FENG Chun
,
FANG Hong-sheng
钢铁研究学报(英文版)
A new hot-rolled low carbon air-cooling bainitic steel containing 0.02%Nb has been developed based on alloying design of the grain boundary allotriomorphic ferrite (FGBA)/ granular bainite (BG) duplex steel.The as-rolled microstructure and mechanical properties of 0.02%Nb bainitic steel were investigated by tensile test, X-ray diffraction(XRD),Optical Microscopy (OM), scanning electron microscopy (SEM) ,and Transmission electron microscopy(TEM). The results show that (1) The addition of 0.02% niobium improves the strength obviously without sacrificing toughness of the FGBA/BG steel. Compared with Non-Nb FGBA/ BG steel, 0.02% Nb increases the tensile strength and yield strength about 20% (From 780Mpa to 937Mpa)and 17%(From 557Mpa to 650Mpa) respectively, remaining 18% elongation and 83J Akv. (2) Small addition of Nb(0.02%) not only refines the allotriomorphic ferrite grain but also promotes the nucleation of intragranular ferrite, both of which in turn contribute to the refinement of granular bainite cluster including its ferrite platelets and M-A islands. Compared with Non-Nb steel, the volume fraction of M-A island in 0.02%Nb steel increases from 21% to 31%, and the average size of M-A island decreases from 1.2μm to 0.95um.(3)There is hardly any Nb(C,N) has been observed in 0.02%Nb steel. It is suggested that the strengthening effect of 0.02%Nb can be mainly attributed to the influence of the segregation of Nb to γ/α phase boundaries(solute drag-like effect) on the phase transformation rather than the precipitation strengthening of Nb(C,N).
关键词:
Low carbon air cooling bainitic steel;Small addition of Nb;Microstructure;Mechanical properties
FANG Hongsheng
,
FENG Chun
,
ZHENG Yankang
,
YANG Zhigang
,
BAI Bingzhe
钢铁研究学报(英文版)
The development and mechanical performances of new type aircooled Mn series bainitic steels including granular bainitic steels, FGBA/BG duplex steels, CFB/M duplex steels, medium carbon bainite/martensite steels, cast bainitic steels invented by the authors are summarized. The novel series of bainitic steels are alloyed with Mn, and several series bainitic duplex microstructures can be easily obtained under the condition of air cooling through unique composition design. The invented idea, the principle of alloying design, the strengthening mechanism, and the evolution of the microstructure of new type aircooled Mn series bainitic steels are presented. Furthermore, the applications in different fields of these Mn series aircooled bainitic steels with different strength level are also introduced. It is suggested that the significance of the development of the aircooled Mn series bainitic steel can be summarized as follows: reducing costs of both raw materials and production; good combination of strength and toughness; selfhardening with high bainitic hardenability by air cooling from hot working without additional quenchingtempering treatment or quenching procedure; large savings in energy resources; and reduced environmental pollution.
关键词:
bainite;bainitic steel;microstructure;mechanical property;air cooling