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Microstructure of 11%Cr ferritic/martensitic steel in normally heat-treated state before and after irradiation

Wo Jianxing, Shen Yinzhong

Heat Treatment of Metals 2025, 50 (1): 6-11. doi:10.13251/j.issn.0254-6051.2025.01.001

Abstract （109）

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The microstructure of 11%Cr ferritic/martensitic steel in the normally heat-treated state before and after irradiation was experimentally studied by using transmission electron microscopy and energy dispersive spectroscopy. The results show that the primary microstructure of the 11%Cr ferritic/martensitic steel before and after irradiation consists of tempered martensitic along with a small amount of δ-ferrite. Before irradiation, a small amount of precipitates with a relatively small size are present at martensite boundaries and within martensite laths. Some irregular, blocky, large black particles are present at the interface of δ-ferrite and matrix. There are no precipitates within δ-ferrite grains. After irradiation, a large number of rod-like and blocky precipitates appear at the boundaries and interior of the martensitic lath, while the number and size of precipitates significantly increase compared to that before irradiation. The number of irregular blocky black particles at the interface of δ-ferrite and matrix increase compared to that before irradiation. Inside the δ-ferrite, a large number of blocky and needle-like precipitates are formed which may be Cr-rich nitrides, Cr-rich carbonitrides and Fe-W type precipitates. After irradiation, the precipitates inside the martensitic laths are Cr-rich M₂₃C₆ phase. Compared with the Cr-rich M₂₃C₆ phase before irradiation, the Cr and Ta contents in the M₂₃C₆ phase slightly decrease, while the Fe and Nd contents slightly increase after irradiation. However, overall, the changes in the average metal element composition of the Cr-rich M₂₃C₆ phase are relatively small.

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Microstructure and properties of high-strength corrosion-resistant Fe-based medium entropy alloys

Dai Chunduo, Li Jiangwen, Guo Chengyu, Zhang Yong, Sun Meihui, Li Tianyi, Gong Li, Pan Yue

Heat Treatment of Metals 2025, 50 (1): 12-21. doi:10.13251/j.issn.0254-6051.2025.01.002

Abstract （68）

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Using Python language to edit Thermal-Calc instructions for efficient calculation of alloy phase composition, two iron-based medium entropy alloys with L2₁ precipitation ratio greater than 15% were obtained according to design principles. Adopting large deformation cold rolling combined with medium temperature aging process for microstructure control to achieve excellent strength plasticity matching. The results show that the tensile strength and elongation of No.1 alloy are 1592 MPa and 17.50%, respectively, while that of No.2 alloy are 1682 MPa and 13.50%, respectively. At the same time, both the alloys form stable passivation films in a 3.5wt% NaCl solution, with a pitting potential close to 0 V(vs SCE) and good corrosion resistance. The main matrix phase of the two alloys is FCC solid solution, with a small amount of BCC phase. The combination of large deformation cold rolling and medium temperature aging results in the alloy having an incomplete recovery of fine grain structure, accompanied by the formation of multiphase and multi-scale precipitation phases, which form a soft and hard coordination with the FCC matrix to improve the strength and plasticity of the alloy. The combined effect of precipitation strengthening, dislocation strengthening and grain refinement strengthening enhances the strength of alloys. The high plasticity of the alloy is due to the relief of stress concentration during medium temperature aging. The good plasticity of the FCC matrix can effectively slow down the formation and propagation of cracks. In addition, the low mismatch between Heusler_L2₁ phase and the matrix can also slow down the formation of microcracks at the phase boundary, allowing the two medium entropy alloys to maintain high plasticity.

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Research progress of κ-carbide in Fe-Mn-Al-C low density steels

Li Changhao, Liu Zhi, Zhang Xiaofeng, Yang Yong, Zhou Huasheng, Zhao Xinlei

Heat Treatment of Metals 2025, 50 (1): 22-30. doi:10.13251/j.issn.0254-6051.2025.01.003

Abstract （69）

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As a new generation of automotive steel, the Fe-Mn-Al-C system low-density steel is a potential material for future automotive light-weighting research due to its advantages of high strength, low density, and good plasticity and toughness. As a result of κ-carbide affect the comprehensive mechanical properties of the steel, the characteristics and formation mechanism of κ-carbides in Fe-Mn-Al-C low-density steels and the effect of differences in the content of alloying elements on κ-carbides were expounded, and the effect of solution and aging treatments on κ-carbides and the effect of κ-carbides on the toughening mechanism were described in detail. It is concluded that the mass fraction of Al and Mn in Fe-Mn-Al-C steel should be reasonably controlled to provide driving force for κ-carbide precipitation, and the solution treatment temperature should be 900-1100 ℃, after which the aging should be carried out in the range of 450-600 ℃, and the aging time should be 1-2 h, to avoid the precipitation of coarse κ-carbides at the grain boundaries to deteriorate the material properties.

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Effect of heating time on surface oxidation and decarburization of 60Cr13 stainless steel cutting tools

Ji Xianbin, Pan Jixiang, Li Zhaoguo, Wei Haixia, Qian Zhangxin

Heat Treatment of Metals 2025, 50 (1): 31-35. doi:10.13251/j.issn.0254-6051.2025.01.004

Abstract （57）

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Effect of different heating time (20, 40 min) on surface oxidation and decarburization of 60Cr13 stainless steel cutting tools at 1050 ℃ was studied. The results show that at heating temperature of 1050 ℃, a longer holding time results in severe internal oxidation and grain boundary oxidation on the surface of the 60Cr13 stainless steel cutting tools, with an oxide layer thickness of 15-17 μm. In addition, extending the heating time intensifies the oxidation reaction in high-temperature environments, the oxygen continuously diffuses into the interior of the steel, while the carbon atoms in steel migrate outward. Due to the diffusion rate of carbon atoms exceeding the oxidation rate, the surface decarburization process is intensified, reducing the carbon content in the surface layer, resulting in a decrease in the surface hardness of the 60Cr13 stainless steel cutting tools.

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Effect of vanadium on microstructure and properties of hypereutectoid tool steel

Yang Yu, Wang Tianxiao, Ai Chengshen, Xu Cheng

Heat Treatment of Metals 2025, 50 (1): 36-41. doi:10.13251/j.issn.0254-6051.2025.01.005

Abstract （44）

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In order to study the role of vanadium in hypereutectoid tool steels, microstructure observation, mechanical property test, heat treatment test and abrasive wear test were used to compare and analyze the microstructure and properties of the two hypereutectoid tool steels with and without vanadium after hot rolling and heat treatment. The results show that under the same hot rolling process condition, fine VC particles with a diameter of not more than 10 nm are precipitated in the V-containing steel, the colony size of the pearlite are smaller and with finer lamellar spacing, the yield strength, tensile strength and hardness are 116 MPa, 179 MPa and 3.2 HRC higher than those of the V-free steel, respectively. When tempered at temperatures below 550 ℃, with the increase of tempering temperature, the hardness of the two tested steels gradually decreases and the wear rate gradually increases. Under the same heat treatment process conditions, the hardness of V-containing steel is higher, the wear rate is smaller, and the tempering resistance is better. The tempered hardness at 450 ℃ still reaches more than 53 HRC, and the wear rate is less than 23 mg·km^-1. Tempering at 500 ℃ is a turning point in the deterioration of wear resistance of the V-containing steel. When tempered at 500 ℃ and above, VC particles with a size of above 100 nm precipitate in the V-containing steel, resulting in a significant increase in wear rate and deterioration of wear resistance.

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Magnetic properties and interaction of nanocomposite Nd₂Fe₁₄B/PrCo₅ melt-spun ribbons

Bo Yu, Zuo Jianhua, Wang Hao, Lu Wei

Heat Treatment of Metals 2025, 50 (1): 42-46. doi:10.13251/j.issn.0254-6051.2025.01.006

Abstract （30）

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The nanocomposite Nd₂Fe₁₄B/PrCo₅ melt-spun ribbons were prepared by induction melting and melt-spinning technique, and the effect of PrCo₅ addition on the phase structure, magnetic properties and exchange coupling was investigated. The XRD test results indicate that the ribbons has dual hard magnetic phases of Nd₂Fe₁₄B and PrCo₅, and no oxidation or formation of new phases occur during the preparation process. The content of PrCo₅ has an obvious effect on magnetic properties, and the appropriate addition of PrCo₅ can help improve coercivity. However, the remanent and maximum magnetic energy product decrease with the increase of PrCo₅ content. Research on the recoil loops shows that the "opening" phenomenon of the recoil loops is related to the content of PrCo₅, and the δ_M curve test shows that there is a strong exchange coupling effect in the Nd₂Fe₁₄B/PrCo₅ ribbons. Comprehensive analysis shows that optimal magnetic properties of the nanocomposite Nd₂Fe₁₄B/PrCo₅ ribbons can be obtained at 12%PrCo₅ content, with remanent M_r of 8.73 kGs, coercive H_cj of 11.03 kOe, and the maximum magnetic energy product (BH)_Max of 15.83 MGOe.

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Effect of rare element Ce on microstructure and mechanical properties of 32MnMoNiCu cast steel

Li Jianguo, Jia Dongsheng, Zhao Yinhu, Liu Yubao, Wang Xu, Zhao Leicheng, Lan Yueguang

Heat Treatment of Metals 2025, 50 (1): 47-52. doi:10.13251/j.issn.0254-6051.2025.01.007

Abstract （32）

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By adding rare earth cerium iron alloy in the 32MnMoNiCu cast steel, the effect of rare earth Ce on microstructure and mechanical properties of the cast steel was investigated by using scanning electron microscopy observation, tensile and impact testing methods. The results show that rare earth Ce can refine the ferrite phase, transform inclusions shape from long strip into nodular, and decrease the size of inclusions. Rare earth Ce mainly exists in the form of CeAlO₃, and does not react with MnS inclusions. Precipitation strengthening and fine-grained strengthening which are caused by rare earth Ce in the cast steel result in 12.3% and 23.4% increase in tensile strength and yield strength, respectively. However, the increase fraction of lath ferrite by adding rare earth Ce result in 11.1% and 7.4% decrease in elongation and impact absorbed energy, respectively.

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Hot deformation behavior of TiAl-V-Cr alloy near-α phase region

Liu Hongwu, Gao Fan, Feng Xiangzheng, Li Zhenxi, Dai Songyan, Wang Qingfeng

Heat Treatment of Metals 2025, 50 (1): 53-57. doi:10.13251/j.issn.0254-6051.2025.01.008

Abstract （36）

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Hot deformation behavior and microstructure evolution of Ti-44Al-5V-1Cr alloy deformed near the α-phase region (at 1250 ℃) under different conditions as various initial microstructure, strain rates and deformation were investigated by means of thermophysical simulation, SEM, EBSD and OM characterization. The results show that when the deformation temperature is 1250 ℃, the difference of flow stress variations in initial microstructure of the alloy under identical deformation rate are smaller. However, under the same microstructural condition, the strain rate has a relatively significant effect on the flow stress. As the strain rate decreases, the flow stress decreases noticeably. When the alloy is deformed near the α-phase region, the dynamic recrystallization of α phase is dominant, and the dynamic recovery is supplemented, while the β phase effectively suppresses the growth of α grains. In addition, increasing the deformation can facilitate the refinement of α grain size. After extrusion at 1250 ℃ with a high extrusion ratio, the alloy achieves a fine and uniform fully lamellar structure with average lamellar colony sizes of 12-23 μm.

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Determination and analysis of SHCCT curve of EH36 steel for offshore platform

Wang Chengming, Bai Lijuan, Song Yue, Liu Lijun, Gu Xiurui, Li Huimin

Heat Treatment of Metals 2025, 50 (1): 58-62. doi:10.13251/j.issn.0254-6051.2025.01.009

Abstract （35）

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Offshore platform steel EH36 was taken as the research object, and the welding process of the tested steel was simulated by DIL805L quenching dilatometer. The SHCCT curve of the tested steel was established by means of thermal expansion method combined with metallography method and Vickers hardness test, and the influence of different cooling rates on the microstructure transformation law of the welding heat affected zone was studied. The results show that in the whole cooling rate range, there are four types of microstructure transformation in the HAZ of the tested steel: ferrite+pearlite, ferrite+pearlite+bainite, bainite and martensite+bainite, and the hardness value increases from 164 HV10 to 277 HV10 with the increase of cooling rate. When the cooling rate is lower than 5 ℃/s, the hardness of the HAZ of the tested steel is lower than that of the base metal. In order to ensure that the tested steel obtains good welding joint properties, the cooling rate should be controlled in the range of 10-20 ℃/s (that is, the t_8/5 time is controlled in the range of 15-30 s).

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Microstructure transformation of SCM415H steel for high strength automotive fasteners

Chu Feng, Li Zhanwei, Yu Xuesen, Zhang Jiming

Heat Treatment of Metals 2025, 50 (1): 63-67. doi:10.13251/j.issn.0254-6051.2025.01.010

Abstract （31）

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The phase transformation characteristics of the SCM415H steel for automotive fasteners were studied by thermal simulation. The cooling rate of 0.25 ℃/s produces a microstructure of ferrite and pearlite, while the bainite and martensite occurs with the cooling rate reaches 0.5 ℃/s. The cooling rate of 5 ℃/s results in a microstructure of mainly martensite and bainite, and that of 15 ℃/s or above results in a microstructure of mainly martensite. The pearlitic transformation temperature is 700-575 ℃ during isothermal conditions. The nose tip temperature is about 660 ℃, and completion time of the phase transformation is about 428 s. Based on the tested results, the steel wires with a diameter of 24 mm were successfully produced, and then grade 10.9 automobile fasteners were successfully produced after one spheroidizing annealing and two drawing processes.

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Effect of Ce content on inclusions and as-cast microstructure and hardness of S355NL low alloy steel

Yang Jiandong, Xie Bijun, Xu Bin, Sun Mingyue, Li Dianzhong

Heat Treatment of Metals 2024, 49 (12): 122-127. doi:10.13251/j.issn.0254-6051.2024.12.021

Abstract （40）

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Effects of adding different contents high-purity rare earth Ce element on the inclusions, as-cast microstructure and hardness of high-purity S355NL low alloy steel were investigated. The types, sizes and shapes of inclusions, as well as the as-cast microstructure and hardness were analyzed and evaluated by using scanning electron microscopy, optical microscopy, and Vickers hardness testing. The results indicate that with the Ce addition ranging from 0.0011% to 0.0049%, the irregularly shaped large Al₂O₃ and MnS inclusions in the S355NL low alloy steel are modified into fine spherical rare earth inclusions. When Ce is added at levels between 0.0011% and 0.0049%, it initially reacts with O and S to form small spherical rare earth oxysulfides. However, with the increase of Ce content, excess Ce can react with As and P, leading to larger irregular rare earth inclusions. Additionally, the incorporation of Ce refines the dendritic structure of the S355NL low alloy steel and enhances its hardness. Considering both the inclusion modification and hardness optimization, the optimal range for Ce addition in the S355NL low alloy steel is determined to be 0.0011% to 0.0049%.

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Hot deformation behavior of Fe-13Mn-4.4Al-0.64C-0.1Ti low density steel

Gan Wenxuan, Wu Wenping, Chen Gang, Yang Yong, Li Tianrui, Zhang Xiaofeng, Huang Zhenyi

Heat Treatment of Metals 2024, 49 (12): 128-136. doi:10.13251/j.issn.0254-6051.2024.12.022

Abstract （36）

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Hot compression experiments were carried out on Fe-13Mn-4.4Al-0.64C-0.1Ti low density steel at deformation temperature of 900-1100 ℃ and strain rate of 0.01-0.1 s^-1 by Gleeble-3500 thermal simulation testing machine. The strain-compensated constitutive equation was established on the basis of the traditional constitutive model. The hot deformation behavior of the experimental steel was studied by verification and analysis. The influence of deformation conditions on hot deformation behavior and microstructure evolution was studied by electron backscattering diffraction. The results show that the deformation behavior of the Fe-13Mn-4.4Al-0.64C-0.1Ti low density steel is dynamic recrystallization type at the temperature of 900-1100 ℃ and strain rate of 0.01-0.1 s^-1. The flow stress decreases with the increase of deformation temperature or the decrease of strain rate. The migration of small angle boundary to large angle boundary promotes dynamic recrystallization. The hot deformation activation energy of the material is 396.44 kJ/mol. The relative absolute error of the strain-compensated constitutive equation is 5.4%, and the linear fitting correlation coefficient is 0.987, which indicates that the constructed strain-compensated constitutive equation can accurately predict the flow stress behavior of the low density steel under different deformation conditions.

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Determination and analysis of CCT curve of LC3 cryogenic cast steel

Chen Kun, Gong Wenguo, Chang Xueting, Yin Yansheng

Heat Treatment of Metals 2024, 49 (12): 137-141. doi:10.13251/j.issn.0254-6051.2024.12.023

Abstract （28）

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DIL 805A type fully automatic phase transformer was used to determine the expansion curve of LC3 cryogenic cast steel under different cooling rates between 0.05-150 ℃/s, and the tangent method was used to determine the phase transformation point Ac₁ of 700 ℃ and Ac₃ of 849 ℃. Combined with microstructure analysis and microhardness to determine the actual transformation products, and the CCT curve was plotted using Origin software. The results show that the microstructure is ferrite + pearlite when the cooling rate is 0.05-2 ℃/s, ferrite + pearlite +bainite when it is 5-20 ℃/s, bainite + martensite when it is 30-50 ℃/s, martensite + retained austenite when it is 80 ℃/s, and martensite when it is 100-150 ℃/s. Hardness of the LC3 cryogenic cast steel gradually increases from 168 HV10 to 453 HV10 with the increasing of cooling rate. Martensite critical cooling rate is about 80 ℃/s.

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Continuous cooling transformation curves of undercooled austenite of medium carbon Cr-Mn-Si low alloy steel

Gao Xin, Ning Jing, Su Jie, Gao Qi, Jiang Qingwei

Heat Treatment of Metals 2024, 49 (12): 142-147. doi:10.13251/j.issn.0254-6051.2024.12.024

Abstract （36）

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Thermal expansion curves of a medium carbon Cr-Mn-Si low alloy steel under different cooling rates were determined by using Formast-FⅡ dilatometer, and the continuous cooling transformation (CCT) curve of the undercooled austenite of the tested steel was plotted in combination with the observation of the metallographic microstructure. The effect of cooling rate on the microhardness and the onset temperature of the undercooled austenite phase transformation of the tested steel was investigated, and the microstructure and properties of the medium carbon Cr-Mn-Si low alloy steel large forgings at different positions after heat treatment were analyzed. The results show that Ac₃=855 ℃, Ac₁=770 ℃, Ms=375 ℃ and Mf=200 ℃ for the medium carbon Cr-Mn-Si low alloy steel. When the cooling rate is less than or equal to 0.28 ℃/s, the ferrite and pearlite transformation mainly occurs in the high temperature zone, and the bainite transformation occurs in the middle temperature zone. When the cooling rate is 0.28-0.83 ℃/s, the bainite transformation mainly occurs in the middle temperature zone, and the martensite transformation occurs in the low temperature zone. When the cooling rate is greater than or equal to 1.66 ℃/s, only the martensite transformation occurs. With the increase of cooling rate, the microhardness of the tested steel firstly rises linearly and then increases slowly, and the phase transformation start temperature firstly decreases sharply and then basically remains stable. The edge of heat-treated medium carbon Cr-Mb-Si low alloy steel large forgings microstracture is martensite and bainite complex, the positions at R/2 and the core microstracture are bainite, the tensile strength (1467.0 MPa) and hardness (475 HV5) values at the edge position are the highest, indicating that appropriate amount of martensite can significantly improve the strength of bainite structure while maintaining good plasticity.

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Thermodynamic calculation and experimental analysis of precipitated phase of Nimonic 80A alloy

Wang Yunhai, Xin Ruishan, Gong Zhihua, Zhao Jiqing, Yang Gang, Bao Hansheng

Heat Treatment of Metals 2024, 49 (12): 148-156. doi:10.13251/j.issn.0254-6051.2024.12.025

Abstract （34）

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Variation of equilibrium phases with temperature of Nimonic 80A alloy with different element contents was calculated by Thermo-Calc thermodynamic simulation software, and the effects of main elements on the types of precipitates, precipitation temperature and precipitation content were analyzed. In order to verify the reliability of thermodynamic calculation, the microstructure characteristics, qualitative and quantitative analysis of aged alloy samples were carried out by means of SEM, TEM, XRD and so on. The results show that the equilibrium precipitates of Nimonic 80A alloy are γ, γ', M₂₃C₆, MX and M₇C₃ phases. Decreasing C content cannot only increase the precipitation temperature of M₇C₃ phase, but also promote the precipitation amount of γ'phase; increasing the content of Al and Ti increases the precipitation temperature of M₇C₃, γ' and M₂₃C₆ phases, and promotes the precipitation of γ'and M₂₃C₆ phase, in which the effect of single Al element is higher than that of Ti element; increasing the total content of Ti+Al increases the precipitation temperatures of M₂₃C₆ and γ' phases, and the precipitation content of γ' phase increases significantly. With the increase of Ti/Al ratio, the precipitation content of γ' phase decreases gradually. Under 1060 ℃×8 h air cooling, 845 ℃×24 h air cooling and 700 ℃×16 h air cooling double aging process, a large number of M₇C₃, M₂₃C₆ and γ' phases are precipitated. The γ' phases of different sizes strengthened the precipitation strengthening of the alloy, and the carbides strengthened the grain boundary strengthening of the alloy. Within the prescribed range of alloy composition, the lower limit of C content(0.05%-0.075%), the middle limit of Al content(1.3%-1.6%) and the upper limit of Ti content(2.3%-2.7%) were selected. The upper limit of the total amount of Ti+Al(3.65%-4.46%) and the middle limit of the specific content of Ti/Al(1.76) can obtain a good distribution ratio of precipitated phase.

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Effect of Mn content on continuous cooling transformation of ultra-low carbon bainitic steel

Mei Tao, Liu Jing, Chai Xiyang

Heat Treatment of Metals 2024, 49 (12): 157-162. doi:10.13251/j.issn.0254-6051.2024.12.026

Abstract （35）

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Phase transition points of three ultra-low carbon bainitic steels with Mn contents of 1.5%, 1.8%, and 2.1%, respectively, were determined using a thermal expansion meter, and the continuous cooling transformation(CCT) curves of the three tested steels were plotted in conjunction with optical microscopy(OM) and scanning electron microscopy(SEM) observation and Vickers hardness measurements. The effects of Mn content on phase transformation points, CCT curves, microstructure and hardness were analyzed. The results show that the change of Mn equivalent caused by the increase of Mn content affects the bainite transformation temperature. In addition, the increase of Mn content makes the Ac₃ of the tested steel show a downward trend, and the hardness is also improved.

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Aging precipitation behavior of 445 ultra-purified ferritic stainless steel with different Mo contents

Li Jianchun, Jia Yuanwei

Heat Treatment of Metals 2024, 49 (12): 163-168. doi:10.13251/j.issn.0254-6051.2024.12.027

Abstract （33）

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Types of equilibrium precipitated phases in 445 ultra-purified ferritic stainless steel with different Mo content (0.68%, 1.79% and 2.37%) were analyzed by Thermo-Calc thermodynamic software. The specimens were annealed at 1020 ℃ for 10 min and aged at 700 ℃/870 ℃ for 1 h. The SEM and TEM methods were used to study the precipitation of second phases in the 445 stainless steel after annealing and aging. The results show that the types of equilibrium precipitates calculated by Thermo-Calc are basically consistent with the experimental results of microstructure observation and phase analysis. The second phases with different morphologies are precipitated in the aged 445 stainless steel, including Laves phase Fe₂(Nb, Mo) with strip-like shape distributing inside the grain and (Nb, Ti)C carbides with irregular granular shape presenting inside the grain and at the grain boundaries. There is remarkable difference in sensitivity of precipitated phases for the 445 ultra-purified ferritic stainless steel with different Mo contents. As the Mo content increases, the precipitation temperature of second phase rises and the amount of second phase precipitation also increases at the same aging temperature.

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Effect of C, N contents on microstructure and properties of 12%Cr ferritic heat resistant steel

Ma Tingwei, Hao Xianchao, Wang Ping, Zhu Jingyi

Heat Treatment of Metals 2024, 49 (12): 169-174. doi:10.13251/j.issn.0254-6051.2024.12.028

Abstract （25）

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Effect of C and N contents on microstructure and mechanical properties of 12%Cr ferritic heat-resistant steel was studied by observing the microstructure and tensile tests at room temperature and high temperature of three groups of 12%Cr ferritic heat resistant steel with different C and N contents. The results show that when the C content increases from 0.14% to 0.20%, the size of martensite laths decreases, δ-ferrite disappears, and the effect of martensite lath refinement improves the strength of the steel. When the N content increases from 0.004% to 0.02%, the prior austenite grain size and martensite lath width decrease, and the number of MX precipitates in the laths increases. The solution strengthening and the second phase strengthening enhance the strength of the steel, while the δ-ferrite reduces the strength, and the change of C and N contents has little effect on the plasticity. According to production practice, when the C content is reduced to 0.14% and the N content is controlled at 0.02%, the tensile properties of the tested steel is optimal. The yield strength, tensile strength and elongation at room temperature are 573.5 MPa, 763.0 MPa, and 24%, respectively. When the tensile test temperature is 550 ℃, the yield strength, tensile strength, and elongation are 344.5 MPa, 414.0 MPa, and 34%, respectively.

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Continuous cooling transformation curve of the third generation aviation bearing steel CSS-42L

Tian Zhongjie, Zhang Yunfei, Cao Wenquan, Zhao Yingli, Wang Yan, Bai Lijuan, Cui Yi

Heat Treatment of Metals 2024, 49 (12): 175-178. doi:10.13251/j.issn.0254-6051.2024.12.029

Abstract （41）

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Critical point and the continuous cooling transformation test of the third generation aviation bearing steel CSS-42L at cooling rate of 0.02-40 ℃/s were carried out by DIL805A quenching dilatometer with dilatometric method. The static CCT curve was drawn, and the microstructure and Vickers hardness at room temperature were analyzed. The results show that the critical points Ac₁ and Ac₃ of the CSS-42L steel are 655 ℃ and 738 ℃, respectively. In the process of continuous cooling, only martensitic transformation occurs at different cooling rates, and the starting temperature of martensitic transformation decreases with the decrease of cooling rate. The tested CSS-42L steel has a maximum microhardness of 330 HV50 at the cooling rate of 1.6 ℃/s.

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Effect of Ce modification and annealing on microstructure and properties of ADC12 aluminum alloy for automobile

An Shiqi, Hao Zengtian

Heat Treatment of Metals 2024, 49 (12): 179-183. doi:10.13251/j.issn.0254-6051.2024.12.030

Abstract （32）

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Effects of modification with different amounts of Ce on microstructure and hardness of the as-cast ADC12 aluminum alloy were studied by using OM, hardness testing, conductivity testing and other methods, as well as the changes in microstructure, hardness, and conductivity after annealing at different temperatures. The results show that within the range of 0% to 0.6%Ce, with the increase of Ce addition, the size of the α-Al phase and that of eutectic Si phase in the tested ADC12 aluminum alloy continuously decrease, and the hardness increases to 67.8 HBS, indicating a better modification effect. When the Ce addition continues to increase to 0.8%, the modification effect for the tested ADC12 aluminum alloy deteriorates, and the optimal Ce addition amount is 0.6%. Annealing treatment of the 0.6% Ce modified ADC12 aluminum alloy at 450, 480, 510, and 540 ℃ can refine the eutectic Si phase in the as-cast ADC12 aluminum alloy, enhance the hardness and conductivity of the alloy. When the annealing temperature is 510 ℃, the hardness and conductivity of the ADC12 aluminum alloy reach their optimal values of 84.5 HBS and 22.61 MS/m, respectively.

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