2014年, 第21卷, 第8期　刊出日期：2014-08-15

  

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Metallurgy and Metal Working
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  CO2 Gasification Characteristics of High and Low Reactivity Cokes

  Bing GAO,Jian-liang ZHANG,Hai-bin ZUO,Cheng-lin QI,Yan RONG,Zhe WANG

  中国钢铁期刊网. 2014, 21(8): 723-728.
  https://doi.org/10.13228/j.boyuan.issn1006-706x.20120481

  摘要 ( )   可视化   收藏

  In order to effectively utilize the high reactivity coke, the gasification characteristics of high and low reactivity cokes were investigated at 1100 ℃. Low reactivity coke A and high reactivity coke B were chosen and charged into the reaction tube in two methods. The results indicated that the mass loss ratio of high reactivity coke in mixed cokes was more significant than that of single high reactivity coke in the middle stage of reaction. Nevertheless, the mass loss ratio of low reactivity coke in mixed cokes was less than that of single low reactivity coke. It was mainly attributed to gas diffusion and internal reaction of coke. When high and low reactivity cokes were mixed, the practical average mass loss ratio was nearly the same as the weighted average. The microscopic structures of coke indicated that with the increase of reaction time, the external and internal layers of low reactivity coke reacted more uniformly with CO2, whereas the reaction degree of external layer of high reactivity coke was obviously higher.
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  Numerical Simulation on Blast Furnace Operation with Hot Burden Charging

  Tong-lai GUO,Man-sheng CHU,Zheng-gen LIU,Hong-tao WANG

  中国钢铁期刊网. 2014, 21(8): 729-736.
  https://doi.org/10.13228/j.boyuan.issn1006-706x.20130381

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  Blast furnace operation with hot burden charging was numerically simulated to preliminarily analyze its advantages and disadvantages. Multi-fluid blast furnace model was utilized to simulate hot burden charging operations under the conditions that the charging temperatures of pellet and coke were supposed separately or simultaneously as 800 ℃. The results showed that, with hot burden charging, the furnace top temperature significantly increased in comparison to the conventional operation with cold burden charging. However, in-furnace temperature decreased, which decelerated the reduction rate of ferrous burdens. The concentrations of reducing gases were decreased in the furnace. The height of cohesive zone shifted downwards. When the charging temperatures of pellet and coke were simultaneously 800 ℃ (PC800), coke rate, fuel rate and carbon emission rate were decreased by 13.4, 22.1 and 19.25 kg·t-1, respectively. The ratio of ore to coke, solid burden charging rate and hot metal productivity were increased by 4.79%, 7.55 kg·s-1 and 6.38%, respectively. Heat taken away by top gas and energy consumption per ton hot metal were increased by 68.97% and 6.40%, respectively. Generally speaking, hot burden charging was adverse to energy utilization of blast furnace.
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  Effect of Slab Subsurface Microstructure Evolution on Transverse Cracking of Microalloyed Steel during Continuous Casting

  Yun-feng LI,Guang-hua WEN,Ping TANG,Jian-quan LI,Cheng-li XIANG

  中国钢铁期刊网. 2014, 21(8): 737-744.
  https://doi.org/10.13228/j.boyuan.issn1006-706x.20130155

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  As to the continuous casting process of low carbon microalloyed steel, subsurface microstructure evolution plays an important role in the slab surface cracking. In order to study the effect of the slab subsurface microstructure evolution on the transverse cracking, three different secondary cooling patterns (i.e., mild cooling, strong cooling and controlled cooling) were performed in the corresponding slab curved continuous caster. Based on the metallographic results, three transformation regions were found to be formed with the evolution of microstructures at different depths in the slab subsurface. The three regions are strong cooling transformation (SCT) region, double phase transformation (DPT) region and mild cooling transformation (MCT) region, respectively. Meanwhile, it was also found that the crack index used for evaluating slab surface cracking susceptibility was decreased when the range of the DPT region was increased. This can be explained by the fact that the double phase transformation (austenite-ferrite-austenite) occurred resulting from thermal cycling in DPT region, which resulted in promoting the refinement of prior austenite grains and inhibiting the precipitation of film-like ferrite and chain-like precipitates. Under the controlled cooling pattern, the widely-distributed DPT region was formed in the range of 3.5-8.0 mm to the slab surface. And compared with other cooling patterns, the cracking susceptibility is lowest with a crack index of 0.4.
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  Effect of Boron Mud and CaF2 on Surface Tension and Density of CaO-SiO2-B2O3 Ternary Slag Systems

  Li-li YANG,,Hong-ming WANG,,Xiang ZHU,,Gui-rong LI,

  中国钢铁期刊网. 2014, 21(8): 745-748.
  https://doi.org/10.13228/j.boyuan.issn1006-706x.20130019

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  The effect of boron mud and CaF2, which were used as fluxing agents, on surface tension and density of CaO-SiO2-B2O3 ternary slag systems was investigated. The surface tension and density were measured by using the ring detachment method and Archimedean method, respectively. The results indicated that surface tension and density of the slag systems decreased with increasing temperature in the range of 1380-1480 ℃. When 5%-10% CaF2 was employed as fluxing agent, the surface tension and density of slag were decreased with increasing CaF2 content, and the surface tension changed from 0.3 to 0.6 N/m, while the density changed from 3.4 to 4.1 g/cm3. However, when using 5%-10% boron mud as fluxing agent, the surface tension was enhanced, whereas the density decreased with the increase of boron mud content, and the variation range was 0.4-0.6 N/m for surface tension and 3.2-3.9 g/cm3 for the density. As a conclusion, using boron mud as fluxing agent to substitute for CaF2 did not cause significant changes in slag surface tension and density.
Material
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  Microstructure and Mechanical Properties of TWIP Steel Joints

  Li-li MA,Ying-hui WEI,Li-feng HOU,Bin YAN

  中国钢铁期刊网. 2014, 21(8): 749-756.
  https://doi.org/10.13228/j.boyuan.issn1006-706x.20130356

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  As a new type of high manganese steel, the twinning induced plasticity (TWIP) steels have attracted a growing interest in the automotive industry due to their good performance. Thin plates of TWIP steel were welded by laser beam welding (LBW) and gas tungsten arc welding (GTAW). The microstructure result shows that GTAW joint has obvious heat-affected zone (HAZ), while the HAZ of LBW joint is almost invisible. The X-ray diffraction result shows that the phase compositions of both joints are austenitic and no phase transition occurs. Energy dispersive spectrometry result shows that there is violent evaporation of Mn element in LBW joint, while the proportion of Mn element in GTAW joint is almost unchanged. Tensile tests and micro-hardness measurements were performed to take into account the mechanical properties of joints manufactured by the two different processes. The micro-hardness profiles of both joints present a typical saddle distribution, and the hardness of GTAW seam is lower than that of LBW seam. The failure positions of LBW joints are all located in base metal while the GTAW joints are all at the weld toe due to the softening of HAZ. By means of scanning electron microscopy, a typical ductile fracture is observed in LBW joint, while a brittle fracture with quasi-cleavage fracture characteristic is observed in GTAW joint.
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  Austenite Grain Refinement and Isothermal Growth Behavior in a Low Carbon Vanadium Microalloyed Steel

  Geng-wei YANG,,,Xin-jun SUN,Qi-long YONG,Zhao-dong LI,Xiao-xian LI,

  中国钢铁期刊网. 2014, 21(8): 757-764.
  https://doi.org/10.13228/j.boyuan.issn1006-706x.20130068

  摘要 ( )   可视化   收藏

  The austenite grain refinement through control of the grain growth during reheating process after thermo-mechanical controlled process (TMCP) in a vanadium microalloyed steel was achieved. The formation of ultra-fine grained austenite was attributed to the high density of austenite nucleation at the ferrite/martensite structure and to the inhibition of austenite growth by (Ti,V)C particles at the relatively low reheating temperature. Corresponding with the precipitation behavior of (Ti,V)C with temperature, the growth behavior of austenite in the vanadium microalloyed steel could be divided into two regions. At lower reheating temperature, austenite grains grew slowly, and ultra-fine grained austenite smaller than 5 μm was successfully obtained. By contrast, the austenite grains grew rapidly at high temperature due to the dissolution of (Ti,V)C particles. According to the measured and predicted results of austenite growth kinetics, two models were developed to describe the growth behavior of austenite grains in two different temperature regions, and the apparent activation energy Qapp for grain growth was estimated to be about 115 and 195 kJ/mol, respectively.
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  Microstructure Evolution and Mechanical Properties of HR3C Steel during Long-term Aging at High Temperature

  Bin WANG,,Zheng-dong LIU,Shi-chang CHENG,Chun-ming LIU,Jing-zhong WANG

  中国钢铁期刊网. 2014, 21(8): 765-773.
  https://doi.org/10.13228/j.boyuan.issn1006-706x.20130089

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  Microstructure evolution and the changes in mechanical properties of HR3C steel during long-term aging at 650, 700 and 750 ℃ were investigated. The precipitated phases of the aging steel included M23C6 carbides, Z-phase and a trace amount of Nb(C,N). The M23C6 carbides were distributed mainly at the grain boundary, while Z-phase was mainly inside the grains. Amounts of both M23C6 carbides and Z-phase during the aging process increased with increasing aging period and temperature. Coarsening of M23C6 carbides was influenced significantly by aging time and temperature, while the size of the Z-phase was relatively less affected by the aging time and temperature, which had a steady strengthening effect. Coarsening of the M23C6 carbides was the main reason for the decline in high temperature yield strength during long-term aging at 750 ℃. The M23C6 carbides were linked into a continuous chain along the grain boundary which accounted for the decrease of toughness during aging.
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  Corrosion Performance of High Strength 15Cr Martensitic Stainless Steel in Severe Environments

  Xiang-hong L,Fu-xiang ZHANG,Xiang-tong YANG,Jun-feng XIE,Guo-xian ZHAO,Yan XUE

  中国钢铁期刊网. 2014, 21(8): 774-780.
  https://doi.org/10.13228/j.boyuan.issn1006-706x.20130169

  摘要 ( )   可视化   收藏

  High pressure and high temperature corrosion performance of high strength 15Cr martensitic stainless steel was studied in different severe environments—live acid (10%HCl+1.5%HF+3%HAc+5.1% corrosion inhibitor), spent acid and formation water containing CO2. The results show that the corrosion of high strength 15Cr martensitic stainless steel in live acid is most serious, and the uniform corrosion rate is far greater than those in spent acid and formation water containing CO2 corrosion environments, but all of them can be acceptable for oilfield. Acidizing corrosion inhibitor displays a good matching ability with the high strength 15Cr martensitic stainless steel in terms of decreasing the uniform corrosion rate, which changes mainly the anodic process of high strength 15Cr martensitic stainless steel. The corrosion potential moves to the positive direction, thus the corrosion current density decreases significantly. There are some different degrees of pitting of high strength 15Cr martensitic stainless steel after corrosion tests in live acid, spent acid and formation water containing CO2, and the pitting density aggravates significantly and the maximum pit depth decreases in the corrosion sequence.
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  Role of Mn and P in Texture of Bake Hardening Steel during Heat Treatment

  Hua WANG,,Hong-lin YANG,Lin LI,Li WANG

  中国钢铁期刊网. 2014, 21(8): 781-786.
  https://doi.org/10.13228/j.boyuan.issn1006-706x.20130105

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  Samples of three ultra-low carbon bake hardening (ULC-BH) steels (BH-0, BH-Mn, and BH-P) were prepared by two annealing processes followed by water quenching and overaging. The texture evolution in the as-treated steels was explored via EBSD and ODF, and the roles of Mn and P elements as well as heat treatment processes in the texture orientation and intensity were investigated. It is found that overaging significantly increases texture intensity of BH-0 and BH-Mn steel, while markedly hinders the texture development in BH-P steel. Based on the microstructure analysis, it can be deduced that the texture variations in BH-0 and BH-Mn steels mainly contribute to carbide (in BH-0 and BH-Mn steels) and manganese containing compound (in BH-Mn steel) or partially to C segregation to dislocation, while the texture variation in BH-P steel is mainly caused by the P and C co-segregation formed during quenching.
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  Effect of Boron on CGHAZ Microstructure and Toughness of High Strength Low Alloy Steels

  Han YANG,Xi-xia WANG,Jin-bo QU

  中国钢铁期刊网. 2014, 21(8): 787-792.
  https://doi.org/10.13228/j.boyuan.issn1006-706x.20130141

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  Effect of boron on the microstructure and impact toughness in the coarse-grained heat-affected zone (CGHAZ) of two high strength low alloy steels, boron-free and boron-containing, was investigated by means of weld thermal simulation test. The result shows that, for the boron-free steel, a microstructure consisting of grain boundary ferrite degenerates pearlite and granular bainite for longer t8/5 (the cooling time from 800 to 500 ℃), while lath bainite for shorter t8/5. For the boron-containing steel, granular bainite is dominant for a wide range of t8/5. Continuous cooling transformation (CCT) study on the CGHAZ indicates that the transformation start temperature decreases by about 50-100 ℃ under different t8/5, for the boron-containing steel compared with the boron-free steel. The presence of boron suppresses the nucleation of ferrite at prior austenite grain boundaries and hence enlarges the range of t8/5 for granular bainite transformation. However, the addition of boron deteriorates the impact toughness of CGHAZ, which may be due to a markedly increased fraction of martensite-austenite (M-A) constituents and decreased fraction of high angle grain boundaries.
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  Compressive Behavior of Porous Titanium Fiber Materials

  Shi-feng LIU,,Zheng-ping XI,Hui-ping TANG,Xin YANG,Zhao-hui ZHANG

  中国钢铁期刊网. 2014, 21(8): 793-796.
  https://doi.org/10.13228/j.boyuan.issn1006-706x.20140029

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  Porous titanium fiber materials with the fiber sizes of 70-120 μm in diameter were prepared by vacuum sintering technology. The morphology and compressive properties of porous titanium fiber materials were investigated by using a scanning electron microscope (SEM) and an MST 858 compression testing machine in quasi-static condition. The results show that porous titanium fibers form complex micro-networks. The stress-strain curves of porous titanium fiber materials exhibit elastic region, platform region and densification region and no collapse during platform region. The yield strength of porous titanium fiber materials decreases with increasing the porosity and increasing the fiber diameter.
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  Combined Effects of Different Overload Ratios and Nitriding Process on Fatigue Crack Growth of AISI 4140 Steel

  A. B. Sengül,A. elik

  中国钢铁期刊网. 2014, 21(8): 797-803.
  https://doi.org/10.13228/j.boyuan.issn1006-706x.20130077

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  The combined effects of different overload ratios (OLRs) and nitriding process on fatigue crack growth (FCG) were analyzed. Steel compact tension specimens made of AISI 4140 steel were subjected to the plasma nitrification process using a gas mixture of 50% N2 and 50% H2 at 500 ℃ for 2 h. Structural properties of the samples were studied by scanning electron microscopy, optical microscopy, microhardness testing and digital imaging. Plasma nitriding slowed down FCG, but the crack growth retardation caused by the overload was reduced when the OLR was 2.0 and 2.5. Nitriding did not take effect when the OLR was 1.5 and 3.0.
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  Inhibition Effects of Chloroquinolines on Corrosion of Mild Steel in Hydrochloric Acid Solution

  A. V. Shanbhag,T. V. Venkatesha,B. M. Praveen,S. B. Abd Hamid

  中国钢铁期刊网. 2014, 21(8): 804-808.
  https://doi.org/10.13228/j.boyuan.issn1006-706x.20130272

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  The corrosion inhibition efficiencies of four compounds namely N-［(1E)-(2-chloroquinolin-3-yl)methylene］-N-phenylamine(CQMA), N-(1E)-(2-chloroquinolin-3-yl) methylene］-N-(4-fluorophenyl)amine (CQMFA), N-(4-chloro phenyl)-N-［(1E)-(2-chloroquinolin-3-yl)methylene］amine (CQMCA),and N-(4-bromo phenyl)-N-［(1E)-(2-chloroquinolin-3-yl)methylene］amine (CQMBA) on mild steel corrosion in hydrochloric acid media were investigated using mass loss, potentiodynamic polarization and electrochemical impedance spectroscopy. For all the studied inhibitors the inhibition efficiency values were found to increase with increasing concentration up to 5.00×10-4 mol·dm-3. Scanning electron microscopic technique showed the formation of a thick film on the steel surface in the presence of inhibitors.