Data-driven algorithms for predicting mechanical properties with small datasets are evaluated in a case study on gear steel hardenability.The limitations of current data-driven algorithms and empirical models are iden...Data-driven algorithms for predicting mechanical properties with small datasets are evaluated in a case study on gear steel hardenability.The limitations of current data-driven algorithms and empirical models are identified.Challenges in analysing small datasets are discussed,and solution is proposed to handle small datasets with multiple variables.Gaussian methods in combination with novel predictive algorithms are utilized to overcome the challenges in analysing gear steel hardenability data and to gain insight into alloying elements interaction and structure homogeneity.The gained fundamental knowledge integrated with machine learning is shown to be superior to the empirical equations in predicting hardenability.Metallurgical-property relationships between chemistry,sample size,and hardness are predicted via two optimized machine learning algorithms:neural networks(NNs)and extreme gradient boosting(XGboost).A comparison is drawn between all algorithms,evaluating their performance based on small data sets.The results reveal that XGboost has the highest potential for predicting hardenability using small datasets with class imbalance and large inhomogeneity issues.展开更多
In the 20CrMnTi steel production process, the nitrogen content increased by 19 × 10-6 and 29 × 10-6, respectively, during ladle furnace(LF) refining and during the casting process from ladle to tundish. The ...In the 20CrMnTi steel production process, the nitrogen content increased by 19 × 10-6 and 29 × 10-6, respectively, during ladle furnace(LF) refining and during the casting process from ladle to tundish. The protective casting is the key to decrease the N content. The results of thermodynamic calculations and a growth kinetics investigation show that TiN formation occurs only when the solidification fraction is greater than 0.533 under the controlled conditions used in this study for the manufacture of 20CrMnTi steel; the radius of TiN particles decreases as the Ti and N contents decrease and as the cooling rate increases. Furthermore, the theory of austenite grains controlled by second-phase particles was analyzed. The elemental analysis results showed that the Ti content was controlled at 0.04wt%–0.06wt% and the N content decreased to 0.005wt%, which satisfy the requirements for grain refinement but can also effectively prevent the precipitation of TiN inclusions in 20CrMnTi steel.展开更多
The effect of compressive deformation of austenite on continuous cooling transformation microstructures for 22CrSH gear steel has been investigated using a Gleeble 1500 thermal simulator. The experimental results show...The effect of compressive deformation of austenite on continuous cooling transformation microstructures for 22CrSH gear steel has been investigated using a Gleeble 1500 thermal simulator. The experimental results show that the deformation of austenite promotes the formation of proeutectoid ferrite and pearlite, and leads to the increase of critical cooling rate of proeutectoid ferrite plus pearlite microstructure. The grain boundary allotriomorphic ferrite occupies the austenite grain surfaces when the prior deformation takes place or the cooling rate is decreased, which causes a transition from bainite to acicular ferrite. The deformation enhances the stability of transformation from austenite to acicular ferrite, which results in an increase of M/A constituent.展开更多
Using a Gleeble 1500 hot simulator, the dynamic recrystallization (DRX) behavior of Mn-Cr type gear steel was investigated. The experimental results show that the Mn-Cr gear steel exhibits a typical DRX behavior at hi...Using a Gleeble 1500 hot simulator, the dynamic recrystallization (DRX) behavior of Mn-Cr type gear steel was investigated. The experimental results show that the Mn-Cr gear steel exhibits a typical DRX behavior at higher deformation temperature, lower strain rate and smaller initial austenite grain size. The DRX takes place under the conditions that Zener-Hollomon parameter (Z) is less than a critical value Z_c. The DXR grains are formed by the bulging mechanism. Activation energy and stress exponent were calculated to be 378.6 kJ·mol -1 and 5.8 respectively by regression analysis.展开更多
The equilibrium reaction between CaO -Al_2O_3-SiO _2-MgO slag and 28 MnC r5 molten steel was calculated to obtain the suitable slag composition which is effective for decreasing the oxygen content in molten steel. The...The equilibrium reaction between CaO -Al_2O_3-SiO _2-MgO slag and 28 MnC r5 molten steel was calculated to obtain the suitable slag composition which is effective for decreasing the oxygen content in molten steel. The dissolved oxygen content [O] in molten steel under different top slag conditions was calculated using a thermodynamic model and was measured using an electromotive force method in slag–steel equilibrium experiments at 1873 K. The relations among [O], the total oxygen content(T.O), and the composition of the slag were investigated. The experimental results show that both [O] and T.O decrease with decreasing SiO_2 content of the slag and exhibit different trends with the changes in the CaO /Al_2O_3 mass ratio of the slag. Increasing the CaO /Al_2O_3 mass ratio results in a decrease in [O] and an increase in T.O. To ensure that T.O ≤ 20 ppm and [O] ≤ 10 ppm, the SiO _2 content should be controlled to <5wt%, and the CaO /Al_2O_3 mass ratio should be in the range from 1.2 to 1.6.展开更多
The prediction of the hardenability and chemical composition of gear steel was studied using artificial neural networks. A software was used to quantitatively forecast the hardenability by its chemical composition or ...The prediction of the hardenability and chemical composition of gear steel was studied using artificial neural networks. A software was used to quantitatively forecast the hardenability by its chemical composition or the chemical composition by its hardenability. The prediction result is more precise than that obtained from the traditional method based on the simple mathematical regression model.展开更多
The influence of ingot segregation on quenching distortion of gear steel was investigated in this paper.The results show that the shape of ingot segregation of rod steel depends on the shape of continuous casting (CC)...The influence of ingot segregation on quenching distortion of gear steel was investigated in this paper.The results show that the shape of ingot segregation of rod steel depends on the shape of continuous casting (CC) molds,and that the distortion of gear steel with square ingot segregation is uniform,while that of gear steel with rectangular ingot segregation is anisotropic.After quenching,the outer circle of the ring sample with a large rectangular segregation area is distorted into an oval shape.No obvious element segregation has been found in the rod steel produced through the rectangular CC mold.Obvious difference in density has been detected at the cross section of rod steel.It suggests that center porosity may be the main reason for the strong impact of segregation on heat treatment distortion of gear steel.展开更多
A 3D/2D hybrid multi-physical-field mathematical model,which takes into consideration the thermosolutal buoyance,was developed to predict the macrosegregation of gear steel 20CrMnTi continuously cast by a curved bille...A 3D/2D hybrid multi-physical-field mathematical model,which takes into consideration the thermosolutal buoyance,was developed to predict the macrosegregation of gear steel 20CrMnTi continuously cast by a curved billet caster with size of 160 mm×160 mm,and investigated the effect of final electromagnetic stirring(F-EMS)on the fluid flow,heat transfer and solute distribution in the liquid core of continuously cast steel.The results show that the application of F-EMS eliminates the effect of thermosolutal buoyancy on the asymmetric distribution of carbon concentration in the cross section of billet and accelerates the final solidification of resident molten steel in the liquid core of strand,but promotes the negative carbon segregation near the billet center.When the gear steel 20CrMnTi is cast at the temperature of 1803 K and speed of 1.7 m/min,the solidification end advances forward from 9.84 to 9.72 m,and center carbon segregation ratio of billet decreases from 1.24 to 1.17 with the increase in current density of F-EMS from 0 to 350 A.展开更多
Shot-peened,case-hardened gears can fail in the tooth root due to crack initiation below the surface of the steel matrix.Here,the crack is initiated at a non-metallic inclusion in the center of a so-called fisheye.Thi...Shot-peened,case-hardened gears can fail in the tooth root due to crack initiation below the surface of the steel matrix.Here,the crack is initiated at a non-metallic inclusion in the center of a so-called fisheye.This failure type can lead to a reduced endurance fatigue limit of the gears.It is for this reason that,over the last decade,much effort has been invested by steel manufacturers to reduce the non-metallic inclusion content of gear steels so as to mitigate or even completely prevent such crack initiation.These ultra-clean gear steels were achieved by various measures in the steel production process.However,as a result,the remaining non-metallic inclusions are inhomogeneously distributed in the steel volume in terms of both size and location.However,due to the inhomogeneity of ultra-clean steels,the question arose if the values derived according to the standards are still representative of ultra-clean steel batches.The results show that the standards can still be applied,but more effort must be applied.To determine the degree of cleanliness,six microsections are currently evaluated according to steel test specification(SEP)1571,method K.It is shown that an examination of 24 microsections starting from size class 0 seems beneficial to get more reliable and comparable results of the degree of cleanliness of these ultra-clean gear steels.In addition,it is shown that a high degree of cleanliness has been achieved for all steel batches investigated with the measures taken in the steel production process.展开更多
High temperature carburization is becoming more and more attractive because it can remarkably reduce processing time and increase productivity.However,the commonly used gear steels which are microalloyed by Al are not...High temperature carburization is becoming more and more attractive because it can remarkably reduce processing time and increase productivity.However,the commonly used gear steels which are microalloyed by Al are not suitable for high temperature carburization due to abnormal grain coarsening.The gear steel 20CrMnTiNb,which is microalloyed with 0.048%Nb and 0.038%Ti,has been compared with the gear steel 20CrMn in terms of microstructure in the case of hardened layer and in the core after carburizing at 1000℃for 4hand mechanical properties after carburizing and pseudo-carburizing.The results indicate that the fine austenite grains exist in the carburized case of 20CrMnTiNb steel,while there is abnormal coarsening and duplex grain structure in the case and core of steel 20CrMn.The average prior austenite grain sizes are 19.5and 34.2μm for the steels 20CrMnTiNb and20CrMn,respectively.In addition,the mechanical properties of 20CrMnTiNb steel are superior to those of 20CrMn steel.In particular,the HV hardness of the former is higher than that of the latter by about 40-70in the range of less than 0.7mm in depth.Therefore,the steel 20CrMnTiNb is suitable for high temperature carburization.展开更多
The considerable heat treatment induced runout value in the end face of the automobile main reducer gear is always dimensionally out of tolerance.It directly affects the dimensional accuracy,the grade of carburized an...The considerable heat treatment induced runout value in the end face of the automobile main reducer gear is always dimensionally out of tolerance.It directly affects the dimensional accuracy,the grade of carburized and hardened gears,and the post-quenching manufacturing costs.In this study,three dimensional numerical models were developed to simulate the carburizing-quenching process of gear based on the multi-field coupling theory using DEFORM software.The results indicated that the ununiform cooling rate of the gear caused by the asymmetry of the web structure would result in the ununiform distribution of martensite,leading to the large runout value at the end face of the gear.Therefore,a novel method was proposed to minimize the heat treatment induced runout value.It was found that the heat treatment induced runout value could be effectively controlled by the addition of a compensation ring and the support of a rod structure.Further experiments showed that the average runout value of the gear end face before and after the proposed heat treatment method were about 0.023 mm and 0.059 mm respectively,which was in good agreement with the simulated results.The novel approach proposed in this study led to a reduction of the gear runout value by 70.0%‒76.9%compared to that of the original heat treatment process,which may serve as a practical and economical way to predict and minimize the heat treatment induced distortion in drive gear.展开更多
In consideration of the composition characteristics and quality requirements of sulphurous free-cutting gear steel, the rational measures of sulfur control, calcium treatment and key technologies of continuous casting...In consideration of the composition characteristics and quality requirements of sulphurous free-cutting gear steel, the rational measures of sulfur control, calcium treatment and key technologies of continuous casting process are applied in the development of a full-line operation of LD-Billet continuous casting on steelmaking with semi-steel, which suggests an economic production of the steel has been realized. Test results show that the average retrieval rate of sulphurous alloy in the process of RH treatment is 95.3% and sulfur content of products is stability. Otherwise, content of T[O] in casting billet is in the range of 11×10-6 ~ 18×10-6 with average value is 14.7×10-6.Based on this, the billets have good surface quality and internal quality.展开更多
In view of process conditions of Vanadium Recovery and Steelmaking Plant, PanGang Group Panzhihua steel and Vanadium Co.,Ltd., and on the basis of making choice of a reasonable deoxidization process, some measures hav...In view of process conditions of Vanadium Recovery and Steelmaking Plant, PanGang Group Panzhihua steel and Vanadium Co.,Ltd., and on the basis of making choice of a reasonable deoxidization process, some measures have been taken to the development of automobile gear steel (20CrMoH) such as the pre-refining technology during converter tapping, "white slag" refining in LF, RH Vacuum treatment, and even protective casting technology. Also different and suitable models of argon blowing from bottom of ladle were adopted in the platform after converter, LF refining and calcium treatment. Test results show that the high cleanness 20CrMoH gear steel slab with T[O] ≤15×10-6(The average T[O] is 11.8×10-6) could be obtained through all these measures.展开更多
文摘Data-driven algorithms for predicting mechanical properties with small datasets are evaluated in a case study on gear steel hardenability.The limitations of current data-driven algorithms and empirical models are identified.Challenges in analysing small datasets are discussed,and solution is proposed to handle small datasets with multiple variables.Gaussian methods in combination with novel predictive algorithms are utilized to overcome the challenges in analysing gear steel hardenability data and to gain insight into alloying elements interaction and structure homogeneity.The gained fundamental knowledge integrated with machine learning is shown to be superior to the empirical equations in predicting hardenability.Metallurgical-property relationships between chemistry,sample size,and hardness are predicted via two optimized machine learning algorithms:neural networks(NNs)and extreme gradient boosting(XGboost).A comparison is drawn between all algorithms,evaluating their performance based on small data sets.The results reveal that XGboost has the highest potential for predicting hardenability using small datasets with class imbalance and large inhomogeneity issues.
基金supported by the National Natural Science Foundation of China (No. 51274029)
文摘In the 20CrMnTi steel production process, the nitrogen content increased by 19 × 10-6 and 29 × 10-6, respectively, during ladle furnace(LF) refining and during the casting process from ladle to tundish. The protective casting is the key to decrease the N content. The results of thermodynamic calculations and a growth kinetics investigation show that TiN formation occurs only when the solidification fraction is greater than 0.533 under the controlled conditions used in this study for the manufacture of 20CrMnTi steel; the radius of TiN particles decreases as the Ti and N contents decrease and as the cooling rate increases. Furthermore, the theory of austenite grains controlled by second-phase particles was analyzed. The elemental analysis results showed that the Ti content was controlled at 0.04wt%–0.06wt% and the N content decreased to 0.005wt%, which satisfy the requirements for grain refinement but can also effectively prevent the precipitation of TiN inclusions in 20CrMnTi steel.
基金Item Sponsored by National Basic Research Programof China (G2000067208-4)
文摘The effect of compressive deformation of austenite on continuous cooling transformation microstructures for 22CrSH gear steel has been investigated using a Gleeble 1500 thermal simulator. The experimental results show that the deformation of austenite promotes the formation of proeutectoid ferrite and pearlite, and leads to the increase of critical cooling rate of proeutectoid ferrite plus pearlite microstructure. The grain boundary allotriomorphic ferrite occupies the austenite grain surfaces when the prior deformation takes place or the cooling rate is decreased, which causes a transition from bainite to acicular ferrite. The deformation enhances the stability of transformation from austenite to acicular ferrite, which results in an increase of M/A constituent.
文摘Using a Gleeble 1500 hot simulator, the dynamic recrystallization (DRX) behavior of Mn-Cr type gear steel was investigated. The experimental results show that the Mn-Cr gear steel exhibits a typical DRX behavior at higher deformation temperature, lower strain rate and smaller initial austenite grain size. The DRX takes place under the conditions that Zener-Hollomon parameter (Z) is less than a critical value Z_c. The DXR grains are formed by the bulging mechanism. Activation energy and stress exponent were calculated to be 378.6 kJ·mol -1 and 5.8 respectively by regression analysis.
基金financially supported by the Program for New Century Excellent Talents in Universities of China(No.NCET-07-0650)
文摘The equilibrium reaction between CaO -Al_2O_3-SiO _2-MgO slag and 28 MnC r5 molten steel was calculated to obtain the suitable slag composition which is effective for decreasing the oxygen content in molten steel. The dissolved oxygen content [O] in molten steel under different top slag conditions was calculated using a thermodynamic model and was measured using an electromotive force method in slag–steel equilibrium experiments at 1873 K. The relations among [O], the total oxygen content(T.O), and the composition of the slag were investigated. The experimental results show that both [O] and T.O decrease with decreasing SiO_2 content of the slag and exhibit different trends with the changes in the CaO /Al_2O_3 mass ratio of the slag. Increasing the CaO /Al_2O_3 mass ratio results in a decrease in [O] and an increase in T.O. To ensure that T.O ≤ 20 ppm and [O] ≤ 10 ppm, the SiO _2 content should be controlled to <5wt%, and the CaO /Al_2O_3 mass ratio should be in the range from 1.2 to 1.6.
文摘The prediction of the hardenability and chemical composition of gear steel was studied using artificial neural networks. A software was used to quantitatively forecast the hardenability by its chemical composition or the chemical composition by its hardenability. The prediction result is more precise than that obtained from the traditional method based on the simple mathematical regression model.
文摘The influence of ingot segregation on quenching distortion of gear steel was investigated in this paper.The results show that the shape of ingot segregation of rod steel depends on the shape of continuous casting (CC) molds,and that the distortion of gear steel with square ingot segregation is uniform,while that of gear steel with rectangular ingot segregation is anisotropic.After quenching,the outer circle of the ring sample with a large rectangular segregation area is distorted into an oval shape.No obvious element segregation has been found in the rod steel produced through the rectangular CC mold.Obvious difference in density has been detected at the cross section of rod steel.It suggests that center porosity may be the main reason for the strong impact of segregation on heat treatment distortion of gear steel.
基金The authors gratefully acknowledge the financial support of the National Key Research and Development Plan(Nos.2017YFB0304100 and 2016YFB0300105)National Natural Science Foundation of China(Nos.51674072,51704151,and 51804067)Fundamental Research Funds for the Central Universities(Nos.N182504014,N170708020,and N172503013).
文摘A 3D/2D hybrid multi-physical-field mathematical model,which takes into consideration the thermosolutal buoyance,was developed to predict the macrosegregation of gear steel 20CrMnTi continuously cast by a curved billet caster with size of 160 mm×160 mm,and investigated the effect of final electromagnetic stirring(F-EMS)on the fluid flow,heat transfer and solute distribution in the liquid core of continuously cast steel.The results show that the application of F-EMS eliminates the effect of thermosolutal buoyancy on the asymmetric distribution of carbon concentration in the cross section of billet and accelerates the final solidification of resident molten steel in the liquid core of strand,but promotes the negative carbon segregation near the billet center.When the gear steel 20CrMnTi is cast at the temperature of 1803 K and speed of 1.7 m/min,the solidification end advances forward from 9.84 to 9.72 m,and center carbon segregation ratio of billet decreases from 1.24 to 1.17 with the increase in current density of F-EMS from 0 to 350 A.
基金The underlying research work was funded in equal proportions by the“Arbeitsgemeinschaft industrieller Forschungsvereinigungen e.V.(AiF)”,the German Federal Ministry of Economics and Technology(BMWi,IGF no.16662 N)and the FVA.The results presented in this paper were taken from the FVA research project 293 III“Späte Zahnfußbrüche/Reinheitsgrad”.More detailed information on the influence of non-metallic inclusions is given in the final report.
文摘Shot-peened,case-hardened gears can fail in the tooth root due to crack initiation below the surface of the steel matrix.Here,the crack is initiated at a non-metallic inclusion in the center of a so-called fisheye.This failure type can lead to a reduced endurance fatigue limit of the gears.It is for this reason that,over the last decade,much effort has been invested by steel manufacturers to reduce the non-metallic inclusion content of gear steels so as to mitigate or even completely prevent such crack initiation.These ultra-clean gear steels were achieved by various measures in the steel production process.However,as a result,the remaining non-metallic inclusions are inhomogeneously distributed in the steel volume in terms of both size and location.However,due to the inhomogeneity of ultra-clean steels,the question arose if the values derived according to the standards are still representative of ultra-clean steel batches.The results show that the standards can still be applied,but more effort must be applied.To determine the degree of cleanliness,six microsections are currently evaluated according to steel test specification(SEP)1571,method K.It is shown that an examination of 24 microsections starting from size class 0 seems beneficial to get more reliable and comparable results of the degree of cleanliness of these ultra-clean gear steels.In addition,it is shown that a high degree of cleanliness has been achieved for all steel batches investigated with the measures taken in the steel production process.
基金Item Sponsored by National High Technology Research and Development Program(863)of China(2006AA03Z526)
文摘High temperature carburization is becoming more and more attractive because it can remarkably reduce processing time and increase productivity.However,the commonly used gear steels which are microalloyed by Al are not suitable for high temperature carburization due to abnormal grain coarsening.The gear steel 20CrMnTiNb,which is microalloyed with 0.048%Nb and 0.038%Ti,has been compared with the gear steel 20CrMn in terms of microstructure in the case of hardened layer and in the core after carburizing at 1000℃for 4hand mechanical properties after carburizing and pseudo-carburizing.The results indicate that the fine austenite grains exist in the carburized case of 20CrMnTiNb steel,while there is abnormal coarsening and duplex grain structure in the case and core of steel 20CrMn.The average prior austenite grain sizes are 19.5and 34.2μm for the steels 20CrMnTiNb and20CrMn,respectively.In addition,the mechanical properties of 20CrMnTiNb steel are superior to those of 20CrMn steel.In particular,the HV hardness of the former is higher than that of the latter by about 40-70in the range of less than 0.7mm in depth.Therefore,the steel 20CrMnTiNb is suitable for high temperature carburization.
基金National Key R&D Program of China(Grant No.2019YFB2004700)State Key Laboratory of High Performance Complex Manufacturing of China(Grant No.ZZYJKT2019-08)China Postdoctoral International Exchange Program(Grant No.140050004).
文摘The considerable heat treatment induced runout value in the end face of the automobile main reducer gear is always dimensionally out of tolerance.It directly affects the dimensional accuracy,the grade of carburized and hardened gears,and the post-quenching manufacturing costs.In this study,three dimensional numerical models were developed to simulate the carburizing-quenching process of gear based on the multi-field coupling theory using DEFORM software.The results indicated that the ununiform cooling rate of the gear caused by the asymmetry of the web structure would result in the ununiform distribution of martensite,leading to the large runout value at the end face of the gear.Therefore,a novel method was proposed to minimize the heat treatment induced runout value.It was found that the heat treatment induced runout value could be effectively controlled by the addition of a compensation ring and the support of a rod structure.Further experiments showed that the average runout value of the gear end face before and after the proposed heat treatment method were about 0.023 mm and 0.059 mm respectively,which was in good agreement with the simulated results.The novel approach proposed in this study led to a reduction of the gear runout value by 70.0%‒76.9%compared to that of the original heat treatment process,which may serve as a practical and economical way to predict and minimize the heat treatment induced distortion in drive gear.
文摘In consideration of the composition characteristics and quality requirements of sulphurous free-cutting gear steel, the rational measures of sulfur control, calcium treatment and key technologies of continuous casting process are applied in the development of a full-line operation of LD-Billet continuous casting on steelmaking with semi-steel, which suggests an economic production of the steel has been realized. Test results show that the average retrieval rate of sulphurous alloy in the process of RH treatment is 95.3% and sulfur content of products is stability. Otherwise, content of T[O] in casting billet is in the range of 11×10-6 ~ 18×10-6 with average value is 14.7×10-6.Based on this, the billets have good surface quality and internal quality.
文摘In view of process conditions of Vanadium Recovery and Steelmaking Plant, PanGang Group Panzhihua steel and Vanadium Co.,Ltd., and on the basis of making choice of a reasonable deoxidization process, some measures have been taken to the development of automobile gear steel (20CrMoH) such as the pre-refining technology during converter tapping, "white slag" refining in LF, RH Vacuum treatment, and even protective casting technology. Also different and suitable models of argon blowing from bottom of ladle were adopted in the platform after converter, LF refining and calcium treatment. Test results show that the high cleanness 20CrMoH gear steel slab with T[O] ≤15×10-6(The average T[O] is 11.8×10-6) could be obtained through all these measures.
