Wen-hao Gong, De-hong Lu, Guang-yu He, Wei Ma, Qing-hua Yan
Effect of volume fraction of metal matrix composites framework on compressive mechanical properties of 3D interpenetrating ZTAp/40Cr architectured composites
The effect of the volume fraction of 3D-metal matrix composites (MMC) framework on the compressive properties of 3D interpenetrating hierarchical ZrO
particle (ZTAp)/40Cr steel composites was investigated. The results showed that the compressive properties of the material tended to decrease as the volume fraction of 3D-MMC framework increased. The composite with 35 vol.% 3D-MMC had a yield strength of 1455.2 MPa and compressive strength of 1612.8 MPa, which occurred at a strain value of 5.6%. Compared to the homogeneously dispersed composite material, the composite with 35 vol.% 3D-MMC had a 144.7% higher yield strength, which occurred at a 20% higher strain. An analysis of the cracks inside the material revealed that the crack was hindered and deflected by the matrix during propagation, which lengthened the crack propagation path and consumed more energy, thus leading to toughening. The results indicated that 3D interpenetrating hierarchical structure had a strengthening and toughening effect on ZTAp/40Cr composites.
2022 Vol. 29 (5): 859-865.
De-kun Liu, Jian Yang, Yin-hui Zhang, Long-yun Xu
Effect of Mo content on nano-scaled particles, prior austenite grains and impact toughness of CGHAZ in offshore engineering steels
The effect of Mo on nano-scaled particles, prior austenite grains and impact toughness of coarse-grained heat-affected zone (CGHAZ) in offshore engineering steels with Ca deoxidation was studied. The heat-affected zone (HAZ) toughness of Mo16 steel is obviously higher than that of Mo8 steel at all the heat inputs of 50, 100, 150 and 200 kJ/cm, with HAZ toughness of both steels decreased with increasing the welding heat input. When the Mo content is increased from 0.08 to 0.16%, the size of nano-scaled particles in HAZ is decreased from 18 to 15 nm, and their number density is increased from 0.7 to 0.9 μm
. Thus, the Zener pinning force is increased, and the prior austenite grain size (PAGS) is decreased, leading to the improved HAZ toughness. Microstructural characterizations show that the nano-scaled particles in both steels are Ti(C, N) with the solute elements of Nb and Mo. The calculated critical particle size of TiN is 10.2 and 8.4 nm in Mo8 and Mo16 steels at 1350 °C, and the particles larger than the critical size are stable during the welding process. From the Zener pinning force calculation, Ti(C, N) particles play the more important role in the pinning effect on the prior austenite grain growth. Based on the regression analysis by the MATLAB results, the predicted values of PAGS at different heat inputs are well fitted with the experimental data.
2022 Vol. 29 (5): 846-858.
Bing Han, Wei-hao Wan, Dan-dan Sun, Cai-chang Dong, Lei Zhao, Hai-zhou Wang
A deep learning-based method for segmentation and quantitative characterization of microstructures in weathering steel from sequential scanning electron microscope images
Microstructural classification is typically done manually by human experts, which gives rise to uncertainties due to subjectivity and reduces the overall efficiency. A high-throughput characterization is proposed based on deep learning, rapid acquisition technology, and mathematical statistics for the recognition, segmentation, and quantification of microstructure in weathering steel. The segmentation results showed that this method was accurate and efficient, and the segmentation of inclusions and pearlite phase achieved accuracy of 89.95% and 90.86%, respectively. The time required for batch processing by MIPAR software involving thresholding segmentation, morphological processing, and small area deletion was 1.05 s for a single image. By comparison, our system required only 0.102 s, which is ten times faster than the commercial software. The quantification results were extracted from large volumes of sequential image data (150 mm
, 62,216 images, 1024 × 1024 pixels), which ensure comprehensive statistics. Microstructure information, such as three-dimensional density distribution and the frequency of the minimum spatial distance of inclusions on the sample surface of 150 mm
, were quantified by extracting the coordinates and sizes of individual features. A refined characterization method for two-dimensional structures and spatial information that is unattainable when performing manually or with software is provided. That will be useful for understanding properties or behaviors of weathering steel, and reducing the resort to physical testing.
2022 Vol. 29 (5): 836-845.
J.L. Guo, T.J. Chen
Effect of surface layer softening from previous electrochemical corrosion on electrochemical cold drawing of Q235 steel bar
The effects of H2SO4 concentration and current in electrochemical corrosion on surface layer softening or plasticizing of Q235 steel bar and their effects on subsequent electrochemical cold drawing (ECD) were investigated. The results indicate that the electrochemical corrosion can soften or plasticize the surface layer of Q235 steel bar and then make the subsequent ECD be conducted more easily. The softening degree and thickness of the surface layer are continuously enhanced with increasing corrosion rate, i.e., increasing H2SO4 concentration or current, due to the generation of more vacancy clusters in deeper regions of surface layer. These vacancy clusters then relax dislocations through being absorbed during ECD, and the formation and movement of additional dislocation flux are thereby enhanced, resulting in the further obvious decrease in the drawing force. It is also due to the enhanced formation and movement of additional dislocation flux that the dislocation density and thus the hardness of the surface layer are decreased, as well as that the texture structure is weakened. These behaviors are enhanced as the corrosion rate increases.
2022 Vol. 29 (5): 819-835.
Xiao-xiao Liu, Zheng Zhang, Jie Zhang, Ran Yang, Cheng-shuang Yu, Jun-wei Qiao, Li-na Han
Enhanced strength and toughness in 40CrNiMo steels by austempering below martensite start temperature
The austempering above and below martensite transition temperature (
) was employed in a medium-carbon low-alloy 40CrNiMo steel, and the bainite and martensite multiphase microstructures with different volume fractions were obtained. Here, the effect of pre-existing martensite on subsequent transformation of bainite microstructure and mechanical properties is focused and researched. The microstructure with a volume fraction of pre-existing martensite (V
), bainite (V
), and martensite/austenite (V
) constituents of approximately 28%, 46%, and 26%, respectively could be obtained by austenitizing below Ms (280 °C) for 1 h, and an optimum combination of strength, ductility, and impact toughness (yield strength of 1420 MPa, ultimate tensile strength of 1795 MPa, total elongation of 7.9%, and V-notch impact value of 37 J) was achieved. The considerable enhancement of mechanical properties in the sample austenitized below Ms is mainly ascribed to the formation of the pre-existing martensite, resulting in an effective reduction in the size of the bainite plates and martensite/austenite constituents.
2022 Vol. 29 (5): 810-818.
Jin-wen Zhang, Yan-guang Cao, Cheng-guo Zhang, Zhao-dong Li, Wen-xian Wang
Effect of Nb addition on microstructure and mechanical properties of 25CrNiMoV (DZ2) steel for high-speed railway axles
The microstructure, precipitates and properties of 25CrNiMoV (DZ2) steel for high-speed railway axles with different Nb contents were investigated by means of optical microscopy, scanning electron microscopy, electron back-scattering diffraction, transmission electron microscopy and physicochemical phase analysis. The results show that the grain size of the original austenite of the test steels decreases from 20.5 to 14.2 and 10.8 μm after adding 0.026 and 0.039 wt.% Nb to a 25CrNiMoV steel, respectively. Moreover, the block width of the tempered martensite in the test steels is refined from 1.91 to 1.72 and 1.60 μm, respectively. MC-type precipitates in 25CrNiMoV steel are mainly VC, while (Nb,V)C gradually precipitates when Nb is microalloyed, and the amount of precipitates increases with increasing Nb content. Through strengthening mechanism analysis, it is found that grain refinement strengthening is the primary way to increase the strength. The improvement in the yield strength with increasing Nb content is attributed to a significant increase in precipitation strengthening, grain refinement strengthening and dislocation strengthening.
2022 Vol. 29 (5): 802-809.
Xin-tian Wang, Hui-bin Wu, Yang Gu, Li-xiong Xu, Peng-cheng Zhang, Qi-bo Tang
Tensile deformation behavior of nickel-free high-manganese austenitic cryogenic-temperature steel
Nickel-free high-manganese austenitic Fe–24.4Mn–4.04Al–0.057C steel was produced by smelting, and the homogenized forged billet was hot-rolled. The plastic deformation mechanism was investigated through tensile testing of the hot-rolled sample. Different characterization techniques such as scanning electron microscopy, transmission electron microscopy, electron backscattered diffraction, and X-ray diffraction were used to analyze the microstructural evolution of steel under different strain levels. The steel had a single austenite phase, which was stable during deformation. After hot rolling, annealing twins were observed in the microstructure of the steel. The steel showed an excellent combination of mechanical properties, like a tensile strength of 527 MPa, impact energy of 203 J at - 196 °C, and an elongation of 67% till fracture. At the initial deformation stage, the dislocations were generated within the austenite grains, entangled and accumulated at the grain boundaries and annealing twin boundaries. Annealing twins participated in plastic deformation and hindered the dislocation movement. As the deformation progressed, the dislocation slip was hindered and produced stress concentration, and the stacking faults evolved into mechanical twins, which released the stress concentration and delayed the necking.
2022 Vol. 29 (5): 793-801.
Hui Wang, Chao Liu, Hong-wei Xing, Jin-hu Wu, Wen-long Lin, Shuo Li, Guo-hui Ding, Yu-zhu Zhang
High-temperature modification and air-quenching granulation of steel slag
To solve the problem of difficult utilization of steel slag, the liquid steel slag was modified and the air-quenching granulation process was carried out to make steel slag into a value-added end product: air-quenching granulated steel slag. The granulated slag was tested to analyze the variation rule of slag properties under different modification conditions. Based on the phase diagram of CaO–Si
slag system, the feasibility of blast furnace (BF) slag as modifier was determined. When the addition of BF slag was increased from 0% to 35%, following results were obtained. The slag fluidity was improved, and the air-quenching temperature range was expanded. Then, the yield of air-quenched steel slag increased, while the granulation rate, the degree of sphericity, the compactness were decreased. Furthermore, the air-quenching granulation process could substantially improve the stability and the amorphous content of steel slag. The maximum removal rate of free CaO was above 80% and the amorphous content was up to 95%. Taking the factors of yield and properties of granulated steel slag into full consideration, the optimum proportion of BF slag is around 15%.
2022 Vol. 29 (5): 783-792.
Bao Liu, Jin Li, Qian-qian Ren, Shuang Cai, Xue Yang, Ya-nan Zeng, Jun-guo Li
Leaching behavior and mineralogical evolution of vanadium released from sodium roasted-acid leaching tailing of vanadium slag
The sodium roasted-acid leaching tailing (SRALT) of vanadium slag with a certain amount of vanadium exhibits potential environmental risk. To investigate the leaching behavior of vanadium from the SRALT, neutral batch leaching tests were performed. The evolution of vanadium concentration, pH, redox potential (Eh), dissolved oxygen, and conductivity as a function of time was measured. Pourbaix diagrams of V–H
O system with different vanadium concentrations were obtained to identify the ionic speciation of vanadium in leachate. X-ray diffraction, X-ray photoelectron spectroscopy, field emission-scanning electron microscopy, and thermogravimetry–differential scanning calorimetry analysis were conducted to investigate the mineralogical evolution of the SRALT during the leaching process. It was found that the major minerals of the original SRALT are titanomagnetite, spinel, olivine, and augite. The valence states of V existing in the original SRALT are V
The pH and Eh values of the obtained leachates are 10.00–10.58 and (-43)–(+67) mV, respectively. In this pH and Eh region, the released vanadium is mainly present as HVO
. The FeOOH and CaCO
would form during the leaching process. The HVO
would be mainly adsorbed by the FeOOH and slightly incorporated into the CaCO
, resulting in the decline in the vanadium concentration. The vanadium concentration above 27 mg L
and the dissolved oxygen value below 5.0 mg L
can be obtained after a short leaching period. As a V(V)-releasing and oxygendepleting substance, the leaching toxicity of the SRALT should not be ignored.
2022 Vol. 29 (5): 772-782.
Fu-bin Liu, Jun-zhe Gao, Hai-bo Cao, Hua-bing Li, Zhou-hua Jiang, Xin Geng, Cong-peng Kang, Kui Chen, Rui-dong An
Effect of slag composition on elements oxidation behavior of GH984G superalloy for electroslag remelting withdrawal process
The composition of a slag system has been shown to be particularly important and influential for the new technology of electroslag remelting withdrawal process. The oxidation of the GH984G alloy elements, in contact with different contents of CaF
in various slag systems, has been investigated in the present study by performing slag–metal equilibrium experiments and ion and molecule coexistence theory analysis. The results show that CaF
and MgO have only a minor effect on the oxidation rates of Al and Ti in the GH984G superalloys. However, it was found that SiO
would intensify the oxidation degree of Al and Ti, and Al was found to become easier oxidized than Ti. Moreover, CaO was found to reduce the activity of SiO
and, thereby, also the oxidation degree of Al and Ti. Also, TiO
was found to reduce the oxidation rate of Ti and instead increase the oxidation rate of Al. Finally, the effect of Al
on the oxidation of Al and Ti was observed to be opposite to that of TiO
. The calculated results were found to be in good agreement with experimental measurements. Moreover, viscosity experiments showed that CaO would rapidly increase the viscosity of the slag at low temperatures, and that the viscosity of the slag would increase with an increase in SiO
2022 Vol. 29 (5): 761-771.
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