2018年, 第25卷, 第10期　刊出日期：2018-10-15

  

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  Influence of process parameters on interfacial tensile strength of crosswedge rolling of 42CrMo/Q235 laminated shafts

  Wen-fei Peng, ? Chao Yan, ? Xiao Zhang, ? Xue-dao Shu, ? Guang-xing Huang, ? Dong-ming Xu,

  . 2018, 25(10): 1003-1009.

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  Through rolling experiments and interfacial tensile strength tests of cross-wedge rolled laminated shafts of 42CrMo/Q235 composites, the influence of process parameters, including forming angle, spreading angle, area reduction, rolling temperature and core material diameter on the interfacial shear strength was analyzed. The results show that the sequence of process parameters in order of greatest influence on interfacial tensile strength was rolling temperature, area reduction, core material diameter, forming angle and spreading angle. At the interface of the combined materials, tensile strength decreased as forming angle and spreading angle increased, whereas the tensile strength first increased and then decreased as area reduction, rolling temperature and core material diameter increased.
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  Cooling phenomena in blast furnace hearth

  Ke-xin Jiao, ? Jian-liang Zhang, ? Zheng-jian Liu, ? Yong Deng, ? Chun-lin Chen

  . 2018, 25(10): 1010-1016.

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  Cooling water provides the best protection for refractory in the blast furnace hearth. Stable and suitable water quality and abundant cooling water are the basis for long service life of the hearth. Some phenomena about cooling system in the commercial blast furnaces were described, and reasonable explanations of these phenomena were analyzed. The results show that increasing the amount of cooling water and reducing the inlet temperature of cooling water can increase the cooling effect significantly in the case of water scaling. Heat flux in the blast furnace hearth is the average heat flux of cooling stave, and the erosion of carbon brick is uneven. There is no direct connection between the actual erosion condition and the heat flux in the hearth. The change trend of thermocouple temperature and heat flux in the hearth can reflect whether the gaps exist among the bricks or not, providing an effective guidance for industrial production and the evaluation of safety state in the hearth. And, the film boiling will not occur in the normal cooling system in the blast furnace hearth.
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  Strengthening granulation behavior of specularite concentrates based on matching of characteristics of iron ores in sintering process

  Sheng-li Wu ? Zhi-gang Que ? Kai-lang Li

  . 2018, 25(10): 1017-1025.

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  Specularite concentrates have advantages of high ferrous grade, less harmful impurities and low price. However, the small size and poor granulation behavior of specularite concentrates could consequently deteriorate the permeability of sinter bed and reduce the productivity of sinter, resulting in un-effectively utilizing in sintering process. In this paper, granulation experiments were carried out when specularite concentrates matched with five kinds of fine or coarse ores, and the effects of surface property and wettability of fine or coarse ores on granulation behavior of specularite concentrates were investigated. Then the optimized ore blending recipes were proposed to strengthen the granulation behavior of specularite concentrates. Results can be summarized as follows. The growth index increased with increasing the specific surface area of fine ores, and had a positive linear correlation with the circularity degree of coarse ores. In addition, it was found that there were negative correlations between the growth index and the contact angle of fine or coarse ores. Compared to the scheme of blending ores containing 15 mass% specularite concentrates, the growth index increased by approximately 22 % in the case of using Ore-A and Ore-E with greater surface property and higher wettability to replace all of Ore-B and half of Ore-D respectively. Furthermore, the vertical sintering speed and the productivity of sinter improved by approximately 23 % and 20 %. This study could be beneficial to effectively use of the specularite concentrates in sintering process.
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  Texture and inhibitor features of grain-oriented pure iron produced by different cold-rolling processes

  Jian-jun Deng, ? Hai-jun Wang, ? Zhe Rong ? Li Xiang ? Sheng-tao Qiu ? Yong Gan

  . 2018, 25(10): 1026-1032.

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  To promote the manufacture of grain-oriented pure iron, the texture and inhibitor features of two samples A and B produced by different cold-rolling processes were studied by optical microscopy, X-ray diffraction, and transmission electron microscopy. The results showed that a higher content of inhibitor elements directly resulted in a greater number of fine inhibitors, which exhibited strong inhibitory ability, leading to more fine precipitates of appropriate size effectively inhibiting the growth of primary grains in decarburized bands (sheets) during the single-stage cold-rolling process. The formation of the component with {110}\001[ Goss orientation was greatly suppressed in the stage of primary recrystallization, and this component could hardly be observed in the decarburized band; by contrast, the {411}\148[-oriented grains grew. During the process of high-temperature annealing, abnormal growth occurred and secondary recrystallized grains (Goss orientation) merged with other matrix grains such as {111}\112[and {411}\148[. The magnetic induction of samples A and B at 800 A/m was 1.939 T and 1.996 T, respectively.
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  Effect of heat input on microstructure and toughness of rare earthcontained C–Mn steel

  Ming-ming Song, ? Bo Song ? Sheng-hua Zhang ? Zhan-bing Yang ? Zheng-liang Xue, ? Sheng-qiang Song, ? Run-sheng Xu, ? Zhi-bo Tong

  . 2018, 25(10): 1033-1042.

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  Gleeble-1500D thermal simulator was used to simulate the thermal cycle of different welding processes in C–Mn steel. The toughness of steel matrix and heat-affected zone (HAZ) was investigated, and the microstructure and inclusion were characterized as well. The results showed that the welding process has a great influence on the microstructure in HAZ. When t8/5 (the cooling time from 800 to 500 C) value of the welding process is less than 111 s, the microstructure in HAZ is mainly bainite/Widmansta¨tten in spite of the addition of rare earth. However, when t8/5 value is more than 250 s, there are a lot of acicular ferrites in the steel containing rare earth, while the main microstructures are grain boundary ferrite and bainite/Widmansta¨tten in the steel without rare earth. The impact toughness of the HAZ at ambient temperature first decreases and then increases with the increase in t8/5 value. The impact toughness is the worst when t8/5 value is 111 s. Rare earth can improve the impact performance of HAZ at ambient temperature, especially when t8/5 value of the welding process is 445 s. After the rare earth treatment, the cooling rate of forming acicular ferrite is about 0.5–7.5 C/s. Acicular ferrite can form even during the welding process with larger t8/5 value up to 600 s in rare earth-treated steel.
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  Effect of coarse TiN inclusions and microstructure on impact toughness fluctuation in Ti micro-alloyed steel

  Tao Liu,? Mu-jun Long, ? Deng-fu Chen, ? Hua-mei Duan, ? Lin-tao Gui, ? Sheng Yu, ? Jun-sheng Cao, ? Hua-biao Chen, ? He-lin Fan,

  . 2018, 25(10): 1043-1053.

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  Toughness is an important property for steels used in engineering applications. However, recent toughness testing has shown the existence of a significant fluctuation in toughness in a single rolled plate of titanium microalloyed steel (0.17 wt.% C, > 0.05 wt.% Ti, 13 Ti/N ratio). The underlying causes of this fluctuation were investigated by fractography, analysis of microstructure, and measurement of inclusions. Coarse, distributed TiN inclusions were responsible for the toughness variation, as they tended to act as the potent cleavage initiators, forming microcracks. From a calculation of the local fracture stress, the critical size of coarse TiN inclusions for dominating microcrack propagation was 4.93 μm, and similarly the critical size of ferrite grains for dominating microcrack propagation was 36.6 μm. Under current casting and thermo-mechanically controlled processing (TMCP) schedules, the toughness fluctuation of rolled steel plates can be attributed primarily to the fraction of coarse TiN inclusions larger than 5 μm. A corresponding relationship between impact energy and the proportion of coarse TiN inclusions was established in this study. Finally, a normalizing treatment was applied to refine the ferrite grains of rolled steel plates. Despite the presence of coarse TiN inclusions, this refinement in ferrite grains minimized the toughness fluctuation and improved the uniformity of the impact properties of the steel plates.
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  Characterization of hot deformation behavior of wear-resistant steel BTW1 using processing maps and constitutive equations

  Peng-tao Liu,, ? Qing-xue Huang,, ? Li-feng Ma, ? Tao Wang

  . 2018, 25(10): 1054-1061.

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  In order to predict flow instability of wear-resistant steel BTW1, the hot compressions of wear-resistant steel BTW1 were firstly performed at the temperature of 900–1150 C and at the strain rate of 0.05–15 s-1. Then, the constitutive relation was established based on Arrhenius-type hyperbolic sine equation. The results demonstrated that the flow stress depended on the deformation temperature and strain rate. When the deformation temperature kept constant, the flow stress increased as the strain rate increased. When the strain rate remained constant, the flow stress decreased as the temperature increased. The flow stresses calculated by constitutive equations were in a good agreement with experimental results. The apparent activation energy for deformation in the above processing region was estimated to be 369 kJ mol-1. A processing map could be obtained by the superimposition of an instability map on a power dissipation map. Based on the analysis of processing map and the microstructures, the rheological instability regimes of strain rate and temperature for hot deformation of wear-resistant steel BTW1 had been identified.
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  Microstructure and mechanical properties of nanobainitic steel subjected to multiple isothermal heat treatments

  Ning Liu? Xin Zhang ? Jing Ding ? Jun He ? Fu-xing Yin

  . 2018, 25(10): 1062-1067.

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  Nanostructured bainite in 62MnSiCr steel was prepared by two-stage transformation process at different temperatures for less than 2 h. Microstructures, phase distribution and mechanical properties of the obtained steel were investigated. The results showed that the thickness of bainite plate and the amount of retained austenite decreased obviously after the twostage transformation, while the carbon concentration in the retained austenite showed a small change. With increase in the second holding temperature within the bainite transformation range, all of them increased slightly. The additional formation of bainite at the second transformation stage is beneficial to refining the austenite and further enriching it with carbon, resulting in the enhancement of the mechanical stability. Bainite transformed in two-stage process showed a better comprehensive performance. Absorbed impact energy of 88 J and an ultimate tensile strength of 1818 MPa have been achieved by isothermal heat treatment at 300 C followed by 260 C. Meanwhile, there was a slight change in mechanical properties when the second transformation temperature varied from 260 to 220 C.
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  Microstructure evolution and mechanical properties of 316L austenitic stainless steel with aluminum addition by warm rolling

  Xin Guo,? Pei-qing La, ? Heng Li ? Yu-peng Wei ? Xue-feng Lu

  . 2018, 25(10): 1068-1077.

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  In this present contribution, microstructure evolution and mechanical properties of 316L austenitic stainless steel with aluminum by warm rolling at 550 °C are investigated. It is found that specimen is composed of an ashen austenite matrix, a gray black ferrite phase and a small number of NiCx. The average grain sizes are 21.62, 19.66 and 19.49 μm for samples with the rolling deformation of 30%, 50% and 70%, respectively. The yield strength and tensile strength of samples with solid solution time of 30 min and deformation of 70% are higher. The fracture modes are similar and belong to toughness fracture. The fracture surfaces of the samples are composed of relatively large equal-axis ductile dimples (5-15 μm) and fine scattered ones around the dimples (< 5μm). As the rolling deformation increases, the quantity of subgrain boundary increases and the <101> orientation is more prominent. {100} and {111} cube textures are present in ferrite phase of samples and weak Goss texture formed in austenite pole images.
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  Effect of cooling time t8/5 on microstructure and toughness of Nb–Ti– Mo microalloyed C–Mn steel

  Xiao-nan Wang ? Xia-ming Chen ? Feng Wen ? Peng-fei Guo ? Lei Yang ? Qian Yan ? Hong-shuang Di

  . 2018, 25(10): 1078-1085.

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  In order to further optimize welding process of Nb–Ti–Mo microalloyed steel, welding thermal cycles on coarse-grained heat-affected zone (CGHAZ) of welded joints were simulated using Gleeble 1500. The microstructure and low-temperature impact fracture were investigated using a scanning electron microscope and a pendulum impact machine, respectively. Moreover, the relationship between cooling time t8/5 and the microstructure of CGHAZ was discussed, and the effect of microstructure on impact toughness was also studied. As cooling time increased, martensite fraction decreased from 97.8% (3 s) to 3.0% (60 s). The fraction of martensite/austenite (M/A) constituent increased from 2.2% (3 s) to 39.0% (60 s), its shape changed from granular to strip, and the maximum length increased from 2.4 lm (3 s) to 7.0 lm (60 s). As cooling time increased, the prior austenite grain size increased from 34.0 lm (3 s) to 49.0 lm (60 s), the impact absorption energy reduced from 101.8 J (5 s) to 7.2 J (60 s), and the fracture mechanism changed from quasi-cleavage fracture to cleavage fracture. The decreased toughness of CGHAZ was due to the reduction of lath martensite-content, coarsening of original austenite grain, and increase and coarsening of M/A constituent. The heat input was controlled under 7 kJ cm-1 during actual welding for these steels.
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  Precipitation kinetics of complex precipitate in multicomponent systems

  Yong Yang ? Tian-rui Li ? Tao Jia ? Zhao-dong Wang

  . 2018, 25(10): 1086-1093.

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  A kinetic model based on the classical nucleation and growth theory has been proposed to predict the precipitation behavior of complex precipitate. The method for calculating absolute solution temperature, which is an important guidance for determining solution treatment temperature, is also proposed based on thermodynamic model. In the model, nucleation of the second phase is assumed to be controlled by the effective diffusion, which involves the bulk diffusion and dislocation pipe diffusion, and growth is controlled by the bulk diffusion of forming elements. The interfacial energy of complex precipitate is calculated by the linear interpolation method, and the effects of alloying elements on precipitation behavior are manifested using weighted means of their diffusivities and concentration. The predictions were compared with the experimental measurements, and a good agreement was obtained.
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  Corrected stress field intensity approach based on averaging superior limit of intrinsic damage dissipation work

  Hao-ran Li? Yan Peng ? Yang Liu ? Ming Zhang

  . 2018, 25(10): 1094-1103.

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  In the present paper, corrected stress field intensity obtained by averaging of the superior limit of intrinsic damage dissipation work in critical domain, which considers thoroughly thermodynamic consistency within irreversible thermodynamic framework, is proposed for predictions of high-cycle fatigue endurance limits. Simultaneously, the effect of mean stress, additional hardening behavior related of non-proportional loading paths and stress gradients on multiaxial high-cycle fatigue are taken into account in the proposed approach. The approach is an extension of the general stress field intensity (GSFI) proposed by Yao and co-workers in 1996. For a better comparison, existing multiaxial high-cycle fatigue criteria (proposed by Freitas, Papadoulous and Yao) were employed to predict the endure limits of different metallic materials subjected to different multiaxial loading paths, and it is shown that our proposal performs better from statistical value of error indexes. The approach of corrected stress field intensity (CSFI) and its associated concepts in the present paper provide a new conception to predict endurance limits of multiaxial high-cycle fatigue with high accuracy.