low temperature impact toughness of the critical components is a key performance indicator of the material.This article focus on research and study of fundamental factors of this material when it's applied to mass production.The critical temperature factors of this 400-18 LT low temperature fine impact ferrite based ductile iron are Temperature of ductile brittle transition(DBT),temperature of actual working environment and precise measurement of the testing temperature.This article focus also on the study of influence of low temperature impact,chemical composition and heat treatment to this material.The inflection point of low temperature impact of this material has been discovered and determined by the test.The DBT of this ductile iron material according to dimple surface occupies 50% of the fracture surface is-72.4?.Impact fracture happened above this temperature should be classified as ductile fracture,on the other hand,those fracture happened below this temperature is considered as brittle facture.Through a series of low temperature impact experiment,a common methodology of material research has been summarized.This methodology can be applied as fundamental in the future for analysis of both low temperature impact of other ductile iron material and other similar metal material.By making analysis and comparison of the picture of low temperature fracture surface scanned by SEM,key factors of the material manufacturing like heat treatment,add of alloy elements,chemical composition is studied.After heat treatment,the low temperature toughness can be improved,all the base of the material is converted to ferrite phase.At the same time,heat treatment can also refine the grain size,improve the layout of graphite nodule.As one of the vital alloy element added,Nickel plays solution strengthening in the material.The composition of alloy materialis strictly controlled in the low temperature ductile iron,in this way,Nickel can also make the material stronger without sacrificing the low temperature toughness.Concerning mass production procedure,except heat treatment process,chosen of raw material,smelting process and nodulizing-inoculating process are also the key factors to the production of low temperature ductile iron.This article focus more on the mass production application of the research.The key factors of usage and production are summarized during the series of test.It is proved that the quality of the material can be guaranteed under sufficient quality control.Through observing and studying the micro-appearance(SEM)of the fracture from 0? to-120?,we try to find out the mechanism of impact fracture and ductile brittle transition(DBT).Finally we get the low temperature impact curve of the material and measured the ductile brittle transition temperature.At the same time,the factor those will affect the mechanism are analyzed.The production procedure is then promoted according to the analysis.The low temperature impact value goes down when the test temperature decreases.Per study of impact curve,the temperature of ductile brittle transition is-74.3?.When the test temperature goes down,rate of the crystalline area of the fracture surface is increasing,the fracture surface morphology shapes from dimple to cleavage plane.Considering the fact that on the other curve the DBT is-72.4?.We consider the test is successful and matches the realistic.