Stress relaxation behavior of two turbine bolt steels was evaluated by the manual-controlled tensile stress relaxation test (TSRT) at high temperature. First, feasibility and the procedure of the manual-controlled ten...Stress relaxation behavior of two turbine bolt steels was evaluated by the manual-controlled tensile stress relaxation test (TSRT) at high temperature. First, feasibility and the procedure of the manual-controlled tensile stress relaxation test (TSRT) is discussed and carried out on a general creep testing machine. And then, the experimental results from such type of test were compared to the existing data provided by certain Laboratory U.K. Overall good agreement between the results of manual-controlled TSRT method and the existing data provides confidence in the use of the proposed method in practice. Finally, the experimental results of turbine bolt steels from TSRT were compared with that of bending test. It is observed that great difference exists between the results from two different type stress relaxation tests. It is therefore suggested that the results from TSRT method be adopted in turbine bolt design in engineering.展开更多
By the increase in Mo content,the addition of microalloying elements V and Nb and by reducing the contents of Mn,P and S based on the composition of steel 42 CrMo,we have developed a 1 300 MPa-grade high strength stee...By the increase in Mo content,the addition of microalloying elements V and Nb and by reducing the contents of Mn,P and S based on the composition of steel 42 CrMo,we have developed a 1 300 MPa-grade high strength steel(ADF1)for bolts.The sustained load bending test,sustained load tensile test and stress corrosion cracking test have been carried out to evaluate the delayed fracture resistance of steel ADFl and commercial steel 42 CrMo.The results showed that steel ADF1 has superior delayed fracture resistance to that of 42 CrMo steel.It's concluded that the superior delayed fracture resistance of ADF1 is mainly due to the increase of tempering temperature,fine homogeneously distributed MC carbide and fine prior austenite grain size.展开更多
In this study, the effect of vanadium addition(0.25%) on microstructure and hydrogen embrittlement(HE) was investigated in grade 12.9 bolt steels, and hydrogen diffusion was analyzed by hydrogen permeation.The results...In this study, the effect of vanadium addition(0.25%) on microstructure and hydrogen embrittlement(HE) was investigated in grade 12.9 bolt steels, and hydrogen diffusion was analyzed by hydrogen permeation.The results show that the addition of 0.25% vanadium in bolt steels can significantly improve the HE resistance.Vanadium addition can form a large number of vanadium precipitates, resulting in the uniform distribution of hydrogen and reduction of hydrogen accumulated at local grain boundaries, which promotes the inhibition of hydrogen-induced cracking.展开更多
The hydrogen-induced delayed fracture(HIDF)behavior of a 1300-MPa-grade high-strength bolt steel 42CrMoV containing 0.42 wt.%Cu was investigated by constant load tensile test in a pH 3.5 Walpole solution.It is shown t...The hydrogen-induced delayed fracture(HIDF)behavior of a 1300-MPa-grade high-strength bolt steel 42CrMoV containing 0.42 wt.%Cu was investigated by constant load tensile test in a pH 3.5 Walpole solution.It is shown that the addition of Cu is beneficial to enhance the HIDF resistance by~13%.The observation of the fracture surface revealed that the area fraction of brittle crack initiation zone decreased remarkably for the Cu-added steel.Both the corrosion pit depth and the corrosion rate of the Cu-added steel in the Walpole solution are notably decreased,which is primarily because of the formation of a Cu-rich protective compact rust layer and slightly higher corrosion potential.As a result,the absorbed hydrogen content in that solution was also decreased by~21%.It is concluded that the improvement in the HIDF resistance of the tested steel is primarily due to the increase in corrosion resistance and resultant decrease in the absorbed diffusible hydrogen content in the acidic condition.展开更多
The loading capacity in the axial direction of a bolted thin steel plate was investigated.A refined numerical model of bolt was first constructed and then validated using existing experiment results.Parametrical analy...The loading capacity in the axial direction of a bolted thin steel plate was investigated.A refined numerical model of bolt was first constructed and then validated using existing experiment results.Parametrical analysis was performed to reveal the influences of geometric parameters,including the effective depth of the cap nut,the yield strength of the steel plate,the preload of the bolt,and shear force,on the ultimate loading capacity.Then,an analytical method was proposed to predict the ultimate load of the bolted thin steel plate.Results derived using the numerical and analytical methods were compared and the results indicated that the analytical method can accurately predict the pull-through capacity of bolted thin steel plates.The work reported in this paper can provide a simplified calculation method for the loading capacity in the axial direction of a bolt.展开更多
文摘Stress relaxation behavior of two turbine bolt steels was evaluated by the manual-controlled tensile stress relaxation test (TSRT) at high temperature. First, feasibility and the procedure of the manual-controlled tensile stress relaxation test (TSRT) is discussed and carried out on a general creep testing machine. And then, the experimental results from such type of test were compared to the existing data provided by certain Laboratory U.K. Overall good agreement between the results of manual-controlled TSRT method and the existing data provides confidence in the use of the proposed method in practice. Finally, the experimental results of turbine bolt steels from TSRT were compared with that of bending test. It is observed that great difference exists between the results from two different type stress relaxation tests. It is therefore suggested that the results from TSRT method be adopted in turbine bolt design in engineering.
基金Sponsored by National Key Fundamental Research Project(G1998061503)
文摘By the increase in Mo content,the addition of microalloying elements V and Nb and by reducing the contents of Mn,P and S based on the composition of steel 42 CrMo,we have developed a 1 300 MPa-grade high strength steel(ADF1)for bolts.The sustained load bending test,sustained load tensile test and stress corrosion cracking test have been carried out to evaluate the delayed fracture resistance of steel ADFl and commercial steel 42 CrMo.The results showed that steel ADF1 has superior delayed fracture resistance to that of 42 CrMo steel.It's concluded that the superior delayed fracture resistance of ADF1 is mainly due to the increase of tempering temperature,fine homogeneously distributed MC carbide and fine prior austenite grain size.
文摘In this study, the effect of vanadium addition(0.25%) on microstructure and hydrogen embrittlement(HE) was investigated in grade 12.9 bolt steels, and hydrogen diffusion was analyzed by hydrogen permeation.The results show that the addition of 0.25% vanadium in bolt steels can significantly improve the HE resistance.Vanadium addition can form a large number of vanadium precipitates, resulting in the uniform distribution of hydrogen and reduction of hydrogen accumulated at local grain boundaries, which promotes the inhibition of hydrogen-induced cracking.
基金This work was financially supported by the National Natural Science Foundation of China(Grant No.52071010).
文摘The hydrogen-induced delayed fracture(HIDF)behavior of a 1300-MPa-grade high-strength bolt steel 42CrMoV containing 0.42 wt.%Cu was investigated by constant load tensile test in a pH 3.5 Walpole solution.It is shown that the addition of Cu is beneficial to enhance the HIDF resistance by~13%.The observation of the fracture surface revealed that the area fraction of brittle crack initiation zone decreased remarkably for the Cu-added steel.Both the corrosion pit depth and the corrosion rate of the Cu-added steel in the Walpole solution are notably decreased,which is primarily because of the formation of a Cu-rich protective compact rust layer and slightly higher corrosion potential.As a result,the absorbed hydrogen content in that solution was also decreased by~21%.It is concluded that the improvement in the HIDF resistance of the tested steel is primarily due to the increase in corrosion resistance and resultant decrease in the absorbed diffusible hydrogen content in the acidic condition.
基金The work described in this paper was financially supported by the Project funded by China Postdoctoral Science Foundation(No.2017M621156)the State Key Research Development Program of China(Nos.2016YFC0801404 and 2016YFC0600704).
文摘The loading capacity in the axial direction of a bolted thin steel plate was investigated.A refined numerical model of bolt was first constructed and then validated using existing experiment results.Parametrical analysis was performed to reveal the influences of geometric parameters,including the effective depth of the cap nut,the yield strength of the steel plate,the preload of the bolt,and shear force,on the ultimate loading capacity.Then,an analytical method was proposed to predict the ultimate load of the bolted thin steel plate.Results derived using the numerical and analytical methods were compared and the results indicated that the analytical method can accurately predict the pull-through capacity of bolted thin steel plates.The work reported in this paper can provide a simplified calculation method for the loading capacity in the axial direction of a bolt.