20 February 2018, Volume 42 Issue 2
    

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  • Effect of Microaddition of Vanadium on Superplasticity of CrNiMo Series Forged Steel
    GUO Hongwei, HAN Jianmin, LI Zhiqiang, LIU Xiaolong
    Materials For Mechanical Engineering. 2018, 42(2): 1-7,94. https://doi.org/10.11973/jxgccl201802001
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    The tensile properties at 25,400,600,800℃ and tensiled microstructure evolution of CrNiMo series forged steel with and without vanadium were studied and compared. The effect of vanadium on the superplasticity of the tested steels was analyzed. The results show that with the test temperature rising, the strength decreased and the plasticity increased of the two tested steels. The elongation at 800℃ of the tested steel without vanadium was 71%, while that after the addition of vanadium reached 154%, indicating a superplasticity. The microstructure of the tested steel without vanadium was homogeneous lath martensite, while that with vanadium was mainly martensite+retained austenite+vanadium carbide. Vanadium carbide provided fine grain strengthening and precipitation strengthening. High temperature softening weakened the strengthening effect of vanadium carbide but enhanced its plasticizing effect.
  • Crack Propagation Behavior of TiB+TiC+La2O3 Ternary Particulate Reinforced IMI834 Titanium Matrix Composite
    FENG Jiahao, HAN Yuanfei, HUANG Guangfa, MAO Jianwei, LÜ Weijie
    Materials For Mechanical Engineering. 2018, 42(2): 8-12. https://doi.org/10.11973/jxgccl201802002
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    TiB+TiC+La2O3 ternary particulate reinforced IMI834 titanium matrix composite was in-situ synthesized, and then forged and treated by stress relief annealing. The microstructure, tensile properties and the crack propagation behavior of the composite were investigated. The results show that the in-situ synthesized TiB, TiC and La2O3 reinforcements dispersed homogenously in the titanium alloy matrix, forming a clean interface, and some TiB reinforcements were broken. The yield and tensile strength of the composite were 1 010 MPa and 1 150 MPa, respectively, improved by 9% and 8% compared with those of IMI834 titaniuim alloy. Intergranular crack propagation mainly occurred in the region containing fewer defects of the composite, and the crack propagation path was tortuous. In the region containing more defects, defects caused by broken reinforcements changed the crack propagation direction.
  • Dissolution of Second Phase during Austenitization and Characteristics of Quenching Phase Transformation in SV30 Bearing Steel
    FANG Zhibo, ZHANG Yanjun, MIN Yongan, GU Jiaming, CHEN Pengfei
    Materials For Mechanical Engineering. 2018, 42(2): 13-17,68. https://doi.org/10.11973/jxgccl201802003
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    SV30 bearing steel was quenched at 990-1 070℃ for 10 min and at 1 030℃ for 0-100 min by DIL805A dilatometer. The microstructure, hardness, residual austenite content of the tested steel before and after quenching were studied. The dissolution of second phase and characteristics of quenching phase transformation were analyzed. The results show that when the quenching temperature rose from 990℃ to 1 070℃, the dissolution rate of M23C6 carbides in the steel became quicker. M2N nitrides dissolved in large quantities only when the temperature reached 1 050℃ or higher. When holding at 1 070℃ for 10 min, the carbides were completely dissolved into the austenite while about 6.3wt% nitrides still remained undissolved. After quenching at 1 010-1 030℃ for 10-30 min, the hardness of the tested steel reached over 58 HRC; after quenching at 1 030-1 070℃, the residual austenite of about 30vol%-50vol% were retained in the tested steel.
  • Effects of Brazing Temperature on Microstructure and Mechanical Properties of Brazing Joint between YG8 Cemented Carbide and 1Cr18Ni9Ti Stainless Steel
    CHEN Sijie, YAN Ruifeng, LI Bao
    Materials For Mechanical Engineering. 2018, 42(2): 18-21,26. https://doi.org/10.11973/jxgccl201802004
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    Using L304 silver solder as brazing filler metal, YG8 cemented carbide and 1Cr18Ni9Ti stainless steel were welded by high temperature argon gas-shielding brazing. The effects of brazing temperature on microstructure and mechanical properties of the brazing joint were studied by microstructure observation, energy spectrum analysis, hardness test and room-temperature shear test. The results show that with the increase of brazing temperature, the microstructure of joint was getting more and more uniform and compact. The brazing filler metal was melted gradually and filled the weld seam fully, and the brazing quality was improved. However, when the brazing temperature was higher than 920℃, the brazing joint exhibited overheating phenomenon, the microstructure became coarse and the brazing quality became poor. With the increase of brazing temperature, the shear strength and micro-hardness of brazing joint increased first and then decreased. When the brazing temperature was 910℃, the shear strength of brazing joint was 147.5 MPa and the micro-hardness was 194 HV, indicating that the brazing joint had the best comprehensive mechanical properties.
  • Microstructure of Pressure Boundary Welded Joint of CAP1400 Steam Generator
    XUE Xiaohuai, WANG Zhiying, LI Tianyu, LI Zhiyuan, YANG Juwen, ZHANG Wenyang, ZHANG Maolong
    Materials For Mechanical Engineering. 2018, 42(2): 22-26. https://doi.org/10.11973/jxgccl201802005
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    Microstructures of the pressure boundary welded joint of CAP1400 steam generator were studied with optical microscope and scanning electron microscope. The pressure boundary joint is made up of SA508Gr.3Cl.2 steel base metal, heated affected zone, surfacing layer and butt weld. The results show that the base metal of the joint had a fine tempered bainite microstructure and the heat affected zone had a coarse martensite microstructure. The microstructure of the stainless steel surfacing layer was mainly composed of columnar austenite and little ferrite, and that of the nickel based alloy surfacing and butt weld mainly consisted of columnar austenite. Austenite recrystallization occurred both in the stainless steel surfacing layer and in the nickel based alloy butt weld because of the thermal cycling effect of the multi-layer and multi-pass welding. The carbides precipitated in the austenite matrix.
  • Work-Hardening/Softening Behavior and Temperature Evolution of AZ31B Magnesium Alloy During High Cycle Fatigue Process
    LIU Fei, YAN Zhifeng, HE Xiuli, WANG Fenglan, WANG Zhongnan, LI Chenghao, LI Yonglian
    Materials For Mechanical Engineering. 2018, 42(2): 27-30,34. https://doi.org/10.11973/jxgccl201802006
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    The temperature evolution of AZ31B magnesium alloy in fatigue and tensile processes was measured with infrared imager. The work-hardening/softening behavior of the alloy during fatigue process was studied by conducting tensile tests on the fatigued AZ31B magnesium alloy samples. The results show that the temperature evolution process of the AZ31B magnesium alloy during fatigue was divided into five stages including initial temperature rising, temperature falling, temperature stabilizing, rapid temperature rising and natural temperature falling after fracture in sequence when the maximum stress during fatigue was higher than the fatigue strength of the alloy. The tensile strength of the fatigued sample increased and then decreased and then increased with the number of cycles increasing, due to the fact that the work-hardening and softening occurred in turn of the samples. With the increase of the cyclic maximum stress, the tensile strength of the fatigued sample increased because of the different work-hardening levels caused with the different stress levels during fatigue.
  • Micro-mechanical Properties at Grain Boundaries of IF Steel and Their Effect on Macro-mechanical Properties
    SHEN Yu, ZHANG Ke, CEN Feng, CHU Feng
    Materials For Mechanical Engineering. 2018, 42(2): 31-34. https://doi.org/10.11973/jxgccl201802007
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    The micro-mechanical properties at grain boundaries of interstitial-free steel (IF steel) with different grain size were characterized by nanoindentation technique, and the Vickers hardness and tensile properties of the steel were tested. The effect of micro-mechanical properties at the grain boundaries on the macro-mechanical properties was discussed. The results show that the nanoindentation hardness and elastic modulus of the grains with different size were basically the same. The average nanoindentation hardness of the sample containing relatively fine grains was about 3.12 GPa, higher than that (2.36 GPa) with relatively coarse grains, and the elastic modulus was about 205 GPa, lower than that (210 GPa) with relatively coarse grains. The Vickers hardness and tensile strength of the sample containing relatively fine grains were also higher than those containing relatively coarse grains. The nanoindentation hardness at the grain boundaries (above 3.25 GPa) was higher than that (2.61 GPa) in the grains while the elastic modulus was slightly lower, which was the main reason for the difference between the macro-mechanical properties.
  • Dissolution Behavior of Second Phase Particles in 960 MPa Grade Nb-Ti Microalloyed Ultra-High Strength Steel
    HUI Yajun, PAN Hui, LI Wenyuan, LIU Kun, CHEN Bin, CUI Yang
    Materials For Mechanical Engineering. 2018, 42(2): 35-39. https://doi.org/10.11973/jxgccl201802008
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    The dissolution behavior of second phase particles in 960 MPa grade Nb-Ti microalloyed ultra-high strength steel after heat treatment at different temperatures for different times was studied by transmission electron microscope and energy dispersive X-ray analyzer. The results show that the test steel contained square TiN particles with size greater than 1 μm precipitated during solidification, square and ellipsoidal TiS or Ti (C, S) particles with size of 200 nm-1 μm, and square, spherical and ellipsoidal (Nb, Ti) (C, N) precipitates with size less than 500 nm precipitated by strain during forging. With the increase of heating temperature, the number of the second phase particles decreased and the size increased. With the extension of holding time, the number of the small second phase particles decreased, while that of large second phase particles increased and whose edges became blurred. These particles were composite precipitates containing niobium and titanium. Considering the full dissolution of carbonitride containing niobium and titanium and the suitable grain size of austenite, heating at 1 250℃ for 80 min was relatively appropriate for 960 MPa grade Nb-Ti microalloyed ultra-high strength steel.
  • Continuous Cooling Transformation of Austenite in 15CrNiMn Steel for Drilling Bit
    HOU Huanyu, LIANG Aiguo, AN Zhiguo, CHEN Hongwei, SHI Yuan
    Materials For Mechanical Engineering. 2018, 42(2): 40-42. https://doi.org/10.11973/jxgccl201802009
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    The austenite continuous cooling transformation (CCT) curves of 15CrNiMn steel for drilling bit were determined by DIL805L dilatometer. The phase transformation, microstructure and hardness of the tested steel at different cooling rates were studied. The results show that the bainite structure was obtained in the tested steel over a large range of cooling rates, and the transformation zones of ferrite or pearlite and bainite were separated completely. With the cooling rate increasing, the microstructure of the tested steel became finer and the hardness increased obviously.
  • Continuous Cooling Transformation of Supercooled Austenite of 46MnVS6 Non-quenched and Tempered Steel
    SHI Yuan, DAI Guanwen, AN Zhiguo, LUO Yang
    Materials For Mechanical Engineering. 2018, 42(2): 43-46,73. https://doi.org/10.11973/jxgccl201802010
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    The microstructure and micro-hardness of complete austenitization 46MnVS6 non-quenched and tempered steel were analyzed after cooling to room temperature at different cooling rates by using thermal dilatometer, optical microscope and Vickers hardness tester. The continuous cooling transformation (CCT) curves of supercooled austenite were tested. The influence of alloying element and cooling rate on the continuous cooling transformation of supercooled austenite was discussed. The results show that the CCT curve could be divided into high temperature transition region, middle temperature transition region and low termperature transition region, and the middle temperature transition region and low temperature transition region were separated. The microstructure was mainly ferrite and pearlite when the cooling rate was below 2℃·s-1. With the increase of cooling rate, the content and average grain size of ferrite and pearlite decreased, and the content of martensite increased. The main microstructure was martensite when the cooling rate was over 5℃·s-1. With the increase of cooling rate from 0.5℃·s-1 to 60℃·s-1, the micro-hardness of 46MnVS6 steel increased from 285 HV1 to 683 HV1.
  • Formation Mechanism and Solutions of Coarse Intermetallic Compound in Modified 3003 Aluminum Alloy
    ZHANG Haifeng, CHEN Qin
    Materials For Mechanical Engineering. 2018, 42(2): 47-51,57. https://doi.org/10.11973/jxgccl201802011
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    The morphology and effect on properties of coarse intermetallic compound in modified 3003 aluminum alloy were studied by chemical composition analysis, microstructure observation, micro-hardness testing, scanning electron microscopy observation and energy spectrum analysis, and the forming mechanism was discussed. The solutions of controlling the coarse intermetallic compound were proposed. The results show that there was coarse intermetallic compound with average size larger than 100 μm in modified 3003 aluminum alloy ingot. The average hardness of the intermetallic compound was 315 HV and much higher than that of matrix. The formation of the intermetallic compound was related to the segregation of iron, titanium and manganese elements. When the mass fraction of iron element in the modified 3003 aluminum alloy was controlled below 0.13%, the coarse intermetallic compound could be avoided.
  • In-situ Synthesized TiN/Ti3Al Composite Coating by Laser Gas Nitriding and Its High-Temperature Erosion Resistance
    SU Guanqun, FU Yao, ZHANG Xiancheng, WANG Zhengdong, TU Shantong
    Materials For Mechanical Engineering. 2018, 42(2): 52-57. https://doi.org/10.11973/jxgccl201802012
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    TiN/Ti3Al composite coating was in-situ synthesized on the surface of Ti-6Al-4V alloy by laser gas nitriding technique with the aluminium powder mixed in the nitrogen. The micromorphology, phase composition, hardness distribution and the anti-erosion performance with high-temperature high-velocity steam containing SiC and SiO2 particles of the coating were studied. The results show that the surface hardness of the coating was (1 400±50) HV, four times higher than that of Ti-6Al-4V titanium alloy. After erosion with SiC particles during a relatively short period or with SiO2 particles, the erosion mass loss of the coating increased with the increase of erosion angle, while that of the Ti-6Al-4V titanium alloy decreased. At the same erosion angle, the erosion mass loss of the coating increased with the increase of erosion particle hardness, and that of the Ti-6Al-4V titanium alloy followed this rule at relatively small erosion angles while changed little at relatively large erosion angles.
  • Preparation,Characterization and Adsorption Capacity to Rhodamine B of Activated Carbon/Expanded Graphite Composite
    FU Meng, LIU Peng, CHEN Zhigang
    Materials For Mechanical Engineering. 2018, 42(2): 58-63. https://doi.org/10.11973/jxgccl201802013
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    Activated carbon/expanded graphite (AC/EG) composite was prepared by impregnation activation process using fructose as precursor and phosphoric acid as activating agent. The microstructure and adsorption capacity to Rhodamine B of the composite were studied by using X-ray diffraction, scanning electron microscope, nitrogen adsorption-desorption tester, Fourier transform infrared spectroscope and ultraviolet-visual spectrophotometer. The formation mechanism of AC membrane was discussed. The results show that the good flowability of fructose as precursor was the key factor for achieving the EG coated with AC membrane. AC/EG composite had features of hierarchical porous and pores connected with each other. The specific surface area and mesopore volume of composite were both the largest which were 863.34 m2·g-1 and 0.396 cm3·g-1, respectively, and the adsorption capacity to Rhodamine B was 626.12 mg·g-1 when the mass of added phosphoric acid was 7.2 g, activation temperature was 500℃ and activation time was 2 h.
  • Process Optimization of QPQ Complex Salt Bath Treatment of Ti6Al4V Titanium Alloy
    LIU Xiang, LIU Liguo, SUN Baoyong, LI Bingyue, KE Xuefeng
    Materials For Mechanical Engineering. 2018, 42(2): 64-68. https://doi.org/10.11973/jxgccl201802014
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    The microstructure and phase composition of Ti6Al4V titanium alloy after QPQ (quenching-polishing-quenching) complex salt bath treatment were analyzed by scanning electron microscope and X-ray diffractometer. The effect of carbonitriding time, carbonitriding temperature, oxidation time and oxidation temperature on wear resistance of the titanium alloy was studied by using orthogonal test and compared with titanium alloy samples treated with salt bath nitrocarburizing. The results show that after QPQ complex salt bath treatment, a permeation layer formed on the surface of Ti6Al4V titanium alloy. There were oxidation layer, compound layer and diffusion layer from the surface to the interior of the permeation layer. When the titanium alloy was carbonitrided at 610℃ for 1.5 h and oxidated at 400℃ for 40 min, the average wear amount of titanium alloy was the minimum, which was 1.11 mg and reduced by 38.3% of the carbonitriding sample. When the titanium alloy was carbonitrided at 580℃ for 3.5 h and oxidated at 400℃ for 40 min, the average friction coefficient was the minimum, which was 0.246 7 and reduced by 21.8% of the carbonitriding sample. The wear resistance of titanium alloy treated by optimized QPQ complex salt bath treatment was improved obviously.
  • Microstructure and Properties of Bobbin Tool Friction Stir Welded Joint of 5 mm Thick 6005A-T6 Aluminum Alloy
    DAI Zhongchen, YUN Zhonghuang, FU Ningning, JI Hua, ZHU Jun, DENG Jianfeng, GUO Weiqiang
    Materials For Mechanical Engineering. 2018, 42(2): 69-73. https://doi.org/10.11973/jxgccl201802015
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    Five-millimeter thick 6005A-T6 aluminum alloy was butt-welded by friction stir welding with self-designed bobbin tool. The microstructure and properties of the joint were studied. The results show that the weld was formed well. The welded joint consisted of weld nugget, thermo-mechanically affected zone, heat affected zone and base metal. A distinct boundary existed between the heat affected zone and thermo-mechanically affected zone at the advancing side. The microhardness at cross-section of the joint showed a W-shape distribution and reached the lowest value of 60 HV at the interface between thermo-mechanically affected zone and heat affected zone at the advancing side. The tensile strength of the joint was 205 MPa. The joint fractured in a ductile manner at the interface between thermo-mechanically affected zone and heat affected zone at the advancing side. The conditional fatigue limit of the joint was 96.6 MPa. The cracks initiated at the oxide inclusion near the upper surface. The catastrophic rupture region of the fatigue fracture showed dimple morphology.
  • Influence of Surface Explosion Spraying WC Coating on Fatigue Resistance of GCr15 Bearing Steel
    XIONG Xiaochen, YAN Nu, JIANG Yu
    Materials For Mechanical Engineering. 2018, 42(2): 74-77. https://doi.org/10.11973/jxgccl201802016
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    A layer of WC coating was coated on the surface of GCr15 bearing steel by explosion spraying technique. The fatigue resistance of the bearing steel after explosion spraying was studied by fatigue tests and compared with that of bearing steel without explosion spraying. The results show that the fatigue resistance and fatigue life of GCr15 bearing steel decreased after explosion spraying. The fatigue cracks of the bearing steel without explosion spraying mainly originated from the surface machining tiny scratches, non-metallic inclusions and crystal slip belts. The fatigue cracks of the bearing steel after explosion spraying mainly originated from the cavity defects in the WC layer or non-metallic inclusions in the bearing steel near the interface.
  • Comparison between Microstructures and Properties of Weldox960 Steel Welded Joints by Laser-MAG Welding and MAG Welding
    LI Yi, ZHU Pengxiao, CHEN Bo, FAN Huiji, CUI Haixia, TANG Cai, JIN Xin
    Materials For Mechanical Engineering. 2018, 42(2): 78-81,87. https://doi.org/10.11973/jxgccl201802017
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    Weldox960 steel plates were welded by laser-metal active gas arc welding (Laser-MAG welding) and MAG welding, and then the microstructures and properties of the welded joints by two processes were compared and analyzed. The results show that the average grain size in coarse-grained heat affected zone of the Laser-MAG welded joint was relatively small, which was 48 μm, while that of the MAG welded joint was 95 μm. The microstructures of the two welded joints were basically the same; the weld metal was composed of fine granular bainite, the fine grained zone consisted of fine lath martensite and granular bainite, and the partial phase transition zone consisted of ferrite and granular bainite. The heat affected zone of the Laser-MAG welded joint was narrower than that of the MAG welded joint and had a relatively narrow softening band. The tensile performance and impact performance were better than those of the MAG welded joint, and the conditional fatigue limit was 320 MPa, higher than that of the MAG welded joint.
  • Corrosion Behavior of 2205 Duplex Stainless Steel in Severe Environment of Oilfield
    ZHAO Guoxian, WANG Yaqian, JI Ling, LIANG Jianjun, XIE Junfeng, LÜ Xianghong
    Materials For Mechanical Engineering. 2018, 42(2): 82-87. https://doi.org/10.11973/jxgccl201802018
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    The corrosion behavior of 2205 duplex stainless steel under the simulated conditions of the whole process of simulated acidification well completion and production was studied by the combination of electrochemical analysis. The results show that the test steel exhibited slightly uniform corrosion in the formation water containing CO2. When the CO2 partial pressure was 4.80 MPa and the experimental temperature was 220℃, the corrosion rate was only 0.002 1 mm·a-1. The test steel had an obvious ferrite phase selective dissolve corrosion during corrosion in the whole process of acidification well completion, with a lowest corrosion rate of 0.523 6 mm·a-1, which was much higher than that in the formation water containing CO2. The test steel was activated in the fresh prepared acid solution, and the corrosion rate was relatively high. In the formation water containing 0.1 MPa CO2, the anodic polarization zone of the test steel showed a passivation phenomenon, and thus the corrosion rate was reduced significantly.
  • Microstructure and Corrosion Resistance of Ni-Co Based Cladding Layers on Surface of ZG45 Steel
    WANG Jianru, YANG Guirong, SONG Wenming, WANG Fuqiang, ZHANG Yufu, LI Jian, MA Ying
    Materials For Mechanical Engineering. 2018, 42(2): 88-94. https://doi.org/10.11973/jxgccl201802019
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    The Ni-Co based cladding layers with different proportions of Ni and Co and those with different mass fractions of WC, graphite (G)+WC were fabricated on the surface of ZG45 steel substrate by vacuum cladding technique. The microstructures, phase composition and corrosion resistance in NaCl solution of the cladding layers were studied. The results show that all the cladding layers had dense microstructures and were metallurgically bonded to the substrate. The main phases of the G+WC/Ni-Co alloy cladding layer were Cr7C3, Cr23C6, Ni3Si, CrB, FeW3C, WC, C and γ-Ni-C solid solution. The corrosion resistance of Ni-Co alloy cladding layers was better than that of substrate and increased with the Co content increasing. The free corrosion current density of both WC/Ni-Co alloy cladding layer and G+WC/Ni-Co alloy cladding layer decreased and then increased with the increase of WC or G content. Localized corrosion mainly occurred on the surface of G+WC/Ni-Co alloy cladding layer, and the localized corrosion pits appeared in the WC and G particle concentrated area.
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