Analysis on Drop-Dregs Defect of C70S6 Fracture Splitting Connecting Rod
The drop-dregs defect is the main quality problem of C70S6 non-quenched and tempered steel fracture splitting connecting rod.In order to explore the causes of drop-dregs,the chemical composition and content of two C70S6 connecting rods with and without drop-dregs were compared and analyzed.The fracture morphology,non-metallic inclusions and microstructure of the steels near the fracture were observed and analyzed by means of metallographic microscope and scanning electron microscope.The results show that the content of N in the 1#(drop-dregs)steel is low.Properly increasing the content of N is conducive to improve the expansion and fracture performance of connecting rod.The non-metallic inclusions in the connecting rods are mainly MnS.The inclusions in the 2#connecting rod are smaller and more numerous than those in the connecting rod 1#,especially at the end of the fracture,and it causes the plasticity of the 2#(without drop-dregs)connecting rod is lower than that of the connecting rod 1#,and it is conducive to fracture splitting.The microstructure of C70S6 fracture splitting connecting rod is ferrite+pearlite,and 1#connecting rod pearlite accounts for 97%-99%.There is mixed crystal structure with different grain sizes in the middle area.Too high pearlite content and mixed crystal structure are the main reasons for connecting rod drop-dregs defect.
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