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Report on China titanium industry in 2022

An Zhongsheng, Chen Yan, Zhao Wei

2023, 44(3): 1-8. doi: 10.7513/j.issn.1004-7638.2023.03.001

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Abstract:
The overall situation of China titanium industry was analyzed on the basis of capacity, output, application, and import and export amount of titanium concentrate, titanium sponge, titanium ingot and titanium materials in 2022. The existed problems and the corresponding suggestions were also proposed.

Separation of V and Mn in calcification roasting-acid leachate of V slag by simultaneous amine extraction and CO₂ mineralization

Hu Ke, Han Huiguo, Wu Pan, He Jian, Jiang Wei, Liu Changjun, Liang Bin

2023, 44(3): 9-15. doi: 10.7513/j.issn.1004-7638.2023.03.002

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The efficient separation of vanadium and manganese from an acid leachate of the calcification roasting vanadium slag is quite difficult and costly, particularly for those leachates with high vanadium and manganese concentrations. A novel process was investigated for the separation of vanadium and manganese using trioctylamine and CO₂. The chemical separation basic of V and Mn was discussed. The distribution law of the major metallic components, particularly V and Mn, of the acid leachate in organic phase, aqueous phase and precipitated phase were quantified. The effects of concentrations of vanadium and manganese, and the recycle of trioctylamine on the separation efficiency were elucidated. The techno-economic feasibility of the new process was discussed. The results show that a vanadium extraction rate of 99% can be achieved even for an acid leachate with high concentration of manganese. The vanadium extraction rate of 97% and manganese precipitation rate of 96% are maintained after 5 regeneration cycles. The new process is techno-economically applausive.

Biomass pyrolysis product-enhanced selective reduction-magnetic separation of iron sand

Huang Zhucheng, Shu Yang, Li Yixin, Tang Tingting, Xie Chenxi

2023, 44(3): 16-22. doi: 10.7513/j.issn.1004-7638.2023.03.003

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Using clean, carbon neutral, highly reactive and renewable biomass as a reducing agent, limiting the escape of pyrolysis products by hermetic gas plugs, the direct reduction behavior of the biomass allotted within the iron sand was studied. The results show that a pressure of 60 kPa is rapidly developed in the reaction tank as a result of limiting the escape of pyrolysis products (CO、H₂、CO₂、H₂O 、C_xH_yO_z) from biomass pyrolysis, which facilitates the participation of H₂, CO in the reduction. The tar has higher activity and guarantees the source of H₂ in the later stage, which promotes the rapid reduction of iron sand at low temperature. Under the conditions of reduction temperature of 1120 °C and reduction for 80 min, the iron powder with 97.81% metallization and 97.81% Fe recovery can be obtained, as well as the titanium-rich slag with a TiO₂ recovery of 69.98% and a V₂O₅ recovery of 59.93%.

Production of high-purity rutile titanium dioxide by leaching water-quenched titanium-bearing blast furnace slag with hydrochloric acid

Huang Xianliang, Zhong Shan, Tang Siyang, Song Lei, Li Hongjiao, Liang Bin

2023, 44(3): 23-32. doi: 10.7513/j.issn.1004-7638.2023.03.004

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Abstract:
Hydrochloric acid method was used for the leaching of water-quenched titanium-bearing blast furnace slag in this work. According to the leaching and solid-liquid separation process, valuable elements including titanium and aluminum were concentrated in the solution. With further hydrolysis and precipitation, high-purity rutile titanium dioxide and alumina oxide can be obtained. In order to obtain optimized leaching processing parameters, the effects of acid concentration, liquid-solid ratio, reaction temperature and reaction time on the leaching efficiency of different elements in titanium-bearing blast furnace slag were systematically investigated. When the leaching temperature is 90 °C, hydrochloric acid concentration is 33%, liquid-solid ratio is 15 : 1 (mL : g), and leaching time is 30 min, the leaching efficiency of titanium reaches 75.3%. By hydrolysis at 130 °C and following drying process, rutile titanium dioxide with a purity of 97.7% can be obtained. This method can be directly applied for the recovery of valuable titanium from the water-quenched titanium-bearing blast furnace slag and for the production of high purity titanium dioxide, with short process and low energy consumption, which can provide practical support for the resourceful utilization of titanium-bearing blast furnace slag.

Preparation of titania with high surface area by industrial titanyl sulfate solution and its properties study

Pu Hong, Zhang Huan

2023, 44(3): 33-38. doi: 10.7513/j.issn.1004-7638.2023.03.005

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Abstract:
Titania with high surface area was prepared by hydrothermal method using industrial titanyl sulfate solution as raw material. The influence of hydrothermal reaction time and calcination temperature on the specific surface area of titania were investigated. The samples were characterized by BET, XRD, XPS, SEM, TEM, FT-IR, UV-Vis DRS and the visible photocatalytic activity was evaluated by the degradation of model compound Rhodamine B. The results show that the proper hydrothermal reaction time and low calcination temperature are beneficial to the preparation of titania with high specific surface area. The titania obtained by hydrothermal reaction for 3 h and calcination temperature at 300 ℃ has the highest specific surface area, up to 214.3 m²/g. And the visible light degradation activity of Rhodamine B is significantly better than that of commercial titanium dioxide P25, which is because the prepared titania has a higher specific surface area and better visible light absorption, its degradation rate reached 90.3% in 2 h.

Study on the effect of coke particle size on titanium slag smelting

Li Kaimao, Xiao Jun, Ma Yong, Song Bing, Qiu Shuxing

2023, 44(3): 39-44. doi: 10.7513/j.issn.1004-7638.2023.03.006

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Abstract:
According to the characteristics of free settling movement of particles in the fluid, the theoretical calculation results show that the maximum size of coke particles taken out under the condition of continuous feeding smelting titanium slag is 0.06 mm. Combined with the industrial application, the size range of coke for test is 2～8 mm. Based on this, the influence of coke particle size on titanium slag smelting was investigated. The results show that under the condition of constant power, the flue gas temperature and CO concentration fluctuate greatly in the smelting process, and the electrode position rises rapidly at the beginning of smelting, which is caused by the large coke particle size and relatively delayed reaction. As a result, the consumption per ton of slag coke, the time consumption per hundred tons of material, and the power consumption per ton of slag are respectively 24 kg, 0.18 h, 52.07 kWh more than the reference period. By contrast, the power is increased from 17.67 MW/h to 18.14 MW/h (increased by 0.47 MW/h), thermodynamic and kinetic conditions are improved, coke is fully reacted, carbon residue in the furnace is eliminated, and smelting is more stable. At the same time, coke consumption per ton of slag and power consumption per ton of slag are reduced by 26 kg and 128.12 kWh respectively compared with "unraised power test period". The narrow and uniform coke particle size distribution is conducive to the titanium slag smelting process and quality stability control, while the increase of power can effectively reduce the adverse effect of relatively large coke particle size on titanium slag smelting.

Effect of intermediate pass annealing on the microstructures and properties of Ti-3Al-2.5V tubes

Zhu Xiaoyong, Xing Yuan, Jiang Jian, Wang Ying, Luan Baifeng

2023, 44(3): 45-51. doi: 10.7513/j.issn.1004-7638.2023.03.007

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By using EBSD and TEM techniques, the microstructures of the deformation and annealed samples were characterized. After that, the recrystallization process of the tubes during the heat treatments was examined, and the changes in the texture during the various heat treatments were analyzed using polar and inverse polar figures. The experimental results show that when the heat treatment temperature is below 580 ℃, the tube mainly recovers and the microstructure is mainly consisted of the deformed grains. The complete recrystallization process of the tube will occur only when the heat treatment is conducted at 750 ℃. The research demonstrates that the cold-rolled tubes produce a basal bimodal texture with a circumferential (TD) tilt, and that the type of basal bimodal texture produced remains constant as the heat treatment temperature rises, while the recrystallization texture <${11{\bar 2}0 }$>//AD gradually replaced the deformation texture <${10{\bar 1}0}$>//AD. The mechanical properties of the alloy tubes after annealing at 620 ～ 650 ℃ change obviously, which is ascribed to the sharp increase in the recrystallization ratio with the rise in temperature.

Effects of mean load and load amplitude on biaxial dwell fatigue behavior of commercial pure titanium

Hu Changqun, Zhao Jiayu, Chang Le, Zhou Changyu, He Xiaohua

2023, 44(3): 52-60. doi: 10.7513/j.issn.1004-7638.2023.03.008

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Based on biaxial dwell fatigue tests at room temperature, effects of different mean loads and load amplitudes on the biaxial dwell fatigue behavior of commercial pure titanium were studied. The results show that the mean strain and strain rate increase with the increase of mean load and load amplitude under the same dwell time. When the load amplitude remains constant, the creep strain increases with the increase of the mean load. However, when the mean load remains constant, the creep strain decreases with the increase of the load amplitude. By analyzing the interaction between biaxial ratcheting and creep strain, it is found that ratcheting strain and creep strain are always restricted by each other. Fracture surface analysis shows that with the increase of mean load and load amplitude, the fatigue strip characteristics disappear gradually, and the number of dimples and tearing ridges significantly increases, exhibiting ductile failure mode. Meanwhile, with the increase of mean load or load amplitude, equivalent strain amplitude is increased, leading to the decrease of fatigue life. Compared with the effect of mean load, fatigue life is more sensitive to the variation of load amplitude. Maximum principal strain, maximum shear strain, Mises equivalent strain, maximum principal stress and SWT models are used to perform biaxial dwell fatigue life prediction, among them SWT model has the highest prediction accuracy.

Research on the preparation of Al-Ti-B master alloy

Li Jun, Wu Enhui, Hou Jing, Xu Zhong, Li Hong, Gong Hao

2023, 44(3): 61-67. doi: 10.7513/j.issn.1004-7638.2023.03.009

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Al-Ti-B master alloy is commonly used as grain refining agent to endow aluminum with better organizational properties. In this paper, TiO₂ and B₂O₃ are used as raw materials for the one-step synthesis of Al-Ti-B master alloy by aluminum thermal reduction. The results show that Al-Ti-B master alloy was successfully prepared under the conditions of Al₂O₃∶CaO∶CaF₂=1∶1∶1, roasting temperature 1550 ℃, roasting time 30 min and Al/TiO₂>0.9. The yield of Ti and B is higher than 80%. The Al and B contents of the alloy can be adjusted according to the amount of Al and B₂O₃ in the raw material. The phase of the alloy changes to TiAl and TiB₂ with the increase of the amount of Al and B₂O₃.

Effects of pre-strain on tensile mechanical properties of commercially pure titanium TA2 welded joint

Zhao Qing, Chang Le, Zhou Changyu, Pu Jiang, Zheng Yixiang, Wang Zhicheng, Wang Bumei

2023, 44(3): 68-74. doi: 10.7513/j.issn.1004-7638.2023.03.010

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In this paper, room temperature tensile mechanical properties of commercially pure titanium TA2 welded joint after pre-straining were studied. The results show that stress-strain curves rises and yield strength and tensile strength increase with the degree of pre-strain. With considering effects of pre-strain and strain rate, the empirical expression for the strength of the material after pre-strain was developed. According to Hollomon constitutive equation, the variations of strain rate sensitivity index and strain hardening exponent were analyzed. Meanwhile, the tensile constitutive equation for the pre-strained samples was determined. The observation of fracture surface indicates that the reduction of fracture surface and the size of dimples decreases after pre-straining due to the decrease of elongation of the material.

Effect of pickling on surface contamination layer and chemical composition of ZTA15 titanium alloy

Han Yunfei, Sun Bing, Liu Yihui, Hou Peihua, Yuan Bingbing, Qiao Haibin

2023, 44(3): 75-79. doi: 10.7513/j.issn.1004-7638.2023.03.011

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Abstract:
The ZTA15 titanium alloy test bars were prepared by investment casting technology. The thickness of the surface contamination layer was observed and measured by metallography, and then the pickling amount was determined. Before and after pickling, the removal of the contaminated layer was determined by the two-point diameter measurement and metallographic method. After pickling treatment, vacuum annealing was also carried out. The chemical composition was tested from the surface of test bars in three states to detect the change of hydrogen and oxygen content. The effect of acid pickling on the surface contamination layer and chemical composition of ZTA15 titanium alloy was studied. The results show that the thickness of the contaminated layer on the surface of ZTA15 titanium alloy is 0.1～0.2 mm. When hydrofluoric acid, nitric acid and hot water in the pickling solution are prepared according to the mass ratio of 30%: 30%: 40%, the temperature is 40～60 ℃, the pickling time is within 60 min, and the pickling amount is (0.25±0.05 )mm, the α contaminated layer with high hardness and low plasticity can be completely removed to avoid embrittlement or crack during subsequent deformation or stress, and improve its service performance. After pickling, the surface of ZTA15 titanium alloy has slight hydrogen absorption, no obvious change in oxygen content. Hydrogen evolution occurs after vacuum annealing, but the hydrogen content on the surface always meets the requirement of <0.01%. Hydrogen embrittlement and other adverse conditions on the composition performance are not to be generated.

Study on property and microstructure of Ti-6Al-4V extrusion

Teng Kui

2023, 44(3): 80-83. doi: 10.7513/j.issn.1004-7638.2023.03.012

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Properties and microstructure tests were carried out in Ti-6Al-4V extrusion under different transections to investigate the strength, damage tolerance and fatigue behaviors of different thickness of extrusion, as well as the contrastive analysis on microstructure of Ti-6Al-4V extrusion. The results indicate that tensile strength is lower while the thickness is higher, the fracture toughness is higher while the thickness is higher, the ‘T’ extrusion with higher thickness has higher fatigue and fracture toughness properties. In thicker cross-section of Ti-6Al-4V extrusion, there are clear grain boundary structures, and the mechanical properties are lower while fatigue and fracture toughness performances are higher, therefore, Ti-6Al-4V extrusion parts could be designed referring to the relationship between material properties and cross-section thickness in engineering.

Review on technology developments of titanium-steel clad plates based on global patent analysis

Zhang Weina, Li Jun, Peng Lin, Wu You, Liang Guangfen

2023, 44(3): 84-92. doi: 10.7513/j.issn.1004-7638.2023.03.013

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The development of key technologies of titanium-steel clad plates is reviewed based on a comprehensive mining of global patent applications. The results show that China and Japan are the major technology sources of titanium-steel clad plates. While Japan started earlier, China later rank first in patent applications in the world. Titanium-steel clad plate processing technologies are research hot spots, among which the direct rolling process route holds the largest share in a patent portfolio. The aims of the patented technologies is primarily to reduce the cost and improve the bonding strength. Based on the above findings, some suggestions about technological innovation and product development are proposed from a patent strategic perspective.

Study on the strength and toughness mechanism of multilayered gradient ultrafine-grained titanium

Liu Jiawen, Fang Hongmei, Cao Lili, Zhang Ya, Yang Dengke

2023, 44(3): 93-99. doi: 10.7513/j.issn.1004-7638.2023.03.014

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In view of the poor toughness and work hardening performance of ultra-fine grained (UFG) metals at room temperature, we designed and prepared the micro multilayer hierarchical structure (MHS) of metal materials using low-temperature rolling and surface mechanical attrition treatment (SMAT) processes, which improved the mechanical properties and work hardening ability of UFG Ti. The microstructure observation and mechanical properties testing, combined with fracture surface analysis, show that the multilayer gradient microstructure can improve the work hardening ability of ultrafine-grained metal, achieving a more moderate stress distribution and an improved resistance of the workpiece to failure cracks. A fracture mechanics model is proposed to explain the crack arrest effect of the MHS.

Mechanism analysis of the production of sublimated sulfur in the tail gas of acidolysis of titanium concentrate

Xiang Quanjin, Quan Yuanxia, Quan Xuejun, Li Li, Wang Haibo, Chen Xinhong, Li Ping

2023, 44(3): 100-104. doi: 10.7513/j.issn.1004-7638.2023.03.015

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In order to prevent the continuous production of titanium dioxide from being blocked by sublimated sulfur in the process of titanium dioxide acidolysis by sulflate process, this paper starts from the structural composition analysis of titanium concentrate, combined with the main chemical reactions that may exist in the acidolysis process and the specific acidolysis process conditions in actual production by calculating the change of Gibbs free energy of related reactions. The potentio-pH diagram of the system under the condition of acid hydrolysis was drawn, and the mechanism of the occurrence of sublimated sulfur in the tail gas of acid hydrolysis was explored. The results show that the elemental sulfur in the tail gas of acidolysis mainly come from the pyrrhotite (FeS) in titanium concentrate. The pyrrhotite is oxidized in the complex environment of acid hydrolysis at high temperature (180～220 ℃) and high acidity (pH: ?1.51～?1.47) to produce elemental sulfur, which is cooled and solidified to form sublimated sulfur after the reaction. Therefore we can start from the specific process, change the acid hydrolysis environment (change the chemical potential, reduce the environmental pH value) without reducing the acid hydrolysis rate in order to avoid or reduce the occurrence of sublimation sulfur in production, reduce the effect of sublimation sulfur on the sulfate process titanium white.

Preparation and properties of calcium silicate sound insulation board from vanadium-titanium iron ore tailings

Wang Changlong, Jing Jianlin, Qi Yang, Zhang Yuewen, Zheng Yongchao, Ma Jintao, Ping Haoyan, Zhai Yuxin, Liu Feng

2023, 44(3): 105-113. doi: 10.7513/j.issn.1004-7638.2023.03.016

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In order to promote the comprehensive utilization of vanadium-titanium iron ore tailings (VTIOTs) with weak gelling activity, the preparation of calcium silicate sound insulation board (CSSB) using VTIOTs as the main raw material was investigated. Through particle size analysis, mechanical properties and other testing methods, the grinding characteristics of VTIOTs were studied, then composite cementitious materials (CCM) were prepared with VTIOTs, silica fume and cement, and then CSSB were prepared by steam curing with waste rubber powder and steel fiber as reinforcement materials, and the effects of reinforcement materials and layer structure on the properties of CSSB were explored. The results show that alkali melting can effectively improve the activity of silicon and aluminum in VTIOTs, and the highest concentrations of Si⁴⁺and Al³⁺are 17.27 mg/L and 6.80 mg/L, respectively. When the mix proportion of CCM∶VTIOTs∶cement∶SF = 2∶7∶1, the cement sand ratio = 1∶3, the water cement ratio = 0.5, and the 28-day compressive strength is 39.7 MPa. For the CSSB prepared from VTIOTs, when the volume content of steel fiber or rubber powder in the single layer sound insulation plate is 0.93% or 1%, the flexural strength reaches 8.0 MPa and 8.8 MPa, respectively, while for the dual addition the flexural strength is 6.1 MPa. The maximum flexural strength of multilayer structural plates prepared by pouring slurry with different ingredients in layers is 8.2 MPa. The flexural strength of CSSB prepared from VTIOTs meets the requirements of GB/T 7019-2014 and JC/T 564.1-2018 standard.

Experimental study on iron concentrate separation from a low-grade vanadium-titanium magnetite in Panxi area

Cao Yuchuan

2023, 44(3): 114-117. doi: 10.7513/j.issn.1004-7638.2023.03.017

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In order to reduce the grinding cost and improve the grade of iron concentrate, the mineral composition, occurrence state of main elements and distribution characteristics of main minerals of the ore were studied by means of chemical analysis, optical microscopy, automatic mineral analyzer (MLA) combined with chemical analysis and chemical multielement analysis. The results show that: ① Part of ilmenite and spinel crystals whitch were wrapped in titanium magnetite were fine in size (-0.02 mm) and difficult to be dissociated; ② the iron concentrate with iron grade of 54.64%, iron recovery of 68.87% was obtained by adopting the process of ore grinding, low intensity magnetic separation, regrinding, low intensity magnetic separation, elutriation.

Experimental study on mechanical properties of high-titanium heavy slag tunnel shotcrete

Yang He, Chen Wei, Ma Shuangshi, Xie Xiaopeng, Li Fuliang, Guo Junhuai

2023, 44(3): 118-122. doi: 10.7513/j.issn.1004-7638.2023.03.018

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Using high-titanium heavy slag as aggregate to make high-titanium heavy slag tunnel shotcrete. Experiments show that when the content of fly ash and steel fiber is constant, within the range of water-binder ratio of 0.34 to 0.4, the suitable water-binder ratio of high titanium heavy slag tunnel shotcrete is 0.38. The addition of wave-shaped steel fibers can enhance the mechanical properties of the high-titanium heavy slag tunnel shotcrete and reduce the rebound rate of the high-titanium heavy slag tunnel shotcrete. High-titanium heavy slag tunnel sprayed concrete spray products are mainly C-S-H gel and ettringite. C-S-H gel and ettringite fill the gap between high-titanium heavy slag crushed stone and high-titanium heavy slag sand, and wrap steel fibers to form The denser whole improves the flexural strength and splitting strength of the high-titanium heavy slag tunnel shotcrete, and reduces the rebound rate of the high-titanium heavy slag tunnel shotcrete.

Study on the corrosion behavior of a 600 MPa corrosion-resistant steel barin a chloride environment

Li Pei, Yuan Jing, Huang Jixiang, Yan Bo, Yin Shubiao, Lei Ting

2023, 44(3): 123-130. doi: 10.7513/j.issn.1004-7638.2023.03.019

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The effect of Cr and V elements on the corrosion behavior of the ordinary 600 MPa grade high-strength seismic steel bar HRB600E and the same grade corrosion-resistant steel bar after alloy regulation was studied by the cyclic immersion tests, electrochemical tests, surface analysis, and phase analysis in a chloride environment. The results show that the addition of corrosion-resistant alloy promotes the formation of bainite in the matrix and slows down the corrosion process of the ferrite anode. The synergistic effect of V and Cr elements can hinder the infiltration of Cl^?, effectively delaying the growth rate of the rust layer, and the corrosion rate of corrosion-resistant steel bars decreases after 360 hours of cyclic immersion. Under the control of Cr-V elements, the self-corrosion potential of the electrochemical properties of corrosion-resistant steel bars increases, while the potential shifts positively after passivation, and the corrosion current density decreases. The AC impedance value of the corrosion-resistant steel bar is significantly improved after passivation, and it shows excellent corrosion resistance in the alkaline environment of concrete. The regulation of alloying elements improves the phase composition of corrosion products of the steel bars. The proportion of α-FeOOH and γ-FeOOH in the later corrosion products of the corrosion-resistant steel bars is higher and the internal rust layer is enriched with spinel-structured product FeCr₂O₄, which increases the density and stability of the internal rust layer.

Dynamic in-situ observation of solidification process of GH5188 alloy

Jiang Shichuan, Zhang Jian, Pei Binghong, Chen Qi, Wang Fu

2023, 44(3): 131-137. doi: 10.7513/j.issn.1004-7638.2023.03.020

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The solidification process of the GH5188 alloy at cooling rates of 10-200 ℃/ min was dynamically in-situ observed by high-temperature confocal laser scanning microscopy (CLSM). The effects of cooling rates on the solidification process, structure and precipitates of the GH5188 alloy were studied. The results show that the solidification process for the GH5188 alloy is slow-rapid-slow solidification. The higher the cooling rate, the greater the peak solidification rate is obtained. The cooling rate affects the solidification temperature of the alloy, and the solidification temperature decreases with the increase in the cooling rate. With the increase in cooling rate, the secondary dendrite arm spacing of the alloy after solidification decreases. The size of precipitates is more uniform and refined, which is conducive to reducing the crack sensitivity of the alloy during solidification. The secondary dendrite arm spacing prediction formula is obtained under different cooling rates.

Effect of tempering temperature on microstructure and impact properties of low-carbon high-alloy bearing steel

Wu Zhiwei, Wu Xueting, Zhang Jun, Li Wei

2023, 44(3): 138-143. doi: 10.7513/j.issn.1004-7638.2023.03.021

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The effect of tempering temperature on microstructure and impact toughness of low-carbon, high-alloy bearing steel was studied by OM, SEM, and XRD. The results show that the metallographic microstructure for the low-carbon, high-alloy bearing steel consisted of tempered martensite and retained austenite when the tempering temperature is 200, 300, 400, 500 ℃, respectively. Furthermore, martensite degradation occurs, and the microstructure consists of tempered soxbite and retained austenite when the tempering temperature increases to 600 ℃ and 700 ℃. After tempering at 200-700 ℃, the impact toughness of low-carbon, high-alloy bearing steel tempered at 300 ℃ is the highest, that tempered at 600 ℃ is the lowest, and the tempering temperature should not exceed 500 ℃. The fracture characteristics of low-carbon, high-alloy bearing steel after tempering at 200-500 ℃ are quasi-dissociative fractures, and the tempering at 600 ℃ and 700 ℃ are brittle fractures.

Optimization of flow control device on twin channel induction heating tundish by simulation

Gao Wenxing, Yuan Jibai, He Junfeng, Liang Richeng, Li Yuanyuan

2023, 44(3): 144-151. doi: 10.7513/j.issn.1004-7638.2023.03.022

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In order to solve the problems of low volume utilization, short average residence time and poor consistency of each flow of the twin channel induction heating tundish without flow control devices, weirs with different diversion holes and heating twin channels were designed. The flow field and temperature field of tundish are simulated by numerical simulation and water simulation. Simulation results show that the flow of molten steel can be improved by setting a wall in the tundish. For Scheme A2 (two diversion holes are opened on the splayed wall, with diameter of 130 mm and a horizontal inclination of 5° to the retaining wall, an elevation of 25° for the lower hole and 15° for the upper hole), the average residence time is extended by 207.2 s, the dead zone volume is reduced by 23.89%, and the maximum temperature difference between the edge nozzle and the middle nozzle is 3 ℃. Scheme E2 (Runway type heating twin channel) can achieve better heating effect on tundish. The production practice has proved that the maximum temperature difference between the edge water outlet and the middle water outlet is about 3～4 ℃.The optimized flow control device improves the fluidity inside the tundish.

Control and research on original lump carbides and their inheritance of continuous casting bearing steel billets

Xu Bin, Cheng Pengfei, Xiao Guohua, Jin Guobing, Hao Zhichao, Chen Tao, Sun Junxi

2023, 44(3): 152-158. doi: 10.7513/j.issn.1004-7638.2023.03.023

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The morphology, distribution and relationship between the original bulk carbides and carbon segregation index of GCr15 bearing steel continuous casting billets under different continuous casting factors (superheat, drawing speed, secondary cooling strength, electromagnetic stirring conditions) were investigated by Image-Pro Plus software and metallographic method. The results show that the heritability of the original bulk carbide of different types of billets, intermittently distributed or individually distributed billet bulk carbide after the existing rolling heating process, the liquid precipitation carbide level is 0-0.5, which guides the best matching process parameters for continuous casting is the drawing speed 0.95 m/min, superheating degree 20-25 ℃, cooling intensity 0.35 L/kg, end electromagnetic stirring 350 A/7 Hz.

Evolution mechanism of inclusions in GH4169 produced by vacuum induction melting

Li Jing, Jiang Shichuan, Qi Huilin, Zhou Yang

2023, 44(3): 159-164. doi: 10.7513/j.issn.1004-7638.2023.03.024

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Inclusion had been considered as main factor affecting metallurgical quality and mechanical property of Ni-based superalloys. In this work the evolution mechanism of inclusions during the preparation of GH4169 Ni-based superalloy by vacuum induction melting (VIM) was studied. A method of ASPEX automatic scanning electron microscope was utilized to characterize the inclusions in GH4169 Ni-based superalloy prepared by vacuum induction melting (VIM). The phases, compositions, morphologies, formation mechanism and evolution mechanism of the inclusions were analyzed. The results indicate that the inclusions of single phase in GH4169 include mainly Al₂O₃、MgAl₂O₄ and MgO. The inclusions of composite phases include mainly MgAl₂O₄-Ti(C,N)-NbC and MgO-Ti(C,N)-NbC. Al₂O₃ forms during melting period, MgAl₂O₄ forms during refining period, and MgAl₂O₄-Ti(C,N)-NbC forms after alloying with Nb, Al and Ti, and MgO and MgO-Ti(C,N)-NbC form after alloying with Mg. As smelting process going, the number density of inclusions firstly increases and then decreases, and the number density of inclusions reaches a peak value of 211.42/mm² during the refining period. After the refining period, the number of inclusions decreases, and the number density of inclusions before pouring is 46.57/mm².

Study of the heating rate effect on the oxidation kinetics of the corrosion-resistant rebar

Wang Baoshan, Zhang Hongliang, Ma Jian, Feng Guanghong

2023, 44(3): 165-170. doi: 10.7513/j.issn.1004-7638.2023.03.025

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Abstract:
The oxidation behavior of corrosion-resistant rebar at various heating rates in air was studied by thermogravimetric analysis and microstructural observation, and the results were compared with those of isothermal oxidation. It is showed that there were no significant microstructural differences at different heating rates, but the oxidation thickness increased with the decrement of the heating rate. Meanwhile, the oxide scale displayed a two-layer structure when the heating rates were under 10 ℃/min, but there was almost a single layer of the oxide at the heating rate of 20 ℃/min. A new calculation method for the oxidising activation energy was established through the constant heating rate tests. The relative errors of the heat rates of 5, 10 ℃/min, and 20 ℃/min were 4.14%, 5.12%, and 32.13% respectively, compared to the values obtained by the isothermal oxidation tests. Thus, in order to ensure the accuracy of the new method, tests should be carried out at comparatively low heating rates.

Effect of titanium content on hydrogen embrittlement behavior of bainite/martensite dual-phase steel

Li Zhengjie, Zhang Wei, Liu Xiaojun

2023, 44(3): 171-176. doi: 10.7513/j.issn.1004-7638.2023.03.026

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Abstract:
Three kinds of bainite/martensite dual-phase steels with different titanium content (0, 0.9, and 1.8 wt%) were smelted in this paper. The bainite content in the samples was changed by heat treatment to maintain the same strength level. The effect of bainite content on the hydrogen embrittlement resistance of bainite/martensite dual-phase steel was studied by electrochemical hydrogen charging and a slow strain rate tensile test. The results show that the test steel with a titanium content of 1.8 wt% has the highest bainite content and the best resistance to hydrogen embrittlement, mainly due to the capture of hydrogen atoms by irreversible traps such as cementite ferrite interface dislocations. In order to improve the hydrogen embrittlement resistance of bainite/martensite dual-phase steel, the number of fine cementite particles in the bainite structure can be increased, which provides more irreversible hydrogen traps for hydrogen migration during plastic deformation.

Effect of deoxidizer on non-metallic inclusions in M50NiL steel

Li Bing, Wu Zhiwei, Chen Wenxiong, Wang Xiaoqiang, Lang Dong, Zhang Jun, Mao Jian

2023, 44(3): 177-182. doi: 10.7513/j.issn.1004-7638.2023.03.027

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Abstract:
Different deoxidizers were used for deoxidation in the vacuum smelting process of aero-engine bearing steel M50NiL, and the influence of different deoxidizer types on the morphology, type, size and number density of inclusions in the steel were studied. The results indicate that without adding deoxidizer, the inclusions in steel are mainly Al₂O₃ and Al-Mg spinel. After using Al-RE as deoxidizer, the main types of inclusions in steel are rare earth inclusions. When Al-RE-Si-Mn is used as deoxidizer, the type, size and distribution characteristics of inclusions in steel are basically similar to those of Al-RE deoxidizer. The addition of rare earth elements can significantly improve the type and morphology of inclusions in steel, where the main inclusion types are transformed from Al₂O₃-rich inclusions with angular and irregular shapes to nearly spherical rare earth inclusions, while reduce the maximum size of inclusions in steel and the number of large-sized Al₂O₃ inclusions. However, excessive addition of rare earth causes the agglomeration of rare earth inclusions in steel.

Thermodynamic study on equilibrium phase transformation and precipitation of 12Cr1MoVG steel

Wen Li, Ai Liqun, Lei Yue, Li Yaqiang, Hong Lukuo, Zhu Guangpeng, Wang Xufeng

2023, 44(3): 183-190. doi: 10.7513/j.issn.1004-7638.2023.03.028

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Abstract:
The phase transformation and precipitation behavior of 12Cr1MoVG steel during cooling were studied by thermodynamic software JMatPro, and the effect of alloying elements in the steel on longitudinal crack sensitivity was analyzed. The results show that the transformation path of 12Cr1MoVG steel from 1600 ℃ to 400 ℃ is L→ L+δ→ L+δ+γ→ δ+γ→ γ→ γ+MnS→ γ+MnS+MN→ γ+MnS+M(C,N)→ γ+α+MnS+M(C,N)→ γ+α+MnS+M(C,N)+AlN→ γ+α+MnS+M(C,N)+M(C,N)+AlN+M₂₃C₆→ α+MnS+M(C,N)+M(C,N)+AlN+M₂₃C₆. With the increase of P, S, Mo, V and Cr contents in the steel, the longitudinal crack sensitivity increases. While, the longitudinal crack sensitivity decreases with the increase of Mn and Si contents. Based on the temperature range of the (α+γ) two-phase region and the precipitation behavior of M (C, N), the low-temperature brittleness temperature range is calculated to be in the range of 747.6～869 ℃, which is basically consistent with the tensile testing results.

Analysis of the gear shaft broken teeth of the reducer

Dong Xuejiao

2023, 44(3): 191-196. doi: 10.7513/j.issn.1004-7638.2023.03.029

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Abstract:
Aiming at the broken phenomenon of the gear shaft in a reducer, the chemical composition of the gear shaft was analyzed; the internal microstructure of the gear shaft and the causes of defects were studied by metallographic analysis technology. The fracture morphology was observed by scanning electron microscope, and the hardened layer depths of the tooth were calculated by the hardness calculation method, and the carburized and quenched hardened layers on the tooth top were mathematically verified. The results show that the high temperature of the gear during quenching and heating leads to the appearance of coarse martensite and network carbide in the gear. There is a serious internal oxidation phenomenon on the tooth surface, resulting in the embrittlement of the tooth material, and then intergranular cracking and blocks falling. In addition, the phenomenon of broken teeth occurs under the synergistic effect of the eccentric loads and low hardness.

2023 Vol. 44, No. 3