FU Changpu HAN Yong Shaanxi Mechanical Engineering Institute
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Xi'an
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China FU Changpu
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associate professor
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Department of Materials Engineering
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Shaanxi Mechanical Engineering Institute
,
Xi'an 710048
,
China
金属学报(英文版)
Studies were made of the effect of tempering at temperatures from 25 to 750℃ for 0.5 to 100 h on changes of hardness,precipitated phase and its alloying element content as well as activation energy of tempering for quenched steel 20Cr11MoVNbNB.Tempering of the steel at temperatures below 400℃ may be controlled by the diffusion of C atoms in α-Fe,and above 400℃,by diffusion of Cr,also Mo or V,in α-Fe.
关键词:
steel 20Cr11MoVNbNB
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FU Changpu HAN Yong
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L(?) Shuangyun AN Yunzheng Shaanxi Mechanical Engineering Institute
,
Xi'an
,
ChinaPAN Jingda DU Wenfeng Beijing Heavy Electric Machine Works
,
China associate professor
,
Department of Materials
,
Shaanxi Mechanical Engineering Institute
,
Xi'an 710048
,
China
金属学报(英文版)
Studies were made of the creep properties and structure change of steet 20Cr11MoVNbNB at 550-650℃.It is found that at 550℃ when creep stress>180 MPa there exists linear rela- tion with two different slopes β_1 and β-2 between transitional creep strain ε_β and creep time t~(1/3),and β_1(in initiol period)>β_2(in later period).The Creep rate of stable stage at 550℃ can be expressed by =Aσ exp(-Q_ /RT),where,n=4.7.A exp(-Q_ /RT)= 5.37×10~(-16).Apparent creep activation energy Q_ =430 kJ/mol at 550-650℃,which is much higher than the self-diffusion activation energy of atoms for matrix Fe.In creep process,as the creep stress and time increase,the total weight of precipitated phases and rela- tive weight of Cr,Mo and V increase,but those of Fe and Nb decrease in precipitated phases,
关键词:
20Cr11MoVNbNB
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TAN Yuxu REN Liping LI Gang Xi'an Jiaotong University
,
Xi'an
,
China TAN Yuxu Associate Professor
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Institute of Metallic Materials and Strength
,
Xi'an Jiaotong University
,
Xi'an 710048
,
China
金属学报(英文版)
In the strengthened layer of stainless steel after shot peening,there are a great amount of deformation microtwins which may act as structural strengthening factor and prevent the gradual relaxation of surface residual stress during fatigue,so as to keep its rather high level of bending fatigue strength.However,in the strengthened surface layer of low carbon steel, dislocation cell structure is so unstalbe during fatigue that its surface residual stress relaxation cannot be retarded.Therefore,the bending fatigue strength of the low carbon steel can not be improred by shot peening.
关键词:
substructure
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JING Xiaotian LOU Bingzhe GU Chenqing SHEN Fusan Shanxi Institute of Mechanical Engineering
,
Xi'an
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China Dept.of Materials
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Shanxi Institute of Mechanical Engineering
,
Xi'an 710048
,
China
金属学报(英文版)
The morphology of the retained austenite in the carburized case of 20CrNiMo steel and its transformation during fatigue crack propagation through the case were investigated by using X-ray and TEM analysis.In the carburized case both film and block shaped retained austenite were found.Due to the crystallographic orientation relationship at the interface,the fatigue crack is inclined to pass through the block shaped retained austenite and thereby stim- ulates its strain-induced martensitie transformation.During the process of the fatigue frac- ture,most of the retained austenite structures on the crack path are transformed into the martensite,and the untranaformed parts on the fracture surface remain less than 6%.The transformation of the retained austenite,which is restrieted mainly within the plastic zone,oc- curs only during the proeess of fracture,and is independent of the magnitudes of the external stress,stress ratio and cyclic number.The volume expansion accompanying the transforma- tion creates an additional residual displacement of about 0.44μm on fracture surfaces,which is equivalent to the magnitude of the plasticity-induced residual displacement.The phase transformation induced fatigue crack closure is believed to be an important factor affecting the fatigue crack behaviors in the high carbon laver of the carburized case.
关键词:
retained austenite
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