2021年, 第28卷, 第03期　刊出日期：2021-03-25

  

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  Synthesis of high-quality ferrovanadium nitride by carbothermal reduction nitridation method

  Ying‑cong Zhou, Yu Wang, Kuo‑chih Chou, Guo‑hua Zhang

  钢铁研究学报(英文版). 2021, 28(03): 255-262.
  https://doi.org/10.1007/s42243-020-00425-w

  摘要 ( )   可视化   收藏

  High-quality ferrovanadium nitride (FeV45N, FeV55N and Fe65N) was fabricated using the raw materials of Fe₃O4, V₂O₅ and graphite via carbothermal reduction nitridation method. Compared with the traditional methods, it shortens the production process of ferrovanadium nitride by avoiding the preparation of ferrovanadium. The effects of C/O molar ratio and reaction temperature on phase transition, density, carbon, oxygen and nitrogen contents and microstructure were investigated. The appropriate C/O molar ratio is crucial to obtain the products with high nitrogen content. It is also found that a higher temperature is beneficial for the densification, and the density of the products obtained at 1550 °C is much higher than that at 1500 °C. Moreover, a higher temperature contributes to the increase in nitrogen content owing to the higher reaction kinetics. The carbothermal reduction nitridation method is proved to be a facile route to fabricate cost-effective ferrovanadium nitride and is possible to be applied for industrial production.
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  Effect of process parameters on dry centrifugal granulation of molten slag by a rotary disk atomizer

  Ri-jin Cheng, Hua Zhang, Yang Li, Qing Fang, Bao Wang, Hong-wei Ni

  钢铁研究学报(英文版). 2021, 28(03): 263-271.
  https://doi.org/10.1007/s42243-020-00523-9

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  Dry centrifugal granulation (DCG) experiments for blast furnace slag (BFS) were performed by means of a rotary disk atomizer since water quenching method can create a series of problems. The results showed that the DCG method can granulate the BFS, but the results are easily affected by the slag flow rate, disk rotating speed, disk radius, disk material and slag falling height. The granulating parameters with an excessive flow rate, low rotating speed, SiN–SiC disk, stainless steel disk and low slag falling height are detrimental to the granulation process. The most suitable parameters for granulation are a slag flow rate of 5.1 9 10-5 m3/s, a disk rotating speed of 1500–2300 r/min, a slag falling height of 0.8 m and a smooth graphitic disk with the radius of 0.1 m. In the absence of an off-center flow, the overall best granulating effect produces round particles with mean diameter of 3.43 mm without creating slag fiber. The vitreous content of the BFS particles granulated by graphite disks is 92%, which meets the requirements of cement raw materials. The Bond work index of dry granulated BFS is 18.4 kWh/t, and the grindability of dry granulated slag and water-quenched slag is similar.
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  Effect of soft reduction process on segregation of a 400 mm thick high-alloy steel slab

  Ren-sheng Chu, Zhan-jun Li, Jin-gang Liu, Yong Fan, Yang Liu, Chang-wen Ma

  钢铁研究学报(英文版). 2021, 28(03): 272-278.
  https://doi.org/10.1007/s42243-020-00542-6

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  During the solidification of high-alloy steel (0.4C–1.5Mn–2Cr–0.35Mo–1.5Ni), the high temperature gradient of solidified shell as well as the columnar crystal development would contribute to the centre segregation and cracking due to the high carbon and alloy contents. The effect of soft reduction process on the segregation of a 400 mm thick high-alloy steel slab was analysed. Industrial trials in a steel mill were performed combining with segregation analysis. The inner quality of the high-alloy steel slab produced through the optimised soft reduction procedures and had a significant improvement in centre segregation. The reduction amount is increased from 20% of solid phase fraction, to avoid the segregation due to the long liquid core, and the reduction rate is deceased from 1.35 to 0.88 mm/m as well. This operation would contribute to the symmetrical distribution of solute element and decrease the segregation to avoid the cracking. An obvious improvement in centre segregation to mainly 1.0 class of high-alloy slab after procedure optimization was achieved. The quality improvement of slab would ensure the quality of downstream forging.
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  Research and application of approximate rectangular section control technology in hot strip mills

  Hai-nan He, Jian Shao, Xiao-chen Wang, Quan Yang, Yang Liu, Dong Xu, You-zhao Sun

  钢铁研究学报(英文版). 2021, 28(03): 279-290.
  https://doi.org/10.1007/s42243-021-00558-6

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  Profile requirements of silicon steel strip are extremely high and the thickness difference of cold-rolled products is usually less than 7 lm, and the profile quality of hot-rolled strip is the key to ensure the thickness difference of cold-rolled products. In order to produce the silicon steel strip with high-precision shape, the concept of quasi-rectangular rolling during hot continuous rolling was put forward; the equipment configuration and technical method of approximate rectangular section control were studied. Through the roughing multi-target load distribution technology and the roll configuration technology for uniform wear of a 4-high rolling mill, the strip crown of transfer bar was reduced and the profile control stability was guaranteed. Configuring variable contact back-up roll technology on all stands in the finishing rolling process, equipped with symmetry variable taper work roll and long-stroke intelligent shifting strategy in the downstream stands, and using side rolling lubrication technology can make the roll wear more uniform, reduce the edge drop of silicon steel strip, improve the profile quality, and make the strip section of finishing exit ‘‘quasi-rectangular’’. In addition, induction furnace and side heater were also equipped to guarantee the temperature uniformity of the strip, so as to improve the stability of profile control. The whole control technology is based on the 1580-mm hot continuous rolling production line, designed, and developed according to the characteristics of equipment and products, and has been successfully applied, which can obtain the approximate rectangular strip section satisfying the flatness quality, and improve the strip section precision of silicon steel and other products.
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  Longitudinal profiled plate straightening process based on curvature integral method

  Jian-liang Sun, Kai Li, Meng-qian Sun, Xiang-hui Lu, Yan Peng

  钢铁研究学报(英文版). 2021, 28(03): 291-302.
  https://doi.org/10.1007/s42243-020-00538-2

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  Considering the variable cross section thickness of longitudinal profiled plate and the dynamic reductions of straightening rolls, an analytical model combining curvature integral method with linear decreasing straightening scheme was proposed to investigate the longitudinal profiled plate straightening process. Moreover, the calculation flow and solution algorithm of longitudinal profiled plate straightening process were presented. To verify the proposed model, calculated straightening forces were compared with the measured values, and very good agreements were achieved. Then, the reduction, contact angle, reverse bending curvature, residual curvature, straightening force and straightening moment of longitudinal profiled plate in the straightening process were calculated and analyzed, and the calculated results show that the curvature integral method can be used to reveal the mechanism of longitudinal profiled plate straightening.
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  Multi-class classification method for steel surface defects with feature noise

  Mao-xiang Chu, Yao Feng, Yong-hui Yang, Xin Deng

  钢铁研究学报(英文版). 2021, 28(03): 303-315.
  https://doi.org/10.1007/s42243-020-00501-1

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  Defect classification is the key task of a steel surface defect detection system. The current defect classification algorithms have not taken the feature noise into consideration. In order to reduce the adverse impact of feature noise, an anti-noise multi-class classification method was proposed for steel surface defects. On the one hand, a novel anti-noise support vector hyper-spheres (ASVHs) classifier was formulated. For N types of defects, the ASVHs classifier built N hyper-spheres. These hyper-spheres were insensitive to feature and label noise. On the other hand, in order to reduce the costs of online time and storage space, the defect samples were pruned by support vector data description with parameter iteration adjustment strategy. In the end, the ASVHs classifier was built with sparse defect samples set and auxiliary information. Experimental results show that the novel multi-class classification method has high efficiency and accuracy for corrupted defect samples in steel surface.
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  Effect of thermal cycles on microstructure of reduced activation steel fabricated using laser melting deposition

  Qian An, Zhi-xin Xia, Chi Zhang, Zhi-gang Yang, Hao Chen

  钢铁研究学报(英文版). 2021, 28(03): 316-326.
  https://doi.org/10.1007/s42243-020-00442-9

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  Reduced activation steel was successfully fabricated by laser melting deposition employing a Gaussian and a ring-shaped laser. The microstructure evolution of the reduced activation steel was investigated using the scanning electron microscope, transmission electron microscope and electron backscatter diffraction. The experimental results showed that the grains close to the substrate were smaller than the grains in the upper layers. Compared to those deposited using a Gaussian laser, the samples deposited using a ring-shaped laser showed a more homogeneous microstructure. Furthermore, a finite element analysis (FEA) model was applied to reveal the thermal history during laser melting deposition. The simulation results were well validated with the experimental results. FEA results indicate that the peak temperature increases and the cooling rate decreases, as the layer gets further from the substrate. Additionally, the temperature and the cooling rate resulting from the Gaussian laser model were higher at the midline of the samples and lower around the edges, whereas those of the ringshaped laser model were consistent with both at the center and around the edges.
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  Formation mechanism of surface oxide layer of grain-oriented silicon steel

  Jia‑long Qiao, Fei‑hu Guo, Sheng‑tao Qiu, Xing‑zhong Zhang, Hai‑jun Wang

  钢铁研究学报(英文版). 2021, 28(03): 327-334.
  https://doi.org/10.1007/s42243-020-00464-3

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  The surface oxide layer of grain-oriented electrical steels was investigated by scanning electron microscopy. The formation mechanism and the influence on the glass flim of the surface oxide layer were analyzed by the calculation of thermodynamics and kinetics. The surface oxide layer with 2.3 μm in thickness is mainly composed of SiO₂, a small amount of FeO and Fe₂SiO₄. During the formation of surface oxide layer, the restriction factor was the diffusion of O in the oxide layer. At the initial stage of the decarburization annealing, FeO would be formed on the surface layer. SiO₂ and silicate particles rapidly nucleated, grew and formed a granular oxide layer in the subsurface. As the oxidation layer thickens, the nucleation of new particles decreases, and the growth of oxide particles would be dominant. A lamellar oxide layer was formed between the surface oxide layer and the steel matrix, and eventually formed a typical three-layer structure. During the high temperature annealing, MgO mainly reacted with SiO₂ and Fe₂SiO₄ in the surface oxide layer to form Mg₂SiO₄ and Fe₂SiO₄ would respond first, thus forming the glass film with average thickness of 4.87 μm.
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  Isothermal transformation and precipitation behaviors of titanium microalloyed steels

  Xiang‑dong Huo, Kang He, Ji‑nian Xia, Lie‑jun Li, Song‑jun Chen

  钢铁研究学报(英文版). 2021, 28(03): 335-345.
  https://doi.org/10.1007/s42243-020-00479-w

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  The microstructure transformation and precipitation behavior of nano-carbides in Ti microalloyed steel during isothermal process were studied by a compression test on a Gleeble 3800 thermomechanical simulator and analyzed by optical microscopy, transmission electron microscopy and other methods. The results show that γ→ α phase transformation and TiC precipitation take place in Ti microalloyed steel during the isothermal process, and time–temperature–transformation curve and precipitation–time–temperature (PTT) curve are all of “C”-type. During the isothermal process, the interphase precipitation of TiC mostly occurs at the period of the phase transformation, and the random precipitation of TiC mostly occurs on the ferrite after the phase transformation. The increment in yield strength at the initial stage of isothermal transformation mainly comes from phase transformation strengthening. With the increase in isothermal time, the precipitation hardening effect becomes more important for nucleation and growth of titanium carbides and eventually reaches the maximum value at the precipitation finished point of the PTT curve.
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  Microstructure, property and deformation and fracture behavior of 800 MPa complex phase steel with different coiling temperatures

  Jian-zhong Xue, Zheng-zhi Zhao, Di Tang, Hui Li, Hao-hong Wu, Wei-liang Xiong, Liang Liang, Yao Huang

  钢铁研究学报(英文版). 2021, 28(03): 346-359.
  https://doi.org/10.1007/s42243-020-00502-0

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  The microstructure characteristics and properties (especially hole expansion property) of 800 MPa hot-rolled complex phase steel with different coiling temperatures were studied. The microstructure consisted of polygonal ferrite and precipitates when the steel was coiled at 550 °C, and when the steel was coiled between 460–520  °C, the microstructure was composed of granular bainite and martensite and austenite (M/A) islands. The morphology of the crack was analyzed by scanning electron microscopy, and the in situ scanning electron microscope tensile test was used to find out the fracture mechanism and deformation behavior of the steel with different coiling temperatures. When the steel was coiled at 550 °C, the cracks initiated at the ferrite grain boundary and propagated through the grains or along the grain boundaries. When the steel was coiled at 520 °C, the cracks first initiated at the junction of ferrite and M/A island and then propagated through the grains. The steel coiled at 520 °C has quite good mechanical properties and relatively high hole expansion ratio.
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  Microstructure and mechanical properties in core of a carburizing 20CrNi2MoV bearing steel subjected to cryogenic treatment

  Chang-sheng Li, Bin-zhou Li, Xin Jin, Yu Wang

  钢铁研究学报(英文版). 2021, 28(03): 360-369.
  https://doi.org/10.1007/s42243-020-00516-8

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  Microstructure and mechanical properties in core of a carburizing 20CrNi2MoV bearing steel subjected to cryogenic treatment were investigated. Conventional treatment sample was quenched and tempered at 180 °C for 2 h. Cryogenic treatment samples were quenched, cryogenically treated at - 80 and - 196 °C for 4 h, slowly returned to room temperature and thereafter tempered at 180 °C for 2 h, and finally tempered at 180 °C for 2 h. The scanning electron microscope, electron backscattering diffraction, X-ray diffraction and transmission electron microscope were adopted for microstructure characterization. The results show that cryogenic treatment increases the fraction of high-angle grain boundaries and the precipitation of finely dispersed carbides in the matrix, decreases the volume fraction of inter-lath retained austenite, and hence improves the strength and hardness. Compared with the conventional treatment, the hardness, yield strength and ultimate tensile strength of the steel after cryogenic treatment are increased by 11.7%, 12.6% and 18.3%, respectively, while the impact energy is decreased by 9.8%.
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  Effects of traditional heat treatment and a novel deep cryogenic treatment on microstructure and mechanical properties of low-carbon high-alloy martensitic bearing steel

  Dong-hui Li, Wen-chao He, Xu Zhang, Mao-guo Xiao, Shao-hong Li, Kun-yu Zhao, Mao-sheng Yang

  钢铁研究学报(英文版). 2021, 28(03): 370-382.
  https://doi.org/10.1007/s42243-020-00527-5

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  The effects of traditional heat treatment (quenching and then tempering) and deep cryogenic treatment on the microstructure and mechanical properties of a low-carbon high-alloy martensitic bearing steel were studied by Rockwell hardness test, X-ray diffractometry, scanning electron microscopy and transmission electron microscopy. The results show that the deep cryogenic treatment promotes the transformation of the retained austenite to martensite during cooling, which leads to the hardness of the sample after deep cryogenic treatment higher than that at the quenched state. Also, the carbon content in the martensite matrix after different treatments was calculated and the results indicated that deep cryogenic treatment can promote the segregation of carbon atoms in martensite to dislocations. The segregated carbon atoms act as and grow into nuclei for the formation of fine carbide particles during subsequent tempering. And this resulted in the fact that the hardness of the tempered experimental steel after deep cryogenic treatment is higher than that without deep cryogenic treatment.