The effect of tempering temperature on the microstructure and mechanical properties of ultra-high strength, copperbearing, low-carbon bainitic steel has been investigated in the experiment. The results showed that the...The effect of tempering temperature on the microstructure and mechanical properties of ultra-high strength, copperbearing, low-carbon bainitic steel has been investigated in the experiment. The results showed that the microstructure was mainly the laths of bainite in the as-quenched steel. The bainitic laths were restored and combined after the steel tempered at various tempera- tures. There were rnartensite/austenite （M/A） islands and numerous dislocations within and between the bainitic laths, while very t-me precipitates of ε-Cu were also observed within the laths. With increasing the tempered temperature from 400 to 600℃, the yield strength （YS） increased from 877 to 957 MPa, whereas the ultimate tensile strength （UTS） decreased from 1020 to 985 MPa. The Charpy V-notch （CVN） varied from 68.5 to 42 J, and the value was minimal for the steel tempered at 500℃. 2008 University of Science and Technology Beijing. All rights reserved.展开更多
Ethylenediamine with two-NH2 functional groups was used as a critical complexing agent in chemical mechanical polishing(CMP)slurries for a high carbon chromium GCr15 bearing steel(equivalent to AISI 52100).The polishi...Ethylenediamine with two-NH2 functional groups was used as a critical complexing agent in chemical mechanical polishing(CMP)slurries for a high carbon chromium GCr15 bearing steel(equivalent to AISI 52100).The polishing performance and corresponding mechanism of-NH2 functional groups were thoroughly investigated as a function of pH.It is revealed that,when polished with ethylenediamine and H2O2-based slurries,the material removal rate(MRR)and surface roughness Ra of GCr15 steel gradually decrease as pH increases.Compared with acidic pH of 4.0,at alkaline pH of 10.0,the surface film of GCr15 steel has much higher corrosion resistance and wear resistance,and thus the material removal caused by the pure corrosion and corrosion-enhanced wear are greatly inhibited,resulting in much lower MRR and Ra.Moreover,it is confirmed that a more protective composite film,consisting of more Fe3+hydroxides/oxyhydroxides and complex compounds with-NH2 functional groups of ethylenediamine,can be formed at pH of 10.0.Additionally,the polishing performance of pure iron and a medium carbon 45 steel exhibits a similar trend as GCr15 steel.The findings suggest that acidic pH could be feasible for amine groups-based complexing agents to achieve efficient CMP of iron-based metals.展开更多
Effects of annealing time on microstructure of cold-roiled niobium-titanium bearing micro-alloyed steel strips were investigated by optical microscopy, scanning electron microscopy, electron back-scatter diffraction ...Effects of annealing time on microstructure of cold-roiled niobium-titanium bearing micro-alloyed steel strips were investigated by optical microscopy, scanning electron microscopy, electron back-scatter diffraction （EBSD） and transmission electron microscopy. The complete recrystallization annealing temperature of 670 ℃ and complete annealing time of 9 min were determined using Vickers-hardness testing and EBSD analysis. The ferrite mi-crostructure with spheric cementite particles and nano-scale precipitates of Nb（C,N） in matrix was obtained. The ki-netics of the ferrite grain growth is lowered due to ferrite grain boundaries pinned by the cementite particles, so the ferrite grain size of 5.5 μm remains unchanged among the annealing time ranging from 9 to 30 min. In addition, the strength of tested steel also keeps unchanged with the increase of annealing time. The higher yield strength of ap-proximately 420 MPa can be obtained by grain refinement and precipitation hardening and the higher elongation of approximately 40% and work-hardening exponent of approximately 0.2 can be gained due to grain refinement and presence of cementite particles, indicating that the balance of strength, ductility and forming property is realized.展开更多
In the present work, an ultrahigh strength bearing steel（AISI 52100） was subjected to surface mechanical rolling treatment（SMRT） at room temperature. Microstructural observations showed that martensitic laths, twi...In the present work, an ultrahigh strength bearing steel（AISI 52100） was subjected to surface mechanical rolling treatment（SMRT） at room temperature. Microstructural observations showed that martensitic laths, twins and cementite particles in the initial microstructure underwent distinct plastic strains and were gradually refined into nanostructures. Consequently, a gradient nanostructured（GNS） surface layer with a mean grain size of -24 nm at the top surface was obtained on the bearing steel, resulting in an increment of -20% in the surface hardness. Analyses based on microstructural evolution, phase constitution and in-depth hardness distribution revealed a mechanically induced formation mechanism of the GNS surface layer. The multiple surface severe plastic deformation under fine lubrication and cooling during SMRT contributed to the formation of a thick hardened surface layer on the bearing steel.展开更多
5 heats of GCr15 bearing steel of different sulfur contents ranging from 0.009-0.092% （wt.）were smelted. The role of sulfur in bearing steel and its effect on contact fatigue properties andfracture toughness K<su...5 heats of GCr15 bearing steel of different sulfur contents ranging from 0.009-0.092% （wt.）were smelted. The role of sulfur in bearing steel and its effect on contact fatigue properties andfracture toughness K<sub>IC</sub>Were studied. It was shown that as the sulfur content increases the sulfur content dissolved in the steelsubstrate remains unchanged. The best contact fatigue property appears at the sulfur content of0.045% （wt.）, and the influence of sulfur content on the fracture toughness of bearing steel is notobvious. Finally, the mechanism of the role of sulfur was investigated.展开更多
文摘The effect of tempering temperature on the microstructure and mechanical properties of ultra-high strength, copperbearing, low-carbon bainitic steel has been investigated in the experiment. The results showed that the microstructure was mainly the laths of bainite in the as-quenched steel. The bainitic laths were restored and combined after the steel tempered at various tempera- tures. There were rnartensite/austenite （M/A） islands and numerous dislocations within and between the bainitic laths, while very t-me precipitates of ε-Cu were also observed within the laths. With increasing the tempered temperature from 400 to 600℃, the yield strength （YS） increased from 877 to 957 MPa, whereas the ultimate tensile strength （UTS） decreased from 1020 to 985 MPa. The Charpy V-notch （CVN） varied from 68.5 to 42 J, and the value was minimal for the steel tempered at 500℃. 2008 University of Science and Technology Beijing. All rights reserved.
基金The authors are grateful for the financial supports by National Natural Science Foundation of China(51975488,51991373,and 51605396)National Key R&D Program of China(2018YFB2000400)+2 种基金Science Challenge Project(TZ2018006)Tribology Science Fund of State Key Laboratory of Tribology(SKLTKF16A02)Laboratory of Precision Manufacturing Technology CAEP(ZD17005).
文摘Ethylenediamine with two-NH2 functional groups was used as a critical complexing agent in chemical mechanical polishing(CMP)slurries for a high carbon chromium GCr15 bearing steel(equivalent to AISI 52100).The polishing performance and corresponding mechanism of-NH2 functional groups were thoroughly investigated as a function of pH.It is revealed that,when polished with ethylenediamine and H2O2-based slurries,the material removal rate(MRR)and surface roughness Ra of GCr15 steel gradually decrease as pH increases.Compared with acidic pH of 4.0,at alkaline pH of 10.0,the surface film of GCr15 steel has much higher corrosion resistance and wear resistance,and thus the material removal caused by the pure corrosion and corrosion-enhanced wear are greatly inhibited,resulting in much lower MRR and Ra.Moreover,it is confirmed that a more protective composite film,consisting of more Fe3+hydroxides/oxyhydroxides and complex compounds with-NH2 functional groups of ethylenediamine,can be formed at pH of 10.0.Additionally,the polishing performance of pure iron and a medium carbon 45 steel exhibits a similar trend as GCr15 steel.The findings suggest that acidic pH could be feasible for amine groups-based complexing agents to achieve efficient CMP of iron-based metals.
基金Sponsored by Fundamental Research Funds for Central Universities of China(N110607003)
文摘Effects of annealing time on microstructure of cold-roiled niobium-titanium bearing micro-alloyed steel strips were investigated by optical microscopy, scanning electron microscopy, electron back-scatter diffraction （EBSD） and transmission electron microscopy. The complete recrystallization annealing temperature of 670 ℃ and complete annealing time of 9 min were determined using Vickers-hardness testing and EBSD analysis. The ferrite mi-crostructure with spheric cementite particles and nano-scale precipitates of Nb（C,N） in matrix was obtained. The ki-netics of the ferrite grain growth is lowered due to ferrite grain boundaries pinned by the cementite particles, so the ferrite grain size of 5.5 μm remains unchanged among the annealing time ranging from 9 to 30 min. In addition, the strength of tested steel also keeps unchanged with the increase of annealing time. The higher yield strength of ap-proximately 420 MPa can be obtained by grain refinement and precipitation hardening and the higher elongation of approximately 40% and work-hardening exponent of approximately 0.2 can be gained due to grain refinement and presence of cementite particles, indicating that the balance of strength, ductility and forming property is realized.
基金supported financially by the National Key Research and Development Program of China (No.2017YFA0204400)Shenyang National Laboratory for Materials Science(No. 2015RP04)
文摘In the present work, an ultrahigh strength bearing steel（AISI 52100） was subjected to surface mechanical rolling treatment（SMRT） at room temperature. Microstructural observations showed that martensitic laths, twins and cementite particles in the initial microstructure underwent distinct plastic strains and were gradually refined into nanostructures. Consequently, a gradient nanostructured（GNS） surface layer with a mean grain size of -24 nm at the top surface was obtained on the bearing steel, resulting in an increment of -20% in the surface hardness. Analyses based on microstructural evolution, phase constitution and in-depth hardness distribution revealed a mechanically induced formation mechanism of the GNS surface layer. The multiple surface severe plastic deformation under fine lubrication and cooling during SMRT contributed to the formation of a thick hardened surface layer on the bearing steel.
文摘5 heats of GCr15 bearing steel of different sulfur contents ranging from 0.009-0.092% （wt.）were smelted. The role of sulfur in bearing steel and its effect on contact fatigue properties andfracture toughness K<sub>IC</sub>Were studied. It was shown that as the sulfur content increases the sulfur content dissolved in the steelsubstrate remains unchanged. The best contact fatigue property appears at the sulfur content of0.045% （wt.）, and the influence of sulfur content on the fracture toughness of bearing steel is notobvious. Finally, the mechanism of the role of sulfur was investigated.
