The addition of boron（B） is frequently adopted to increase the hardenability of bainitic steels. Although it is well known that B can retard the bainitic transformation kinetics, it is still not clear how the B affe...The addition of boron（B） is frequently adopted to increase the hardenability of bainitic steels. Although it is well known that B can retard the bainitic transformation kinetics, it is still not clear how the B affects the bainitic transformation kinetics after ausforming. By systematic high-resolution dilatometry tests, the present work reveals that the bainitic transformation kinetics is accelerated in a low C steel with B addition after ausforming from all aspects including incubation time, transformation velocity and transformed volume fraction. In contrast, for the same steel without B addition, both transformation velocity and transformed volume fraction are retarded after ausforming. It is proposed that ausforming can reduce B segregation at prior austenite grain boundaries as some boron can interact with dislocations and therefore enhance bainite nucleation rate. Furthermore, auforming can refine the average volume of bainitic sheaf. Based on the competing mechanisms between increase of nucleation rate and refinement of bainitic sheaf, the effects of B and ausforming on the bainitic transformation kinetics are discussed.展开更多
基金the financial support by the Steel Joint Funds of the National Natural Science Foundation of China(Grant No.U1560204)National Natural Science Foundation of China(Grant No.51301148)+2 种基金the Research Grants Council of Hong Kong(Grant Nos.HKU719712E,HKU712713E,17203014)Shenzhen Science,the Technology and Innovation Commission(Grant No.JCYJ20150629151046886)financial support from National Natural Science Foundation of China(Grant No.51574080)
文摘The addition of boron（B） is frequently adopted to increase the hardenability of bainitic steels. Although it is well known that B can retard the bainitic transformation kinetics, it is still not clear how the B affects the bainitic transformation kinetics after ausforming. By systematic high-resolution dilatometry tests, the present work reveals that the bainitic transformation kinetics is accelerated in a low C steel with B addition after ausforming from all aspects including incubation time, transformation velocity and transformed volume fraction. In contrast, for the same steel without B addition, both transformation velocity and transformed volume fraction are retarded after ausforming. It is proposed that ausforming can reduce B segregation at prior austenite grain boundaries as some boron can interact with dislocations and therefore enhance bainite nucleation rate. Furthermore, auforming can refine the average volume of bainitic sheaf. Based on the competing mechanisms between increase of nucleation rate and refinement of bainitic sheaf, the effects of B and ausforming on the bainitic transformation kinetics are discussed.
