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General model for kinematic analysis of swash plate axial piston pump WANG Jian-sen, CAO Wei-dong, HE Xin-long, WANG Zheng-rong, ZHANG Zhi-wei Journal of Lanzhou University of Technology    2021, 47 (5): 59-64.   Abstract （545）      PDF（pc） （3701KB）（775）       Knowledge map    Save Based on the comprehensive consideration of swash plate angle, cross angle and piston inclination angle of the swash plate axial piston pump, the general piston kinematics model is established by coordinate transformation method. The analysis results show that the cross angle of swash plate and the inclination angle of piston will increase the maximum amplitudes of displacement, velocity and acceleration of piston, and then increase the displacement of pump, the maximum transient flow velocity in the piston chamber and the inertia force of piston; the cross angle of swash plate will change the phase of piston movement and make the internal and external dead points deflect, which will change the pre-compression and pre-expansion angle of valve plate; the inclination angle of piston will affect the movement of the piston, the smaller the inclination angle of the plunger, the closer the movement of the plunger is to the simple harmonic motion, on the contrary, the larger the deviation is, the maximum deflection angle of internal and external dead center is 90°, the smaller the absolute value of the cross angle is, the smaller the deflection angle of internal and external dead center changes in the range of big swash plate angle, and the greater the gradient of change when swash plate angle is close to zero displacement. Reference | Related Articles | Metrics

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Cleaning and modeling of abnormal data of wind farm power curve CAO Li-xin, LIU Wei-min, GUO Hu-quan Journal of Lanzhou University of Technology    2022, 48 (4): 64-70.   Abstract （469）      PDF（pc） （3178KB）（764）       Knowledge map    Save The wind speed and power data of wind farms usually contain a large number of abnormal data, which is difficult to reflect the real working conditions of wind turbines, affect the accuracy of wind power prediction, and then cause certain economic losses. To solve this problem, the characteristics of abnormal data are analyzed, a slip-quartile abnormal data elimination method is proposed, and the wind speed power curve of the eliminated data is modeled by using high-order polynomial and Logistic function. Finally, the applicability and effectiveness of this method are verified by variance, root means square error and determination coefficient. The analysis in the example shows that the method is simple, efficient and versatile, and can significantly improve the accuracy of wind turbine power characteristic analysis. Reference | Related Articles | Metrics

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A machine learning methods for identifying the properties of Chinese medicinal materials from infrared spectrum data TIAN Chun-ting, ZHAO Ning, QIN Jian-wei, MENG Xiao-feng Journal of Lanzhou University of Technology    2023, 49 (3): 55-59.   Abstract （307）      PDF（pc） （2953KB）（710）       Knowledge map    Save There are great differences in the characteristics of near-infrared and mid-infrared spectra of different kinds of traditional Chinese medicine. Due to the different chemical components such as inorganic elements and organic substances, even if the origin of the same traditional Chinese medicine is different, the labeling effect under near-infrared and mid-infrared spectral irradiation will have different spectral characteristics which can be used to classify Chinese herbal medicine and identify the origin of Chinese herbal medicine. With the help of MATLAB software tool and K-means clustering algorithm in SPSS classification tool, unsupervised machine learning is carried out on traditional Chinese medicine to classify traditional Chinese medicine; Using SPSS neural network multilayer perceptron and the random forest algorithm provided by Python language, 70% of the data set is used as the training set and 30% as the verification set to train the supervised machine learning model which is finally used to identify and predict the origin of traditional Chinese medicine. Reference | Related Articles | Metrics

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Mechanical resonance suppression of permanent magnet servo system based on shaft torque compensation BAO Guang-qing, DU He-xuan, QI Wu-gang Journal of Lanzhou University of Technology    2022, 48 (4): 76-82.   Abstract （193）      PDF（pc） （2877KB）（690）       Knowledge map    Save Flexible drive will cause mechanical resonance in the AC permanent magnet servo system and degrade the dynamic performance and control accuracy of the system. Therefore, a Kalman filter-based resonance suppression method for shaft torque compensation is proposed. In this method, the shaft torque estimation value of the flexible drive device is obtained by Kalman filter, which is converted into a current signal and compensated to the given current loop, so as to eliminate the influence of the flexible transmission on the motor speed and improve the dynamic performance of the system. Finally, the effectiveness of the method is verified by simulation. Reference | Related Articles | Metrics

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Research on DR digital imaging automatic detection method of blade air film hole processing defects LIU Tao, SHI Yu, LI Chun-kai, SUN Zhong-chen, MAN Yue-e, LV Jian Journal of Lanzhou University of Technology    2021, 47 (5): 19-23.   Abstract （357）      PDF（pc） （3987KB）（685）       Knowledge map    Save Air film holes are one of the important cooling structures in turbine blades, it has great significance to improve the cooling efficiency of aircraft engines, reduce the temperature of the combustion chamber and even increase the service life of the engine. However, in the actual course of working, it is easy to have internal defects such as unopened air film holes, deflection, and damage to the inner wall due to external factors. Traditional detection methods mainly use artificial film X-ray method to detect internal defects, but there are problems such as low detection efficiency, high cost and high dependence on the experience and skills of the inspectors. This paper proposes an automatic detection method for air film hole defects based on X-ray digital imaging technology. By studying the equivalence of DR digital images and film images, the law of the effect of the transillumination angle on defect recognition and the optimization of the detection process, key technologies based on deep learning neural network defect self-recognition, high-precision detection and intelligent recognition of blade air film hole processing defects are realized. Reference | Related Articles | Metrics

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First principles on the effect of Cr content on the electronic structure and mechanical properties of Fe 3Al alloy LI Ya-min, ZHANG Jun-xia Journal of Lanzhou University of Technology    2022, 48 (2): 1-8.   Abstract （462）      PDF（pc） （4161KB）（673）       Knowledge map    Save Effect of Cr content on the electronic structure and mechanical properties of DO 3-Fe 3al alloy was investigated by using the first principle method based on density functional theory. The occupation of Cr in the supercell model was determined by calculating the formation heat and binding energy of the system before and after doping, and the micro mechanism of the effect of Cr on the mechanical properties of Fe 3Al alloy was revealed by calculating the elastic modulus, population, density of states and differential charge density. The results showed that Fe Ι bit is preferentially occupied when the Cr content is 3.125 at.%, while the content is 6.25 at.%), it tends to occupy Fe Ι and Al bit. The doping of Cr improves the stability of the system and the brittleness of the alloy, and the toughening effect increases with the increase of Cr content. Cr doping changes the distribution of electrons between atoms, with the increase of Cr content, the number of p-d hybrid electrons between Fe and Al decreases and the covalent bond decreases, at the same time, the charge transferring between atoms increases, the increase of Fe-Fe bond and the existence of Fe-Cr and Al-Cr anti bonds enhance the metallicity of the system, in addition, decrease of the covalent bond on the (100) plane but the increases of bonding strength between atoms on the (010) plane are all the essential reasons that the addition of Cr can improve the toughness of Fe 3Al alloy. Reference | Related Articles | Metrics

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Influence of high rate charge and discharge cycle on the electronic performance and thermal safety of lithium ion battery LI Dong-qi, ZHANG Qing-song, ZHENG Shao-shuai Journal of Lanzhou University of Technology    2023, 49 (3): 30-35.   Abstract （459）      PDF（pc） （2624KB）（654）       Knowledge map    Save Lithium-ion batteries are widely used in electric vehicles and various energy storage devices. In this paper, cyclic aging and thermal runaway experiments under different charge-discharge rates were carried out, and the effects of large-rate charging and discharging on the performance and thermal safety of single lithium-ion batteries were studied. The results showed that the actual capacity of single lithium-ion battery is attenuated under the large-rate charge-discharge cycle, and the degree of attenuation is positively relevant to the charge-discharge rate. With the charge-discharge rate increasing, the constant current ratio is stepwise attenuation, but the coulombic efficiency still maintains in the range of 99%-100%, indicating that the reversible performance of lithium-ion batteries is normal. With the increase of the magnification, the thermal runaway trigger time, explosion pressure and jet flame temperature first increase and then decrease. The average surface temperature of the battery during explosion is 655.8 ℃, which is close to the melting point of aluminum. The explosion injection powder products are mainly metal aluminum, graphite and lithium cobalt oxide. Reference | Related Articles | Metrics

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Fatigue strength analysis of high-strength bolts for tower flange of wind turbine LIANG Yuan, WANG You-liang, WEI Tai, LIU Jian-hui Journal of Lanzhou University of Technology    2023, 49 (2): 65-69.   Abstract （250）      PDF（pc） （1391KB）（637）       Knowledge map    Save An analysis method for high-strength bolts of wind turbine tower flange was established by considering the influence of external load on fatigue damage. Firstly, the maximum load section was determined with the aid of the tower equivalent model according to the damage parameters of the stress state on the connection section. Secondly, the external load on any sector of the tower was obtained by Schmidt-Neuper algorithm. Afterwards, the fatigue damage distribution model of high-strength bolts was established and the relationship between the external load and the internal stress of high-strength bolts was explored based on the finite element model. Finally, the optimal bolt pretightening force was determined with comparing the fatigue cumulative damage values with different bolt pretightening forces by considering the influence of pretightening forces. The results show that the positions of the maximum fatigue cumulative damage of flange bolts were －4.17° and 175.87°, and the bolt pretightening force was the most suitable value when the bolt pretightening force ratio was 70%. Reference | Related Articles | Metrics

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Dynamic output feedback control of cyber-physical systems under false data injection attacks ZHU Chao-qun, ZHU Yi-rong Journal of Lanzhou University of Technology    2023, 49 (1): 74-82.   Abstract （256）      PDF（pc） （1259KB）（622）       Knowledge map    Save In this paper, an H-infinity dynamic output feedback control strategy with attack defense ability is investigated to deal with the problem of security control of cyber-physical system (CPS) under false data injection (FDI) attacks, which is taken as a special kind of external disturbance. Firstly, the effect of FDI attacks in the measurement channel and random time-delay on the communication network is considered, and a closed-loop system model with FDI attack, random time-delay, and external disturbance is established. Secondly, the sufficient conditions for the asymptotic stability of the closed-loop system under FDI attacks are derived based on the Lyapunov stability theory, and then the design scheme of H-infinity dynamic output feedback controller by utilizing linear matrix inequality technology is presented. Finally, a simulation example is given to demonstrate the feasibility and effectiveness of the proposed method. Reference | Related Articles | Metrics

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Design of virtual and real interactive monitoring system for CNC machine tools based on digital twins HUANG Hua, LI Jia-ran, LI Dian-lun Journal of Lanzhou University of Technology    2023, 49 (1): 36-43.   Abstract （423）      PDF（pc） （5660KB）（612）       Knowledge map    Save Aiming at the problem that the actual operating status of CNC machine tools is not directly reflected by traditional monitoring technology and virtual simulation technology, a virtual-real interactive monitoring system for CNC machine tools based on digital twins technology is designed by combining the new generation of information technology and the concept of digital twins. In addition, taking a CNC machine tool as example, the system architecture and related functions are first designed through Portal software. Based on that, the information collected by the sensor is transmitted to the system through PLC and Ethernet for analog conversion; and the digital twins data in the system is connected with the digital twins to realize the reception and transmission of information, then the combination of virtual and real are completed through OPC-DA. Finally, this method is used to monitor the vibration signal of the machine tool in real time and design a remote control panel. The experimental results show that the system using the virtual-real interactive monitoring system and digital twins of the CNC machine tool to double monitor the machining process can reflect the actual operating status of the machine tool more effectively and intuitively. Meanwhile the digital twins is virtually controlled by the virtual-real interactive monitoring system, and the application field of digital twins technology is further expanded. Reference | Related Articles | Metrics

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Sentiment analysis of Chinese text based on feature fusion ZHAO Hong, FU Zhao-yang, WANG Le Journal of Lanzhou University of Technology    2022, 48 (3): 94-102.   Abstract （284）      PDF（pc） （1771KB）（598）       Knowledge map    Save To address the problems that the existing methods cannot comprehensively consider the semantic information of text in terms of syntactic structure, contextual information and local semantic features, a feature fusion-based Chinese text sentiment analysis method is proposed. Firstly, Jieba word segmentation tool is used for word segmentation and part of speech tagging of the review text, and a word vector training tool GloVe is used to obtain pre-trained word vectors with part of speech. Then, the word vector is used as the input of BiGRU and TextCNN with self attention respectively. The global features are extracted from the syntactic structure and the contextual information of the text using BiGRU with Self-Attention, and the local semantic ones are extracted using TextCNN. Finally, the global features and local semantic features are integrated, and Softmax is used for text sentiment classification. The experiment result shows that the proposed method can effectively improve the accuracy of text sentiment analysis. Reference | Related Articles | Metrics

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Research on noise addition and precision analysis in differential privacy WANG Xiao-shi, KANG Hai-yan Journal of Lanzhou University of Technology    2023, 49 (3): 94-103.   Abstract （269）      PDF（pc） （2751KB）（595）       Knowledge map    Save Differential privacy, as a definition of privacy protection with a strong mathematical background and rigorous mathematical derivation, has received great attention and has been widely studied. However, up to now, there is a lack of strict and clear proof and derivation processes for the definition of differential privacy and the basic mechanism used in China, which makes it difficult for scholars to get started. Therefore, in this paper, the Laplace and exponential mechanism in differential privacy are analyzed in detail by means of analysis, proof, and application examples, and a complete mathematical derivation process and application examples are given to address this gap. It is pointed out that there is a problem of excessive scaling in the accuracy formula of the Laplace and exponential mechanism. After proving the accuracy formula of Laplace and the exponential mechanism, the reason why this paper considers excessive scaling is given. It is not difficult to conclude from experiments that the Laplace mechanism precision formula and the exponential mechanism precision formula are formulas with an excessive range of accuracy. Reference | Related Articles | Metrics

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Dynamic response analysis of wind turbine structure under wind and sand load excitation LI Wan-run, HUANG Jie, DING Ming-xuan, LI De-qiang, WANG Xue-ping, DU Yong-feng Journal of Lanzhou University of Technology    2022, 48 (2): 107-114.   Abstract （293）      PDF（pc） （2758KB）（544）       Knowledge map    Save To study the damage of wind-sand load to wind turbine, the dynamic response analysis of wind turbine under the load was analyzed. Based on 2 MW wind turbine, three finite element models are established, which do not consider blades, consider blade rotation, and consider soil-structure interaction. The Davenport wind speed spectrum and harmonic superposition method are used to simulate the pulsating wind speed time history, and the dynamic calculation model of wind and sand load is established by the law of conservation of momentum and wind and sand flow density. The dynamic responses of the model under the action of wind load and wind sand load are simulated by ANSYS. The results show that: the response of wind power generation structure under wind sand load is large, and its effect can not be ignored. The results obtained by numerical simulation with simplified lumped mass model are unsafe, and soil-structure interaction has obvious amplification effect on the displacement response under wind load and wind sand load. Reference | Related Articles | Metrics

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Investigation on obstacle detection and recognition of façade-cleaning robot based on convolutional neural network GUO Run-lan, SHI Fang-qing, FAN Ya-qiong, HE Zhi Journal of Lanzhou University of Technology    2022, 48 (4): 83-89.   Abstract （208）      PDF（pc） （4742KB）（540）       Knowledge map    Save Combined with the working principle of the robot and the application of convolutional neural network (CNN) of image classification, a wall obstacle detection and recognition algorithm based on CNN is proposed. Firstly, with the goal of accurate recognitionof wall obstacles, the image database of wall obstacles is constructed, and then the simplified VGG-16 network is optimized to obtain a CNN model, which is suitable for accurate recognition of wall obstacles. On this basis, the network is designed to be composed of an input layer, four convolutional layers, two pooling layers, a fully-connected layer and an output layer. Further, the training samples are convolved using 3×3 convolution kernels, and the acquired feature maps are pooled in 2×2 domains. After repeating the above operations, the optimal network model is obtained by learning and the network model parameters are further determined. The experimental results show that the recognition accuracy of obstacles can reach 99.0%, which has good recognition ability. Reference | Related Articles | Metrics

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Effect of slotted blade on cavitation performance of axial flow pump ZHAO Wei-guo, XUE Zi-yang, KANG Yan-dong, CHENG Chao, LI Qing-hua Journal of Lanzhou University of Technology    2022, 48 (4): 49-55.   Abstract （218）      PDF（pc） （5356KB）（519）       Knowledge map    Save In order to investigate the effect of the slotted blade on the cavitation control of the axial flow pump, the 350ZQ-70-H submersible axial flow pump is taken as the research object, and the flow field under different cavitation margins is simulated by steady and unsteady constant values. The velocity vector distribution, pressure distribution, internal void volume fraction and void volume change of the original model and the improved model are compared and analyzed. The results show that the slotted blade can improve the efficiency and head of the axial flow pump, and enhance the performance of the axial flow pump. The slotted blade increases the flow area at the blade inlet, reduces the flow velocity at the blade inlet, improves the pressure distribution in the axial flow pump impeller, and thus suppresses cavitation. In each stage of cavitation, the cavity volume fraction distribution of the slotted model is reduced, especially in the initial stage of cavitation, which is 30.4% lower than the original model, effectively inhibited the development of cavitation and significantly improved the cavitation performance. Reference | Related Articles | Metrics

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Experimental study on modal parameters of pedestrian bridge with static crowd-structure interaction MA Fa-rong, ZHU Qian-kun, ZHANG Qiong, DU Yong-feng Journal of Lanzhou University of Technology    2022, 48 (2): 115-122.   Abstract （220）      PDF（pc） （6083KB）（519）       Knowledge map    Save In this paper, the effect of modal parameters of pedestrian bridge under static crowd-structure interaction is studied, and the steel structure pedestrian glass bridge is used as the research platform. The research contents are as follows: the dynamic parameter of the pedestrian bridge under the excitation of the test environment and the dynamic parameters of the structure under different positions are changed under the action of the static crowd in different positions of the pedestrian bridge. The results show that under the static population-structure interaction, with the increase of the number of people acting, the natural frequency of the structure decreases and the damping ratio increases gradually. The sitting posture has the greatest influence on the structural frequency, the natural vibration frequency of the structure decreases from 4.381Hz to 3.643Hz, which is decreased by 16.8% under the action of four people, and the semi-squatting position has the greatest effect on the damping ratio. The damping ratio of the structure increases from 0.660% to 4.888%, which is increased by 640.6% under the action of four people. When the static population is located at the peak point of a certain order mode, the frequency of the corresponding modal structure is the smallest and the damping ratio is the largest. Reference | Related Articles | Metrics

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Study on effect of laminate thickness on bridging and interlaminar fracture toughness ZHANG Yong-gui, MA Qi-wen, LIU Jian-hui Journal of Lanzhou University of Technology    2022, 48 (4): 43-48.   Abstract （210）      PDF（pc） （3399KB）（514）       Knowledge map    Save Accurate simulation and analysis of delamination propagation behavior of composite laminates is extremely significant for the structural design of laminates. In view of the deficiency that the existing research does not quantitatively describe the relationship between mode Ⅰ interlaminar fracture toughness and laminate thickness, a plane strain model was established with the help of ABAQUS finite element software. The iterative method was used to determine the influence of specimen thickness on the traction separation behavior in the bridging zone by controlling the ratio of the thickness to the layer number. At the same time, considering the cohesive constitutive relationship,when the thickness was 2, 4 and 8 mm,the delamination propagation behavior of unidirectional carbon/epoxy composites was studied by finite element method. The results show that the steady-state fracture toughness become higher with the increase of specimen thickness. However, the initial fracture toughness is independent of specimen thickness. The effect of specimen thickness on interlaminar fracture toughness of laminates is further verified, and the analytical results are in good agreement with the experimental values. Reference | Related Articles | Metrics

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Study on life extension strategy based on real-time life prediction of feedback control system LI Wei, LI Zong-ren, MAO Hai-jie Journal of Lanzhou University of Technology    2021, 47 (6): 74-83.   Abstract （325）      PDF（pc） （3371KB）（504）       Knowledge map    Save Aiming at the problem that the performance of the feedback control system cannot meet the time limit of the control task due to the implicit degradation of the actuator, a dynamic matrix control (DMC) life extension method based on the real-time life prediction of the feedback system is proposed. Firstly, based on the Wiener and Poisson process, a composite model more suitable for the actual degradation process of actuator is established. Secondly, by analyzing the impact of the implicit degradation of the actuator on the performance of the control system, the analytical solution of the remaining life (RUL) of the system is given, and the real-time and rapid prediction of system RUL is realized. Then, based on the RUL prediction information and combined with the DMC method, the RUL of the system is extended by the online targeted adjustment of the element values of the constraint matrix Q and R, so as to ensure the achievement of the time limit requirements of control tasks. Finally, the effectiveness of the proposed method is verified by a double tank liquid level system, and the life extension effect and robustness are better than the existing LQR method. Reference | Related Articles | Metrics

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A fatigue life prediction model of multi-axial notched specimens with notch effect LIU Jian-hui, PAN Xue-mei, LU Xin, ZI Rong, CHEN Xiao-chuang Journal of Lanzhou University of Technology    2021, 47 (6): 56-60.   Abstract （235）      PDF（pc） （1412KB）（490）       Knowledge map    Save In order to study the multi-axial fatigue of notched specimens, based on the theory of damage mechanics and the idea of von Mises equivalent rule, a multi-axial damage constitutive equation considering notch effect was established, which comprehensively considers the effect of normal stress and shear stress in the multi-axial damage process; and further, a multi-axial fatigue life prediction model that can be applied to metal notched parts was proposed in this paper. The model was evaluated by the multi-axial notched fatigue test data of GH4169 nickel-based superalloy, SAE1045 steel and LY12CZ aluminium alloy. The results show that the multi-axial fatigue life predicted by the proposed model was in good agreement with the test results, and the prediction accuracy was significantly improved compared with the traditional local stress strain approach. At the same time, the model is easy to calculate and is convenient for engineering application. Reference | Related Articles | Metrics

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Thermodynamical analysis of TiN precipitation in 21Cr ultra pure ferrite stainless steel SHENG Jie, WEI Jia-fu, MENG Ya-hui, LI Yu-feng, MA Guo-cai, LA Pei-qing Journal of Lanzhou University of Technology    2023, 49 (5): 1-9.   Abstract （299）      PDF（pc） （2905KB）（480）       Knowledge map    Save Number density and size distribution of non-metallic inclusion have important influences on processability and service behaviors of steel. The numerical modeling of TiN precipitation condition in 21Cr ultra-pure ferrite stainless steel was solved based on the basic solidification theory. Thermodynamic and kinetic formation conditions and precipitation laws of TiN were investigated theoretically. The findings showed that TiN is precipitated free in molten steel. Ti and N elements solute segregation occurs on the solid/liquid interface in the processing of solidification, which promote TiN precipitation starting as f s=0.15. The precipitate size of TiN is affected by Ti, N content, and cooling rate. TiN radius can be reduced by decreasing the initial content of Ti, N and increasing the solidification cooling rate, Ti, N element contents are more sensitive to the effect of TiN size, so the timing of the precipitation of TiN inclusions during solidification can be significantly delayed by reducing the initial content of N in molten steel. Therefore, the addition amount of Ti in molten steel can be adjusted to make the quantity and size of TiN more reasonable in manufacture. Reference | Related Articles | Metrics