The Splitting Fracture Defects And Nb-microalloyed Of Air-cooled Medium Carbon Forging Steel Connecting Rod

In recent years,with the rapid development of automobile industry,manufacturing method of automobile engine connecting rod and technology at domestic and overseas to get more and more attention.In order to adapt to the development of lightweight and high power engine developed in carbon connecting rod material as a new material,a typical representative of 36MnVS4 and 46MnVS5,because the material in the comprehensive with the traditional mechanical performance has improved significantly,the current international is gradually popularized as a mainstream material of engine connecting rod.The connecting rod fracture splitting processing technology is a new technology of processing in the 20 century in Germany in 90 s was used in the manufacture of engine connecting rod.Compared with traditional processing the method has been improved in reducing energy consumption,showing great advantages to reduce the process and improve the quality.In this paper,the connecting rod of medium carbon air-cooled and tempered steel 36MnVS4 and 46MnVS5 production as the research object,from the composition,analysis of fractured connecting rod defect microstructure and properties,and finally through the Nb-Microalloyed defect on the connecting rod 46MnVS5 to improve.The main work are as follows.The microstructure,fracture morphology observation and determination of mechanical properties,analysis of the main reasons of 36MnVS4 defects of the connecting rod is of less uniformity.the emergence of a large number of bainite,the content reached 58.5% and 70.6% respectively.The connecting rod fracture uneven austenite grain grain size is too small,8.5~9.0 far more than the standard requirements of more than 6.The surface defects of the connecting rod have different degrees of decarburization,depth of 100~300?m;at the same time,the defects of the connecting rod plastic indexes meet the requirements,and a large amount of surplus,after the reduction of area reached 52.4~57.8%.Through the analysis on the microstructure and properties of 46MnVS5,the defects of the connecting rod research shows that the main reason is that 46MnVS5 fractured connecting rod defects,the organization uniformity is poor.The defects of the connecting rod plastic indexes meet the requirements,and a large amount of surplus,expanding continuously and jagged rod broken behind shrinkage were 39.5% and 43.8%.100?m and 120?m decarburization layer appeared in the connecting rod.Continuous expansion rod bainite reached an average of 86.5%.In order to improve the defects of fractured connecting rod,respectively adding 0.02% Nb and 0.03%Nb addition on microstructure and properties of 46MnVS5 steel.The sample at 900~1250? for 1 hours,46MnVS5 steel grain coarsening temperature without Nb is about 950?.46MnVS5-0.02%Nb and 46MnVS5-0.03%Nb grain coarsening temperature is 1000?.0.02% and 0.03% Nb can improve 50? of the grain coarsening temperature,and with the increase of temperature the grain size trend is basically the same.The maximum decarburization layer is 869?m of the material does not contain Nb,the maximum decarburization layer is 809?m of 46MnVS5-0.02%Nb containing material,and the maximum decarburization layer is 779?m of 46MnVS5-0.03%Nb.With the increase of Nb content,the depth of decarburization layer decreases.Therefore,the addition of Nb can reduce the decarburization layer.Therefore,the addition of 0.03%Nb has a more obvious effect on the improvement of the bulging defect of the 46MnVS5 connecting rod.