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Continuous cooling transformation behavior of austenite in 0.6Ni alloyed medium carbon steel

Jiang Bo, Hu Xuewen, Zhou Leyu, Wang Zhilin, Zhao Haidong, Liu Yazheng

Heat Treatment of Metals 2020, 45 (4): 10-15. doi:10.13251/j.issn.0254-6051.2020.04.003

Abstract （147）

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The dynamic and static continuous cooling transformation and effects of deformation and nickel in 0.6Ni medium carbon steel were carefully investigated by means of hot simulation tests, optical microscope and SEM observations and Vickers hardness test. Experimental results show that the ferrite and pearlite transformations are effectively suppressed while the bainite and martensite transformations are greatly promoted by the deformation in austenite region of the tested steel. Then, the critical cooling rate of full martensite is also lowered from 5 ℃/s to 3 ℃/s. The hardness of full martensite is 810 HV0.1 at the cooling rate of 3 ℃/s under the dynamic continuous cooling condition. However, the hardness of full martensite is 689 HV0.1 at the cooling rate of 5 ℃/s under the static continuous cooling condition. The improvement of martensite hardness can be attributed to the refinement of martensite due to the deformation recrystallization of austenite. The ferrite and pearlite transformations are suppressed and the bainite and martensite transformations are promoted by the addition of 0.6Ni because of the improvement of austenite stability. Then, the Ms temperature is lowered from 329 ℃ to 304 ℃ and also the critical cooling rate of martensite transformation is reduced from 0.5 ℃/s to 0.3 ℃/s. Compared with that of the addition of 0.4Mn, the ferrite and pearlite transformation is largely hindered and the Ms temperature is lowered from 320 ℃ to 304 ℃ by the addition of 0.6Ni. At the same time, the microstructure after cooling is also effectively refined.

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Effect of 0.2%Sn addition on microstructure and mechanical properties of Al-Si-Mg alloy

Yin Xin, Yin Dengfeng, Wang Kaixian, Li Jilin, Chi Guoming, Cao Hanquan

Heat Treatment of Metals 2020, 45 (4): 16-21. doi:10.13251/j.issn.0254-6051.2020.04.004

Abstract （112）

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Effect of 0.2%Sn addition on the microstructures and mechanical properties of Al-Si-Mg alloy with as-cast and T6 heat treated state was studied by optical microscopy (OM), scanning electron microscopy (SEM), energy spectrum analysis (EDS) and tensile testing. The results show that the addition of 0.2%Sn refines the morphology of the eutectic silicon phase and makes the primary α-aluminum grains more uniform, which reduces and improves the morphology and distribution of harmful impurities. At T6 state (solution treatment at 535 ℃ for 6 h+aging at 160 ℃ for 5 h), the proof strength, plastic extension and tensile strength of the alloy reach 262.3 MPa and 305.1 MPa respectively, is increased by 9.8% and 12.4% higher than that of the base alloy without Sn addition, and the elongation is 4.32%, which is increased by 22.6%.

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Microstructure and properties of Mo_f/TiAl composites prepared by foil-fiber-foil method

Tao Guidong, Li Hengkui, Xu Zhongxuan, Chen Zhiyuan, Sun Hongliang

Heat Treatment of Metals 2020, 45 (4): 22-28. doi:10.13251/j.issn.0254-6051.2020.04.005

Abstract （80）

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Mo_f/Ti48Al composite was successfully prepared by foil-fiber-foil method and hot pressing sintering, and the effects of Mo fiber on the microstructure and mechanical properties of the TiAl alloy were analyzed. The results show that through the two-step low temperature hot pressing of 635 ℃, 3 MPa for 10 h+680 ℃, 3 MPa for 4 h, the Al has fully reacted and the TiAl foil laminated material forms a dense Ti/TiAl₃ plate nearly void-free. Then in the high temperature reaction annealing at 1200 ℃ for 36 h, Ti and TiAl₃ continue to react to form γ-TiAl and α-Ti₃Al phases. The diffusion reaction of Mo fiber with matrix alloy after high temperature annealing forms a diffusion region, in which the main phases are TiMo and AlMo₃. The Mo fiber and matrix alloy are closely combined through diffusion, and there are no voids or cracks formed in the interface. Compared with the alloy without adding Mo fiber, the flexural properties of the composite with 10vol% Mo fiber are obviously improved, and the Mo fiber plays a toughening role in the alloy.

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Effects of Zr, Mn and Cr addition on microstructure and properties of Al-Zn-Mg alloy

Deng Ke, Sun Daxiang, Tang Weixue, Wan Li, Cai Zhizhi, Zhou Sigen

Heat Treatment of Metals 2020, 45 (4): 29-33. doi:10.13251/j.issn.0254-6051.2020.04.006

Abstract （86）

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Effects of Zr, Mn and Cr additions on microstructure and properties of Al-Zn-Mg alloy were investigated by means of optical microscopy, scanning electron microscopy, transmission electron microscopy and tensile test. The results show that the combined addition of Zr, Mn and Cr in the Al-Zn-Mg alloys leads to precipitates of a large number of (Al,Cr)₃Zr particles with 10-20 nm size, which coherent with the matrix. These irregularity dispersoids can strongly pin the dislocation, and hinder the dislocation movement and subgrain boundary migration and significantly inhibit grain recrystallization and growth of subgrain. The tensile strength and yield strength of Al-Zn-Mg alloy added with Zr, Mn and Cr are increased by 34 MPa and 19 MPa, respectively, which has better processability and mechanical properties.

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Effect of nitrogen content on microstructure and properties of 25Mn2CrVS bainite type non-quenched and tempered steel

Cai Mengru, Duan Meiqi, Hong Zhiwei, He Yizhu, Wang Ruizhen

Heat Treatment of Metals 2020, 45 (4): 34-39. doi:10.13251/j.issn.0254-6051.2020.04.007

Abstract （76）

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Effect of nitrogen content (mass fraction of 0.016%, 0.029% and 0.049% respectively) on the microstructure and mechanical properties of 25Mn2CrVS bainite type non-quenched and tempered steel was studied. The results show that the microstructure of all the tested steels consists of lath bainite, granular bainite and ferrite. When the nitrogen content increases from 0.016% to 0.029%, the strength and toughness of the tested steel increase, and the microstructure is refined. When the nitrogen content increases to 0.049%, the strength of the steel is basically unchanged, but the toughness drops sharply, the microstructure is obviously coarsened, and the grain boundary ferrite is formed. Vanadium in solid solution can promote the formation of lath bainite at grain boundary, and VN particles precipitated from austenite can promote the formation of acicular ferrite.

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Effect of Mg₂Si phase on microstructure and mechanical properties of as-extruded AZ31 magnesium alloy

Zheng Liuwei, Liang Wei, Zhang Huiyun, Nie Huihui, Hao Xinwei

Heat Treatment of Metals 2020, 45 (4): 40-44. doi:10.13251/j.issn.0254-6051.2020.04.008

Abstract （74）

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Mg₂Si phase was introduced into AZ31 magnesium alloy by replacing Al with Al-Si master alloy combined with hot extrusion. Effect of Mg₂Si phase on the microstructure and mechanical properties of AZ31 magnesium alloy was studied by optical microscope (OM), scanning electron microscopy (SEM), X-ray diffraction analysis (XRD) and electronic universal testing machine.The results show that the Mg-3(Al-Si)-Zn extrusion microstructure presents obvious bimodal distribution, and the Mg₂Si particle phase can promote dynamic recrystallization by particle stimulated nucleation (PSN), and the microstructure is refined dramatically around Mg₂Si particles. The yield and tensile strength of Mg-3(Al-Si)-Zn alloy are improved to 175 MPa and 269 MPa, respectively, while the elongation decreases slightly after the introduction of Mg₂Si strengthening phase.

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Recrystallization law of micro-carbon low alloy deep drawing dual phase steel

Zhou Liutao, Pan Hongbo, Pan Shuo, Wu Jiewen

Heat Treatment of Metals 2020, 45 (4): 45-50. doi:10.13251/j.issn.0254-6051.2020.04.009

Abstract （73）

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Recrystallization microstructure evolution and recrystallization kinetics of a micro-carbon low alloy steel during batch annealing were studied. According to the calculation of the Johnson-Mell theory and the Arrhenius recrystallization activation energy, the thermodynamic model of the relationship between recrystallization volume fraction and annealing temperature and isothermal time was established, and so was the dynamic model of the relationship between the annealing temperature and the time required for complete recrystallization. The results show that the two models verify each other and the recrystallization incubation period and completion time are shortened with the increase of annealing temperature. At the same temperature, the volume fraction of recrystallization increases until complete recrystallization with the increase of holding time. In addition, it is found that there is a competition phenomenon between recrystallization and phase transformation when annealing temperature is near Ac₁. The recrystallization process is the main phenomenon as the holding time is short while phase transformation process has a perfectly advantage as the holding time is long.

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Comparison and analysis of cooling transformation for 2.25Cr-1Mo and 2.25Cr-1Mo-0.25V steels

Hou Jingchao, Li Jie, Wu Yanyang, Yuan Jincheng, Yin Weijiang, Niu Hongxing

Heat Treatment of Metals 2020, 45 (4): 51-54. doi:10.13251/j.issn.0254-6051.2020.04.010

Abstract （86）

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Cooling transformations of 2.25Cr-1Mo and 2.25Cr-1Mo-0.25V steels were researched by phase change instrument, OM and SEM, and the effect of V on the cooling transformation was analyzed. The results show that compared with the CCT curves of 2.25Cr-1Mo steel, both the ferrite and the bainite transformation zones of the CCT curves for 2.25Cr-1Mo-0.25V steel shift right. Pearlite transformation zone is unable to be observed under existing test conditions. Adding V into 2.25Cr-1Mo steel improves the hardenability. 2.25Cr-1Mo-0.25V steel can transform into martensite partially under 48 000 ℃/h cooling rate. V can refine microstructure of the steel, the microstructure of 2.25Cr-1Mo-0.25V steel is finer than that of 2.25Cr-1Mo steel under 800 ℃/h cooling rate.

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