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	2020 Vol. 55 No. 3
	Published: 2020-03-15



	Technical Reviews Raw Material and Ironmaking Steelmaking Metal Forming Materials Technology Exchange

Technical Reviews

	1	WU Sheng-li, QUE Zhi-gang, AI Xian-bin
		Research process on regulating reaction behaviors of calcium-containing compounds for reducing NO_x emission in sintering process
		How to cost-effectively reduce NO_x emissions of the iron ore sintering process is a new challenge for iron and steel industries at present. Since there exists a working condition for the reduction of NO to N₂ in the sintering bed, and calcium-containing compounds have a catalytic effect on the NO reduction reaction, the thermodynamics and kinetics of the main reduction reactions of NO are first discussed. It was concluded that the NO-CO reduction reaction had great advantages in thermodynamics and kinetics. Then, the catalytic mechanisms of NO-CO reduction reaction by calcium-containing compounds, such as CaO and calcium ferrites minerals were analyzed. Moreover, the influence of the reaction behavior regulations of primary calcium-containing compounds such as lime/limestone and secondary calcium-containing compounds such as calcium ferrites minerals on NO reduction in the sintering bed were discussed in detail. In addition, the development directions of promoting NO reduction were proposed by clarifying the main influencing factors of NO-CO reaction, the adsorption behaviors of CO and NO by calcium ferrite minerals, and the regulations of changing the height of the sinter bed combined with optimizing the reaction behaviors of calcium-containing compounds, respectively.
		2020 Vol. 55 (3): 1-8 [Abstract] ( 393 ) [HTML 1KB] [PDF 1070KB] ( 829 )

Raw Material and Ironmaking

	9	ZHANG Xiao-hua, ZHAO Kai, BAI Geng-chen, ZHANG Yu-zhu, GAO Jian-jun, ZHANG Ying-yi
		Thermal analysis of rotary kiln-oxygen combustion melting furnace under multi-constraint conditions
		To solve the problem of the long smelting process and large pollutant discharge in the traditional blast furnace ironmaking process, non-blast furnace ironmaking technology has attracted extensive attention from scholars at home and abroad. By establishing a mathematical model coupling the heat and material balance, the material balance and heat balance of the rotary kiln pre-reduction-oxygen combustion furnace were calculated, revealing the process parameters under different metallization rates, gas oxidation degrees and blast oxygen contents. The variation law was finally carried out. The thermal analysis of the process was carried out using Lingo software, and the relationship between the pre-reduction metallization rate in the rotary kiln and the suitable coal consumption of the melting furnace was determined. The results show that increasing the metallization rate, gas oxidation degree and blasting oxygen content can reduce the coal consumption and oxygen consumption of the process, but the gas volume and gas calorific value will not be optimal with the increase of operating parameters. After the optimal solution of the working condition parameters, it was known that the rotary kiln-oxygen combustion melting furnace condition was used when the charge metallization rate is 70%, the melting furnace gas oxidation degree is 16%, and the blast oxygen content is 100%, which is the best condition.
		2020 Vol. 55 (3): 9-15 [Abstract] ( 358 ) [HTML 1KB] [PDF 1045KB] ( 562 )

	16	SUN Jun-jie, ZHANG Yong-jie, XU Ji
		Segregation of sinter particles in sinter shaft cooler
		The process of recycling the sensible heat of sinter by using a sinter shaft cooler is a new technology. The shaft cooler is a typical powder bed with gas-solid countercurrent heat transfer. Considering environmental protection and energy conservation, the process of sinter shaft cooler was introduced into Meishan Steel to replace the traditional ring cooler. Focusing on the segregation of particles in the surge bunker and the furnace, the DEM (Discrete Element Method) is used to study how to decrease the first segregation and the secondary segregation on an industrial scale. The result of the simulation indicates two conclusions. Firstly, the particle pit is formed in the center region of surge bunker after adding a plate for separating the particles and the particle size in the pit is bigger than other regions. This phenomenon can decrease the first segregation. Secondly, the landing position in the furnace can be controlled in a beneficial direction after adding a shunt on the bottom of the feeding pipe and the purpose of decreasing the secondary segregation can be achieved. In addition, the behavior of secondary segregation can be further optimized by adjusting the tilt angle of the shunt.
		2020 Vol. 55 (3): 16-22 [Abstract] ( 400 ) [HTML 1KB] [PDF 4506KB] ( 666 )

	23	WANG Xin, PAN Jian, ZHU De-qing, GUO Zheng-qi, TIAN Hong-yü
		Process of pelletization of nickel laterite and chromite
		The use of cheap low grade chromite concentrate and laterite nickel ore to prepare composite pellets containing nickel and chromium for the production of nickel and chromium stainless steel master alloys in blast furnace is of great significance for the sustainable development of China's stainless steel industry. The preparation process of nickel-containing and chrome-containing pellets was systematically studied, and the effects of adding nickel laterite,chromite,and additive were carried out. The results show that, the compressive strength of fired nickel laterite pellet can reach over 2 500 N/pellet while preheating at 1 000 ℃ for 12 min and firing at 1 220-1 250 ℃ for 12 min. The mixture contained 45% of nickel laterite, 15% of chromite and 40% of iron ore, by adding with 7.7% of additive and pretreated by high-pressure roller grinding. The product pellet can be used as a high-quality burden for blast furnace to manufacture Fe-Cr-Ni alloys.
		2020 Vol. 55 (3): 23-28 [Abstract] ( 420 ) [HTML 1KB] [PDF 6047KB] ( 537 )

Steelmaking

	29	LIU Zhen-tong, YANG Wen, REN Ying, ZHANG Li-feng, WANG Wei-jian
		Analysis of influencing factors on effect of calcium treatment in Al-killed steels
		Due to the insufficient understanding of the influencing factors of calcium treatment, the effect of calcium treatment in different enterprises is different. In order to improve the precision of calcium treatment,influencing factors and influencing rules of the effect of calcium treatment of Al-killed steels are briefly described in the current work from the composition of molten steel and slag, the types and carriers of calcium alloys, the operation of calcium treatment process and the timing of calcium treatment. Many factors are affecting the effect of calcium treatment, and the main factors different enterprises facing are also different. The results can help steel enterprises to understand the main influencing factors of their calcium treatment operation, and then realize the precise control of calcium treatment, which improves the product quality and reduces the production costs.
		2020 Vol. 55 (3): 29-34 [Abstract] ( 446 ) [HTML 1KB] [PDF 1576KB] ( 648 )

	35	ZHU Tan-hua, ZHOU Qiu-yue, REN Ying, DUAN Hao-jian, ZHANG Li-feng
		Inclusion evolution in IF steel during tundish reoxidation
		In the current study,the composition of IF molten steel and the properties of inclusions at different time in tundish during the continuous casting process were systematically analyzed to reveal the effect of tundish reoxidation on cleanliness of IF steels. The evolution mechanism of inclusions during the reoxidation of IF steels was aslo predicted by thermodynamic calculation. It was found that the reoxidation during the casting process was mainly caused by the absorption of air,increasing the Al₂O₃ content in inclusions. One part of alumina inclusions are formed by homogeneous nucleation,which results in the formation of more small Al₂O₃ inclusions in steels. The other part is of alumina inclusions are formed by heterogeneous nucleation, which results in the formation of a pure Al₂O₃ layer on the surface of the original Al₂O₃ core,and increase the size of the inclusions.
		2020 Vol. 55 (3): 35-39 [Abstract] ( 475 ) [HTML 1KB] [PDF 2857KB] ( 623 )

	40	CHEN Deng-fu, XU Pei, LONG Mu-jun, DUAN Hua-mei, YANG Jie, WU Shi-xin
		Development and investigation of advanced process model for secondary cooling in continuous casting of molten steel
		The effect of secondary cooling in molten steel continuous casting will directly influence the quality of the strand. To control the secondary cooling process reasonably,several kinds of static and dynamic control process models have been proposed. The development of static and dynamic control process models for secondary cooling is systematically reviewed,for example,the secondary cooling control process model of the linear or quadratic relationship between water flow and casting speed in the secondary cooling zone,the dynamic control process model of secondary cooling based on the modified effective casting speed,and the dynamic control process model of secondary cooling based on on-line heat transfer calculation method etc.. Besides,the advanced process model of secondary cooling control based on the superheat of molten steel and inlet temperature of secondary cooling,and the dynamic process model of secondary cooling control based on on-line temperature measurement and then feedback regulation of water flow in every circuit are proposed. With the development of secondary cooling control process models,the real-time control,reliability,accuracy,and stability of operation are gradually improved,thus laying a necessary foundation for high-quality slab manufacturing and intelligent secondary cooling control.
		2020 Vol. 55 (3): 40-49 [Abstract] ( 348 ) [HTML 1KB] [PDF 1033KB] ( 736 )

Metal Forming

	50	SUN Ming-han, ZHENG Yi, QU Chun-tao, JIN Shi-zhe, XU Zhi-qiang, DU Feng-shan
		Numerical simulation of temperature field in ultra-fast cooling process of hot rolled plate
		The ultra-rapid cooling process is the core technology for the production of hot-rolled steel sheets,which is of great significance for improving the structure of the plate products and improving the performance of the products. In the ultra-rapid cooling process of medium-thick steel plates,the difference in cooling speed between the core and the surface causes the steel plate to form an internal and external temperature difference in the thickness direction,but the heat transfer mechanism of the steel plate surface in the ultra-rapid cooling is complicated. Therefore,all of them increase the difficulty of defining the cooling mechanism of the plate. In order to improve the calculation accuracy of the ultra-fast cooling model of medium and heavy plates and improve its heat exchange system,this article establishes a mathematical model for the inverse method of equivalent heat transfer coefficient in the ultra-rapid cooling process of medium-thick steel plates after rolling. The model relies on the discrete analytical method,the thermal differential equation and the state characteristics of the normal phase of the object. The model transforms the obtained transcendental equation root into the equivalent heat transfer coefficient,and the result is used as the boundary condition of the ultra-fast cold temperature field model. On this basis, a super-fast cooling temperature field simulation model was constructed to verify the temperature field under the ultra-fast cooling mechanism of 20 mm steel plates. The results showed that the mathematical model of the inverse heat transfer coefficient inverse method could be applied to the ultra-fast cooling process of medium-thick steel plates.
		2020 Vol. 55 (3): 50-57 [Abstract] ( 469 ) [HTML 1KB] [PDF 1095KB] ( 570 )

Materials

	58	DAI Xin-yu, FANG Xu-dong, XU Fang-hong, WEI Ying-hui, HOU Li-feng, DU Hua-yun
		Research progress on low cycle fatigue properties of austenitic heat resistant steel
		In order to study the austenitic heat-resistant steel in depth,the research progress in low cycle fatigue property of austenitic heat resistant steel was introduced. The fatigue fracture characteristic of austenitic heat-resistant steel at room and high temperature was compared. Interstitial atoms,strain,temperature and stacking fault energy have great influence on the fatigue property of austenitic heat-resistant steel. In the high temperature fatigue-creep process,the key factors affecting material crack propagation and fatigue fracture is temperature and stress. In terms of fatigue life prediction,many models have been established,but there will be some deviations for some new materials. A suitable life-predicted model needs to be established.
		2020 Vol. 55 (3): 58-67 [Abstract] ( 361 ) [HTML 1KB] [PDF 2428KB] ( 515 )

	68	XING Xian-qiang, CAO Wen-quan, WANG Cun-yu
		Bond structure of 55SiCr steel used for coil springs of automotive suspension system
		In order to study the effect of central segregation on the microstructure and properties of spring steel,the elemental segregation behavior,banded structure and mechanical properties of 55SiCr spring steel were studied by means of metallographic microscope,scanning electron microscope and electron probe. The results show that the content of Mn,Cr and Si in the banded structure is more than 1 times higher than that in the matrix. The segregation of alloying elements causes the banded structure. Cracks in the tensile specimens of spring steel originate from the segregated banded structure and eventually fracture through the growth of the banded structure. The banded segregation is an important factor affecting the mechanical properties of high strength spring steel.
		2020 Vol. 55 (3): 68-73 [Abstract] ( 404 ) [HTML 1KB] [PDF 11418KB] ( 554 )

	74	ZHU Li-guang, ZHENG Shi-wei, ZHANG Qing-jun, CAO Sheng-li
		Influence of oxide metallurgy and pulsed magnetic field parameters on steel microstructure
		Pulsed magnetic field treatment and oxide metallurgy technology are two common methods for refining microstructure and improving material properties,the organic combination can further optimize the performance of steel materials. A self-developed high-frequency induction coil heating furnace and a pulsed magnetic field generating device are used to non-contact apply a pulsed magnetic field to the solidification process of titanium-treated mild steel. The metallographic microscope,multifractal software and Vickers hardness tester are used. The effect of different pulsed magnetic field parameters on the solidification structure is investigated. The results show that the pulsed magnetic field induction intensity is 135-190 mT,and the magnetic field action time is 5-10 min,the metallographic structure of the test is the smallest and uniform. The original austenite grains are remarkably refined,the area reduced from 15.79 to 1.25 mm²,and the hardness of the test increased from 118.1 to 165.4HV. The pulsed magnetic field under this parameter has the best refinement of the solidification structure.
		2020 Vol. 55 (3): 74-79 [Abstract] ( 379 ) [HTML 1KB] [PDF 28785KB] ( 450 )

	80	ZHOU Ren-yuan, ZHU Li-hui, LI Shi-xian, ZHAI Guo-li
		Improvement of reheat-cracking susceptibility and microstructure of T23 steel
		The high reheat-cracking susceptibility of T23 severely endangers the safety of Ultra-super critical power plants. In order to decrease the reheat-cracking susceptibility of T23,the mass percent of elements such as C and W was optimized. The simulated coarse-grained heat-affected zone (CGHAZ) in T23 and modified T23 was produced via thermal simulation of welding,and the reheat-cracking susceptibility was evaluated by isothermal slow strain rate tensile test on Gleeble. The microstructure of CGHAZ in T23 and modified T23 was investigated by optical microscope (OM),scanning electron microscope (SEM) and transmission electron microscope (TEM). The effect of microstructure on the reheat-cracking susceptibility of modified T23 was discussed. The result shows that the reheat-cracking susceptibility of modified T23 is greatly decreased,and the mechanical properties meet the requirements of ASME specification. Compared with T23,there are less intergranular M₂₃C₆ precipitates and intragranular MX particles in modified T23. At the same time,the mass percent of C and W in the grain interiors is decreased in modified T23. Therefore,the difference between intergranular and intragranular strength is small in modified T23,leading to the improved reheat-cracking susceptibility. In addition,smaller grains and fewer M-A constituents in modified T23 help to decrease the reheat-cracking susceptibility. The decreased number of M₂₃C₆ at grain boundaries slows down the micro-void connection and crack propagation. The composition of modified T23 steel can provide reference for further improving the reheat-cracking susceptibility of T23 steel.
		2020 Vol. 55 (3): 80-86 [Abstract] ( 355 ) [HTML 1KB] [PDF 5714KB] ( 449 )

	87	LI Bo, YANG Fei-fei, LIU Hua-song, LUO Ming, ZHANG Zhong-hua, ZHANG Jia-quan
		Effect of solidification structure on banded defects of high strength corrosion resistant tubes
		As-cast spot segregation is the origin of banded defects in oil tube products,which will be harmful to the corrosion resistance of the tubes in service. The influence of solidified structure on the large banded defects in hot rolled and QT tubes was studied based on the C110 steel for controlling the banded defects. The results show that the spot segregation exists in the center equiaxed crystal region,which has a fine secondary dendritic structure but with severe speckle like segregation. The spot segregation will be inherited into the hot rolled tubes and appear as wide band defects. Such banded defects are difficult to remove by heat treatment and therefore inherited into the final QT products. Reducing the equiaxed crystal zone in the round castings is beneficial to control the formation and growth of the spot segregation,thereby significantly reducing the large band defects in the hot rolled and QT tubes. The hardness measurement results show that the hardness uniformity of both hot rolled and QT tubes can be obviously improved with the decrease of the as-cast center equiaxed crystal area.
		2020 Vol. 55 (3): 87-95 [Abstract] ( 323 ) [HTML 1KB] [PDF 16379KB] ( 691 )

	96	LU Wei, WAN Zhen-zhen, JIN Ying
		Austenite grain growth behavior in 25Cr2Mo1VA steel
		The austenite grain growth behavior of 25Cr2Mo1VA steel was investigated at different heating temperatures and holding time,then the grain size,distribution,precipitate type and its size distribution of austenite were adopted to study the effects of different heating temperature and holding time by metallographic microscopy,TEM,EDS and intercept method.The results shows that the austenite grain size increases with heating temperature,and the austenite grain size grows slowly under 900 ℃;but"mixed crystal" phenomenon is appeared at 950℃,subsequently the grain size of austenite grows quickly at over 1 000 ℃. In addition,it is also found that the austenite grain size slowly increases with the prolonging of holding time,but the effect is not much obvious than temperatures. And connecting with the scanning electron microscope analysis,it confirmes that the similar ball precipitation in the test steel is V-rich M₈C₇precipitated phase.According to the existing model of Anelli correction,relationship between the pinning force and the second phase particles on austenite grains,the behavior and causes of the 25Cr2Mo1VA steel grain growth are analyzed.
		2020 Vol. 55 (3): 96-103 [Abstract] ( 342 ) [HTML 1KB] [PDF 5180KB] ( 464 )

Technology Exchange

	104	LI Xiao-ming, LI Yi, XING Xiang-dong
		Particle growth characteristics of metallic iron in direct coal-based reduction of nickel slag
		The secondary resources in nickel slag can be effectively utilized by direct coal-based reduction. The growth characteristics and rules of metallic iron particles during the direct coal-based reduction of nickel slag under different conditions was described quantitatively, providing theoretical support for the development of subsequent grinding and magnetic separation processes, so as to achieve the purpose of efficient resource utilization of nickel slag. The microstructure of iron particles was observed by the scanning electron microscope. Image-Pro Plus Image analysis software was used to detect and analyze the size of metallic iron particles. The metallization rate of the reduced samples was measured. The results indicate that the coal-based direct reduction technology can effectively reduce the iron resources in nickel slag; the metallization rate of products shows a trend of first increasing and then stabilizing, and finally reaches 91.89% at 1 250 ℃ and 60 min;the average size of metallic iron particles in the reduced samples of nickel slag increases with the increase of time and temperature, and the increase of temperature is beneficial to the aggregation and growth of metallic iron particles in nickel slag; the average size of iron particle in the reduced samples increases up to 10.3 μm when the temperature is 1 250 ℃ and the reduction time is 60 min.
		2020 Vol. 55 (3): 104-109 [Abstract] ( 405 ) [HTML 1KB] [PDF 5577KB] ( 558 )

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