The effect of RE-modifier on the microstructure and mechanical properties of high carbon-medium manganese steel has been investigated in present work.The results showed that the RE-modifier can refine the crystalline ...The effect of RE-modifier on the microstructure and mechanical properties of high carbon-medium manganese steel has been investigated in present work.The results showed that the RE-modifier can refine the crystalline grain of high-carbon medium-manganese steel.The shape and distribution of carbides are improved and the columnar grains and phosphide in grain boundary are eliminated.Consequently,the impact toughness of the steel is increased by more than one time,compared with no addition of RE-modifier.展开更多
Many researchers have explored the inclusion modification mechanism to improve non-metallic inclusion modifications in steelmaking. In this study, two types of industrial trials on inclusion modifications in liquid st...Many researchers have explored the inclusion modification mechanism to improve non-metallic inclusion modifications in steelmaking. In this study, two types of industrial trials on inclusion modifications in liquid steel were conducted using ultra-low-carbon Al-killed steel with different Mg and Ca contents to verify the effects of Ca and Mg contents on the modification mechanism of Al_2O_3-based inclusions during secondary refining. The results showed that Al_2O_3-based inclusions can be modified into liquid calcium aluminate or a multi-component inclusion with the addition of a suitable amount of Ca. In addition, [Mg] in liquid steel can further reduce CaO in liquid calcium aluminate to drive its evolution into CaO–MgO–Al_2O_3 multi-component inclusions. Thermodynamic analysis confirmed that the reaction between [Mg] and CaO in liquid calcium aluminate occurs when the MgO content of liquid calcium aluminate is less than 3 wt% and the temperature is higher than 1843 K.展开更多
The delayed fracture behavior of medium carbon high strength spring steel containing different amounts of boron （0. 000 5%, 0. 001 6 %） was studied using sustained load delayed fracture test. The results show that d...The delayed fracture behavior of medium carbon high strength spring steel containing different amounts of boron （0. 000 5%, 0. 001 6 %） was studied using sustained load delayed fracture test. The results show that delayed fracture resistance of boron containing steels is higher than that of conventional steel 60Si2MnA at the same strength level and it increases with the increase of boron eontent from 0. 000 5% to 0. 001 6%. The delayed fracture mode is mainly intergranular in the boron containing steels tempered at 350℃, which indicates that the addition of boron does not change the fracture character. However, the increase of boron content enlarges the size of the crack initia tion area. Further study of phase analysis indicates that most boron is in solid solution, and only a very small quantity of boron is in the M3 （C, B） phase.展开更多
The effect of Al content(0.035 wt%,0.5 wt%,1 wt%,and 2 wt%)on the composition change of steel and slag as well as inclusion transformation of high manganese steel after it has equilibrated with Ca O-Si O_(2)-Al_(2)O_(...The effect of Al content(0.035 wt%,0.5 wt%,1 wt%,and 2 wt%)on the composition change of steel and slag as well as inclusion transformation of high manganese steel after it has equilibrated with Ca O-Si O_(2)-Al_(2)O_(3)-Mg O slag was studied using the method of slag/steel reaction.The experimental results showed that as the initial content of Al increased from 0.035 wt%to 2 wt%,Al gradually replaced Mn to react with Si O_(2)in slag to avoid the loss of Mn due to the reaction;this process caused both Al_(2)O_(3)in slag and Si in steel to increase while Si O_(2)and Mn O in slag to reduce.In addition,the type of inclusions also evolved as the initial Al content increased.The evolution route of inclusions was Mn O→Mn O-Al_(2)O_(3)-Mg O→Mg O→Mn O-Ca O-Al_(2)O_(3)-Mg O and Mn O-Ca O-Mg O.The shape of inclusions evolved from spherical to irregular,became faceted,and finally transformed to spherical.The average size of inclusions presented a trend that was increasing first and then decreasing.The transformation mechanism of inclusions was explored.As the initial content of Al increased,Mg and Ca were reduced from top slag into molten steel in sequence,which consequently caused the transformation of inclusions.展开更多
： Titanium is an impurity element in some special steel grades. The existence of titanium decreases the grain size and lowers the yield strength ,resulting in low quality of these steels with regard to various proper...： Titanium is an impurity element in some special steel grades. The existence of titanium decreases the grain size and lowers the yield strength ,resulting in low quality of these steels with regard to various properties. Thus, the titanium content should be reduced to the minimum. Based on the industrial production of ultra-low carbon A1-Si killed steel, this paper investigated the physical-chemical behaviors of titanium with and without desulfurization during RH refining. The influences of Ti content in hot metal, ladle slag composition, and ladle slag quantity, etc., on the Ti content in refined liquid steel were discussed. The results show that the partition ratio of titanium between ladle slag and liquid steel is inversely proportional to the AI content to the power of 4/3 ,and the empirical formula regressed from practical experience can be expressed as w（TiO2）/WTi=48/w[AI]4/3 Maximum partition ratio of titanium between top slag and liquid steel can be ensured W[Til WIAIIby an optimum slag composition including components of FeOx and A12 03 and an appropriate slag basicity. The contents of FetO and A1203 should be controlled above 6% and below 20% respectively and the slag basicity should be kept within 1.5 to 3.0. Moreover, desulfurization refining in the RH vacuum will decrease the partition ratio of titanium between ladle slag and liquid steel significantly. To keep the Ti content stably below 15 ×10 ^-4% in a 300 ton ladle ,the Ti content in hot metal must be lower than 500 × 10^-4% and the thickness of ladle slag carried over from BOF slag must be less than 50 ram.展开更多
This work investigated the evolution of multiphase microstructure and impact fracture behavior of medium carbon high silicon high strength steel subjected to the austempering treatment at 240,360,and400℃.The results ...This work investigated the evolution of multiphase microstructure and impact fracture behavior of medium carbon high silicon high strength steel subjected to the austempering treatment at 240,360,and400℃.The results show that martensite,bainite,and retained austenite(RA)are the main microstructural phases.The austempering treatments at 360 and 400℃ caused the formation of carbon-poor ferrite in the matrix,and the transformation of ultrafine bainite into coarse lath bainite and granular bainite,respectively.Thick filmy RA was distributed between bainite laths.The polygonal martensiteaustenite islands and blocky RA formed along the grain boundaries.The average carbon concentration in the matrix decreased with the temperature increase,while the impact toughness initially increased and then dropped with temperature.The quasi-cleavage brittle fracture dominated the impact fracture mechanism of the sample austempered at 240℃ by forming tearing surfaces and tearing steps.The microcracks disappeared in the RA on the prior austenite grain boundaries.On the other side,the fracture surface of the sample austempered at 360℃ exhibited ductile fracture with deep dimples and brittle fracture with cleavage river patterns.The polygonal martensite-austenite islands or blocky RA constrained the microcracks.After austempered at 400℃,the brittle fracture was dominant,showing river patterns,and the microcracks propagated through the granular bainite without any resistance.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 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
Titanium is the impurity in some special steel grades.The existence of titanium decreases the grain size,depresses the yield strength,and results in the low quality of these steels in various properties.Thus,titanium ...Titanium is the impurity in some special steel grades.The existence of titanium decreases the grain size,depresses the yield strength,and results in the low quality of these steels in various properties.Thus,titanium should be removed to the minimum.Based on the industrial production of ultra low carbon Al-Si killed steel,the physical-chemical behavior of titanium was investigated in vacuum degassing refining（RH）process with and without desulfurization.The influences of titanium content in hot metal,ladle slag composition,and ladle slag quantity,etc,on titanium content of refined liquid steel were discussed.The results showed that the partition ratio of titanium between ladle slag and liquid steel is in inverse proportion to the 4/3square of aluminum content.The maximum partition ratio of titanium between top slag and liquid steel can be obtained by adjusting an optimum slag composition including contents of FeOxand Al2O3and the slag basicity,and the suitable range of them should be controlled higher than 6%,less than 20%,and within 1.5to 3.0,respectively.Moreover,desulfurization refining by RH decreases the partition ratio of titanium between ladle slag and liquid steel significantly.To ensure the titanium content stably less than 15×10-6 in a 300tladle,the titanium content in hot metal must be less than 500×10-6 and the thickness of basic oxygen furnace（BOF）slag carrying over must be less than 50mm.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
文摘The effect of RE-modifier on the microstructure and mechanical properties of high carbon-medium manganese steel has been investigated in present work.The results showed that the RE-modifier can refine the crystalline grain of high-carbon medium-manganese steel.The shape and distribution of carbides are improved and the columnar grains and phosphide in grain boundary are eliminated.Consequently,the impact toughness of the steel is increased by more than one time,compared with no addition of RE-modifier.
基金financially supported by the Fundamental Research Funds for the Central Universities (No. FRF-TP-16-079A1)the National Science Foundation for Young Scientists of China (No. 51704021)+1 种基金the Joint Funds of National Natural Science Foundation of China (No. U1560203)supported by Beijing Key Laboratory of Special Melting and Preparation of High-end Metal Materials
文摘Many researchers have explored the inclusion modification mechanism to improve non-metallic inclusion modifications in steelmaking. In this study, two types of industrial trials on inclusion modifications in liquid steel were conducted using ultra-low-carbon Al-killed steel with different Mg and Ca contents to verify the effects of Ca and Mg contents on the modification mechanism of Al_2O_3-based inclusions during secondary refining. The results showed that Al_2O_3-based inclusions can be modified into liquid calcium aluminate or a multi-component inclusion with the addition of a suitable amount of Ca. In addition, [Mg] in liquid steel can further reduce CaO in liquid calcium aluminate to drive its evolution into CaO–MgO–Al_2O_3 multi-component inclusions. Thermodynamic analysis confirmed that the reaction between [Mg] and CaO in liquid calcium aluminate occurs when the MgO content of liquid calcium aluminate is less than 3 wt% and the temperature is higher than 1843 K.
基金Item Sponsored by National Key Fundamental Research and Development Programme of China (2004CB619104)
文摘The delayed fracture behavior of medium carbon high strength spring steel containing different amounts of boron （0. 000 5%, 0. 001 6 %） was studied using sustained load delayed fracture test. The results show that delayed fracture resistance of boron containing steels is higher than that of conventional steel 60Si2MnA at the same strength level and it increases with the increase of boron eontent from 0. 000 5% to 0. 001 6%. The delayed fracture mode is mainly intergranular in the boron containing steels tempered at 350℃, which indicates that the addition of boron does not change the fracture character. However, the increase of boron content enlarges the size of the crack initia tion area. Further study of phase analysis indicates that most boron is in solid solution, and only a very small quantity of boron is in the M3 （C, B） phase.
基金financially supported by the Ministry of Industry and Information Technology of China(No.TC180A6MR)China Scholarship Council and the National Natural Science Foundation of China(No.51404020)。
文摘The effect of Al content(0.035 wt%,0.5 wt%,1 wt%,and 2 wt%)on the composition change of steel and slag as well as inclusion transformation of high manganese steel after it has equilibrated with Ca O-Si O_(2)-Al_(2)O_(3)-Mg O slag was studied using the method of slag/steel reaction.The experimental results showed that as the initial content of Al increased from 0.035 wt%to 2 wt%,Al gradually replaced Mn to react with Si O_(2)in slag to avoid the loss of Mn due to the reaction;this process caused both Al_(2)O_(3)in slag and Si in steel to increase while Si O_(2)and Mn O in slag to reduce.In addition,the type of inclusions also evolved as the initial Al content increased.The evolution route of inclusions was Mn O→Mn O-Al_(2)O_(3)-Mg O→Mg O→Mn O-Ca O-Al_(2)O_(3)-Mg O and Mn O-Ca O-Mg O.The shape of inclusions evolved from spherical to irregular,became faceted,and finally transformed to spherical.The average size of inclusions presented a trend that was increasing first and then decreasing.The transformation mechanism of inclusions was explored.As the initial content of Al increased,Mg and Ca were reduced from top slag into molten steel in sequence,which consequently caused the transformation of inclusions.
文摘： Titanium is an impurity element in some special steel grades. The existence of titanium decreases the grain size and lowers the yield strength ,resulting in low quality of these steels with regard to various properties. Thus, the titanium content should be reduced to the minimum. Based on the industrial production of ultra-low carbon A1-Si killed steel, this paper investigated the physical-chemical behaviors of titanium with and without desulfurization during RH refining. The influences of Ti content in hot metal, ladle slag composition, and ladle slag quantity, etc., on the Ti content in refined liquid steel were discussed. The results show that the partition ratio of titanium between ladle slag and liquid steel is inversely proportional to the AI content to the power of 4/3 ,and the empirical formula regressed from practical experience can be expressed as w（TiO2）/WTi=48/w[AI]4/3 Maximum partition ratio of titanium between top slag and liquid steel can be ensured W[Til WIAIIby an optimum slag composition including components of FeOx and A12 03 and an appropriate slag basicity. The contents of FetO and A1203 should be controlled above 6% and below 20% respectively and the slag basicity should be kept within 1.5 to 3.0. Moreover, desulfurization refining in the RH vacuum will decrease the partition ratio of titanium between ladle slag and liquid steel significantly. To keep the Ti content stably below 15 ×10 ^-4% in a 300 ton ladle ,the Ti content in hot metal must be lower than 500 × 10^-4% and the thickness of ladle slag carried over from BOF slag must be less than 50 ram.
基金financially supported by the National Key Research and Development Program of China(No.2016YFB0300105)the Fundamental Research Funds for the Central Universities(No.N180725021)the Fundamental Research Funds for the Central Universities(No.N2024005-4)。
文摘This work investigated the evolution of multiphase microstructure and impact fracture behavior of medium carbon high silicon high strength steel subjected to the austempering treatment at 240,360,and400℃.The results show that martensite,bainite,and retained austenite(RA)are the main microstructural phases.The austempering treatments at 360 and 400℃ caused the formation of carbon-poor ferrite in the matrix,and the transformation of ultrafine bainite into coarse lath bainite and granular bainite,respectively.Thick filmy RA was distributed between bainite laths.The polygonal martensiteaustenite islands and blocky RA formed along the grain boundaries.The average carbon concentration in the matrix decreased with the temperature increase,while the impact toughness initially increased and then dropped with temperature.The quasi-cleavage brittle fracture dominated the impact fracture mechanism of the sample austempered at 240℃ by forming tearing surfaces and tearing steps.The microcracks disappeared in the RA on the prior austenite grain boundaries.On the other side,the fracture surface of the sample austempered at 360℃ exhibited ductile fracture with deep dimples and brittle fracture with cleavage river patterns.The polygonal martensite-austenite islands or blocky RA constrained the microcracks.After austempered at 400℃,the brittle fracture was dominant,showing river patterns,and the microcracks propagated through the granular bainite without any resistance.
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Sponsored by National Natural Science Foundation of China(51104109)
文摘Titanium is the impurity in some special steel grades.The existence of titanium decreases the grain size,depresses the yield strength,and results in the low quality of these steels in various properties.Thus,titanium should be removed to the minimum.Based on the industrial production of ultra low carbon Al-Si killed steel,the physical-chemical behavior of titanium was investigated in vacuum degassing refining（RH）process with and without desulfurization.The influences of titanium content in hot metal,ladle slag composition,and ladle slag quantity,etc,on titanium content of refined liquid steel were discussed.The results showed that the partition ratio of titanium between ladle slag and liquid steel is in inverse proportion to the 4/3square of aluminum content.The maximum partition ratio of titanium between top slag and liquid steel can be obtained by adjusting an optimum slag composition including contents of FeOxand Al2O3and the slag basicity,and the suitable range of them should be controlled higher than 6%,less than 20%,and within 1.5to 3.0,respectively.Moreover,desulfurization refining by RH decreases the partition ratio of titanium between ladle slag and liquid steel significantly.To ensure the titanium content stably less than 15×10-6 in a 300tladle,the titanium content in hot metal must be less than 500×10-6 and the thickness of basic oxygen furnace（BOF）slag carrying over must be less than 50mm.
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.
