2015年, 第22卷, 第4期　刊出日期：2015-04-15

  

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Metallurgy and Metal Working
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  Velocity Preset and Transitional Zone′s Shape Optimization for Tailor Rolled Blank

  Dong-cheng WANG,,Lian-chao DONG,Hong-min LIU,,Yan WANG

  中国钢铁期刊网. 2015, 22(4): 279-287.

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  Tailor rolled blank (TRB) is a type of emerging material to produce lightweight vehicle parts. Transitional zone′s shape is an important parameter for tailor rolled blank. It not only affects mold design and the local carrying capacity of the stamping parts, but also determines the maximum value and variation characteristics of rolling force. How to get the best transitional zone′s shape is a key problem for production of tailor rolled blank. A double power function is put forward using for transitional curve, which is continuous and smooth at all connection points independent of its parameters, so the sudden change of mechanical parameters during rolling and forming process can be avoided. At the same time, the velocity formula and restriction for arbitrary transitional curve are derived to preset vertical velocity of the roller and judge whether the curve can be rolled successfully or not. Then, the finite element method (FEM) is used to verify the precision of velocity formula and study the mechanical characteristics of different curves. Finally, a method to obtain the optimal curve equation is put forward and verified.
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  Model of Iron Ore Sintering Based on Melt and Mineral Formation

  Jun ZHANG,,Xing-min GUO,Yuan-hong QI,Ding-liu YAN

  中国钢铁期刊网. 2015, 22(4): 288-296.

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  A model of iron ore sintering was built with consideration of fuel combustion, catalysis of sinter mixture as well as formation of melt and mineral, which was verified via sintering pot tests and showed a good fit to the experimental results. The effect of bed depth on temperature was reflected by the residence time in high-temperature zone, rather than the top value of the temperature, which was weakened by melt formation as well as hematite decomposition. Moreover, the effect of bed depth, fuel content and distribution on sintering process was different, which was reflected by temperature profiles and the rule of calcium ferrite formation. The formation of melt as well as magnetite was a process which was decided by kinetic factors, while the formation of calcium ferrite was related to fuel blending conditions, which is determined by thermodynamics when the fuel ratio inside sinter granules is low or fuel content is high, otherwise, it is determined by kinetics.
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  Softening and Melting Behavior of Ferrous Burden under Simulated Oxygen Blast Furnace Condition

  Hua-jie ZHANG,Xue-feng SHE,Yi-hua HAN,Jing-song WANG,Fan-bo ZENG,Qing-guo XUE

  中国钢铁期刊网. 2015, 22(4): 297-303.

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  The softening and melting behavior of sinter, pellet and mixed burden was researched through high temperature reaction tests under load simulating traditional blast furnace (T-BF) and oxygen blast furnace (OBF) conditions. The results indicated that compared with T-BF, the softening zone of sinter and pellet became wide, but the melting zone became narrow in OBF. The permeabilities of both sinter and pellet were improved in OBF. Under the condition of OBF, the temperature of softening zone of mixed burden was increased by 63 K, but the temperature of melting zone was decreased by 76 K. Therefore, the permeability of material layer was significantly improved. This was mainly caused by the change of the melting behavior of pellet. In addition, the quality of dripping iron in OBF was much better than that of T-BF.
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  Influence of Cohesive Zone Shape on Solid Flow in COREX Melter Gasifier by Discrete Element Method

  Li-hao HAN,Zhi-guo LUO,Heng ZHOU,Zong-shu ZOU,Yu-zhu ZHANG,

  中国钢铁期刊网. 2015, 22(4): 304-310.

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  Based on the principle of discrete element method (DEM), a 2D slot model of a COREX melter gasifier was established to analyze the influence of cohesive zone shape on solid flow, including mass distribution, velocity distribution, normal force distribution and porosity distribution at a microscopic level. The results show that the cohesive zone shape almost does not affect the particle movement in the upper shaft and deadman shape. The particles in the lower central bottom experience large normal force to support the particles above them, while particles around the raceway and in the fast flow zone exhibit weak force network. The porosity distribution was also examined under three kinds of cohesive zones. Like the velocity distribution, the whole packed bed can be divided into four main regions. With the increase of cohesive zone position, the low porosity region located in the root of cohesive zone increases. And the porosity distribution becomes asymmetric in the case of biased cohesive zone.
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  Solid-phase Decarburization Kinetics of High-carbon Ferromanganese Powders by Microwave Heating

  Li-na GUO,Jin CHEN,Jing ZHAO,Wan-ming LIN,Wen-li SHI,Min LIANG

  中国钢铁期刊网. 2015, 22(4): 311-316.

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  Solid-phase decarburization of high-carbon ferromanganese powders (HCFPs) was conducted using calcium carbonate powders (CCPs) as a decarburizer by microwave heating. Solid-phase decarburization kinetics was investigated by isothermal method. The results show that the HCFPs show excellent microwave absorption at a higher average heating rate of 80 ℃/min, while CCPs exhibit poor microwave absorption at a lower heating rate of 5-20 ℃/min; the heating characteristics are in-between when HCFPs and CCPs are mixed. The average heating rates of the mixture are 32.14, 31.25, 31.43, and 30.77 ℃/min when the mixture is heated up to 900, 1000, 1100, and 1200 ℃, respectively. The good microwave absorption property of the mixed material lays the foundation for the solid-phase decarburization of HCFPs containing CCPs. Solid-phase decarburization of HCFPs containing CCPs is a first-order reaction by microwave heating. Apparent activation energy of solid-phase decarburization is 55.07 kJ/mol, which is far less than that of ordinary carbon gasification reaction and that of solid-phase decarburization under the same decarburization condition by conventional heating. It indicates that microwave heating not only produces thermal effect, but also has non-thermal effect.
Material
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  Abrasive Wear Resistance of Dual Phase Steels DP980 and DP600

  Xiu-lin JI,Ju-yi WANG,Cui-cui JI,Jian-hua ZHAO

  中国钢铁期刊网. 2015, 22(4): 317-323.

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  The abrasive wear resistance of dual phase(DP) steels DP980 and DP600 was investigated by using an ASTM rubber wheel abrasion tester. At 2.40 m·s-1 sliding speed under 19.9 N load with 180-355 μm abrasive sands, the wear rates of DP980 and DP600 were 1.01×10-11 and 0.86×10-11 m3·m-1, respectively, corresponding to about 1.9 and 2.3 times of the relative wear resistance of normal low-carbon steel ASTM A283C. Using directly water quenching from austenitic temperature, the abrasive wear resistance of DP980 samples under 19.9 N load could be improved by 1.65 times. The wear rates of DP980 and DP600 samples decreased respectively with increasing sliding speed and abrasive particle size and decreasing applied load. The experimental results reveal that the effect of martensite on the wear resistance not only depends on the volume fraction but also depends on the morphology, distribution and grain size.
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  Effects of Different Substrates on Microstructures and Mechanical Properties of a Bulk Nanocrystalline Structure Pure Iron Prepared by Aluminothermic Reaction Casting

  Xiao-juan ZHEN,Pei-qing LA,Cui-ling LI,Su-lei HU

  中国钢铁期刊网. 2015, 22(4): 324-329.

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  A simple method was developed to produce the nanocrystalline pure iron by aluminothermic reaction casting. The microstructure of the iron was investigated by optical microscope (OM), transmission electron microscope (TEM), electron probe micro-analyzer (EPMA), scanning electron microscope (SEM) and X-ray diffraction (XRD). The mechanical performances of nanocrystalline pure iron were tested. It is found that the pure iron consists of nanocrystalline ferrite. For different substrates of copper and glass, the average grain size of the ferrite was 38 and 35 nm, respectively, which is larger on copper substrate than that on glass. The hardness, compressive strength, tensile strength, and total elongation are 167 and 137 HB, 400 and 500 MPa, 243 and 185 MPa, 16% and 10% on copper substrate and glass substrate, respectively. The hardness, tensile strength and total elongation are all larger on copper substrate than those on glass substrate, while the compressive strength is lower. The large supercooling in the product solidification provides the condition for high nucleation rate and thus leads to nano-grained austenite and final nano-grained ferrite transformed from those small austenite grains.
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  Carbide Evolution in High Molybdenum Nb-microalloyed H13 Steel during Annealing Process

  Tian-sheng LI,,Fu-ming WANG,Chang-rong LI,Guo-qing ZHANG,Qing-yong MENG

  中国钢铁期刊网. 2015, 22(4): 330-336.

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  Based on the Thermo-Calc thermodynamic software, the type of equilibrium precipitated carbides and their contents in high Mo Nb-microalloyed H13 steel (NMH13 steel) were calculated. The composition, morphology, and distribution of carbides after spheroidal annealing of two forged experimental steels were comparatively examined by means of optical microscopy (OM), scanning electron microscopy (SEM), electron dispersive spectroscopy (EDS) and transmission electron microscopy (TEM). VC, M23C6 and M6C are identified in H13 steel after spheroidizing annealing, while (V,Nb)C, M23C6, M2C and M6C are observed in NMH13 steel. Moreover, it is found that the addition of Nb significantly enhances the stability of MC phase and the high Mo content accelerates the precipitation of small rod-shape M2C phase in NMH13 steel. The amount of the fine carbides in NMH13 steel obviously increased with M2C and M6C precipitated from the ferrite phase, which is in accordance with the results of thermodynamic calculations.
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  Microstructure and Mechanical Properties of Precipitation Strengthened Fire Resistant Steel Containing High Nb and Low Mo

  Zheng-yan ZHANG,,Qi-long YONG,Xin-jun SUN,Zhao-dong LI,Jun-yu KANG,Guo-dong WANG

  中国钢铁期刊网. 2015, 22(4): 337-343.

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  Through the thermo-mechanical control process (TMCP), a high Nb low Mo fire resistant steel with the yield strength (YS) of 521 MPa at room temperature (RT) and 360 MPa at elevated temperature (ET) of 600 ℃ was developed based on MX (M=Nb, V, Mo; X=C,N) precipitation strengthening. A series of tensile and constant load tests were conducted to study the mechanical properties at ET. The dynamic continuous cooling transformation (CCT) as well as precipitation behavior of microalloy carbonitride was investigated by means of thermal simulator and electron microscopy approaches. Results showed that the failure temperature of tested steel was determined as 653 ℃, and the granular bainite was obtained when the cooling rate was higher than 10 ℃/s. In the rolled state, a certain amount of M/A islands was observed. During heating from RT to ET, M/A islands disappeared, and cementites and high dense compound precipitates (Nb,Mo,V)C with size of less than 10 nm precipitated in ferrite at ET (600 ℃), which resulted in precipitation strengthening at ET.
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  Microstructural Evolution and Properties of a High Strength Steel with Different Direct Quenching Processes

  Feng LU,Chao WANG,Long L,Zhao-dong WANG,Guo-dong WANG,Raja Devesh Kumar MISRA

  中国钢铁期刊网. 2015, 22(4): 344-351.

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  A high strength low alloy steel with low carbon equivalent was selected for simulating online direct quenching and coiling (DQ-C) process. The influence of stop quenching temperature on mechanical properties and microstructures was studied and compared with normal direct quenching and tempering (DQ-T) process. The study confirmed that required mechanical properties were obtained for both the processes. Properties of the experimental steel with DQ-C process could reach the same level as that of DQ-T process in general. In the DQ-C process, strength decreased with increase in stop quenching temperature. Martensite was obtained and experienced an aging process at stop quenching temperature below Mf. On fast cooling below Ms, martensite was partially transformed and carbon partitioning occurred during slow cooling. The reduction in solid solution carbon and increased amount of retained austenite led to lower strength compared with the DQ-T process. DQ-C process was more favorable for microalloy carbide precipitation. However, impact toughness under different cooling conditions was adequate because of low carbon equivalent and refined microstructure.
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  Simulated Corrosion Test of Q235 Steel in Diatomite Soil

  Jian LI,,Hang SU,Feng CHAI,Xiao-ping CHEN,Xiang-yang LI,Hui-min MENG

  中国钢铁期刊网. 2015, 22(4): 352-360.

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  Through the study of the corrosion behavior of Q235 steel in actual Yingtan soil and two simulated acidic soils with different water contents, the calculation of corrosion mass losses, and the analysis of the corrosion morphologies and products by means of scanning electron microscope (SEM) and X-ray diffraction (XRD), the results demonstrated that the diatomite soil could simulate the corrosion in actual soil veritably. In both actual soil and simulated soil with 16.4% water content, the corrosion rates of Q235 steel were approximately 0.1 mm/a, the corrosion morphologies were mainly extension and connection of corrosion spots on sample surface, and the corrosion products were composed of α-FeOOH, γ-FeOOH, Fe3O4 and Fe2O3. When other media conditions remained unchanged, the corrosion area of Q235 steel was larger in simulated soil with 34.5% water content, and the corrosion rate reached 0.48 mm/a after 360 h of corrosion, which was nearly 5 times as the value in actual soil. Compared with the corrosion products in actual soil, the proportion of γ-FeOOH in simulated soil with 34.5% water content was higher, and the wα-FeOOH/wγ-FeOOH ratio was 1.4, which was only 1/3 of the value in actual soil.
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  Effects of Pre-strain and Temperature on Bake Hardening of TWIP900CR Steel

  Suleyman KILIC,Fahrettin OZTURK,Tayfun SIGIRTMAC,Gokhan TEKIN

  中国钢铁期刊网. 2015, 22(4): 361-365.

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  The effects of pre-strain and baking temperature on bake hardening behaviour of TWIP900CR steel were investigated. The results reveal that the bake hardening process contributes to an increase in yield strength up to 65 MPa at the baking temperature of 200 ℃. The difference in yield strength between baking temperatures of 170 and 200 ℃ is almost insignificant. It is clearly observed that baking at a high temperature does not result in a significant increase in yield strength. For a reasonable bake hardening, a good combination of pre-strain and baking temperature is necessary. Besides, the toughness of the material is found to decrease with increasing pre-strain.
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  Cementite Characterization with Chromium and Vanadium Contents Using Indentation Technique

  John Jairo CORONADO,Sara Aida RODRGUEZ

  中国钢铁期刊网. 2015, 22(4): 366-370.

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  Cast irons with some kinds of cementite with different chromium and vanadium contents were characterized. Fracture toughness was determined by using an indentation technique, along with microhardness and elastic modulus. The results show that at the load of 1 N, microhardness of the cementite with 5.1% Cr is 10.53 GPa, the microhardness for cementite with 9.2% Cr increased to 11.25 GPa and for cementite with 4.5% V the microhardness is 9.18 GPa. The cementite with 9.2% Cr presented the highest elastic modulus of 230.4 GPa and the cementite with 4% V presented the lowest value of 201.32 GPa. Cementite with 5.1% Cr presented higher fracture toughness than cementite with 9.2% Cr; however, cementite with 4.5% V presented the highest fracture toughness of 2.74 MPa·m1/2 and the lowest brittleness index of 3.35 μm-1/2.