2016年, 第23卷, 第6期　刊出日期：2016-06-15

  

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Review
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  Advances in Investigation of Fe-based Glass-forming Alloy Melts

  Hui GAO,Bang-shao DONG,Shao-xiong ZHOU

  中国钢铁期刊网. 2016, 23(6): 509-515.

  摘要 ( )   可视化   收藏

  Continuous precision casting is an important trend in modern industrialization. Clustering effects in glass-forming metallic liquids tremendously influence the properties of rapidly quenched ribbons; therefore, much attention has been paid to the study of Fe-based glass-forming melts at high temperatures. Recent investigations of these melts are categorized and reviewed. It is concluded that more efforts are still required to reveal the discipline of amorphization brought about by rapid quenching of Fe-based glass-forming melts.
Metallurgy and Metal Working
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  Influence of Screw Design on Burden Descending Velocity and Particle Segregation in COREX Shaft Furnace

  Hai-feng LI,Heng ZHOU,Tao ZHANG,Yang YOU,Zong-shu ZOU,Wan-ren XU

  中国钢铁期刊网. 2016, 23(6): 516-524.

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  COREX shaft furnace (SF) is an industrial system that employs screw feeders; thus, the burden descending velocity and particle segregation in the SF can be directly affected by the design of screw. A three-dimensional actual size model of COREX-3000 SF was established using the discrete element method. Four types of burdens, including pellet, ore, flux and coke, were considered in this model. With this consideration, the effect of screw design on solid flow was investigated. Results showed that, in the base case, burdens fell primarily down from the first flight of the screw. The burden descending velocities were nearly uniform in the peripheral direction and decreased along the radial direction. In addition, the normalized particle size increased in the center area and decreased in the wall area. Reducing the flight diameter of screw benefited an even flow pattern and restrained the rolling tendency of burden from the edge to center areas. An optimized case was also proposed, in which a uniform solid flow profile could be obtained and the evenness of descending velocity along the radius could be greatly improved.
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  Stretch Bending of Z-section Stainless Steel Profile

  Zheng-wei GU,,Meng-meng L,,Xin LI,,Hong XU,

  中国钢铁期刊网. 2016, 23(6): 525-530.

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  The stretch bending properties of a new Z-section stainless steel profile were investigated by simulation. The causes of the forming defects, such as section distortions and poor contour precision, were analyzed, and the corresponding controlling methods were proposed. The results show that the main forming defects for the stretch bending of the Z-section profile were the flange sagging, the sidewall obliquing inward, the bottom surface upwarping, and the bad contour accuracy; the cross-section distortions were mainly induced by the shrinkage of the sidewall, which could be eliminated by increasing the sidewall height of the profile reasonably; the poor contour precision was mainly due to springback, which could be controlled by modifying the die surface based on the springback amount; for the investigated bending beam, the proper sidewall height compensation was 2 mm, and the suitable die surface modification amount was 1.2 times of the springback amount, when the elongation was 10% of the initial profile length. Stretch bending tests were conducted on a new type of die with adjustable bending surfaces, and high quality components were achieved, which verified the effectiveness of the defect controlling measures.
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  Formation Mechanism of Inclusion Defects in Large Forged Pieces

  Rong-sheng QI,Miao JIN,Xin-gang LIU,Bao-feng GUO

  中国钢铁期刊网. 2016, 23(6): 531-538.

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  Nonmetallic inclusions mixed into large forged metal objects destroy the continuity in the metal and affect the quality of the forged product. Research on how inclusions affect the plastic deformation of a matrix shows the significance of the formation mechanism of inclusion defects. For upset forging, the nonlinear finite element model was shown to be appropriate for the ingot hot-forging process by comparing the results with experiments involving plastic and hard inclusions inserted into the forged piece. The high-temperature stress-strain curves of MnS plastic inclusions were obtained experimentally. The results show how, during upsetting, the morphology of MnS plastic inclusions varies from spherical to ellipsoidal, until finally becoming flat in shape. The larger the inclusion is, the larger the degree of deformation of the inclusion is, and large inclusions enhance the risk of the final product failing to pass inspection for inclusion flaws. Strain significantly concentrates in the matrix near a hard inclusion. When the hard inclusion reaches a certain size, conical fractures form on both sides of the inclusion. To pass inclusion-flaw inspection and close hole defects to the extent possible, the flat-anvil upsetting is recommended. Finally, the inclusion-deformation state obtained by finite element simulation is verified experimentally.
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  Mechanism and Improvement of Straight Edge Seam Defect on Hot-rolled Plate Surfaces through Use of Chamfered Slabs

  Hui ZHANG,Peng HU,,Ming-lin WANG

  中国钢铁期刊网. 2016, 23(6): 539-546.

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  To improve the straight edge seam defect on hot-rolled steel plates, the deformation and temperature distribution of rectangular slabs and chamfered slabs during rolling in a pilot rolling experiment were analyzed in detail using the finite element method. The results showed that the crease formed on the lateral side near the edge of the plate as a result of uneven stress during broadside rolling. The creases rose to the surface with unrestricted spread and evolved into a straight edge seam during the subsequent straight rolling. To eliminate the straight edge seam defect, chamfered slabs were developed and investigated for rolling. The use of the chamfered slabs provided two advantages for rolling: the distribution of the temperature near the edge was ameliorated, and the deformation shape was improved by the chamfered shape. As a result, the risk of forming a straight edge seam defect was reduced by the use of a chamfered slab.
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  Influence of Residual Stress on Shape of Heavy-gauge, High-strength Steel Caused by Cooling Process after Hot Rolling

  Shui-ze WANG,,Yong-lin KANG,Guo-ming ZHU,Wen LIANG

  中国钢铁期刊网. 2016, 23(6): 547-552.

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  The cooling process following hot rolling has a significant effect on the shape quality of a hot-rolled strip. The temperature and stress fields in the cooling process for a 14 mm thick strip with yield strength of 500 MPa grade were analyzed by the finite element method and actual test data, and the relationship between residual stress and shape defects was described. Subsequently, the small-crown rolling process and the coil slow cooling process were investigated. The results indicate that these processes improved the shape quality of the final product significantly.
Material
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  Micro-alloying Effects of Yttrium on Recrystallization Behavior of an Alumina-forming Austenitic Stainless Steel

  Wu-xin ZHAO,Yuan WU,Sui-he JIANG,Hui WANG,Xiong-jun LIU,Zhao-ping LU

  中国钢铁期刊网. 2016, 23(6): 553-558.

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  Micro-alloying effects of yttrium on the recrystallization behavior of an alumina-forming austenitic (AFA) stainless steel were investigated. It was found that the grain growth kinetics of the steels doped with different amounts of yttrium (i.e., 0, 0.05 and 0.10 mass% Y) could be described by an Arrhenius type empirical equation. Added Y could interact with carbon and influence the morphology of carbides both inside grains and on the grain boundaries, thus altering the grain boundary mobility and grain growth. The steel doped with 0.05 mass% yttrium showed the highest activation energy of grain growth and the most retarded recrystallization behavior, which mainly resulted from the high density of fine carbides both inside grains and on the grain boundaries. However, excess addition of 0.10 mass% Y induced coarsening and then lowered density of carbides, which alleviated the yttrium effects. The results also manifest that micro-alloying of rare-earth elements such as yttrium is an effective way for controlling grain growth behavior during recrystallization of AFA steels, which may have great implications on engineering applications.
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  Effects of Nb and V on Microstructural Evolution, Precipitation Behavior and Tensile Properties in Hot-rolled Mo-bearing Steel

  Fu-ming LIU,Jian-jun WANG,,Yu-jie LIU,R.D.K. MISRA,Chun-ming LIU,

  中国钢铁期刊网. 2016, 23(6): 559-565.

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  Microstructural evolution, precipitation behavior, and tensile properties of four experimental Mo-bearing steels were studied to elucidate the effects of Nb and V on microstructural properties. The results indicated that the microstructure of hot-rolled steels consisted of polygonal ferrite and degenerate pearlite, and the morphology remained same after holding at 600 ℃ for 1 h. The smallest grain size was obtained in Nb-V-Mo containing steel, followed by Nb-Mo and V-Mo steels. Precipitation was less in the hot-rolled Mo-bearing steel. The maximum volume fraction of precipitates was obtained in Nb-V-Mo bearing steel, and the Nb-V-Mo complex carbonitrides were highly stable at 600 ℃. In the Mo-bearing steel, the yield ratio was lowest at room temperature but highest at 600 ℃, which was attributed to the precipitation of Mo carbides and drag effect of Mo solute on dislocation movement.
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  Effect of Zn Vaporization on Wetting of Al-galvanized Steel in Cold Metal Transfer Process

  Qiao-li LIN,Gao-jun MAO,Qian HUANG,Rui CAO,Jian-hong CHEN

  中国钢铁期刊网. 2016, 23(6): 566-572.

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  The wetting of galvanized steel by molten Al alloys was studied in the cold metal transfer process by the sessile drop method using a high speed video camera. The wetting behavior can be divided into two typical cases, trending of non-wetting by using small wire feeding speed and wetting by using large wire feeding speed. The Leidenfrost effect is caused by the volatilization of Zn, which is responsible for the former case. The enhanced wettability of steel by Al and the weakening of the Leidenfrost effect are responsible for the latter case. Zn is the destabilizing factor for Al-steel joining that needs to be avoided by a reasonable design of process.
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  Effects of Temperature and Alloying Elements on γ Phase Fraction of Grain-oriented Silicon Steel

  Bing FU,,Hai-jun WANG,Jian-xin YAN,,Li XIANG,Sheng-tao QIU,Guo-guang CHENG

  中国钢铁期刊网. 2016, 23(6): 573-579.

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  The effects of temperature and alloying elements on γ phase fraction of grain-oriented silicon steel, which contained 2.97-3.42 mass% Si and 0.028-0.058 mass% C, were studied by microstructure observation and statistics. Furthermore, the quantitative relationships of temperature as well as C, Si, and Mn contents to γ phase fraction were obtained by numerical fitting. The experimental results show that γ phase fraction firstly increases with increasing temperature, reaches a maximum and then decreases in the temperature range of 900-1250 ℃. The temperature corresponding to the maximum γ phase fraction is about 1150-1200 ℃. Meanwhile, the γ phase fractions in steels at the same temperature have some differences because of different contents of various alloying elements. The verification results show that the values of γ phase fractions to C, Si, and Mn contents at the specific temperatures, which were obtained by multiple linear regression method, agree well with the measured values. In addition, the values of γ phase fractions to C, Si, and Mn contents in the temperature range of 900-1250 ℃, which were obtained by binomial regression method, agree with the measured values when the contents of Mn and soluble Al are not more than 0.320 mass% and 0.034 mass%, respectively. The obtained equations can carry out the approximate prediction of γ phase fractions of grain-oriented silicon steels during the hot rolling process.
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  Prediction and Experimental Validation of Forming Limit Curve of a Quenched and Partitioned Steel

  Xue-li GAO,Jun-ying MIN,Ling ZHANG,Quan-chao LI,Chang-wei LIAN,,Jian-ping LIN

  中国钢铁期刊网. 2016, 23(6): 580-585.

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  Forming limit curve (FLC) is an effective tool to evaluate the formability of sheet metals. An accurate FLC prediction for a sheet metal is beneficial to its engineering application. A quenched and partitioned steel, known as QP980, is one of the 3rd generation advanced high strength steels and is composed of martensite, ferrite and a considerable amount of retained austenite (RA). Martensite transformation from RA induced by deformation, namely, transformation induced plasticity (TRIP), promotes the capability of work hardening and consequently formability. Nakazima tests were carried out to obtain the experimental forming limit strains with the aid of digital image correlation techniques. Scanning electron microscopy (SEM) was employed to examine the fracture morphologies of Nakazima specimens of the QP980 steel. The observed dimple pattern indicated that tensile stress was the predominant factor which led to failure of QP980 specimens. Therefore, maximum tensile stress criterion (MTSC) was adopted as the forming limit criterion. To predict the FLC of QP980 steel, Von-Mises yield criterion and power hardening law were adopted according to the tested mechanical properties of QP980 steel. Results were compared with those derived from other three representative instability theories, e.g. Hill criterion, Storen-Rice vertex theory and Bressan-Williams model, which shows that the MTSC based FLC is in better agreement with the experimental results.
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  Relationship between Crystal Structure of Inclusions and Formation of Acicular Ferrites

  Zhi-min CUI,,Li-guang ZHU,,Yuan-liang LI,Qing-jun ZHANG,Chun-liang YAN,Wen-ling MO5

  中国钢铁期刊网. 2016, 23(6): 586-592.

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  The formation mechanism of intragranular ferrites with acicular morphology was discussed. The ferrites were characterized by scanning electron microscopy. The results showed that the ferrites had an acicular structure with radial, symmetrical, and acicular laths, and that the inclusions were the nucleation sites of the intragranular acicular ferrites. Transmission electron microscopy (TEM) was used to characterize the inclusions. The results of TEM with energy dispersive spectroscopy and TEM-selected area electron diffraction indicated that the complex inclusions consisted of Ti-Al complex oxides and MnS. The jagged edges of the complex inclusions can be ascribed to the effects of the crystal structure. The stabilization energy U of the coordination polyhedron growth units varies with the type of connection according to the calculation results. A larger U corresponds to more stable growth units, which induces the preferentially oriented growth of inclusions, at which point acicular ferrites are formed.
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  Effects of TMCP Schedule on Precipitation, Microstructure and Properties of Ti-microalloyed High Strength Steel

  Xiang-dong HUO,Lie-jun LI,Zheng-wu PENG,Song-jun CHEN

  中国钢铁期刊网. 2016, 23(6): 593-601.

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  Using the similar compositions of the Ti-microalloyed high-strength steels produced by the thin-slab casting process of compact strip production (CSP), four thermo-mechanical control processes(TMCP) after the simulated thick-slab casting, i.e. the two hot rolling routes and the two cooling processes, were designed, aiming at achieving the same mechanical properties as the thin strip products. The final microstructures after the four TMCP processes were examined by optical microscope(OM), scanning electron microscope(SEM) and transmission electron microscope (TEM). The tensile properties and Charpy impact energy were measured correspondingly. Strain-induced TiC precipitation was found in the two-stage rolling route with the finish rolling temperature at low levels, leading to grain refinement due to the pinning effect during austenite recrystallization. Precipitation hardening in ferrite was observed when a period of isothermal holding was applied after hot rolling. It could be concluded that both finish rolling temperature and the subsequent isothermal holding temperature were crucial for the achieved strength level due to the combined effect of grain refinement and precipitation hardening. At the same time, it was found that the isothermal holding led to poor impact toughness because of remarkable precipitation hardening. Therefore, it was suggested that the precipitation kinetics of titanium carbides in both austenite and ferrite should be investigated in future.
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  Effect of Cr on Characteristic of Rust Layer Formed on Low Alloy Steel in Flow-accelerated Corrosion Environment

  Feng CHAI,Shan JIANG,Cai-fu YANG

  中国钢铁期刊网. 2016, 23(6): 602-607.

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  The flow-accelerated corrosion experiments were carried out to research the effect of Cr on the rust layers formed on the carbon steel and Cr-containing steel, as well as the structure of rust layer of the two experimental steels. The influence of Cr on the flow-accelerated corrosion resistance and the corrosion morphology of inner rust layer formed on the Cr-containing steel were studied by the methods of polarization curves, scanning electron microscope, transmission electron microscope, and X-ray photoelectron spectroscope. The distribution of Cr and its form of existence in the inner rust layer were analyzed. The results show that corroded mass loss of Cr-containing steel is lower than that of carbon steel and its inner rust layer is compact. Cr exists in the form of Fe2CrO4 and is enriched in the inner rust layer. This concentration could make the inner rust layer exhibit the tendency of amorphous. This phenomenon is related to fine Fe2CrO4. The inner rust layer becomes more compact because of the formation of fine Fe2CrO4, and the protectiveness of inner rust layer could be improved remarkably.
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  Corrosion Behavior of Cr Micro-alloyed Corrosion-resistant Rebar in Neutral Cl--containing Environment

  Dan SONG,,,Wei SUN,Jin-yang JIANG,Han MA,Jian-chun ZHANG,Zhao-jun CHENG

  中国钢铁期刊网. 2016, 23(6): 608-617.

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  A new low-cost corrosion-resistant rebar (HRB400R) was designed and fabricated by Cr micro-alloying. The HRB400R rebar had uniform distribution of Cr element in ferrite grains. The corrosion behavior of the rebar in the neutral Cl--containing environment was studied systematically, and the improved corrosion resistance of the HRB400R rebar was revealed. According to the corrosion-morphology observation and electrochemical monitoring during the constant immersion corrosion in the 3.5 mass% NaCl solution, the HRB400R rebar presented alleviated corrosion damage, nobler Ecorr, lower Icorr, and larger Rt values, and these phenomena were more remarkable in the initial corrosion period. The elevated electrode potential of the rebar, caused by the solid-solution of Cr micro-alloying in the ferrite grains, was the key to the corrosion-resistance improvement. The HRB400R rebar also presented much lower mass-loss rate in the salt spray corrosion test. Besides the elevated corrosion resistance of the matrix, the doping and enrichment of Cr element in the rust layer was another factor for the higher corrosion resistance, which retarded the penetration of aggressive medium through the rust layer.
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  Plasma Transferred Arc Surface Alloying of Cr-Ni-Mo Powders on Compacted Graphite Iron

  Ji-jun FENG,,Chun-xu PAN,Liu-lin LU,Qi-wen HUANG,Hua-tang CAO

  中国钢铁期刊网. 2016, 23(6): 618-624.

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  A Cr-Ni-Mo overlayer was deposited on the surface of compacted graphite iron (CGI) by the plasma transferred arc (PTA) alloying technique. The microstructure of Cr-Ni-Mo overlayer was characterized by optical microscopy (OM), scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy (EDS), and X-ray diffractometer (XRD). Results show that the cross-section consists of four regions: alloying zone (AZ), molten zone (MZ), heat affected zone (HAZ), and the substrate (SUB). The microstructure of AZ mainly consists of cellular γ-(Fe,Ni) solid solution, residual austenite and a network of eutectic Cr7C3 carbide while the MZ area has a typical feature of white cast iron (M3C-type cementite). The martensite/ledeburite double shells are observed in the HAZ. With decreasing the concentration of Cr-Ni-Mo alloys, the fracture mode changes from ductile in the AZ to brittle in the MZ. The maximum hardness of the AZ (450 HV0.2) is lower than that of the MZ (800 HV0.2). The eutectic M3C and M7C3 carbides increase the microhardness, while the austenite decreases that of the AZ.
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  Effect of Alloying Method on Microstructure and Wear Resistance of Fe-Cr-V-B Based Alloy

  Yu MA,Ying LIU,Jun LI,Hui ZHANG,Hao YANG

  中国钢铁期刊网. 2016, 23(6): 625-632.

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  The microstructure and wear behavior of Fe-Cr-V-B based alloy was investigated. Each of the specimens was characterized by metallographic techniques and hardness test. Phase analysis of alloy was performed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The results showed that the microstructure of Fe-Cr-V-B based as-cast alloy containing 8.6 mass% V was composed of α-(Fe,Cr) solid solution, VC carbides, and V3B4 borides, whereas the as-cast alloy containing 24.8 mass% Cr was composed of α-(Fe,Cr) solid solution and V3B4 borides; the eutectic V3B4 borides mainly comprise M2B-type borides (M presents Fe and Cr). The existence of a large amount of V atoms affects the growth pattern of eutectic borides, which mainly display rod-like and grainy structure. The wear behavior of the experimental alloy has been investigated using pin-on-disk type friction and wear apparatus. The comparison of experimental results indicated that the relative wear resistance of the alloy containing 8.6 mass% V after destabilization heat treatment in a conventional furnace at 1373 K for 2 h was about six times higher than that of the high chromium (19 mass%) cast iron.