Effect of bainite microstructure during two-step quenching and partitioning process on strength and toughness properties of a 0.3%C bainitic steel
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The effect of bainite transformation and microstructure on the mechanical properties in 0.3%C bainitic steel was investigated via the heat treatment process of quenching at higher initial temperature and partitioning below martensite-start temperature. The results show that bainite transformation takes place with the partitioning time increasing during partitioning below martensite-start temperature. The microstructure of samples treated by this two-step quenching and partitioning process consists of lath bainite, lath martensite and retained austenite. This kind of multiphase microstructure exhibits better strength of 1420 MPa, ductility of 21.8% and the product of strength and elongation of 30.8 GPa%. Furthermore, the excellent impact toughness of 103 J is exhibited by partitioning at 280 °C for 3 h. In addition, the coalescence of bainite platelets was found in the sample treated by partitioning for 8 h, leading to the deterioration of toughness.
KeywordsQuenching and partitioning Bainitic steel Impact toughness Coalesced bainite
This research was supported by the Science & Technology Department of Sichuan Province, China (No. 2014GZ0087) and the Scientific Research Foundation for Young Teachers of Sichuan University (No. 2014SCU11019). The authors also express their great gratitude to Mr. Xiong-fei Yang from Pangang Group Research Institute Co., Ltd. for the kind help of TEM experiment.
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