Current Issue

• Microstructure and properties of P91 steel pipeline in abnormal low hardness parts

  Fan Deliang, Wang Zhiwu, Ju Guangyu

  2020, 45(3):  1-6.  doi:10.13251/j.issn.0254-6051.2020.03.001

  Abstract ( 83 )   PDF (1849KB) ( 55 )  

  The causes of abnormal low hardness found in some parts of P91 steel main steam pipeline during operation of power plant were analyzed by microstructure observation, short-term mechanical properties test and high temperature creep rupture strength test. The results show that the microstructure in low hardness parts of the P91 steel is composed of ferrite and precipitates. The ferrite has a relatively low dislocation density, while the precipitate phases include coarsened M₂₃C₆ phase aggregating at grain boundary, as well as a new precipitated phase of Laves type. Such a microstructure leads to serious reduction of the short-term mechanical properties and high-temperature durability of the P91 steel.

  Microstructure and anisotropy tensile properties of T5 state 7N01 aluminum alloy extruded profile

  Deng Peng, Sun Hongliang, Chen Zhiyuan, Yang Kang, Cai Zhengkun

  2020, 45(3):  7-10.  doi:10.13251/j.issn.0254-6051.2020.03.002

  Abstract ( 63 )   PDF (1568KB) ( 32 )  

  The microstructure and tensile strength of 7N01 aluminum alloy extruded profiles under T5 heat treatment were studied. The results show that the microstructure of the 7N01 profile has a certain degree of non-uniformity and anisotropy, and the grains in the extrusion direction are elongated to form a deformation texture. Such deformation texture can more effectively resist plastic deformation in the extrusion direction, so the strength in the extrusion direction is higher than that perpendicular to the extrusion direction, and the elongation is reduced by about 2%. The tensile strength and yield strength of the 7N01 aluminum alloy extruded profiles at room temperature is about 368 MPa and about 318 MPa respectively, and the comprehensive properties is good.

  Microstructure and properties of B-Al composite coatings on TC4 titanium alloy

  Gao Shun, Tian Xiaodong, Zhang Mengyao

  2020, 45(3):  11-14.  doi:10.13251/j.issn.0254-6051.2020.03.003

  Abstract ( 61 )   PDF (1384KB) ( 32 )  

  B-Al composite coatings were prepared on the surface of TC4 titanium alloy by boronizing at 1050 ℃ for 4-6 h and subsequent aluminizing at 950-1050 ℃ for 4 h through a two-step pack cementation process. The constituent phases, microstructure, composition, hardness, friction coefficient of the composite coatings were analyzed by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), wavelength dispersive spectrometer (WDS) and energy dispersive spectrometer (EDS), microhardness tester, and friction and wear tester. The results show that the thickness of the B-Al composite coatings is in the range of 37-115 μm, and the coatings mainly consist of TiB₂ and TiAl₃ phases. The outer layer is TiAl₃ layer with dispersed TiB₂; and TiAl₂, TiAl and Ti₃Al intermetallic compound layers with smaller thickness are formed inward in turn. The surface hardness of the B-Al composite coatings is in the range of 1041.7-1429.4 HV0.1, which is about 3.03-4.16 times of the TC4 alloy. By boronizing at 1050 ℃ for 6 h followed by aluminizing at 1050 ℃ for 4 h, the friction coefficient of the B-Al composite coating is about 0.3, lower than that of TC4 alloy by about 25%.

  Evolution of silicon-manganese phase at high temperature and its effect on wear resistance of brasses containing silicon and manganese

  Tian Wu, Dai Jiaoyan, Bao Mingdong, Zhang Lijun, Chang Yongqiang, Wang Shimin, Yu Shengwang

  2020, 45(3):  15-19.  doi:10.13251/j.issn.0254-6051.2020.03.004

  Abstract ( 67 )   PDF (2572KB) ( 28 )  

  Four heat treatment processes on a Si-Mn brass with the Mn/Si ratio of 2 were carried out at 500 ℃ and 800 ℃ respectively for 1 h and 6 h. Then the microstructure, wear scar morphology and mechanical properties of the tested brass samples were analyzed and characterized by scanning electron microscope, white light interference, optical microscope and hardness tester. The results show that the wear resistance of the brass is improved after four kinds of heat treatment, and is the best when the heat treatment temperature is 800 ℃ and the holding time is 6 h. The fine Si-Mn phase in the brass is dissolved at 500 ℃, and more Si-Mn phase is dissolved into the matrix at 800 ℃. The friction and wear properties and hardness of the Si-Mn brass are improved by the precipitated slender and sharp Si-Mn phase.

  Effect of annealing temperature on precipitate and mechanical properties of V-Ti-Mo steel

  Yu Wenchao, Xue Yanjun, Sun Ting, Wang Maoqiu, Shi Jie

  2020, 45(3):  20-24.  doi:10.13251/j.issn.0254-6051.2020.03.005

  Abstract ( 42 )   PDF (1685KB) ( 45 )  

  Microstructure and mechanical properties of V-Ti-Mo steel were characterized after annealing at different temperatures. The results show that pearlite structure begins to decompose, and the amount of MC type precipitate in the experimental steels increases as the annealing temperature increasing. The MC type carbide in the hot rolled steel is mainly Ti(C, N), while (V, Mo)C gradually precipitates by increasing annealing temperature. The yield strength of the tested steel is calculated according to steel strengthening theory, the results show good agreement with the experimental data, which indicates that precipitation strengthening is the main reason for the strength increase after annealing.

  Room temperature creep characteristics of a high strength steel with extremely high yield ratio

  Guo Miao, Ding Xinming, Ning Yanting, Sun Wei

  2020, 45(3):  25-29.  doi:10.13251/j.issn.0254-6051.2020.03.006

  Abstract ( 43 )   PDF (1967KB) ( 41 )  

  The room temperature creep behavior of a high strength steel with yield ratio of 99.7% under different loading stress conditions was studied by using MTS universal testing machine, and the characteristics of microstructure evolution under different creep conditions were analyzed. The results show that under the loading stress lower than the yielding strength, the tested steel shows obvious creep phenomenon at room temperature, and the creep curve shows typical two-stage room temperature creep characteristics based on steady state stage. From the fitting results of the creep curves, it can be found that the curves follow the log law, and the creep rate decreases gradually with the increase of creep time, which may vary by two orders of magnitude. Under different room temperature creep conditions, the change of microstructure of the high strength steel is not obvious in the process of room temperature creep. The grain sizes are very small and most of them are less than 5 μm. Besides, the grain boundary is dominated by the small angular grain boundary below 15°, while the large angle grain boundary is mostly concentrated in the 50°-60° range.

  Microstructure and properties of NiMoSi laser clad layer on surface of 304 stainless steel

  Liu Donghua, Zhou Kangning, Zhou Jinsong, Zhang Binjuan, Chen Lei, Ke Jin, Liu Xiubo

  2020, 45(3):  30-34.  doi:10.13251/j.issn.0254-6051.2020.03.007

  Abstract ( 34 )   PDF (1453KB) ( 43 )  

  In order to improve the tribological properties of 304 stainless steel, two coatings with different composition were prepared on the surface of 304 stainless steel by laser cladding, in which coating A was 20%Ni-48%Mo-32%Si and coating B was 30%Ni-42%Mo-28%Si (mass fraction). The phase composition, microstructure, and tribological properties at room temperature were analyzed by means of XRD, SEM and friction abrasion testing machine. The results show that both coatings have good metallurgical bonding with the matrix, but with some cracks. Both composite coating A and B mainly consist of Mo₅Si₃ and MoSi₂, the microhardness of the coating A (1060.1 HV0.5) and coating B(725.9 HV0.5) is obviously higher than that of the matrix (257.2 HV0.5). The wear rate and friction coefficient of the layer A is lowest.

  Microstructure and mechanical properties of friction stir welding joint of Cu-Cr-Zr alloy

  Zhou Sha, Wang Kuaishe, Wang Wen, Peng Pai, Zhang Shengyi, Huang Liying

  2020, 45(3):  35-40.  doi:10.13251/j.issn.0254-6051.2020.03.008

  Abstract ( 33 )   PDF (3557KB) ( 35 )  

  Friction stir welding (FSW) was conducted on Cu-Cr-Zr alloy plates with 3 mm thickness by using rotation speed of 750 and 1500 r/min and welding speed of 23.5 mm /min, in the state of aged and solid solution treated respectively. The effects of rotation speed and base metal (BM) initial state on the microstructure and mechanical properties of the FSW joints were studied, and the mechanical properties of joints were modeled and quantitatively analyzed. The results show that the grain size of the FSW joint significantly refines, and the precipitated phase is dissolved in the matrix under the high-temperature effect of the stir-welding head. When the initial state of BM is aged state, compared with the specimens of 1500 r/min, the grain size of the 750 r/min specimens is smaller, and there exists precipitate phase in the matrix, so that the 750 r/min specimens have higher mechanical properties mainly due to the comprehensive effect of grain boundary strengthening and precipitation strengthening. When the initial state of BM is solid solution state, compared with the specimens of 1500 r/min, the 750 r/min specimens have smaller grain size and high mechanical properties mainly due to grain boundary strengthening effect. When the FSW speed is the same, the welding joint grain size of the aged state is smaller than that of solid solution state, but the mechanical properties of the aged state is higher than that of solid solution state, which is mainly due to the difference of the initial state microstructures. The comprehensive analysis shows that a welding joint with better performance can be obtained by the FSW process with a lower welding speed.

  Microstructure and properties of multi-track joint Co-based alloy laser clad layer

  Cui Lujun, Yu Jihua, Cao Yanlong, Zeng Wenhan, Guo Shirui, Li Xiaolei, Zheng Bo

  2020, 45(3):  41-45.  doi:10.13251/j.issn.0254-6051.2020.03.009

  Abstract ( 28 )   PDF (2170KB) ( 32 )  

  Co-based alloy powder was used as a cladding material to prepare high performance cladding layer on the surface of 42CrMo substrate by using laser cladding technology. The macromorphology and microstructure of the clad layer were observed by an optical microscope. The microhardness and friction coefficient curves of the substrate and clad layer were measured by microhardness tester, friction and wear tester, and the wear mechanism was analyzed. The results show that the microstructure types of the clad layer are planar, cellular and columnar grains, and distributed as gradient morphology. The average hardness of the clad layer reaches 650 HV0.3, which is 2.7 times the average hardness of the substrate. The friction coefficient of the clad layer is about 0.275, about 0.075 smaller than that of the substrate.

  Mechanical and properties of austenitic heat resistant steel 22Cr-25Ni after high temperature aging

  Wang Zhaomin, Wang Shuo, Shen Lei, Cheng Yi

  2020, 45(3):  46-49.  doi:10.13251/j.issn.0254-6051.2020.03.010

  Abstract ( 24 )   PDF (2191KB) ( 38 )  

  Mechanical properties changes of a novel 22Cr-25Ni austenitic steel after aging at 650 ℃ and 700 ℃ were studied by means of hardness test, tensile test at room temperature, impact test, and the microstructure and impact fracture at room temperature were analyzed by means of optical microscope and scanning electron microscopy. The results show that the hardness and tensile strength are increased with aging time and reach maximum after aging for 1000 h, the aging embrittlement of 22Cr-25Ni steel is obvious, the impact absorbed energy is decreased to below 111 J after aging at 650 ℃ for 100 h from 198 J before aging treatment, the impact absorbed energy is only 47 J after aging at 700 ℃ for 100 h, and with the continuation of aging time, the impact toughness decreases to about 20 J after 3000 h aging and then tends to be steady. The change of mechanical properties is mainly caused by the precipitation phase of CrNbN, M₂₃C₆ and MX after aging at high temperature.

  Hot deformation behaviors of AM355 stainless steel

  Hu Jiaqi, Wang Changjun, Yang Zhe, Liang Jianxiong, Dong Han

  2020, 45(3):  50-58.  doi:10.13251/j.issn.0254-6051.2020.03.011

  Abstract ( 43 )   PDF (6459KB) ( 33 )  

  The isothermal hot compression test of as-forged AM355 stainless steel was conducted by Gleeble-3800 thermo-mechanical simulator in the strain rates range between 0.01-10 s^-1 and the temperatures range between 1173-1423 K. And microstructure after hot deformation was observed by means of OM, EBSD and TEM. The constitutive equations based on Arrhenius model as well as a modified equation with higher accuracy were established by the peak stresses obtained from the stress-strain curves under various conditions. The hot processing maps were constructed based on dynamic materials model (DMM). The hot working window at a strain of 0.9 was determined on the basis of processing map and deformed microstructure. The results show that, the optimum domain for hot forming of AM355 steel is determined in the temperature and strain rate ranges between 1250-1300 K, 0.01-0.03 s^-1 and 1300-1400 K, 0.01-10 s^-1 as well as 1400-1423 K, 0.5-10 s^-1 with the efficiency of endless than 0.36. It is found that the dynamic recrystallization (DRX) completed in this domain. Further, the relationship between austenite grain size of complete DRX (d_drx) and Zener-Holloman parameter (Z) is also given out.

  Effect of Nb and aging time on phosphorus segregation in hot-rolled medium-manganese TRIP steel

  Li Yan, Fu Jixue, Zhao Zengwu, Ding Wei

  2020, 45(3):  59-63.  doi:10.13251/j.issn.0254-6051.2020.03.012

  Abstract ( 42 )   PDF (1421KB) ( 30 )  

  The phosphorus segregation and precipitation behavior in a hot-rolled medium-manganese TRIP steel treated with 650 ℃ annealing for 2 h+550 ℃ isothermal aging were investigated by field emission scanning electron microscopy (FE-SEM). The results show that the grain boundary segregation of P is a non-equilibrium phenomenon. The critical time is about 50 h, which is consistent with the theoretical calculation result of 48 h. C and P co-segregation exists in certain local regions, where the segregations of C and P are both higher. The alloying element Nb has an inhibitory effect on phosphorus segregation in the steel, the maximum P segregation content can be reduced relatively by 6.57%-19.5% within the aging time of 20-70 h. According to the Kikuchi line analysis in the electron backscatter diffraction, P is in solid solution when the content of segregation is less than 2.28at%, while P will be in the precipitated phase when the content of segregation is more than 2.28at%.

  Strengthening effect of nitrogen on tin-plated steel sheet

  Sun Chaofan, Fang Yuan, Wang Yaqing, Wu Zhiguo, Pan Hongwei

  2020, 45(3):  64-67.  doi:10.13251/j.issn.0254-6051.2020.03.013

  Abstract ( 35 )   PDF (1763KB) ( 25 )  

  Content of nitrogen in solid solution and combined nitrogen in three different kinds of tin-plated sheet were studied by physiochemical phase analysis, the contribution of solution strengthening and precipitation strengthening played by nitrogen in the tin-plated sheet were also calculated according to related theory. The results show that with the total nitrogen content increasing from 0.0021% to 0.0103%, the proportion of combined nitrogen in the steel is decreased by 10.1%, but the proportion of the nitrogen in the AlN precipitation is increased by 10.7%. Nitrogen can play an important role in improving the strength of the tin-plated sheet, the yield strength of the steel can be promoted by 30 MPa with the total nitrogen content increased by 0.0082%.

  Effect of Al content on microstructure and properties of AZ series magnesium alloy containing rare earth

  Qin Chen, Zhao Liping, Chen Lichao, Niu Jiaxing, Chen Sheng, Jiang Yajun

  2020, 45(3):  68-72.  doi:10.13251/j.issn.0254-6051.2020.03.014

  Abstract ( 27 )   PDF (1549KB) ( 22 )  

  Taking the AZ series magnesium alloy containing rare earth as the base alloy, specimens with 5%, 7% and 9% Al were prepared, and solution treatment at 435 ℃ for 24 h+aging at 200 ℃ for 24 h was carried out. Then the microstructures of as-cast, solid solution treated and aged specimens were observed, the mechanical properties and corrosion resistance of the specimens after aging were measured. The results show that the as-cast microstructure of the specimens is mainly α-Mg+β-Mg₁₇Al₁₂+Al₁₁ (La,Ce)₃ and (La,Ce)Al₄. With the increase of Al content, the β-Mg₁₇Al₁₂ phase and rare earth compounds increase, and the grain refinement is achieved. After solution treatment, the β-Mg₁₇Al₁₂ phase in the microstructure gradually dissolves, the dissolution becomes uncompleted with the increase of Al content, and the undissolved strengthening phase β-Mg₁₇Al₁₂ and the rare earth compound phase disperse in and near the grain boundary. After aging treatment and with the increase of Al content, β-Mg₁₇Al₁₂ phase continues to precipitate and increases in the microstructure, and the size of rare earth compound phase is refined. With the increase of Al element, the tensile strength and hardness of the specimen increase gradually, while the plasticity and toughness are getting worse, the corrosion resistance is becoming better.

  Influence of Nb on microstructure and mechanical properties of 0.2C-1.5Si-1.8Mn quenching and partitioning steel

  Zhan Hua, Leng Deping, Pan Hongbo, Xiao Yangyang, Liu Yonggang, Cao Jinghua

  2020, 45(3):  73-77.  doi:10.13251/j.issn.0254-6051.2020.03.015

  Abstract ( 24 )   PDF (2221KB) ( 35 )  

  Based on traditional C-Si-Mn Q&P steel, the influence of niobium (Nb) on microstructure and properties of quenching-partitioning steel (Q&P) was investigated by adding moderate microalloying element Nb. The results show that the microstructure of the Nb-added steel consists of ferrite, lath martensite and M/A island, basically being the same as that of Nb-free steel. However, the martensite lath of the Nb-added steel is obviously refined, and the inter-lath spacing is significantly reduced. The addition of Nb promotes the precipitation of ferrite, inhibits the formation of pearlite, thus effectively refines the microstructure and shortens the carbon partitioning distance, facilitates the diffusion of carbon into austenite and increases the stability of austenite. The yield strength and tensile strength of the Nb-added steel are improved after the same Q&P heat treatment, with the tensile strength and elongation reaching to 989.07 MPa and 18.36% respectively, the production of tensile strength and plasticity reaching up to 18.16 GPa·%.

  Phase transformation and precipitation behaviors of Mn18Cr18N austenitic stainless steel during equilibrium solidification

  Wang Yinghu

  2020, 45(3):  78-85.  doi:10.13251/j.issn.0254-6051.2020.03.016

  Abstract ( 21 )   PDF (4345KB) ( 40 )  

  The phase transformation and precipitation behaviors were investigated by using Thermo-calc software in the Fe-(16-19)Cr-(16-19)Mn-(0.4-0.7)N-(0.04-0.1)C-(0.1-0.4)Si-(0.1-0.4)Ni multi-element system relevant to Mn18Cr18N austenitic stainless steel during solidification. The vertical sections of phase diagram of this system were calculated by using the TCFE9 database. Based on these vertical sections, the influence of different elements was analyzed in the phase transformations during solidification and a diagram of the phase-transformation path of Mn18Cr18N austenitic stainless steel was obtained during equilibrium solidification. The test results show that increasing C, N, Si and Ni content can enlarge the stable region of γ phase and the effect of Cr and Mn on stabilizing ferrite is obvious. Phase-transformation path and M₂₃C₆ precipitation temperature mainly depend on C content; Cr₂N precipitation temperature mainly depends on N content and σ precipitation temperature mainly depends on Cr content.

  Effect of aging process on mechanical properties and microstructure of nanostructured 2297 aluminum-lithium alloy

  Li Tingting, Luo Junqian, Liang Sheng, Huang Tianlin, Wu Guilin

  2020, 45(3):  86-91.  doi:10.13251/j.issn.0254-6051.2020.03.017

  Abstract ( 28 )   PDF (2388KB) ( 28 )  

  A hot-forged 2297 aluminum-lithium alloy was solution treated at 535 ℃ for 2 h then water quenched, followed by cold rolling with 95% reduction, and then aged at different temperatures (140-190 ℃) for different time (0-80 h). The effects of aging temperature and time on the microstructure and properties of the alloy were analyzed by means of tensile testing, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that the large plastic deformation prior to aging leads to nanostructure in the alloy and promotes homogenous precipitation of fine T₁ phase, which greatly shortens the time for the alloy to reach peak aging. Consequently, the aluminum-lithium alloy with high strength and high plasticity is successfully obtained. When aging at temperature in range of 120-140 ℃, the higher the aging temperature, the shorter the peak aging time and the higher the strength. After peak aging at 140 ℃ for 40 h, the tensile strength, yield strength, and elongation of the alloy are 525 MPa, 478 MPa, and 7.7%, respectively, and the main reinforcement phase is fine T₁ phase. When aging at temperature in range of 170-190 ℃, the higher the aging temperature, the shorter the peak aging time, but the tensile strength and yield strength decrease rapidly. After peak aging at 170 ℃ for 8 h, the tensile strength, yield strength, and elongation of the alloy are 503 MPa, 462 MPa, and 5.0%, respectively, and the main reinforcement phase is still T₁ phase, but it has obviously coarsened.

  Effect of micro-arc oxidation treatment on adhesion properties between stainless steel and epoxy resin

  Zhao Jiefu, Chu Longsheng, Liu Jun, Gao Peng

  2020, 45(3):  92-96.  doi:10.13251/j.issn.0254-6051.2020.03.018

  Abstract ( 25 )   PDF (1326KB) ( 32 )  

  The surface of stainless steel was aluminized by hot-dip aluminizing process, the influences of dip time and dip temperature on the thicknesses of alloy layer and pure aluminum layer were analyzed to obtain the optimum process parameters, then micro-arc oxidation experiment was carried out. The bonding strength between the oxide film and epoxy resin was measured by the shear method, the microstructure of the micro-arc oxidation film was characterized by using SEM, XRD, and laser confocal microscopy to discuss and analyze the influence of micro-arc oxidation treatment of stainless steel on its adhesion to epoxy resin. The results show that the appropriate hot-dip temperature is 710 ℃, the appropriate hot-dip time is 11 min. The micro-arc oxidation film is mainly composed of α-Al₂O₃ and γ-Al₂O₃, and the oxidation film products are basically the same under different micro-arc oxidation time. Both the surface roughness of ceramic film and the micro-arc oxidation film-epoxy resin bonding strength increase with the increase of oxidation time. When the time increases to 30 minutes, the maximum surface roughness is 1.265 μm, the binding strength increases to the maximum value 33.20 MPa and being 2.8 times that of untreated samples.

  Effect of solution treatment on microstructure and mechanical properties of heat-resisting Ni-based alloy used for ultra-supercritical power plant

  Tian Zhongliang, Chen Zhengzong, He Xikou, Bao Hansheng, Liu Zhengdong

  2020, 45(3):  97-102.  doi:10.13251/j.issn.0254-6051.2020.03.019

  Abstract ( 24 )   PDF (3029KB) ( 34 )  

  A nickel-based heat-resistant alloy used for ultra-supercritical power plants was developed by optimizing commercial Inconel 617 alloy through increasing Al and Ti content with B addition. The effects of solution treatment on the microstructure and properties of this alloy was also investigated. The results show that the average grain size increases from 68 μm to 139 μm and the hardness decreases from 203 HBW to 175 HBW with the solution temperature increasing from 1100 ℃ to 1190 ℃ for 2 h. After solution treatment at 1100 ℃ for 1-4 h, the intragranular carbides can be gradually dissolved, and the discontinuous carbides distributed along grain boundaries with no significantly change. With the increase of solution temperature, both the high temperature tensile property and impact toughness at room temperature of the alloy decrease. Although the high temperature tensile property of furnace-cooled sample is slightly lower than that of water-cooled (WQ) sample, it is obvious higher than that of Inconel 617 alloy. The recommended solution heat treatment for the experimental alloy consists of solution treating at 1100 ℃ for 2 h, and water quenching.

  Effects of cold rolling and heat treatment on microstructure and properties of Al_0.3CoCrFeNi high entropy alloy

  Si Songhua, Zhou Fangying, Wang Jianguo

  2020, 45(3):  103-107.  doi:10.13251/j.issn.0254-6051.2020.03.020

  Abstract ( 24 )   PDF (1642KB) ( 33 )  

  Effects of cold rolling with 75% reduction and different cooling methods (air cooling and furnace cooling) after heat treatment at 1073 K for 1 h on the microstructure and mechanical properties of Al_0.3CoCrFeNi high entropy alloy were studied by means of X-ray diffraction, scanning electron microscopy, transmission electron microscopy and tensile test. The results show that, all the as-cast and cold-rolled Al_0.3CoCrFrNi alloy samples are FCC single-phase structure. After holding at 1073 K for 1 h, both the furnace-cooled and the air-cooled samples are FCC+BCC dual-phase structure. Compared with the as-cast state, the strength of the alloy after cold-rolling increases significantly, but the plasticity decreases greatly. After the heat treatment, the furnace cooling sample has excellent mechanical properties due to fine grain strengthening, twinning and precipitation strengthening. The tensile strength of the furnace cooling sample is 1289 MPa, which is about twice as much as that of as-cast specimen(719 MPa), and the maximum elongation is 28.7%. Because of the increase of the precipitated phase and twin size, the strength of the furnace-cooled sample increases without loss of plasticity compared with that of the air-cooled sample.

  Effect of annealing temperature on microstructure and properties of CrFeCoNiTi_1.5 high entropy alloy

  Jiang Yue, Zhou Guangtai, Cheng Simeng, Li Xiuming

  2020, 45(3):  108-113.  doi:10.13251/j.issn.0254-6051.2020.03.021

  Abstract ( 22 )   PDF (2181KB) ( 39 )  

  In order to study the effect of medium and low temperature heat treatment on properties of CrFeCoNiTi_1.5 high entropy alloy, the high entropy alloy was annealed at 200, 400 and 600 ℃ for 10 h, respectively. The microstructure, surface morphology and segregation of the elements were analyzed by X-ray diffraction, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS). Simultaneously, the dynamic potential polarization curves and Vickers hardness of the high entropy alloy were also tested by microhardness tester and electrochemical workstation. The results show that the increase of annealing temperature is favorable to the precipitation of HCP structure phase of the CrFeCoNiTi_1.5 high entropy alloy. With the increase of temperature, Cr, Fe, Co and Ni gradually aggregate into and distribute inside the grains, while Ti gradually aggregates to the intergranular region. When annealed at 600 ℃, the corrosion resistance of the CrFeCoNiTi_1.5 high entropy alloy reaches the optimal value, and the Vickers hardness is 914 HV0.5.

  Effect of T6 heat treatment on friction and wear properties of SiCp/Al composites

  Zhu Shuang, Liu Yun, Xie Liming, Hao Shiming

  2020, 45(3):  114-118.  doi:10.13251/j.issn.0254-6051.2020.03.022

  Abstract ( 21 )   PDF (1854KB) ( 24 )  

  SiCp/Al composites with different SiC particle volume fractions (30%, 35% and 40%) were prepared by means of powder metallurgy. The changes of average friction coefficient and wear rate of SiCp/Al composites under different volume fraction and T6 heat treatment were studied by using MMU-5GA microprocessor controlled high temperature friction and wear tester. The wear morphology of SiCp/Al composites was analyzed by means of scanning electron microscopy, and the friction and wear mechanism was discussed. The results show that when the volume fraction of SiC particles varies from 30% to 40%, the wear resistance decreases with the increase of the volume fraction. In a certain range of 30%-35%SiC particle volume fraction, SiC particles bond well with the matrix, as a hard point, SiC particles play a dual role in resisting wear and restricting the plastic deformation and wear of the matrix alloy. However, when the SiC content is too high, the bonding between the particles and the matrix is not close, the particles are easy to fall off during wear, and the wear resistance of the composites decreases. The average friction coefficient and wear rate of the composite decrease after heat treatment, because the strength and hardness of the sample after heat treatment are improved, so does the wear resistance of the sample. At room temperature, the wear mechanism of composites is mainly abrasive wear at the early stage of wear and abrasive wear and peeling wear coexist at the wear stage.

  Comparison of microstructure and properties of 50W600 non-oriented silicon steel produced by CSP short process and 2250 mm rolling process

  Dong Lili, Lu Xiaoyu, Yang Yuanyuan, Ma Yonglin, Yang Weiyu

  2020, 45(3):  119-121.  doi:10.13251/j.issn.0254-6051.2020.03.023

  Abstract ( 21 )   PDF (1180KB) ( 27 )  

  The mechanical tensile test, microstructure observation and texture analysis for 50W600 non oriented silicon steel produced by two different hot rolling processes (CSP and 2250 mm semi continuous rolling) were carried out to study the difference of microstructure and comprehensive properties between the two processes. The results show that the microstructure of the non oriented silicon steel 50W600 produced by CSP process is more uniform, the average grain size is larger than that of produced by 2250 mm hot rolling process, and the mechanical properties of the hot rolled plate are slightly lower. The unfavorable texture of 50W600 non-oriented silicon steel produced by short-process CSP after acid rolling and continuous annealing is relatively less, and the magnetic properties are better than that of produced by 2250 mm hot rolling process.

  Effect of cold rolling deformation on texture of Al-Mg-Si aluminum alloy

  Yang Zhengbin, Li Yan, Huang Zhehui, Wang Hongkun, Xiang Jisheng, Zhao Hongjin

  2020, 45(3):  122-127.  doi:10.13251/j.issn.0254-6051.2020.03.024

  Abstract ( 21 )   PDF (3228KB) ( 29 )  

  The effect of cold rolling deformation on the texture of aluminum alloy was studied by means of optical microscope and SEM. The results show that the recrystallization texture Cube{001}<100> will be replaced by deformation textures Copper{112}<111> and S{123}<634> via Goss{011}<100> with the increase of cold rolling deformation, and these deformation textures will be the main and stable orientations, but the volume fraction of Goss texture tends to increase first and then decrease. The texture of deformation band is mainly composed of Copper{112}<111> texture with high intensity and Cube{001}<100> texture with weak intensity. When the cold rolling deformation is less than 20%, the main grain orientations are {001} and {012}, and when the cold rolling deformation is more than 40%, the main orientations are {011}, {112}, and {123}.

  Effect of laser power on quenched microstructure and friction and wear properties of 40CrNiMoA steel

  Yang Zhen, Fan Xiangfang, Qiu Changjun, Li Yong, Liu Ning

  2020, 45(3):  128-132.  doi:10.13251/j.issn.0254-6051.2020.03.025

  Abstract ( 23 )   PDF (2169KB) ( 38 )  

  The surface layer of the coiled spindle main shaft 40CrNiMoA steel base material was tested by laser-quenching with different power. The macroscopic structure of cross-section, surface microstructure, microhardness, and friction and wear properties of the specimens were observed or tested by means of stereo microscope, optical microscope, microhardness tester, vertical universal friction and wear tester. The results show that, the surface structure of the laser hardened specimens at different powers exhibit different levels of refining, and compared with the matrix, the hardness and friction and wear properties are improved. When the power is 1600 W, the laser hardened layer can be clearly observed in the cross-section of the specimens, and the surface layer of the specimens is the most detailed, consisting of fine acicular martensite, a small amount of retained austenite and a finely distributed fine carbide, and the surface hardness can reach 640.3-706.8 HV0.2, which is about 2.8 times of that of the substrate. At the same time, the friction coefficient is stable between 0.40 and 0.60, which is about 50% lower than that of the substrate. The amount of wear is 1.3 mg, which is only 36.1% of the substrate. Under the test conditions of spot size with 12 mm×2 mm, scanning speed with 20 mm/s and laser power with 1600 W, the obtained microstructure and friction and wear properties are optimized after surface laser quenching of 40CrNiMoA steel.

  Effect of annealing on microstructure and properties of hot deformed TC21 alloy

  Yang Chunlin, Zhang Song, Ou Meigui

  2020, 45(3):  133-139.  doi:10.13251/j.issn.0254-6051.2020.03.026

  Abstract ( 22 )   PDF (3487KB) ( 33 )  

  The microstructure and properties of TC21 alloy bar after single and double annealing were studied. The results reveal that the deformed α phase is recrystallized and equiaxed to different extents after the single annealing. With the increase of annealing temperature, α phase is equiaxed more clearly and equiaxed α phase is coarsening. After the double annealing, the microstructure is further equiaxed and homogenized. The double annealing process slightly reduces the strength of the alloy, but significantly improves the plasticity of the alloy. After the treatment of 900 ℃×45 min, AC+590 ℃×4 h, AC, the section shrinkage rate and elongation rate of the alloy are increased by 4.11% and 6.71%, respectively.

  Effect of dual phase accelerated cooling on microstructure and properties of X80 pipeline steel

  Ma Jing, Yu Baiqing, Wang Shenhao, Fan Lifeng

  2020, 45(3):  140-145.  doi:10.13251/j.issn.0254-6051.2020.03.027

  Abstract ( 22 )   PDF (2814KB) ( 26 )  

  X80 pipeline steel was heat treated by using dual phase accelerated cooling (the initial cooling temperature of the accelerated cooling was 700 ℃), and dual-phase structure of bainite and ferrite (B+F) was obtained. Microstructure characterization, mechanical properties test and corrosion resistance in 3.5 wt% NaCl solution were studied. The results show that the microstructure of pipeline steel after heat treatment is composed of lath bainite, polygonal ferrite and a small amount of martensite/austenite islands. The yield ratio and initial work hardening index of (B+F) dual-phase pipeline steel are 0.65 and 0.31, respectively. Compared with that of steel before heat treatment, the uniform elongation of pipeline steel after heat treatment is 8.3%, which indicates that the ductility is significantly improved. The corrosion resistance is also improved due to 52.4% amount of ferrite phase in the dual-phase structure. The coordinated deformation of (B+F) dual-phase structure obtained by dual-phase accelerated cooling during plastic deformation process can meet the needs of high deformation, and the corrosion resistance of the dual-phase structure is excellent, which provides some reference for the actual production of high deformation pipeline steel.

  Effect of solution treatment on microstructure and passivation film properties of 2205 duplex stainless steel

  Xing Shanshan, Qi Haoyu, Zheng Chuanbo

  2020, 45(3):  146-150.  doi:10.13251/j.issn.0254-6051.2020.03.028

  Abstract ( 37 )   PDF (1729KB) ( 32 )  

  Solid solution treatment of 2205 duplex stainless steel was carried out at different temperatures. The relationship between solid solution temperature and microstructure and passivation film characteristics of 2205 duplex stainless steel was studied by means of quantitative metallographic method, hardness method, electrochemical polarization test and electrochemical impedance spectroscopy. The results show that σ phase exists at 950 ℃ and distributes at ferrite/austenite grain boundaries, but disappears at 1000 ℃. Ferrite phase ratio increases with the increase of solid solution temperature, while austenite phase ratio shows the opposite rule. The electrochemical and impedance spectroscopy results show that the passivation film has the worst stability and corrosion resistance when solution treated at 950 ℃, and the passivation film has the best stability and corrosion resistance at 1050 ℃.

  Effect of solution temperature on microstructure and grain boundary distribution characteristic of cold-rolled 690 alloy

  Wang Fangjun, Liu Xuan, Liu Yinglong, Wu Wei

  2020, 45(3):  151-157.  doi:10.13251/j.issn.0254-6051.2020.03.029

  Abstract ( 22 )   PDF (7188KB) ( 34 )  

  Effect of solution temperatures from 950 to 1100 ℃ on microstructure and grain boundary characteristic distribution of 690 alloy with different deformation rate was studied by means of SEM and EBSD. The results show that the grain size of recrystallization increases rapidly when the temperature over 1070 ℃, and the grain size of the heavier deformed specimens is smaller than that of the slighter deformed specimens. Meanwhile, the solution temperature for the slighter deformed 690 alloy should be lower than that of the heavier deformed specimen. Furthermore, the grain boundary distribution is investigated based on the Coincidence Site Lattice (CSL) theory. After solution treatment, the low angel boundary (LAB) which produced by deformation microstructure is replaced by Σ3 grain boundary with the increase of the number of annealing twins based on the statistic results. The statistic results of grain boundary characteristic distribution show that Σ3 grain boundary isn't increased obviously when temperature over 1030 ℃. In addition, the density of Σ3 grain boundary of the heavier deformed specimen is higher than that of the slighter specimens. It is indicated that the heavier deformation is positive to the density of Σ3 grain boundary. From the statistic results of grain orientation, it can be showed that the proportion of Σ3ⁿ is increased in the deformed 690 alloy after 1030 ℃ solution treatment, especially Σ3 grain boundary. At the same time, the amount of Σ3 grain boundary in the heavier deformed alloy is 19% more than that of the slighter deformed alloy with 17%.

  Spray deposition process of wire electrical explosion in protective atmosphere

  Bai Xuehu, Zhu Liang, Han Feng, Wang Xudong

  2020, 45(3):  158-161.  doi:10.13251/j.issn.0254-6051.2020.03.030

  Abstract ( 23 )   PDF (1604KB) ( 26 )  

  A wire electrical explosion spray deposition device was developed with a protective atmosphere, and a pure aluminum wire was used for the electrical explosion spray deposition test on a small diameter cylinder. The influencing factors and the micro-hardness were analyzed. The results show that under the test deposition distance, an electrical explosion is occurred in the constrained groove with a width of 3 mm and a deposition layer with width of about 4 mm is obtained. After the entire cylindrical surface is lapped, the thickness of the deposition layer is tended to be uniform. When the charging voltage of the capacitor is 9 kV and the diameter of the aluminum wire is 0.3 mm, the obtained deposition layer has the smallest void ratio and the highest micro-hardness. The grain size in the deposited layer is about 4 μm.

  Effect of heat treatment process on microstructure and hardness of AuCuAgZn17-7-1 alloy

  Tang Lina, Ren Wei, Wang Yongsong, Zhang Tiande, Wu Guohua

  2020, 45(3):  162-165.  doi:10.13251/j.issn.0254-6051.2020.03.031

  Abstract ( 18 )   PDF (3231KB) ( 34 )  

  Microstructure and microhardness of AuCuAgZn17-7-1 alloy for brush under different solution and aging processes were tested and analyzed by means of optical microscope, scanning electron microscope and microhardness tester. The results show that with the increase of solution temperature, the grain size is increased. The microhardness of the tested alloy after solution at 670 ℃ for 30 min is significantly lower than that of the original material, and the microhardness uniformity is increased, which leads to elimination of the microhardness difference between the edge and the core of contact parts. The second phase is precipitated during aging process, and is gradually increased with the increase of aging temperature. The microhardness is increased first and then decreased, and there is obvious aging hardening effect. The peak-aging microhardness of the alloy is reached at 311.5 HV0.2 after solution treatment at 670 ℃ for 30 min and aging treatment at 250 ℃ for 60 min.

  Effect of two-stage solution treatment on microstructure and properties of 7075 high strength aluminum alloy

  Wang Jiyue, Xu Liping

  2020, 45(3):  166-168.  doi:10.13251/j.issn.0254-6051.2020.03.032

  Abstract ( 40 )   PDF (1143KB) ( 29 )  

  Effects of single-stage and two-stage solution treatment on microstructure and mechanical properties of 7075 aluminum alloy were studied by means of optical microscope, electronic universal testing machine and vickers hardness tester. The results show that the second phase particles of 7075 aluminum alloy treated with two-stage solution are much more dissolved into the matrix and have higher solid solubility than those treated with single-stage solution. After 460 ℃×1 h+480 ℃×0.5 h double-stage solution treatment, the volume fraction of the second phase in 7075 aluminum alloy is 0.303%, the grains are uniform and fine, and the solution effect is ideal. The hardness, tensile strength and elongation of 7075 aluminum alloy reach 199 HV5, 637 MPa and 14.1% respectively after 460 ℃×1 h+480 ℃×0.5 h+120 ℃×24 h solution and aging treatment, and the comprehensive properties are the best.

  Effect of non-isothermal aging process on microstructure and properties of 7050 aluminum alloy

  Chen Geng, Miao Jingguo, Fang Qin, Sun Wenwen, Zhang Guangming, Wang Zhengyun

  2020, 45(3):  169-173.  doi:10.13251/j.issn.0254-6051.2020.03.033

  Abstract ( 25 )   PDF (3082KB) ( 30 )  

  Effects of different non-isothermal aging processes on the microstructure, fracture morphology and properties of 7050 aluminum alloy were studied by using TEM, SEM, Vickers hardness tester, electronic universal testing machine and eddy current conductivity tester, then the properties of the aged alloy were compared with that in T74 state. The results show that, after aging at 190 ℃, the main intracrystalline precipitation phase is η′ and the phase spacing is relatively large. The intragranular precipitates increase and the spacing decreases with the decrease of the aging temperature, and accompanied by secondary precipitation of needle-like precipitates. The precipitates at the grain boundary become coarser continuously, and tend to change from continuous to necklace-like to semi-continuous then to disconnected distribution, and the width of PFZ (precipitate-free zone) has little change. The hardness and tensile strength of the alloy increase first and then decrease, their peak values can be obtained when aged at 130 ℃. The conductivity of the alloy shows a monotonous upward trend and it tends to be stable when aged at 110 ℃. Compared with that in T74 state, the alloy can obtain a better comprehensive properties after solution treatment at (475+3) ℃ for 40 min and non-isothermal aging from 210 ℃ to 130 ℃ by a cooling rate of 20 ℃/h, with a reduction of the process time of 24 h.

  Effect of nitriding temperature on microstructure and properties of QPQ treated 40Cr alloy steel

  Tang Cai, Chen Bo

  2020, 45(3):  174-177.  doi:10.13251/j.issn.0254-6051.2020.03.034

  Abstract ( 28 )   PDF (2284KB) ( 32 )  

  Microstructure of QPQ treated 40Cr alloy steel under different nitriding temperature was observed and analyzed by means of optical microscopy (OM), Vickers hardness test and pin-disc friction and wear test, the hardness gradient and wear weight loss of the carburized layer were carried out, and the morphologies of the worn surface was observed and analyzedby using SEM. The results show that after QPQ treatment at different nitriding temperatures, a surface layer consisting of oxide film, compound layer and diffusion layer is formed on the surface of 40Cr steel. However, with the increase of nitriding temperature, the thickness of nitriding layer increases first and then decreases, and the effective depth of nitriding layer reaches 0.14, 0.20, 0.29 and 0.26 mm when thenitriding temperatures are 580, 600, 620 and 640 ℃, respectively. With the increased of nitriding temperature, the wear loss decreases first and then increases, which reaches the lowest value at 620 ℃. The wear forms are all mainly abrasive wear and adhesive wear under those four nitriding temperatures, but with the increase of nitriding temperature which changes the thickness and hardness of the nitrided layer, the wear degree shows a gradual decreasing trend.

  Heat treatment technologies and its application of heavy duty gears

  Fu Haifeng, Li Qiao, Xu Yueming

  2020, 45(3):  178-185.  doi:10.13251/j.issn.0254-6051.2020.03.035

  Abstract ( 40 )   PDF (786KB) ( 60 )  

  Heavy duty gear refers to the gear with large transmission power, large load, low speed and large impact load. Therefore, it is required to have excellent wear resistance, high contact fatigue strength and bending fatigue strength, so it is necessary to modify its surface in order to improve its surface hardness and service life. The common surface modification methods of the heavy duty gears are carburizing heat treatment, nitriding heat treatment and induction quenching and tempering treatment. In this paper, the research status and progress of the above three kinds of heat treatment of the heavy duty gears are reviewed, and the application prospect of vacuum low pressure carburizing for heavy duty gears is also proposed.

  Effect of doping design on tribological performances of DLC coating in seawater

  Liu Mengqi, Wang Jianqiang, Wang Yu

  2020, 45(3):  186-190.  doi:10.13251/j.issn.0254-6051.2020.03.036

  Abstract ( 29 )   PDF (1192KB) ( 25 )  

  Diamond-like carbon coatings with different doping designs (DLC, Cr/DLC and WC/DLC) were prepared on the silicon wafer and 316 stainless steel substrate surface using UDP650 closed-field unbalanced magnetron sputtering system. The structure and mechanical properties of all the coatings were measured by means of SEM, Raman, hardness tester and scratch tester. The tribological performances of these coatings in the air and seawater environments were examined by friction testing machine. The results show that Cr- or WC-doping can significantly promote the graphitization of the DLC coating. Meanwhile, it can improve the adhesion strength and toughness of the DLC coating. In the friction and wear test, due to the lubricating effect of seawater, the friction coefficient and wear rate of all the coatings in the seawater environment is lower than that in the air environment. At the same time, compared with other coatings, the WC/DLC coating exhibits the best tribological properties, mainly depending on its high degree of graphitization, good adhesion and excellent toughness.

  Effect of annealing temperature on microstructure and hardness of aluminum bronze

  Xie Weibin, Liu Gang, Luo Fuxin, Zhou Zhongming, Yang Zhen

  2020, 45(3):  191-195.  doi:10.13251/j.issn.0254-6051.2020.03.037

  Abstract ( 64 )   PDF (2602KB) ( 30 )  

  The evolution of microstructure and hardness of the Cu-Al-Ni alloy during cold-rolling and annealing were investigated by using optical microscopy, scanning electron microscopy, XRD and Vickers hardness tester. The effect of annealing temperature on annealing softening of the Cu-Al-Ni alloy was analyzed. The results show that the microstructure of Cu-Al-Ni alloy after water quenching at 950 ℃ consists of α phase matrix with fcc structure and β phase with bcc structure. The β distributed at grain boundary has small effect on hardness. The hardness significantly increases to 270 HV0.5 in the alloy after cold rolling due to the increase of dislocation strengthening effect. An obvious softening occurs in the cold-rolled Cu-Al-Ni alloy after annealing above 400 ℃, which is attributed to the decrease in dislocations resulted from the recrystallization process. In addition, the recrystallization temperature of the Cu-Al-Ni alloy is above 300 ℃, which is higher than that of pure copper. It is indicated that the addition of Ni and Al could significantly increase the recrystallization temperature and improve the softening resistance.

  Effect of tempering process on microstructure and properties of 1Cr12Ni3MoVN steel

  Yan Lei, Li Xuming, Li Kaifeng, Ma Fengchun

  2020, 45(3):  196-199.  doi:10.13251/j.issn.0254-6051.2020.03.038

  Abstract ( 61 )   PDF (1861KB) ( 26 )  

  Microstructure and mechanical properties of 1Cr12Ni3MoVN steel were studied by means of microstructure analysis, tensile test at room temperature, impact test and hardness test. The results show that with the increase of tempering temperature, the precipitates of 1Cr12Ni3MoVN steel increase, which has a strengthening effect on strength and impact properties of the material. As the carbides aggregate and grow up, the microstructure of matrix tends to change from martensite to tempered sorbite; the segregation of impurity elements at the grain boundary reduces the fracture resistance of the material, the impact toughness decreases, and therefore the tempering temperature should be lower. With the extension of the tempering time at 565 ℃, the tensile strength, yield strength and hardness of 1Cr12Ni3MoVN steel decrease, the plasticity changes little, the impact absorbed energy increases slightly, so the tempering holding time should not be too long. With the decrease of tempering cooling speed, the strength of 1Cr12Ni3MoVN steel increases first and then decreases, the plasticity changes little, the impact absorbed energy decreases significantly, and the hardness changes little, so it is recommended to use air cooling for tempering cooling. The optimal heat treatment process of tempering is 565 ℃ for 2 h, air cooling.

  Effects of tempering temperature and time on microstructure and properties of 2.25Cr-1Mo-0.25V steel

  Zhang Guangwei, Ma Douqin, Lin Yichou, Kong Yuting, Li Jie, Sun Bin

  2020, 45(3):  200-203.  doi:10.13251/j.issn.0254-6051.2020.03.039

  Abstract ( 24 )   PDF (3642KB) ( 34 )  

  The microstructure, properties and fracture morphology of 2.25Cr-1Mo-0.25V steel tempered respectively at 690 ℃ and 705 ℃ for 1-150 h were studied by using optical microscope, scanning electron microscope, tensile test and impact test. The results show that tempering temperature and tempering time have great influence on the microstructure, strength and toughness of the tested steel. In the studied range of temperature, the strip-like carbides in the microstructure are gradually spheroidized and gathering towards the grain boundary with the extension of tempering time. With the increase of tempering time, the strength index shows a tendency of gradual stability after a sharp decline, but the toughness index first increases, then decreases and stabilized. In this study, the reduction of area and the impact toughness with the change of tempering time show the same trend at tempering temperatures of 690 ℃ and 705 ℃.

  Effect of quenching temperature on metallographic structure and properties of G105 steel

  Luo Xiaowei

  2020, 45(3):  204-207.  doi:10.13251/j.issn.0254-6051.2020.03.040

  Abstract ( 34 )   PDF (1821KB) ( 32 )  

  Microstructure and properties of G105 steel, which was quenched at 890, 910 and 930 ℃ respectively for 150 min then tempered at 630 ℃ for 180 min, were studied by using hardness tester, tensile tester, impact tester and optical microscope. The results show that, with the increase of quenching temperature, the hardness of the steel increases. After the tempering treatment, there is no significant difference in the tempering hardness (33.2 HRC and 32.7 HRC) when the quenching temperature is 890 ℃ and 910 ℃ respectively, while the tempering hardness of tested steel quenched at 930 ℃ increases by about 1.5 HRC. The strength of the steel increases with the increase of quenching temperature, but the impact toughness increases firstly and then decreases, which is due to the precipitate of granular carbides, resulting in the impact toughness decrease. So the G105 steel quenched at 910 ℃ has better comprehensive mechanical properties.

  Determination and analysis of CCT curves of R4 (22MnCrNiMo) steel for mooring chain

  Fang Guangjin

  2020, 45(3):  208-210.  doi:10.13251/j.issn.0254-6051.2020.03.041

  Abstract ( 26 )   PDF (2213KB) ( 29 )  

  The expansion curve of R4 (22MnCrNiMo) steel was measured by DIL805A thermal expansion instrument. CCT curves of the steel were drawn by metallographic and hardness test. The effects of different cooling rates on microstructure transformation of the steel were studied. The results show that the critical transition point of R4 (22MnCrNiMo) steel is: Ar₃=819.5 ℃, Ar₁=778.5 ℃. When the cooling rate is in the range of 0.1-0.5 ℃/s, the microstructure obtained by cooling is mainly lower bainite+retained austenite+small amount of martensite structure, only a small amount of lower bainite structure is obtained when the cooling rate reaches 3 ℃/s, as the cooling rate further increases, the microstructure is lath-like, needle-shaped martensite+residual austenite structure.

  Effect of pierced billet cooling rate before reheating on online normalization process of E470 steel pipes

  Tian Yan, Xia Wenbin, Zhou Yong, Zhao Yinghui

  2020, 45(3):  211-216.  doi:10.13251/j.issn.0254-6051.2020.03.042

  Abstract ( 27 )   PDF (3889KB) ( 20 )  

  When the pierced billets were cooled by two different rates before reheating, the E470 steel pipes manufactured by online normalization process were found to have performance anomaly. The analysis results show that, when the pierced billet cooling rate exceeds the critical cooling rate of bainite during 719-600 ℃, the austenite does not transform into ferrite and pearlite completely during the cooling process but partial undercooled austenite can be found. When the undercooled austenite is reheated, it continues to grow into coarse grains and transforms into bainite during the consequential cooling process, the final microstructure is composed of coarse bainite, ferrite, and pearlite, so that the impact toughness of the material reduces greatly. When the cooling rate of pierced billet does not exceed the critical cooling rate of bainite during 719-600 ℃, the final microstructure is composed of refined ferrite and pearlite, so the good match of strength and toughness can be achieved. In order to ensure the online normalization effect, it is proposed that the cooling rate of the pierced billet after piercing rolling shall be controlled as one important process parameter.

  Development of SCM435 cold heading bainitic steel wire rod

  Li Weilong, Yang Xiaojun, Zeng Fanzheng

  2020, 45(3):  217-219.  doi:10.13251/j.issn.0254-6051.2020.03.043

  Abstract ( 25 )   PDF (1240KB) ( 27 )  

  Adding strong carbide forming elements in SCM435 cold heading steel reduces the diffusion rate of carbon atoms and results in longer spheroidizing annealing time. By controlling the rolling temperature and post-rolling cooling process, bainite-dominated transformation structure can be obtained, and rapid spheroidization of the matrix structure can be achieved in subsequent spheroidizing annealing process. By comparison, the spheroidizing annealing time can be shortened by about 50%, uniform and fine spheroids can be obtained after spheroidizing, which can meet the cold heading performance requirements of the customers, and achieve the goal of energy saving with emission reduction.

  Optimization of extrusion and annealing processes for FeCrAl stainless steel cladding pipes

  Pan Qianfu, Zhao Yong, Zhang Yiyong, Zheng Jiyun, Liu Chaohong, Wang Yurong, Jiang Mingzhong

  2020, 45(3):  220-225.  doi:10.13251/j.issn.0254-6051.2020.03.044

  Abstract ( 32 )   PDF (4726KB) ( 24 )  

  Microstructure and precipitates of the FeCrAl stainless steel before and after extrusion were investigated, the microstructure, precipitates, recrystallization and mechanical properties of it after annealing process were also investigated by using optical microscope (OM), scanning electron microscope (SEM), electron backscattered diffraction (EBSD) and universal tensile testing machine. The results show that the Nb content has a significant impact on the precipitation of secondary phases, especially, the precipitation temperature and amount of the Laves phase both increases under the high Nb content. Decreasing the extrusion temperature has contributed to the formation of fine dispersed second phases of FeCrAl stainless steel cladding pipes. With the increase of annealing temperature, the precipitation quantity of fine dispersed phases increases first and then decreases. Under the same annealing process, the room temperature mechanical properties of 800 ℃ extruded tubes are better than those of 950 ℃ extruded tubes.

  Analysis on residual stress of Q345 steel in laser cladding process

  Liu Xiaodong, Jiang Honglei, Xie Meng

  2020, 45(3):  226-230.  doi:10.13251/j.issn.0254-6051.2020.03.045

  Abstract ( 26 )   PDF (2188KB) ( 24 )  

  Aiming at the problems of cracking on surface of the cladding layer due to residual stress, a reasonable experiment was designed to obtain the residual stress value of the workpiece during the cladding and cooling process. Different process routes are compared according to the value of residual stress, the results show that the pre-bending of the workpiece can significantly reduce the residual stress. The temperature field and stress field of the workpiece are simulated by using ANSYS. It can be concluded that longitudinal stress caused by longitudinal plastic distortion of workpiece is the main component of residual stress.

  Tensile fracture analysis of 5B70 aluminum alloy under different strain rates

  Zhou Wei, Jiang Feng, Lai Songbai, Fang Jie, Tong Mengmeng

  2020, 45(3):  231-234.  doi:10.13251/j.issn.0254-6051.2020.03.046

  Abstract ( 45 )   PDF (2307KB) ( 28 )  

  Tensile fractures of 5B70 aluminum alloy at different strain rates were investigated. The results show that as the strain rate increases, the elongation of the alloy decreases. Fracture analysis shows that the lower the strain rate, the greater are the number of dimples in the fracture and the deeper depth, showing obvious high ductile fracture. With the increase of strain rate, the quasi-cleavage plane appears, the alloy is biased towards brittle fracture. Secondary cracks also occur at lower strain rates. As the strain rate increases, the grain elongation on the side of the alloy fracture decreases, and a fine precipitate phase appears.

  Failure analysis of early cracking of aluminum alloy casting die made of 8418 steel

  Ma Rui, Chen Xichun, Jin Linkui, Yang Weidong, Yang Hao, Li Zhe, Li Liang

  2020, 45(3):  235-239.  doi:10.13251/j.issn.0254-6051.2020.03.047

  Abstract ( 40 )   PDF (4790KB) ( 34 )  

  The chemical composition, surface defect morphology and microstructure of failure parts of the aluminum alloy die-casting mold made of 8418 steel were analyzed by means of direct reading spectrometer, digital Rockwell hardness tester, optical microscope, scanning electron microscope and energy spectrometer. The results show that, the grain size of matrix is coarse. The average diameter of coarse grains is 1647 μm, and the degree of material superheat is extremely serious. The original coarse grains lead to an increase of the quenching stress after the final heat treatment, and thus the fracture morphology of cleavage characteristic and intergranular dimple are observed. Carbides were precipitated along grain boundaries during the subsequent slow cooling, as a result, the intergranular strength is decreased remarkably. Under the influence of the quenching microstructure stress, internal crack along the grain boundary is formed. The reason for the early cracking of the aluminum alloy die-casting mold is the overheated coarse structure and internal crack along the grain boundary, which greatly reduces the strength and toughness of the material. During the use of the mold, it is difficult to withstand the working stress of the die-casting process, and finally the crack is generated at the minimum position of the surface of the mold cavity, that is, the position where the stress concentrated maximumly.

  Medium frequency unilateral induction quenching process of spring lamination and corresponding inductor design

  Liang Bo, Yao Honghan, Hu Xiaofei, Sun Xiaoting

  2020, 45(3):  240-241.  doi:10.13251/j.issn.0254-6051.2020.03.048

  Abstract ( 27 )   PDF (930KB) ( 120 )  

  In order to solve uneven hardness resulted fracture problems of the elastic coupling spring laminations paired with the spline shaft on diesel engine during the running of diesel locomotive, a medium frequency induction hardening process was adopted to replace the original laser surface quenching process, and a new medium frequency quenching inductor with corresponding unilateral induction quenching scheme was designed. The results show a good effect after loading on the locomotives.

  High-frequency vacuum electromagnetic induction pulse carburizing and its application

  Song Kangjie, Zhao Xunfeng, Feng Zhiguo, Liu Jing

  2020, 45(3):  242-246.  doi:10.13251/j.issn.0254-6051.2020.03.049

  Abstract ( 31 )   PDF (1492KB) ( 27 )  

  Aiming at the problems of slow heating rate and long process period of the conventional vacuum resistance heating carburizing equipment, a high-frequency electromagnetic induction vacuum pulse carburizing method was proposed, and an electromagnetic induction vacuum pulse carburizing equipment based on PLC control was independently developed. It has a fast heating rate, short process cycle, online monitoring of pressure and temperature, automatic mixing of different proportions of carburizing atmosphere and program control of the entire process of electromagnetic induction vacuum pulse carburizing. It can complete different “strong seepage-diffusion” time ratios and can change pressure and temperature respectively with time in the range of -80-0 kPa and 300-1300 ℃. By using the equipment, a pulse carburizing process with 8 different “strong seepage-diffusion” time ratios was carried out on 20CrMnTi steel, and a carburized layer containing Fe₃C, Fe and other carbide phases was prepared on the surface of the steel, the highest hardness and the thickness of the carbonized layer reach 835.2 HV0.025 and 1398 μm respectively, which are superior to that obtained by the conventional vacuum resistance carburizing method.