The application of response surface methodology was highlighted to predict and optimize the percentage of dilution of iron-based hardfaced surface produced by the PTA （plasma tratisferred arc welding） process. The e...The application of response surface methodology was highlighted to predict and optimize the percentage of dilution of iron-based hardfaced surface produced by the PTA （plasma tratisferred arc welding） process. The experiments were conducted based on five-factor five-level central composite rotatable design with full replication technique and a mathematical model was developed using response surface methodology. Furthermore, the response surface methodology was also used to optimize the process parameters that yielded the lowest percentage of dilution.展开更多
Mierostrueture of the Fe-based alloy hardfaeing coating reinforced by TiC-VC particles was investigated by means of SEM, TEM, XRD and EPMA. The thermodynamics and effect of elements on the carbides were discussed. The...Mierostrueture of the Fe-based alloy hardfaeing coating reinforced by TiC-VC particles was investigated by means of SEM, TEM, XRD and EPMA. The thermodynamics and effect of elements on the carbides were discussed. The result shows that TiC-VC carbides can be formed during arc welding. Carbides with particle size of 2 ～4μm are uniformly dispersed in the matrix. Evidently the covering components and their amount affect the microstrueture and hardness of the coatings. An excellent microstructure and hardness of hardfacing coating were obtained, while the amount of graphite, FeTi and FeV was controlled within the range of 8%- 10%, 15%- 18% and 8%- 12%, respectively.展开更多
The modifying effect of rare earth (RE) oxide on inclusions in hardfacing metals of medium-high carbon steel was investigated by means of thermodynamics. The thermodynamic analysis for inclusion formation shows that ...The modifying effect of rare earth (RE) oxide on inclusions in hardfacing metals of medium-high carbon steel was investigated by means of thermodynamics. The thermodynamic analysis for inclusion formation shows that RE oxide can be reduced to RE element by carbon, then the RE element can react with oxygen and sulfur to form the RE oxide, RE sulfide and RE oxide-sulfide in hardfacing molten pool. The deoxidization and the desulphurization can be carried out and the liquid metal can be purified. In addition, RE oxide can also react with sulfur to form RE oxide-sulfide directly. Therefore, the harmful effect of sulfur can be decreased.展开更多
After different heat treatment processes, the metal compound, the microstructure and the hardness of the C-Cr-W- Mo-V-RE Fe-based hardfacing layers are investigated by means of metallographic microscope, X-ray diffrac...After different heat treatment processes, the metal compound, the microstructure and the hardness of the C-Cr-W- Mo-V-RE Fe-based hardfacing layers are investigated by means of metallographic microscope, X-ray diffraction （ XRD ）, energy dispersive spectrum（ EDS ）, transmission electron microscope（TEM） and hardness tester. The results show that the hardfacing layers have higher tempering stability and secondary hardening property. After quenching at 820 ℃ ,the hardness value（ HRC37 ） and the microstructure of the layers are similar to that normalized at 820 - 1 000 ℃. The tempering stability and the hardness increases with increasing quench temperature, which is attributed to the amount of the alloy element in the matrix. These results are very helpful for improving the mechanical properties of the hardfacing layers.展开更多
Ni-based composite coatings with a high content of tungsten carbides(Stelcar65composite coatings)were synthesized by plasma transferred arc(PTA)hardfacing.The welding parameters of Stelcar65composite coatings were opt...Ni-based composite coatings with a high content of tungsten carbides(Stelcar65composite coatings)were synthesized by plasma transferred arc(PTA)hardfacing.The welding parameters of Stelcar65composite coatings were optimized by orthogonal tests.The PTA welding parameters including welding current,powder feed rate and welding speed have significant influence on the tungsten carbide degradation.The values for the optimum welding current,powder feed rate and welding speed were determined to be100A,25g/min and40mm/min,respectively.The produced WC/Ni-based composite coatings were crack-and degradation-free.The microstructure of deposited layers,as well as the microstructure and microhardness of the optimal coating were further analyzed.展开更多
The cracking morphology of the hardfacing specimens taken from steel 5CrNiMo was observed. Meanwhile, the residual stress fields were measured and simulated. Based on experiment mentioned above, the improved structure...The cracking morphology of the hardfacing specimens taken from steel 5CrNiMo was observed. Meanwhile, the residual stress fields were measured and simulated. Based on experiment mentioned above, the improved structure and modified inclusion in hardfacing metal with rare earth （RE） oxide were analyzed. The results show that, the hardfacing crack is initiated from the coarse dendritic crystal grain boundary, inclusions and coarse austenite grain boundary in the HAZ and propagated by the residual stress existing in the center of the hardfacing metal and HAZ. The primary columnar grain structure can be refined by adding RE oxide in the coating of the electrode. The inclusion in the hardfacing metal can be modified as well. Meanwhile, if the martensite transformation temperature is decreased, the largest value of the residual tensile stress in the dangerous region can be reduced.展开更多
Niobium, as the most effective second-phase forming element, was added in the Fe-Crl3-C-N hard- facing alloy to get carbonitride precipitates. Morphology and composition of carbonitride in the hardfacing alloy were st...Niobium, as the most effective second-phase forming element, was added in the Fe-Crl3-C-N hard- facing alloy to get carbonitride precipitates. Morphology and composition of carbonitride in the hardfacing alloy were studied by optical microscopy, scanning electron microscopy, and electron probe microanalyzer. The ther- modynamics and the effect on the matrix of the formation of carbonitride were also discussed. It was found that niobium carbonitrides are complex Nb（C, N） precipitate distributed on grain boundary and matrix of the hardfacing alloy. Under as-welded condition, primary carbonitride particles were readily precipitated from the hardfacing alloy with large size and morphology as they were formed already during solidification. Under heat treatment condi- tion, a large number of secondary carbonitrides can pre- cipitate out with very fine size and make a great secondary hardening effect on the matrix. As a result, addition of niobium in the hardfacing alloy can prevent the formation of chromium-rich phase on grain boundaries and inter- granular chromium depletion.展开更多
基金the financial support to carry out this investigation through sponsored research and development project No.2003/20/36/1-BRNS.
文摘The application of response surface methodology was highlighted to predict and optimize the percentage of dilution of iron-based hardfaced surface produced by the PTA （plasma tratisferred arc welding） process. The experiments were conducted based on five-factor five-level central composite rotatable design with full replication technique and a mathematical model was developed using response surface methodology. Furthermore, the response surface methodology was also used to optimize the process parameters that yielded the lowest percentage of dilution.
文摘Mierostrueture of the Fe-based alloy hardfaeing coating reinforced by TiC-VC particles was investigated by means of SEM, TEM, XRD and EPMA. The thermodynamics and effect of elements on the carbides were discussed. The result shows that TiC-VC carbides can be formed during arc welding. Carbides with particle size of 2 ～4μm are uniformly dispersed in the matrix. Evidently the covering components and their amount affect the microstrueture and hardness of the coatings. An excellent microstructure and hardness of hardfacing coating were obtained, while the amount of graphite, FeTi and FeV was controlled within the range of 8%- 10%, 15%- 18% and 8%- 12%, respectively.
文摘The modifying effect of rare earth (RE) oxide on inclusions in hardfacing metals of medium-high carbon steel was investigated by means of thermodynamics. The thermodynamic analysis for inclusion formation shows that RE oxide can be reduced to RE element by carbon, then the RE element can react with oxygen and sulfur to form the RE oxide, RE sulfide and RE oxide-sulfide in hardfacing molten pool. The deoxidization and the desulphurization can be carried out and the liquid metal can be purified. In addition, RE oxide can also react with sulfur to form RE oxide-sulfide directly. Therefore, the harmful effect of sulfur can be decreased.
文摘After different heat treatment processes, the metal compound, the microstructure and the hardness of the C-Cr-W- Mo-V-RE Fe-based hardfacing layers are investigated by means of metallographic microscope, X-ray diffraction （ XRD ）, energy dispersive spectrum（ EDS ）, transmission electron microscope（TEM） and hardness tester. The results show that the hardfacing layers have higher tempering stability and secondary hardening property. After quenching at 820 ℃ ,the hardness value（ HRC37 ） and the microstructure of the layers are similar to that normalized at 820 - 1 000 ℃. The tempering stability and the hardness increases with increasing quench temperature, which is attributed to the amount of the alloy element in the matrix. These results are very helpful for improving the mechanical properties of the hardfacing layers.
基金Project (2016YFB0300502) supported by the National Key Research and Development Program of ChinaProjects (51601129,51775386) supported by the National Natural Science Foundation of China+2 种基金Project (16PJ1410000) supported by Shanghai Pujiang Program,ChinaProject (16ZR1438700) supported by the Natural Science Foundation of Shanghai,ChinaProject (TPL1706) supported by Traction Power State Key Laboratory of Southwest Jiaotong University,China
文摘Ni-based composite coatings with a high content of tungsten carbides(Stelcar65composite coatings)were synthesized by plasma transferred arc(PTA)hardfacing.The welding parameters of Stelcar65composite coatings were optimized by orthogonal tests.The PTA welding parameters including welding current,powder feed rate and welding speed have significant influence on the tungsten carbide degradation.The values for the optimum welding current,powder feed rate and welding speed were determined to be100A,25g/min and40mm/min,respectively.The produced WC/Ni-based composite coatings were crack-and degradation-free.The microstructure of deposited layers,as well as the microstructure and microhardness of the optimal coating were further analyzed.
基金Project supported by Key Project of Science and Technology of Hebei Province (04212201D) and Research Foundationfor theReturned Overseas Chinese Scholars of State Education Ministry
文摘The cracking morphology of the hardfacing specimens taken from steel 5CrNiMo was observed. Meanwhile, the residual stress fields were measured and simulated. Based on experiment mentioned above, the improved structure and modified inclusion in hardfacing metal with rare earth （RE） oxide were analyzed. The results show that, the hardfacing crack is initiated from the coarse dendritic crystal grain boundary, inclusions and coarse austenite grain boundary in the HAZ and propagated by the residual stress existing in the center of the hardfacing metal and HAZ. The primary columnar grain structure can be refined by adding RE oxide in the coating of the electrode. The inclusion in the hardfacing metal can be modified as well. Meanwhile, if the martensite transformation temperature is decreased, the largest value of the residual tensile stress in the dangerous region can be reduced.
基金financially supported by the National Natural Science Foundation of China(No.51101050)Natural Science Foundation of Jiangsu Province of China(No.BK2011257)
文摘Niobium, as the most effective second-phase forming element, was added in the Fe-Crl3-C-N hard- facing alloy to get carbonitride precipitates. Morphology and composition of carbonitride in the hardfacing alloy were studied by optical microscopy, scanning electron microscopy, and electron probe microanalyzer. The ther- modynamics and the effect on the matrix of the formation of carbonitride were also discussed. It was found that niobium carbonitrides are complex Nb（C, N） precipitate distributed on grain boundary and matrix of the hardfacing alloy. Under as-welded condition, primary carbonitride particles were readily precipitated from the hardfacing alloy with large size and morphology as they were formed already during solidification. Under heat treatment condi- tion, a large number of secondary carbonitrides can pre- cipitate out with very fine size and make a great secondary hardening effect on the matrix. As a result, addition of niobium in the hardfacing alloy can prevent the formation of chromium-rich phase on grain boundaries and inter- granular chromium depletion.
