2013年, 第20卷, 第11期　刊出日期：2013-11-15

  

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工艺
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  Correlation Between Radial Growth Rate of Cylindrical Solid and Time in Melt

  CHEN Shu-ying,CHANG Guo-wei,YUE Xu-dong,LI Qing-chun,JIN Guang-can

  中国钢铁期刊网. 2013, 20(11): 1-6.

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  The radial growth of δ-phase in Fe-0. 15%C-0. 8%Mn steel during solidification was in-situ observed under a high-temperature confocal scanning laser microscope (HTCSLM). The correlation between radial growth rate of cylindrical solid and time in melt was investigated, and the expression was deduced. The results indicate that the radius of cellular δ-phase rapidly enlarges at the beginning, and then the enlargement amplitude gradually declines. The variation of radial growth rate vs time is the same for each cellular δ-phase, and the radial growth rate of δ-phase rapidly declines to about 1. 5 μm/s within 10 s at a cooling rate of 2. 7 K/min, after that the growth rate slowly falls. The experimental data of the radial growth rate of cellular δ-phase are consistent with the calculation results for Fe-0. 15%C-0. 8%Mn steel.
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  Numerical Simulation of Fractal Agglomerating-Growth of Al2O3 Inclusions in Tundish

  GUO Luo-fang,,LI Hong,,LING Hai-tao,,WANG Yao,,SONG Wen-chen,

  中国钢铁期刊网. 2013, 20(11): 7-12.

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  Based on the Al2O3 inclusion analysis of low-carbon aluminum killed steel in tundish of a domestic steel company and fractal theory analysis, a mathematical model of fractal agglomerating-growth of Al2O3 inclusions in tundish was established. The results indicated that: large swirl flows exist in both sides of inlet, space between weir and dam, and large zone above outlet, in which monomer and agglomerated inclusion particles accumulate easily; the agglomerated inclusions with hydrodynamic diameter of 6-9. 8 μm were quickly generated less than 16 s, but those inclusions with hydrodynamic diameter more than 11 μm were difficult to form; the number density of agglomerated inclusion rapidly increased first, then slowly reduced, so the form and quantity distribution of agglomerated inclusions can be controlled by controlling the residence time of inclusion particles in tundish.
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  Control of Macrosegregation Behavior by Applying Final Electromagnetic Stirring for Continuously Cast High Carbon Steel Billet

  XIAO Chao,,ZHANG Jiong-ming,,LUO Yan-zhao,,WEI Xiao-dong,WU Lian,,WANG Shun-xi,

  中国钢铁期刊网. 2013, 20(11): 13-20.

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  Solidification behavior of continuously cast high carbon steel billets was investigated with an objective of producing high quality billets by determining the optimum final electromagnetic stirring (F-EMS) parameters. Characteristics of centerline segregation were analyzed for lots of billet samples collected from the plant through obtaining the carbon concentrations of drill chips, which were correlated with the operating parameters of the caster and stirrers, but a problem occurred that segregation control results of trial billets with the same casting and stirring parameters often have drastic fluctuations. An attempt was made to find out the induced reasons of this problem by measuring the electromagnetic torque, analyzing the secondary dendrite arm spacing (SDAS) and the corresponding cooling rate of the typical specimens, and observing the longitudinal profile of etched billet samples. Then a simple dynamic secondary cooling model was developed based on the solidified shell thickness control mode, by which the maximum carbon segregation index was reduced effectively, and thus the segregation fluctuation problem was basically solved. Finally, the most favourable stirring parameters were determined as the casting speed of 1. 65 m/min, the liquid core thickness of 40 mm, stirring current of 360 A and frequency of 12 Hz.
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  Permissible Minimum Thickness in Asymmetrical Cold Rolling

  TANG De-lin,LIU Xiang-hua,LI Xiang-yu,PENG Liang-gui

  中国钢铁期刊网. 2013, 20(11): 21-26.

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  The minimum rolling thickness in asymmetrical rolling was analyzed compared with that in symmetrical rolling. The differential equilibrium equations on forces were established to calculate the asymmetrical rolling force equation by slab method. An implicit expression of the minimum rolling thickness was then derived from the rolling force equation and Hitchcock equation. The results show that permissible minimum rolling thickness of asymmetrical rolling only exists within a specific range of cross-shear ratio, which is termed the cross-shear zone proportion of the whole deformation zone. Numerical computation was carried out to obtain a discrete solution of the minimum rolling thickness. Experiments were designed to investigate the influence factors on cross-shear ratio. Finally, experimental results prove the correctness of the improved formula given.
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  Effects of Transition Metal Oxides on Thermal Conductivity of Mould Fluxes

  QIU Xin,XIE Bing,QING Xue-mei,DIAO Jiang,HUANG Qing-yun,WANG Shui-bo

  中国钢铁期刊网. 2013, 20(11): 27-32.

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  The thermal conductivity of the mould fluxes containing transition metal oxides was measured by hotline method at different temperatures. The relationship between the thermal conductivity of mold fluxes and the contents of transition metal oxides was discussed. The synthetic slags were composed of 30. 0%-35. 4% CaO, 34. 7%-38. 6% SiO2, 6% Al2O3, 9% Na2O, 14. 4% CaF2, 0-4% Cr2O3 and 0-8% MnO in mass percent. The results indicated that Cr2O3 and MnO had a negative effect on thermal conductivity of mold fluxes. The thermal conductivity of mold fluxes was about 0. 25-0. 55 W/(m·K) when the temperature reached 1300 ℃, and it increased sharply to about 1. 32-1. 99 W/(m·K) when the temperature reduced from 1300 to 1000 ℃. The thermal conductivity of mold fluxes containing Cr2O3 and MnO was 10%-25% lower than those of original fluxes. The decrease in thermal conductivity was attributed to the change of molecular structure of mold fluxes. In addition, the poor integrity and regulation of polycrystal structure, complexity of crystal structure, and effects of impurities in the boundary and lattice distortion leaded to the reduction in the thermal conductivity. Na2CrO4, Mn2SiO4 and other minor phases were also found in the samples containing Cr2O3 and MnO, respectively.
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  Comparison and Optimization of Mid-low Temperature Cogeneration Systems for Flue Gas in Iron and Steel Plants

  ZHANG Li-hua,WU Li-jun,ZHANG Xiao-hong,JU Gui-dong

  中国钢铁期刊网. 2013, 20(11): 33-40.

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  Three generation systems, namely, steam Rankine cycle (SRC), organic Rankine cycle (ORC), and steam-organic combined Rankine cycle (S-ORC), were simulated using the Engineering Equation Solver (EES) to efficiently utilize flue gas emissions from 200 to 450 ℃ in iron and steel plants. Based on the simulation results for thermal efficiency, exergy efficiency, and power generation, the performances of the three power generation systems were compared and analyzed. To further utilize waste heat from the turbine exhaust steam of the ORC system, cascade ORC (CORC) was designed for heat sources above 300 ℃. Based on a comprehensive performance comparison, the application of the ORC using R141b is preferable for 200 to 300 ℃ flue gas. For 300 to 450 ℃ flue gas, CORC is an alternative technology to improve the efficiency and quality of waste heat utilization. For flue gas above 450 ℃, S-ORC can achieve higher efficiency and power generation than conventional SRC, with a relatively small negative pressure and high dryness of the turbine outlet steam. Hence, S-ORC can be considered as a substitute for SRC.
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  Numerical Simulation and Experimental Study on Interlock Deformation for Roll Formed U-Section Steel Piling

  FENG Guang-hong,ZHANG Pei,ZHANG Hong-liang,ZHOU Xu-chang,ZHAO Yong

  中国钢铁期刊网. 2013, 20(11): 41-45.

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  The interlock of a roll formed U-section sheet steel piling under loading was analyzed by means of numerical simulation, and meanwhile the tensile failure experiment was conducted. The results indicated that under the same load, the interlock corners of roll formed steel piling are not only the regions with the lowest safety factor, but also the regions with the highest stress; there are two slippages in the tensile instability process of interlock. Each slippage can be regarded as a failure, and different types of failure mode should be used to evaluate the performance of steel pilings according to different applications. Due to the work hardening effect during the roll forming process, the hardness of the interlock material increases by 16% compared with that of the original sheet steel. It was also found that the instability strength obtained in tensile failure test is only 15. 6% of the tensile strength of the original sheet steel.
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  Activity Calculation Model for Ternary Slag System of Al2O3-BaO-B2O3

  ZHOU Jian,WANG Qiang,QIN Zhe,QIU Sheng-tao,GAN Yong,ZHU Guo-ling

  中国钢铁期刊网. 2013, 20(11): 46-50.

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  According to the ion and molecule coexistence theory, the activity model of Al2O3-BaO-B2O3 ternary slag system was established, and the influences of BaO/Al2O3 molar ratio, B2O3 mole fraction and temperature on the activity of the slag system were investigated. Finally, the equal activity curves were drawn with the model results. The results show that with the increase of BaO/Al2O3 ratio, the activity of Al2O3 is significantly reduced, the activity of BaO·Al2O3 is increased obviously, and the activity of 2Al2O3·B2O3 is also decreased. With the increase of B2O3 mole fraction, the activity of BaO·Al2O3 decreased significantly, while the activities of BaO·2B2O3 and 2Al2O3·B2O3 increased. In addition, the influence of temperature on the activities of different components is comparatively smaller than the influence of BaO/Al2O3 ratio and B2O3 mole fraction.
材料
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  Optimization Evaluation Test of Strength and Toughness Parameters for Hot-Stamped High Strength Steels

  YING Liang,LU Jin-dong,CHANG Ying,TANG Xing-hui,HU Ping,ZHAO Kun-min

  中国钢铁期刊网. 2013, 20(11): 51-56.

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  Use of hot-stamped high strength steels (HSHSS) not only reduces the vehicle weight, but also improves the crash safety, therefore more and more mentioned steels are used to produce automobile parts. However, there are several problems especially the low ductility and toughness, which have restricted the application of HSHSS in automobile body. Suitable process parameters are very crucial to improve strength and toughness. In order to study the effect of austenization temperature, soaking time and start deformation temperature on strength and toughness of boron steel 22MnB5, an L9 (34) orthogonal experiment which was analyzed by means of comprehensive evaluation was carried out based on Kahn tear method to obtain the value of fracture toughness. The results indicate that the excellent formability, high strength and toughness of boron steel 22MnB5 with 1. 6 mm in thickness are obtained when the austenization temperature is in the range of 920-950 ℃, the soaking time is 1 min and the start deformation temperature is in the range of 650-700 ℃. The optimal parameters were used for typical hot stamping structural parts tests. Properties of samples such as tear strength, unit initiation energy and ratio of strength to toughness (RST) were improved by 10. 91%, 20. 32% and 22. 17%, respectively. Toughness was increased substantially on the basis of a small decrease of strength.
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  Elasto-Plastic Test of Q235 Steel Bending Beam With Cracking Resistance

  WANG Li-min,FENG Ying,CHEN Fan-xiu,WANG Hai-ying,WANG Dong-xu

  中国钢铁期刊网. 2013, 20(11): 57-66.

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  More than 30 bending beams with rectangular cross-section and different thicknesses and heights were prepared from Q235 steel. The specimen dimensions were about 240 mm (length)×60 mm (height)×70 mm (thickness). Flaws were cut along its middle line with a wire cutter, with lengths ranging from 6 to 35 mm. Each specimen was tested with three-point bend loading, and a process curve was obtained between load and the displacement of the loading point, in order to analyze the fracture process when opening the crack. A deformation near the prefabricated crack was observed in the testing period, and the variation of the fracture characteristic parameters was analyzed for different sizes. For a comprehensive understanding of carbon steel fracture resistance behavior, its elasticity and plasticity were established by determining its Young′s modulus and Poisson′s ratio with an optical strain gauge. This gauge was also used for the loading process test. It was found that the fracture toughness varied with the dimensions, and the toughness of the elastic limit loading was almost constant. Using the relationship of crack resistance stress intensity factor and fracture criterion, the bearing capacity of the material structure could be estimated, which shows a good agreement with the experimental test data.
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  Static Recrystallization Behavior of 316LN Austenitic Stainless Steel

  JIN Miao,LU Bo,LIU Xin-gang,GUO Huan,JI Hai-peng,GUO Bao-feng

  中国钢铁期刊网. 2013, 20(11): 67-72.

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  The static recrystallization of 316LN austenitic stainless steel was studied by double-pass hot compression tests on a Gleeble-3500 thermomechanical simulator. The specimens were compressed at the deformation temperatures of 950, 1050, 1150 ℃, strain rates of 0. 01, 0. 1, 1 s-1, strains of 0. 1, 0. 15, 0. 2, and intervals of 1-100 s. The results show that the volume fraction of static recrystallization of 316LN increases with the increase of deformation temperature, strain rate, strain and interval, which indicates that static recrystallization occurs easily under the conditions of higher deformation temperature, higher strain rate and larger strain. Deformation temperature has significant influence on static recrystallization of 316LN. The volume fraction of static recrystallization could easily reach 100% at higher deformation temperatures. By microstructure analysis, it can be concluded that the larger the volume fraction of static recrystallization, the more obvious the grain refinement. The static recrystallization activation energy of 317882 J/mol and the exponent n of 0. 46 were obtained. The static recrystallization kinetics was established. The predicted volume fraction of static recrystallization is in good agreement with the experimental results.
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  Effect of Temperature on Scale Morphology of Fe-1. 5Si Alloy

  LIU Xiao-jiang,CAO Guang-ming,HE Yong-quan,JIA Tao,LIU Zhen-yu

  中国钢铁期刊网. 2013, 20(11): 73-78.

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  Because of the effect of silicon on the formation of oxide scale, red scale is the main surface defect of hot-rolled Fe-Si plate, making the scale difficult for descaling compared with carbon steel. Thermogravimetric analyzer (TGA) is used to simulate isothermal oxidation process of Fe-1. 5Si alloy for 60 min under air condition, and the temperature range is from 700 to 1200 ℃. Electron probe microanalysis (EPMA) is used to observe cross-sectional scale morphology and analyze elemental distribution of the scale. Relational graph of temperature, scale thickness and scale structure is obtained. It is found that scale structure (outer Fe oxide layer+inner FeO/Fe2SiO4 layer+internal Si oxide precipitates) is almost unchanged with temperature except at 1000 and 1200 ℃. At 1000 ℃ internal Si oxide precipitates cannot be found at the subsurface of the alloy, and at 1200 ℃ FeO/Fe2SiO4 not only forms a layer as usual but also penetrates into the outer Fe oxide layer deeply.
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  Effect of Hot Isostatic Pressing on Fatigue Properties of Laser Melting Deposited AerMet100 Steel

  CHENG Hao,LIU Dong,TANG Hai-bo,ZHANG Shu-quan,RAN Xian-zhe,WANG Hua-ming

  中国钢铁期刊网. 2013, 20(11): 79-84.

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  The ultra-high strength steel AerMet100 was fabricated by laser melting deposition (LMD) process. The effect of hot isostatic pressing (HIP) on high-cycle fatigue properties of the LMD AerMet100 steel was investigated, and the influence of defects on fatigue behavior was discussed. Results showed that the LMD AerMet100 steel had fine directionally solidified cellular-dendrite structure and coarse columnar prior austenite grains. Metallurgical defects such as gas pore and lack-of-fusion porosity were produced during the laser deposition process. After HIP treatment, the number and size of metallurgical defects had remarkably decreased. Moreover, high-cycle fatigue properties of the alloys after HIP treatment were superior to the as-deposited alloys.
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  Influence of Inactivation Treatment of Ship′s Ballast Water on Corrosion Resistance of Ship Steel Plate

  WANG Zi-xi,ZHAO Jing-hui,JIA Xiao-hong,FANG Jian-guo,ZHANG Bo,DING Guo-qing

  中国钢铁期刊网. 2013, 20(11): 85-89.

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  The effect of seawater after ultraviolet inactivation on corrosion of a shipbuilding steel plate was investigated by means of natural corrosion potential experiments and immersion corrosion test. The effects of natural seawater and treated seawater after ultraviolet inactivation on corrosion of the selected steel plate samples were compared with each other. The results showed that there was no obvious change in the chemical composition of treated seawater compared with natural seawater. The corrosion potential slightly increased by 10 mV, whereas the corrosion rate rose significantly by 20%. The experiments verified the naturally formed biofilm in the natural seawater for the inhibition of corrosion on the shipbuilding steel plate. The possible influences of ballast water treatment on biofilm by ultraviolet and electrolysis inactivation under the condition of practical usage were also investigated. And it was found that ballast water treatment methods with no continuous disinfection could protect original tank biofilm structure, reducing the intensity of tank corrosion.
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  Oxidation and Thermal Fatigue Behaviors of Two Type Hot Work Steels During Thermal Cycling

  MIN Yong-an,,Bergstrm Jens,WU Xiao-chun,XU Luo-ping

  中国钢铁期刊网. 2013, 20(11): 90-97.

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  Thermal fatigue test has been carried out on widely used hot work steel 4Cr5MoSiV1 and a low alloyed steel 3Cr3MoV in temperature range of 200 to 700 ℃. Tempering resistance, as well as high temperature hardness/strength of steel specimens, works as a dominating material parameter on thermal fatigue resistance. During the heating period, high hardness can depress the inelastic deformation. This deformation is the origination of tensile stress, which acts as the driving force of heat checking during the cooling period. The cyclic strain-oxidation interaction can speed up the damage on surface defects, which plays an obvious role in initiation of thermal cracks. On 4Cr5MoSiV1 steel specimens, borders between the matrix and inclusions such as titanium compounds, or lager carbides such as primary carbides, are focused by strain and attacked by oxidation, and are main initiating places of cracks. While on 3Cr3MoV steel specimens, larger strain causes plastic deformation concentrating around grain boundaries. Then the following oxidation accelerates this grain boundary damage and creates cracks.
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  Dynamic Recrystallization of Hot Deformed 3Cr2NiMnMo Steel:Modeling and Numerical Simulation

  LI Xia,,WU Xiao-chun,ZHANG Xiao-xun,LI Ming-yao

  中国钢铁期刊网. 2013, 20(11): 98-104.

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  Hot compression tests of 3Cr2NiMnMo steel were performed at temperatures in the range of 850 to 1100 ℃ and with strain rates of 10-2 s-1 to 1 s-1. Both the constitutive equations and the hot deformation activation energy were derived from the correlativity of flow stress, strain rate and temperature. The mathematical models of the dynamic recrystallization of 3Cr2NiMnMo steel, which include the dynamic recrystallization kinetics model and the crystallization grain size model, are based on Avrami′s law and the results of thermosimulation experiments. By integrating derived dynamic recrystallization models with the thermal-mechanical coupled finite element method, the microstructure evolution in hot compressive deformation was simulated. The distribution of dynamic recrystallization grains and grain sizes were determined through a comparison of the simulation results with the experimental results. The distribution of strain and dynamic recrystallization grain is also discussed. The similarity between the experimental results and the simulated results indicates that the derived dynamic recrystallization models can be applied effectively to predict and analyze the microstructure evolution in hot deformed 3Cr2NiMnMo steel.
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  Morphologies and Influential Factors of Forsterite Film in Grain-Oriented Silicon Steel

  FU Yong-jun,,JIANG Qi-wu,WANG Bao-chuan,YANG Ping,JIN Wen-xu

  中国钢铁期刊网. 2013, 20(11): 105-110.

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  The product quality of grain-oriented silicon steel may be affected by each process because of its complicated production technology. Morphologies, compositions and structures of forsterite film formed in different conditions on the samples subjected to high temperature annealing were measured by using a scanning electron microscope, an energy disperse spectroscope, an X-ray diffractometer and Fourier transform infrared technique respectively. The morphologies and influential factors of forsterite film were investigated. The results showed that the major component of forsterite film composed of light-gray spherical particles was Mg2SiO4, and the minor was MgAl2O4. If the amount of MgO coated on the surface of the steel was less, bare holes or even large-scale bare grains for forsterite film appeared. The higher temperature of water bath during decarburization annealing led to gaps of strips in forsterite film. Moreover, MgO coating method had great influence on forsterite film. Roller coating method was beneficial to increase compactness and smoothness of forsterite film, but was disadvantageous to its thickness.
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  Formability of Fe-Mn-C Twinning Induced Plasticity Steel

  HUANG Yao,ZHAO Ai-min,MI Zhen-li,JING Hai-tao,LI Wen-yuan,HUI Ya-jun

  中国钢铁期刊网. 2013, 20(11): 111-117.

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  A comparative analysis of formability was investigated between Fe-Mn-C twinning induced plasticity steel with different Mn contents and interstitial-free steel. Tensile test combing with the morphology of fracture reveals that element Mn is helpful for the forming of inclusion or particles with film or rod shapes inducing the crack initiation and propagation. During stamping process, twinning induced plasticity steel without earing shows better anisotropy than interstitial-free steel because a typical <111> fiber texture forms accompanied by a weaker <100> fiber texture. The difference between the two steels is not evident during Erichsen cone cupping test, but the result of cone cupping test indicates that the twinning induced plasticity steel has superior drawing ability compared with interstitial-free steel. The different performances can be attributed to the different deformation mechanism during cupping test. FLD (forming limit diagram) of tested steels further suggests twinning induced plasticity steel has slightly superior deep drawability but low stretchability than that of IF steel, whose FLD0 value can reach 30%.
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  Modeling Flow Stress of 70Cr3Mo Steel Used for Back-Up Roll During Hot Deformation Considering Strain Compensation

  REN Fa-cai,CHEN Jun

  中国钢铁期刊网. 2013, 20(11): 118-124.

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  A constitutive model incorporating the influence of strain developed based on the Arrhenius equation by considering the variation of material constants as a fifth polynomial function of strain is presented. Materials constants are fit to data from hot compression tests of 70Cr3Mo steel used for back-up roll at the temperatures from 1173 to 1473 K and strain rates from 0. 01 to 10 s-1 by using a Gleeble-1500D thermo-mechanical simulator. The developed constitutive model is then used to predict the flow stress under all the tested conditions. The statistical parameters of correlation coefficient and average absolute relative error are used to analyze the predictable efficiency and the values are 0. 997 and 3. 64%, respectively. The results show a good agreement between experimental stress and predicted stress.
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  Modeling of Hot Deformation Behavior of 55SiMnMo Medium-Carbon Steel

  YAN Tao,,YU En-lin,,ZHAO Yu-qian

  中国钢铁期刊网. 2013, 20(11): 125-131.

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  The hot deformation behavior of 55SiMnMo steel was studied by hot isothermal compression tests at 950-1100 ℃ and strain rates of 0. 01-10 s-1 using a Gleeble 3500 thermal simulation machine. Experimental results show that the peak stress increases with decreasing deformation temperature and increasing strain rate. When the strain rate = 0. 01 s-1, or when =0. 1 s-1 and the deformation temperature T≥1000 ℃, the dynamic recrystallization (DRX) of 55SiMnMo steel occurs. The hot flow stress constitutive equation, peak strain equation, as well as critical stress and strain for DRX initiation are obtained based on the experimental data. A comparison between the theoretical and experimental results verifies the reliability of the flow stress equation.