HU Zhizhong WU Yusheng CAI Heping MA Lihua Xi′an jiaotong University
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Xi′an
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China Senior Engineer
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Res.Inst.for Strength of Metals
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Xi′an jiaotong University
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Xi′an 710049
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China
金属学报(英文版)
Studies have been made of the torsional fatigue fracture life of notched specimens,the macroscopic fractography and microscopic fracture mechanism of steel 40Cr after various tempering treatments under different stresses,With the increase of stress,the fracture model changes from normal stress fracture to longitudinal shear one,and then transversal shear one. Under same stress,with the increase of strength,the fracture mode transfers from shear to normal stress fracture.The mechanism of normal stress fracture may be:transgranular frac- ture→striation+intergranular fracture→dimple+intergranular fracture,and of shear fracture may be:transgranular fracture→shear trace→dimple.Based on the experimental results,a fracture mechanism map of torsional fatigue has been drawn up.
关键词:
mechanism map
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CHEN Zheng Northwestern Polytechnical University
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Xi′an
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China Lab.No.401
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Northwestern Polytechnical University
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Xi′an 710072
金属学报(英文版)
Threshold of fatigue for short through cracks for Al-Li alloy 8090 was evaluated to be lower than that of long cracks,and to decrease with the shortening of the crack length.The correla- tion among the threshold,crack wake,and crack tip shielding of the short fatigue cracks was discussed.The super demarcation length and lowest theoretical threshold of short through fa- tigue cracks were presented.
关键词:
Al-Li alloy
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CHEN Daming KANG Mokuang Northwestern Polytechnical University
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Xi′an
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ChinaTAN Ruobing Institute of Metal Research
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Academia Sinica
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Shenyang
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China
金属学报(英文版)
The microstructure,strength,toughness and fatigue properties of an ultra-high strength steel 40CrMnSiMoVA have been investigated.The so-called meta-bainite,composed of thin re- tained austenite films within or between the bainitic ferrite lathes was found in the steel after isothermally quenched at 300℃ for 1h.In comparison with the martensite structure obtained by isothermally quenching in martensite range,the meta-bainite has more excellent strength and plasticity,lower notch sensitivity,stronger strain harden ability,higher fatigue strength, longer strain or impact fatigue life,slower crack propagation rate and more remarkable overload effect on increasing fatigue life.
关键词:
ultra-high strength steel
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WANG Hongwei MA Jinsheng NAN Junma HE Jiawen Xi′an Jiaotong University
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Xi′an
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China
金属学报(英文版)
The surface yield strength(σ_(ms))for various carbon steels was studied by means of X-ray diffraction method.The results showed that it is.far below the bulk yield strength,and is the resistance against plastic deformation in the surface layer.The smooth fatigue limit is associ- ated with crack initiation which is a result of accumulation of plastic deformation.Experimen- tal results showed the relation of smooth fatigue limit for 50% survival with σ_(ms)is σ_(ms)=0.81 tO 1.02 σ_(-1)for different steels.The smooth fatigue limit of a medium carbon steel for 99.9% survival with σ_(ms)is σ_(ms)=0.98 tO 1.10 σ_(-1).It is less expensive and time consuming to measure σ_(ms)than σ_(-1).
关键词:
X-ray
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WANG Zhaoxia CHAI Donglang LIU Jinghua Xi′an Jiaotong University
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Xi′an
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China
金属学报(英文版)
On the basis of stress-strain analysis under cyclic loading,the mechanism,origin and cyclic number of microcraek nucleation of duplex structure materials,saying ferrite plus martensite, have been experimentally studied and calculated.Both results are in fair mutual agreement. The morphology,distribution,size and relative quantities of the constitutional phase,especial ly strengthening phase,as well as the stress-strain distribution and variation in micro-region are directly influential in the origin of microcracks in duplex structure materials.
关键词:
stress-strain analysis
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WANG Xiaotian YAO Yinliang SHAO Tanhua Xi′an Jiaotong University
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Xi′an
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China
金属学报(英文版)
The microstruetural transformation of steels:20SiMn2V,20SiMn2VRE,40SiMn2V and 40SiMn2VRE during quenching and tempering have been examined by TEM,X-ray diffraction and dilatometer.It was shown that the addition of rare earth metals not only can refine the austenite grains of the low or medium carbon steels and packet of lath martensite and lath size,lower the M_s temperature,but can also raise the relative percentage of disloca- tion substructure of martensite in medium carbon steel,but there is little effect on volume frac- tion and thermal stability of retained austenite quenching and tempering structure of low or medium carbon steels.The rare earth metals may remarkably inhibit the decomposition of low carbon martensite during low temperature tempering,retard the precipitation of cementite plates in lath grains and delay the spheroidization of carbides.They may also restrain obvious- ly the precipitation and spheroidization of cementite in medium carbon martensite during high temperature tempering.
关键词:
rare earth metals
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ZHOU Weixian Northwestern Polytechnical University
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Xi′an
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China
金属学报(英文版)
Based on the experimental data,it was clarified that the plastic strain ratio R-value is not equal to Hill's r-value for Ti sheet.From the non-quadratic orthotropic yield function pro- posed recently by the author,an optimal expression between yield stress and r-value for Ti sheet was developed on overall investigation.The suitable value of exponent in the function seems to be 6—8.Thus,an equation was suggested to estimate strength for the pressure vessel made of Ti sheet.
关键词:
Ti sheet
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YAN Wen Xi′an Institute of Technology
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Xi′an
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China
金属学报(英文版)
The symmetrical superlattice intrinsic stacking faults(SISFs)formed on {111} planes are the predominant crystal defects in polycrystalline Ni_3AI after slight deformation at room temper- ature.The formation of this kind of SISF is resulted from the dipoles which are distributed on the neighboring {111} planes after reorientation,dissociation and annihilation under applied stress.
关键词:
deformed Ni_3Al
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LI Yongjun Xi′an Jiaotong University
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Xi′an
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China
金属学报(英文版)
Fatigue crack propagation rate,da/dN,and threshold stress intensity range,ΔK_(th),of steel 20CrMnMo containing low carbon martensite or low carbon martensite/bainite(LCM/B) duplex structure,obtained by oil quenching and austempered at 360℃,have been measured using specimens under four-point bending.Observation was also made of the crack path and fracture morphology with relation to microstructure.The formation of LCM/B duplex structure,which caused by 20% lower bainite after short-time isothermal treatment,may re- markably increase ΔK_(th)and considerably decrease da/dN.The effect of microstructure on da/dN and ΔK_(th)was discussed with the emphasis on the crack propagation path.
关键词:
low carbon martensite
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