Z.D. Wang
,
J.B. Qu
,
X.H. Liu and G.D. Wang(State Key Lab of Rolling and Automation
,
Northeastern University
,
Shenyang 110006
,
China)
金属学报(英文版)
The influence of hot deformation conditions on continuous cooling bainitic transformation has been investigated for a low carbon microalloyed steel. The CCT diagrams show that deformation in unrecrpstallized austcnite ation can accelerate transformation process. Bainitic transformation in intermediate transformation temperature region is prominent, and the proeutectoid polygonal ferrite transformation at evelated high temperature is suppressed. According to optical and TEM analyses, low carbon bainitic ferrite is characterized by granular and lathlike ferrite, based on the cooling rate and deformation conditions. For nondeformation, groaps of coarse parallel ferrite lath form from the prior austenite grain boundaries with the same crystallographic orientation. For heavy deformaton, cell structure within the austenite grains due to the high dislocation density formed, which provides more nucleation sites for bainite ferrite. So deformation can discontinue the growth of ferrite laths and decrease the length of ferrite laths.
关键词:
bainite
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null
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null
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null
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null
Z.X. Wu and X.F. Sun ( Institute of Applied Mechanics
,
Southwest Jiaotong University
,
Chengdu 610031
,
China State Key Laboratory for Fatigue and Fracture of Materials
,
Institute of Metal Research
,
Chinese Academy of Sciences
,
Shenyang 110015
,
China)
金属学报(英文版)
The behavior of part-through and through short cmcks in single edge blunt notched specimens of a medium carbon steel was investigated by a replication method. It is found that the fatigue failure of these notched specitnensis caused mainly by the growth of short surface cracks originating from the sudece of notch root. More than 70% of the fatigue lofe is spent in the regimes in which short surface cracks initiate and propagate as part-through cracks before joining up to form a single through-thickness cmck. The effect of original crack profile which is forsned through the coalescence of multiple part-through cracks is the main reason causing the "anomalous" propagation behavior of the through-thickness cruck in its early stage.
关键词:
medium carbon steel
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null
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null
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null
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null
钢铁研究学报(英文版)
The fine microstructures of medium and medium-high carbon bainitic steels were observed and analyzed by high resolution electron microscope (HREM). The investigation results show that there are retained austenitic films with different appearances and sizes in bainitic ferrite laths. The boundaries of different structure levels are separated and encircled by retained austenitic films. The fine structure units and their sizes of different structure levels in the bainitic ferrite were determined by retained austenitic films. The bainitic ferrite laths are composed of different structure level sublaths, subunits and elementary units (or so called sub-subunits). The dimensions of most sublaths, subunits and elementary units are 25-80 nm, 2580 nm and 5.0-30 nm, respectively.
关键词:
steel;bainite;ferrite;retained austenitic;microstructure
WANG Yong-Wei
钢铁研究学报(英文版)
The effect of Nb on the microstructure evolution of low carbon Mn series air cooling bainitic steels has been discussed in this paper by using Gleeble 1500D, SEM, and TEM observation. The results show that: The amount of grain boundary allotriomorphic ferrites is relatively higher in non-Nb bearing steel than Nb-bearing steel under same deformation conditions. And the ferrites in Nb bearing steel are more finer. With the decreasing of finishing rolling temperature (FRT), the particles of Nb(CN) precipitating in Nb bearing steel are smaller and more dispersive. The properties of the Nb bearing steel is higher than that of non-Nb bearing steel at same FRT, and it is suggested that the toughness of Nb Micro-alloyed steel will be improved more effectively than that of non-Nb bearing steel with the decreasing of FRT.
关键词:
Mn-series bainitic steel;grain boundary allotriomorphic ferrites;finishing rolling temperature;Nb micro-alloyed;toughness
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
Liangyun LAN
金属学报(英文版)
Thermomechanical process and tempering heat treatment were employed to produce the experimental steel plates. The effect of boron addition on the microstructure and mechanical properties of low carbon bainitic steels was studied in this paper. Microstructure observation and crystallographic features were conducted by using optical microscopy, SEM, TEM and electron back scattering diffraction (EBSD) analysis. The results showed that under the same rolling processes and heat treatment conditions, a substantial increase in strength is obtained by addition of boron into steel, but accompanied by an obvious drop in toughness. New martensite phase forms along the grain boundaries on tempering at 650 ℃ mainly due to boron segregation, which can further deteriorate impact toughness of the boron bearing steel. The EBSD analysis showed that high angle grain boundary is not responsible for the deteriorated toughness of the boron bearing steel because it has relatively higher percentage of high angle grain boundary than the boron free steel. The low toughness of the boron bearing steel is mainly attributed to the coarse boride precipitated particles according to the results of fractograph observation.
关键词:
Low carbon bainitic steel
DU Jiaju TONG Shihua Institute of Solid State Physics
,
Academia Sinica
,
Hefei
,
China [Originally published in ACTA METALL SIN(CHINESE EDN)25(3)1989 pp A226—A228
,
Associate Professor
,
Institute of Solid State Physics
,
Academia Sinica
,
Hefei
,
China
金属学报(英文版)
Optical microscope,SEM and IMMA investigation show that a strong interaction between hydrogen and calcium aluminate inclusions containing MgO may occur in medium carbon steels.This causes the hydrogen accumulating around the inclusions and reducing the ductility of the steel.
关键词:
hydrogen
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null
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null
NIE Yihong
,
HUI Weijun
,
FU Wantang
,
WENG Yuqing
钢铁研究学报(英文版)
The delayed fracture behavior of mediumcarbon high strength spring steel containing different amounts of boron (0000 5%, 0001 6%) was studied using sustained load delayed fracture test. The results show that delayed fracture resistance of boron containing steels is higher than that of conventional steel 60Si2MnA at the same strength level and it increases with the increase of boron content from 0000 5% to 0001 6%. The delayed fracture mode is mainly intergranular in the boron containing steels tempered at 350 ℃, which indicates that the addition of boron does not change the fracture character. However, the increase of boron content enlarges the size of the crack initiation area. Further study of phase analysis indicates that most boron is in solid solution, and only a very small quantity of boron is in the M3(C, B) phase.
关键词:
boron;delayed fracture resistance;mediumcarbon high strength spring steel
