Papers by Author: Bing Zhe Bai

Abstract: The effect of 0.06%Nb on the microstructure and mechanical properties of grain boundary allotriomorphic ferrite (F_GBA) / granular bainite (B_g) air-cooling bainitic steels has been investigated in this paper. The results indicate that the steel acquires superior mechanical properties by adding 0.06%Nb. Compared with Non-Nb steel, the addition of 0.06%Nb increases the tensile strength and yield strength about 37.1% (From 780MPa to 1070MPa)and 26.6%(From 557MPa to 705MPa) respectively, remaining 18.3% elongation and 97J toughness. The addition of 0.06%Nb not only promotes the nucleation of intragranular ferrite but also refines the allotriomorphic ferrite grain , both of which in turn contribute to the refinement of granular bainite cluster including its ferrite platelets and M-A islands. Under the synthetic roles of the microstructure refinement and precipitation strengthening, 148MPa yield strength improvement has been acquired in the low carbon air-cooling bainitic steel by the adding of 0.06%Nb.

Abstract: The origin and development of air-cooled Mn-series bainite steels are introduced. The invented idea, strengthening-toughening mechanism, mechanical performances, development and application of this kind of steel including granular bainitic steels, FGBA / BG duplex steels, CFB/M duplex steels, medium carbon bainite/martensite steels, cast bainitic steels are presented. The invented idea mechanical performances, development and application of second generation of Mn-series bainitic steels, i.e. water-quenched Mn-series bainitic steels invented by the authors newly are introduced. The water quenched Mn-series bainitic steels can meet the performance requirements of most steels used in engineering structure, reduce the amount of alloying content, increase harden capability and improve weldability. It should be pointed out that the application of both air-cold and water- quenched Mn-series bainitic steels are complementary and mutually reinforcing. Some newest technology of Mn-series bainitic steels in China are discussed in this paper. It is suggested that the significance of the development of the Mn-series bainitic steels can be summarized as: significantly reducing costs of both raw materials and production; good combination of strength and toughness; excellent weldability; simple procedure; large savings in energy resources and environmental pollution is reduced.

Abstract: The effect of four different niobium(From 0-0.1%) addition on the mechanical properties of allotriomorphic ferrite (FGBA)/ granular bainite (BG) air cooling bainitic steels has been investigated in this paper. The results show that (1) The 0.06%Nb steel acquired superior strength and toughness combination by applying 1250°C×60min solution treated, finish rolling at 850°C, and air cooling. The corresponding mechanical property of the thick plate (30mm) is: σb>1050MPa, σ0.2>700MPa, δ5>17%, Akv>90J. (2) The addition of niobium refine the grain size of FGBA, and promoted the transformation of bainite structure. With the increase of niobium content, the refinement of ferrite grain and bainitic cluster is improved. (3) More refined M-A island is acquired by the small addition of niobium. According to M-A Analysis tools and transversal methods, with the rise of niobium content, the volume fraction of M-A island increase from 21% to 35%, and the average size of M-A island decrease from 1.1μm to 0.7um. (4) It is suggested that 0.02-0.06% niobium can improve the mechanical properties of the steel obviously. However, excess addition of Nb (0.1%) deteriorates the impact toughness obviously. (5) Under the synthetic roles of the microstructure refinement and precipitation strengthen, 60-160MPa yield strength improvement has been acquired in the low carbon air cooling bainitic steel by the small addition of niobium. (6) This steel is with low production cost since the alloying element Mn is cheap.

Abstract: The effect of four different niobium(From 0-0.1%) addition on the mechanical properties of allotriomorphic ferrite (FGBA)/ granular bainite (BG) air cooling bainitic steels has been investigated in this paper. The results show that (1) The 0.06%Nb steel acquired superior strength and toughness combination by applying 1250°C×60min solution treated, finish rolling at 850°C, and air cooling. The corresponding mechanical properties of the thick plate(30mm) is: σb>1050MPa, σ0.2>700MPa,δ5>17%,Akv>90J. (2) The addition of niobium refine the grain size of FGBA, and promoted the transformation of bainite structure. With the increase of niobium content, the refinement of ferrite grain and bainitic cluster is improved. (3) More refined M-A island is acquired by the small addition of niobium. According to M-A Analysis tools and transversal methods, with the rise of niobium content, the volume fraction of M-A island increase from 21% to 35%, and the average size of M-A island decrease from 1.1μm to 0.7um. (4)It is suggested that 0.02-0.06% niobium can improve the mechanical properties of the steel obviously. However, excess addition of Nb (0.1%) deteriorates the impact toughness obviously. (5)Under the synthetic roles of the microstructure refinement and precipitation strengthen, 60-160MPa yield strength improvement has been acquired in the low carbon air cooling bainitic steel by the small addition of niobium. (6)This steel is with low production cost since the alloying element Mn is cheap.

Abstract: The air cooling rate of the Low Carbon Mn-Si-Cr steel bar with different diameter after austenitizing at 910oC and 960oC was simulated by Formaster-F Phase transforming instrument and Gleeble-1500 thermal /mechanical simulating machine. Microstructure of the specimen was observed by OLYMPUS PME3 optical microscope and FEI QUANTA200F scanning electron microscope. The hardness and impact toughness of the steel was tested by HBRV-187.5 hardness tester and JCSJ300-I instrumented Charpy impact tester. The experimental result showed that with the amount of CFB in CFB+M mixed microstructure increasing the combination of strength and toughness of the steel was improved. The higher the austenitizing temperature of the steel, the wider the air-cooling rate range obtaining CFB+M mixed microstructure. However, the steel produces mixed grain after austenitizing at 960 oC. For obtaining fine prior austenite grain size, Ti and Nb alloying element need to be added.

Abstract: The influence of temperature, strain rate, strain on mechanical parameters and microstructure evolution in isothermal deformation of GH4169 alloy were investigated. Lower resistance is obtained under higher temperature and or lower strain rate. However, coarser microstructure also is gained under such condition. The tensile property at room temperature and elevated temperature, permanent properties at elevated temperature of the GH4169 alloy with the treatment of “direct aging after isothermal deformation” are better than those of the same alloy with the treatment of solid-solution+direct aging after isothermal deformation. Isothermal forming was undertaken for a 1/4 size simulated part of a kind of turbo disk of an aviation engine. Its external is fine and the microstructure of the material was fine and homogeneous for both straightly after forming and after direct aging.