Hardfacing of valve sealings in power plants with Inconel 625 alloy has been reviewed in this paper.The overlaying processes,over-lay microstructures,and weldability issues during the hardfacing process have been anal...Hardfacing of valve sealings in power plants with Inconel 625 alloy has been reviewed in this paper.The overlaying processes,over-lay microstructures,and weldability issues during the hardfacing process have been analyzed.The results indicate that almost all melting welding processes can be used for hardfacing of Inconel 625 alloy.During hardfacing,it is necessary to strictly control the penetration,reduce the overlay dilution rate,so as to prevent the formation of partially mixed zone(PMZ)and solidification crack.From the perspective of controlling the penetration,reducing the overlay dilution rate,and automated hardfacing,the most suitable process for hardfacing Inconel 625 alloy on the valve sealings in power plants is cold metal transfer(CMT)welding process.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
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
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
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 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
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
It is expected that the welding hardfacing of continuous casting rolls has better welding performance and higher wear resistance. A new type of submerged-arc hardfacing flux-cored wire has been developed through nitro...It is expected that the welding hardfacing of continuous casting rolls has better welding performance and higher wear resistance. A new type of submerged-arc hardfacing flux-cored wire has been developed through nitrogen replacing part of carbon and addition of the nitrogen-fixing elements of niobium and titanium. And microstructure, degree of hardness and high-temperature wear resistance of its deposited metal samples were also investigated. It is found that the microstructure is martensite, residual austenite and carbonitride precipitates. As a result, the hardfacing metal with homogeneous distribution of very fine carbonitride particles had high hardness and excellent wear-re- sisting property during high-temperature wear, which could significantly extend the service life of continuous casting rolls.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
The flux cored wires with different rare earth oxide additions for hardfacing the workpieces of medium-high carbon steel were developed. The microstrucmre of the hardfacing layer was observed using the optical microsc...The flux cored wires with different rare earth oxide additions for hardfacing the workpieces of medium-high carbon steel were developed. The microstrucmre of the hardfacing layer was observed using the optical microscopy. The average dimension of primary austenite grains in hardfacing layer was measured by image analyzer. The primary austenite grain growth activation energy and index were calculated according to Sellars＇s mode and Beck formula, respectively. Moreover, the effect of rare earth oxide on the growth dynamics of primary aus- tenite grain was analyzed, and then discussed with the misfit theory. The experimental results showed that, by adding rare earth oxide, the av- erage dimension of primary austenite grains in hardfacing layer of medium-high carbon steel decreased, and it was the smallest when the ad- dition of rare earth oxide was 5.17 wt.%. Meanwhile, at this rare earth oxide addition, the primary austenite grain growth activating energy in hardfacing layer was the largest, while its index was the smallest. The calculated results indicated that the primary austenite grain could be refined because LaAlO3 as heterogeneous nuclei of γ-Fe was the most effective.展开更多
The most effective carbide-forming elements titanium and niobium were added into hardfacing alloy.Formation and composition of carbides in the hardfacing alloy were investigated by means of optical microscope（OM）,sc...The most effective carbide-forming elements titanium and niobium were added into hardfacing alloy.Formation and composition of carbides in the hardfacing alloy were investigated by means of optical microscope（OM）,scanning electron microscope（SEM）,X-ray diffraction（XRD）and energy-dispersive spectrometer（EDS）.Hardness and impact toughness of the hardfacing alloy were measured.The thermodynamics and formation mechanism of carbides were also discussed.It is found that the carbides consist of TiC and NbC which are able to form directly from welding pool during the welding process.The formation mechanism of carbides involves nucleation of TiC followed by epitaxial precipitation of NbC on the surface of TiC.The formation of titanium and niobium carbides can obviously refine the microstructure and deplete the carbon in the matrix.The micros tructure transforms to well-distributed carbides and a tough martensite matrix,contributing to a good combination of high hardness and high toughness in the hardfacing alloy.展开更多
The Fe-Cr-C flux-cored wires with 0 wt.%, 0.63 wt.%, 2.54 wt.% and 5.08 wt.% additions of nano-Y203 were developed in this work. And the different hypereutectic Fe-Cr-C hardfacing coatings were prepared. The phase str...The Fe-Cr-C flux-cored wires with 0 wt.%, 0.63 wt.%, 2.54 wt.% and 5.08 wt.% additions of nano-Y203 were developed in this work. And the different hypereutectic Fe-Cr-C hardfacing coatings were prepared. The phase structures of the coatings were determined by X-ray diffraction. The microstructures were observed by optical microscopy. The morphologies of the hypereutectic Fe-Cr-C hardfacing coatings were observed by a field emission scanning electron microscope equipped with an X-ray energy disper- sive spectrometer. The effectiveness ofY203 as heterogeneous nuclei of primary M7C3 was calculated with the misfit theory. The ex- periment results showed that, the microstructures of the hypereutectic Fe-Cr-C hardfacing coatings consisted of M7C3, ？-Fe and a-Fe phases. With the increase of nano-Y203 additives, primary M7C3 in hypereutectic Fe-Cr-C coatings could be refined gradually. The average size of the primary M7C3 was the minimum, which was 22 pro, when nano-Y203 additive was 2.54 wt.%. The calculated re- sults showed that, the two-dimensional lattice misfit between the face （001） of Y203 and face （100） of orthorhombic M7C3 was 4.911%, which indicated that Y203 as heterogeneous nuclei of M7C3 was middle effective to refine the primary M7C3.展开更多
Hypoeutectic Fe-Cr-B-C hardfacing alloys with different molybdenum( Mo) contents( The design content was 0,2,3. 3 and 4. 5 wt. %,respectively) were deposited using the flux-cored wire by means of metal active gas arc ...Hypoeutectic Fe-Cr-B-C hardfacing alloys with different molybdenum( Mo) contents( The design content was 0,2,3. 3 and 4. 5 wt. %,respectively) were deposited using the flux-cored wire by means of metal active gas arc welding. The effects of Mo on the refinement of microstructures,eutectic microstructure changes and improvement of wear resistance were investigated. The main results were shown as follows: the added Mo could increase the volume fraction of eutectic microstructure and reduce the size of coarse primary austenite as well as the volume fraction. The carboboride of M3( B,C) could be observed in hypoeutectic Fe-Cr-B-C hardfacing alloys at the Mo design content of ≤2. 0 wt. %,while that of M23( B,C)6was formed when 3. 3 wt. % Mo was added.Additionally,the wear resistance of alloys was increased with the increase in Mo content. Specifically,the highest wear resistance of alloys was achieved at 4. 5 wt. % Mo design content,which was 113. 7% higher than that in alloys without Mo.展开更多
The nitrogen-alloying hardfacing alloy of the martensitic stainless steel was deposited on a low carbon steel substrate using hardfacing flux-cored wire. Microstructure and surface hardness of hardfacing alloy were in...The nitrogen-alloying hardfacing alloy of the martensitic stainless steel was deposited on a low carbon steel substrate using hardfacing flux-cored wire. Microstructure and surface hardness of hardfacing alloy were investigated and measured by optical microscope and microhardness tester. Carbonitrides of the hardfacing alloy were observed by electron probe. The wear behaviour of the hardfacing alloy was studied using the belt abrasion test apparatus and the worn surface was analyzed by scanning electron microscopy. The results showed that carbonitride particles in the hardfacing alloy are complex MX （ M： alloy elements ; X： C, N） precipitate with fine size. These carbonitride particles distributed homogeneously in the hardfacing alloy and had a good strengthening effect on the wear property. The wear property of the hardfacing alloy with nitrogen was better than the one without nitrogen.展开更多
Hardfacing coatings involve hard carbide/boride phases dispersed in a relatively soft steel matrix.For the hardness measurements of hardfacing coatings,depending on the microstructure,both the hardness test method and...Hardfacing coatings involve hard carbide/boride phases dispersed in a relatively soft steel matrix.For the hardness measurements of hardfacing coatings,depending on the microstructure,both the hardness test method and the applied load affect the hardness results;therefore,they affect the wear performance predictions of the coating.For this reason,the proper hardness test method should be determined according to the microstructure of the coating,and the reliability of the obtained hardness data should be established.This study aimed to determine the most suitable hardness test method for hypoeutectic and hypereutectic microstructures of hardfacing coatings by analyzing the reliability of Rockwell-C and Vickers hardness test results.Reliability analyses showed that Rockwell-C is not a suitable hardness test method for hypereutectic hardfacing coatings.Based on the relationship between wear resistance and hardness,Vickers hardness method was found more suitable for the considered materials.展开更多
The temperature and residual stress fields of a medium-high carbon steel, welded by a cracking resistance electrode with rare earth (RE) oxide, were measured by thermo-vision analyzer and X-ray stress analyzer respect...The temperature and residual stress fields of a medium-high carbon steel, welded by a cracking resistance electrode with rare earth (RE) oxide, were measured by thermo-vision analyzer and X-ray stress analyzer respectively. Meanwhile, the martensitic transformation temperatures of matrix, hard-face welding (hardfacing) metal welded by conventional hardfacing electrode and that welded by cracking resistance electrode with RE oxide were determined. According to the experimental data and the thermo-physical, mechanical parameters of materials, finite element method (FEM) of temperature and stress fields was established. In this FEM, the effect of martensitic transformation on residual stress of hardfacing metal of medium-high carbon steel was taken into account. The results show that, by adding RE oxide in the coat of hardfacing electrode, the martensitic transformation temperature can be decreased, so that the residual tensile stress on the dangerous position can be decreased. Therefore, the cracking resistance of hardfacing metal can be improved.展开更多
The hardfacing alloys with different concentrations of titanium were deposited on carbon steel substrates by shielded metal arc welding, and the effect of titanium content on the microstructure characteristics of the ...The hardfacing alloys with different concentrations of titanium were deposited on carbon steel substrates by shielded metal arc welding, and the effect of titanium content on the microstructure characteristics of the hardfacing alloys was investigated. The wear resistance test of the hardfacing alloys was carried out by using a slurry rubber wheel abrasion test machine, and the wear behaviour was also studied. The results indicate that the addition of titanium can effectively promote the precipitation of the complex carbides of Nb and Ti due to the prior precipitation of titanium carbide which acts as nucleation sites for complex carbides. With the increase of titanium content, the wear resistance of the hardfacing alloys is increased gradually resulting from the refinement of microstructure and dispersive distribution of fine carbide precipitates. And the wear mechanism is mainly minimum plastic deformation with interrupted grooves due to the strengthening and protecting effects of carbide precipitates.展开更多
After tempering treatment at different conditions, the tempering stability of Fe-base hardfacing layer containing RE and multiple alloying was investigated. The results show that after heat preservation at 560 ℃ and ...After tempering treatment at different conditions, the tempering stability of Fe-base hardfacing layer containing RE and multiple alloying was investigated. The results show that after heat preservation at 560 ℃ and tempering for 4 h the hardness value of Fe-base hardfacing layer containing RE and multiple alloying can reach HRC57; By repeatedly heating circle 700 ℃17 ℃ for 150 times, the hardness value of Fe-base hardfacing layer can reach HRC43, tempering stability is higher and causes the secondary hardening phenomenon. Reasons for higher tempering stability of Fe-base hardfacing layer were analyzed by means of metallographic, XRD, TEM and EDS.展开更多
A new type of non-preheated hardfacing electrode was developed using H08A as the core and the coat contents including ferrotitaninm, ferrovanadium, graphite, rutile etc. The microstrnctures and properties of hardfacin...A new type of non-preheated hardfacing electrode was developed using H08A as the core and the coat contents including ferrotitaninm, ferrovanadium, graphite, rutile etc. The microstrnctures and properties of hardfacing metal were systematically researched. The results show the hardness of hardfacing metal increases with increasing of ferrotitanium, ferrovanadium, graphite in the coat, but the crack resistance and processing weldability become worse. The carbides formed by arc metallurgic reaction are uniformly dispersed in the matrix structure. The phases of hardfacing metal consist of α-Fe, γ-Fe, VC, TiC and Fe3 C.The carbides are compression aggregation of TiC and VC, and their appearances present irregular block. The matrix microstrncture of hardfacing metal is lath martensite. The hardfacing layers with better crack resistance and wearability are achieved and no visible cracks occur when using non-preheated electrode in continuous welding process. Hardness of hardfacing metal is more than 60HRC, and its relative wearability is five times of wearability of D667 electrode in abrasive wear test.展开更多
The hypereutectic Fe-Cr-C hardfacing alloys with different contents of TiB_2 and Nb were prepared by selfshielded flux cored arc welding.The microstructure of a series of hypereutectic Fe-Cr-C hardfacing alloys added ...The hypereutectic Fe-Cr-C hardfacing alloys with different contents of TiB_2 and Nb were prepared by selfshielded flux cored arc welding.The microstructure of a series of hypereutectic Fe-Cr-C hardfacing alloys added with various TiB_2 and Nb contents was investigated by using optical microscopy（OM）,scanning electron microscopy（SEM）and X-ray diffraction（XRD）.In addition,their Rockwell hardness,microhardness and resistance to abrasive wear were tested.The results showed that the microstructure of a series of hypereutectic Fe-Cr-C hardfacing alloys consisted mainly of martensite,austenite,primary M7C3 carbides and eutectic M7C3 carbides.With the addition of TiB_2,a new hard-phase TiC was produced in the hardfacing alloys.And in the alloys added with TiB_2 and Nb,a new hard composite phase TiC-NbC was formed.The microhardness of the matrix was improved by adding TiB_2 and Nb,but the effect on the Rockwell hardness of Fe-Cr-C hardfacing alloys was insignificant.The addition of TiB_2 and Nb can also decrease the size of the primary M7C3 carbides and make the primary M7C3 homogeneous.As a result,the reinforced matrix,the more homogeneous primary M7C3 carbides,and the new hard-phase TiC-NbC all improved the wear resistance of Fe-Cr-C hardfacing alloys.展开更多
文摘Hardfacing of valve sealings in power plants with Inconel 625 alloy has been reviewed in this paper.The overlaying processes,over-lay microstructures,and weldability issues during the hardfacing process have been analyzed.The results indicate that almost all melting welding processes can be used for hardfacing of Inconel 625 alloy.During hardfacing,it is necessary to strictly control the penetration,reduce the overlay dilution rate,so as to prevent the formation of partially mixed zone(PMZ)and solidification crack.From the perspective of controlling the penetration,reducing the overlay dilution rate,and automated hardfacing,the most suitable process for hardfacing Inconel 625 alloy on the valve sealings in power plants is cold metal transfer(CMT)welding process.
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.
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.
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.
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.
基金Item Sponsored by National Natural Science Foundation of China (51101050)Fundamental Research Funds for Central Universities of China (2009B30214)Natural Science Foundation of Jiangsu Province of China (BK2011257)
文摘It is expected that the welding hardfacing of continuous casting rolls has better welding performance and higher wear resistance. A new type of submerged-arc hardfacing flux-cored wire has been developed through nitrogen replacing part of carbon and addition of the nitrogen-fixing elements of niobium and titanium. And microstructure, degree of hardness and high-temperature wear resistance of its deposited metal samples were also investigated. It is found that the microstructure is martensite, residual austenite and carbonitride precipitates. As a result, the hardfacing metal with homogeneous distribution of very fine carbonitride particles had high hardness and excellent wear-re- sisting property during high-temperature wear, which could significantly extend the service life of continuous casting rolls.
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Program supported by National Nature Science Foundation of China(51271163)Key Project of Science and Technology of Hebei Province(09215106D)
文摘The flux cored wires with different rare earth oxide additions for hardfacing the workpieces of medium-high carbon steel were developed. The microstrucmre of the hardfacing layer was observed using the optical microscopy. The average dimension of primary austenite grains in hardfacing layer was measured by image analyzer. The primary austenite grain growth activation energy and index were calculated according to Sellars＇s mode and Beck formula, respectively. Moreover, the effect of rare earth oxide on the growth dynamics of primary aus- tenite grain was analyzed, and then discussed with the misfit theory. The experimental results showed that, by adding rare earth oxide, the av- erage dimension of primary austenite grains in hardfacing layer of medium-high carbon steel decreased, and it was the smallest when the ad- dition of rare earth oxide was 5.17 wt.%. Meanwhile, at this rare earth oxide addition, the primary austenite grain growth activating energy in hardfacing layer was the largest, while its index was the smallest. The calculated results indicated that the primary austenite grain could be refined because LaAlO3 as heterogeneous nuclei of γ-Fe was the most effective.
基金financially supported by the National Natural Science Foundation of China(No.51101050)theFundamental Research Funds for the Central Universities(Nos.2013B18114 and 2015B22614)the Natural Science Foundation of Jiangsu Province of China(No.BK20141156)
文摘The most effective carbide-forming elements titanium and niobium were added into hardfacing alloy.Formation and composition of carbides in the hardfacing alloy were investigated by means of optical microscope（OM）,scanning electron microscope（SEM）,X-ray diffraction（XRD）and energy-dispersive spectrometer（EDS）.Hardness and impact toughness of the hardfacing alloy were measured.The thermodynamics and formation mechanism of carbides were also discussed.It is found that the carbides consist of TiC and NbC which are able to form directly from welding pool during the welding process.The formation mechanism of carbides involves nucleation of TiC followed by epitaxial precipitation of NbC on the surface of TiC.The formation of titanium and niobium carbides can obviously refine the microstructure and deplete the carbon in the matrix.The micros tructure transforms to well-distributed carbides and a tough martensite matrix,contributing to a good combination of high hardness and high toughness in the hardfacing alloy.
基金supported by National Natural Science Foundation of China(51271163,51471148)
文摘The Fe-Cr-C flux-cored wires with 0 wt.%, 0.63 wt.%, 2.54 wt.% and 5.08 wt.% additions of nano-Y203 were developed in this work. And the different hypereutectic Fe-Cr-C hardfacing coatings were prepared. The phase structures of the coatings were determined by X-ray diffraction. The microstructures were observed by optical microscopy. The morphologies of the hypereutectic Fe-Cr-C hardfacing coatings were observed by a field emission scanning electron microscope equipped with an X-ray energy disper- sive spectrometer. The effectiveness ofY203 as heterogeneous nuclei of primary M7C3 was calculated with the misfit theory. The ex- periment results showed that, the microstructures of the hypereutectic Fe-Cr-C hardfacing coatings consisted of M7C3, ？-Fe and a-Fe phases. With the increase of nano-Y203 additives, primary M7C3 in hypereutectic Fe-Cr-C coatings could be refined gradually. The average size of the primary M7C3 was the minimum, which was 22 pro, when nano-Y203 additive was 2.54 wt.%. The calculated re- sults showed that, the two-dimensional lattice misfit between the face （001） of Y203 and face （100） of orthorhombic M7C3 was 4.911%, which indicated that Y203 as heterogeneous nuclei of M7C3 was middle effective to refine the primary M7C3.
文摘Hypoeutectic Fe-Cr-B-C hardfacing alloys with different molybdenum( Mo) contents( The design content was 0,2,3. 3 and 4. 5 wt. %,respectively) were deposited using the flux-cored wire by means of metal active gas arc welding. The effects of Mo on the refinement of microstructures,eutectic microstructure changes and improvement of wear resistance were investigated. The main results were shown as follows: the added Mo could increase the volume fraction of eutectic microstructure and reduce the size of coarse primary austenite as well as the volume fraction. The carboboride of M3( B,C) could be observed in hypoeutectic Fe-Cr-B-C hardfacing alloys at the Mo design content of ≤2. 0 wt. %,while that of M23( B,C)6was formed when 3. 3 wt. % Mo was added.Additionally,the wear resistance of alloys was increased with the increase in Mo content. Specifically,the highest wear resistance of alloys was achieved at 4. 5 wt. % Mo design content,which was 113. 7% higher than that in alloys without Mo.
文摘The nitrogen-alloying hardfacing alloy of the martensitic stainless steel was deposited on a low carbon steel substrate using hardfacing flux-cored wire. Microstructure and surface hardness of hardfacing alloy were investigated and measured by optical microscope and microhardness tester. Carbonitrides of the hardfacing alloy were observed by electron probe. The wear behaviour of the hardfacing alloy was studied using the belt abrasion test apparatus and the worn surface was analyzed by scanning electron microscopy. The results showed that carbonitride particles in the hardfacing alloy are complex MX （ M： alloy elements ; X： C, N） precipitate with fine size. These carbonitride particles distributed homogeneously in the hardfacing alloy and had a good strengthening effect on the wear property. The wear property of the hardfacing alloy with nitrogen was better than the one without nitrogen.
文摘Hardfacing coatings involve hard carbide/boride phases dispersed in a relatively soft steel matrix.For the hardness measurements of hardfacing coatings,depending on the microstructure,both the hardness test method and the applied load affect the hardness results;therefore,they affect the wear performance predictions of the coating.For this reason,the proper hardness test method should be determined according to the microstructure of the coating,and the reliability of the obtained hardness data should be established.This study aimed to determine the most suitable hardness test method for hypoeutectic and hypereutectic microstructures of hardfacing coatings by analyzing the reliability of Rockwell-C and Vickers hardness test results.Reliability analyses showed that Rockwell-C is not a suitable hardness test method for hypereutectic hardfacing coatings.Based on the relationship between wear resistance and hardness,Vickers hardness method was found more suitable for the considered materials.
文摘The temperature and residual stress fields of a medium-high carbon steel, welded by a cracking resistance electrode with rare earth (RE) oxide, were measured by thermo-vision analyzer and X-ray stress analyzer respectively. Meanwhile, the martensitic transformation temperatures of matrix, hard-face welding (hardfacing) metal welded by conventional hardfacing electrode and that welded by cracking resistance electrode with RE oxide were determined. According to the experimental data and the thermo-physical, mechanical parameters of materials, finite element method (FEM) of temperature and stress fields was established. In this FEM, the effect of martensitic transformation on residual stress of hardfacing metal of medium-high carbon steel was taken into account. The results show that, by adding RE oxide in the coat of hardfacing electrode, the martensitic transformation temperature can be decreased, so that the residual tensile stress on the dangerous position can be decreased. Therefore, the cracking resistance of hardfacing metal can be improved.
基金Funded by the National Natural Science Foundation of China(No.51101050)Fundamental Research Funds for the Central Universities,Natural Science Foundation of Jiangsu Province of China(No.BK20141156)Program for Outstanding Innovative Talents in Hohai University
文摘The hardfacing alloys with different concentrations of titanium were deposited on carbon steel substrates by shielded metal arc welding, and the effect of titanium content on the microstructure characteristics of the hardfacing alloys was investigated. The wear resistance test of the hardfacing alloys was carried out by using a slurry rubber wheel abrasion test machine, and the wear behaviour was also studied. The results indicate that the addition of titanium can effectively promote the precipitation of the complex carbides of Nb and Ti due to the prior precipitation of titanium carbide which acts as nucleation sites for complex carbides. With the increase of titanium content, the wear resistance of the hardfacing alloys is increased gradually resulting from the refinement of microstructure and dispersive distribution of fine carbide precipitates. And the wear mechanism is mainly minimum plastic deformation with interrupted grooves due to the strengthening and protecting effects of carbide precipitates.
文摘After tempering treatment at different conditions, the tempering stability of Fe-base hardfacing layer containing RE and multiple alloying was investigated. The results show that after heat preservation at 560 ℃ and tempering for 4 h the hardness value of Fe-base hardfacing layer containing RE and multiple alloying can reach HRC57; By repeatedly heating circle 700 ℃17 ℃ for 150 times, the hardness value of Fe-base hardfacing layer can reach HRC43, tempering stability is higher and causes the secondary hardening phenomenon. Reasons for higher tempering stability of Fe-base hardfacing layer were analyzed by means of metallographic, XRD, TEM and EDS.
文摘A new type of non-preheated hardfacing electrode was developed using H08A as the core and the coat contents including ferrotitaninm, ferrovanadium, graphite, rutile etc. The microstrnctures and properties of hardfacing metal were systematically researched. The results show the hardness of hardfacing metal increases with increasing of ferrotitanium, ferrovanadium, graphite in the coat, but the crack resistance and processing weldability become worse. The carbides formed by arc metallurgic reaction are uniformly dispersed in the matrix structure. The phases of hardfacing metal consist of α-Fe, γ-Fe, VC, TiC and Fe3 C.The carbides are compression aggregation of TiC and VC, and their appearances present irregular block. The matrix microstrncture of hardfacing metal is lath martensite. The hardfacing layers with better crack resistance and wearability are achieved and no visible cracks occur when using non-preheated electrode in continuous welding process. Hardness of hardfacing metal is more than 60HRC, and its relative wearability is five times of wearability of D667 electrode in abrasive wear test.
文摘The hypereutectic Fe-Cr-C hardfacing alloys with different contents of TiB_2 and Nb were prepared by selfshielded flux cored arc welding.The microstructure of a series of hypereutectic Fe-Cr-C hardfacing alloys added with various TiB_2 and Nb contents was investigated by using optical microscopy（OM）,scanning electron microscopy（SEM）and X-ray diffraction（XRD）.In addition,their Rockwell hardness,microhardness and resistance to abrasive wear were tested.The results showed that the microstructure of a series of hypereutectic Fe-Cr-C hardfacing alloys consisted mainly of martensite,austenite,primary M7C3 carbides and eutectic M7C3 carbides.With the addition of TiB_2,a new hard-phase TiC was produced in the hardfacing alloys.And in the alloys added with TiB_2 and Nb,a new hard composite phase TiC-NbC was formed.The microhardness of the matrix was improved by adding TiB_2 and Nb,but the effect on the Rockwell hardness of Fe-Cr-C hardfacing alloys was insignificant.The addition of TiB_2 and Nb can also decrease the size of the primary M7C3 carbides and make the primary M7C3 homogeneous.As a result,the reinforced matrix,the more homogeneous primary M7C3 carbides,and the new hard-phase TiC-NbC all improved the wear resistance of Fe-Cr-C hardfacing alloys.
