| Bainite/Martensite duplex-phase steel has a widely application prospect in the field of rail transportation,construction and machinery for its outstanding mechanical property.This article is based on the “973 Program – Research of new type of bainite wheel-track material of High-performance”,taken the “Natural Science Foundation of China – study on VHCF Behavior and Mechanism of Non-inclusion Induced Crack Initiation of Bainite/Martensite Duplex-phase High Strength Steel‘ as the main content and research objectives of the work,studied character of very high cycle fatigue of typical bainite/martensite duplex-phase steel together with its mechanism of crack initiation.The text takes bainite rail produced by commercial process as experimental subject.In order to acquire different typical bainite/martensite duplex-phase microstructure,three heat treatment process have been designed.The microstructure of SG1 is constitute by acicular bainite,lath bainite and lath martensite,which possesses favourable matching of obdurability.Hence SG1 and SG4(the contrast sample of GG3)have been chosen to conduct ultrasonic fatigue test(vibrational frequency is 20000 Hz)to study the very high cycle fatigue behavior of theirs.Through elaborate observation of non-inclusion crack initiation and the statistics of relationship between fatigue life and fracture parameter,the frequency of inclusion and microstructure to the crack initiation of bainite/martensite duplex-phase steel has been deeply analyzed,at the same time,the mechanism of non-inclusion induced crack initiation of bainite/martensite duplex-phase steel has been studied.The study found that during the process of very high cycle fatigue,crack extension in the GBF zone and Fish eye zone have impacted fatigue life jointly and different failure mode has a enormous influence to the relationship between fatigue life and weight ratio of GBF and Fish eye.The research had proved that M/A island near prior austenite grain boundary would deformation-induced martensitic transformation on the function of cyclic load,and create carbon-rich martensite which would have brittle fracture and create microcrack that would lead to fatigue failure. |
PDF Full Text Request