2009年, 第16卷, 第4期　刊出日期：2009-08-15

  

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Metallurgy and Metal Working
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  Hybrid Modeling for Soft Sensing of Molten Steel Temperature in LF

  TIAN Huixin;MAO Zhizhong;WANG Anna

  中国钢铁期刊网. 2009, 16(4): 1-0.

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  Aiming at the limitations of traditional thermal model and intelligent model, a new hybrid model is established for soft sensing of the molten steel temperature in LF. Firstly, a thermal model based on energy conservation is described; and then, an improved intelligent model based on process data is presented by ensemble ELM (extreme learning machine) for predicting the molten steel temperature in LF. Secondly, the selfadaptive data fusion is proposed as a hybrid modeling method to combine the thermal model with the intelligent model. The new hybrid model could complement mutual advantage of two models by combination. It can overcome the shortcoming of parameters obtained online hardly in a thermal model and the disadvantage of lacking the analysis of ladle furnace metallurgical process in an intelligent model. The new hybrid model is applied to a 300 t LF in Baoshan Iron and Steel Co Ltd for predicting the molten steel temperature. The experiments demonstrate that the hybrid model has good generalization performance and high accuracy.
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  Effect of LowFrequency AC Power Supply During Electroslag Remelting on Qualities of Alloy Steel

  CHANG Lizhong;SHI Xiaofang;YANG Haisen;LI Zhengbang

  中国钢铁期刊网. 2009, 16(4): 7-0.

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  The effect of frequencies of AC power supply on the quality of the electroslagmelted ingot is studied. The results show that with a decrease in the frequency, electromagnetic force becomes more violent, and the temperature in the slag bath becomes more homogeneous, and therefore, the depth of molten metal pool is decreased; electrochemical reactions occur with the decrease in the frequency, and the atomic oxygen electrolyzed dissolves in the molten metal pool; the nonmetallic inclusions, which are distributed dispersively in the ingot, have an increased content, and their size is approximately in the range of 2-3 μm.
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  Application of Numerical Simulation Technique to Casting Process of Valve Block

  MI Guofa;LIU Xiangyu;WANG Kuangfei;FU Hengzhi

  中国钢铁期刊网. 2009, 16(4): 12-0.

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  The numerical simulation technique was applied to the casting process of a valvetype part. The moldfilling and solidification stages of the casting were numerically analyzed. The filling behavior, solidification sequence, and thermal stress distribution were reproduced and the possible defects, such as cold shut and shrinkage, were predicted. Based on the simulation result, the doublegating system was replaced by a singlegating system. Meanwhile, the chills were used to regulate the solidification sequence of casting. To eliminate the cracks in the casting, the sand core was converted into a canulate one. By modifying the original process, the defects were eliminated and the casting with good quality was obtained.
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  Quantitative Study on Nonmetallic Inclusion Particles in Steels by Automatic Image Analysis With Extreme Values Method

  Cássio Barbosa;José Brant de Campos;Jneo Lopes do Nascimento;Iêda Maria Vieira Caminha

  中国钢铁期刊网. 2009, 16(4): 18-0.

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  The presence of nonmetallic inclusion particles which appear during steelmaking process is harmful to the properties of steels, which is mainly as a function of some aspects such as size, volume fraction, shape, and distribution of these particles. The automatic image analysis technique is one of the most important tools for the quantitative determination of these parameters. The classical Student approach and the Extreme Values Method (EVM) were used for the inclusion size and shape determination and the evaluation of distance between the inclusion particles. The results thus obtained indicated that there were significant differences in the characteristics of the inclusion particles in the analyzed products. Both methods achieved results with some differences, indicating that EVM could be used as a faster and more reliable statistical methodology.
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  Analysis of Rolling Pressure in Asymmetrical Rolling Process by Slab Method

  TIAN Yong;GUO Yanhui;WANG Zhaodong;WANG Guodong

  中国钢铁期刊网. 2009, 16(4): 22-0.

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  The plane strain asymmetrical rolling was analyzed using slab method. The contact arc was replaced by parabola, and the constant surface friction status was adopted during the analysis. The deformation area was divided into three zones according to the direction of the friction. Then, the three zones were studied, respectively. A rolling force model and a rolling torque model were developed based on the analysis, and they were used to analyze the influence of asymmetrical rolling factors on deformation area and unit pressure if they had good precision which was determined by comparing the calculated results with the measured ones.
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  Nonlinear Finite Element Analysis of Thin Strip Temper Rolling Process

  SUN Jingna;HUANG Huagui;DU Fengshan;LI Xuetong

  中国钢铁期刊网. 2009, 16(4): 27-0.

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  To reveal the basic deformation mechanisms under the conditions of high friction, small reduction, and long contact length in thin strip temper rolling process, an elastoplastic finite element analysis of plane strain upsetting was made based on the FEM software Marc. The results indicated that a near flat ‘zero reduction’ region was present in the center of the contact arc. The simulation results about the effect of rolling parameters on the central flat region showed that any change of increasing the rolling force could result in or enlarge the central flat region in the deformation zone. Stress distribution results illustrated that the metal was in triaxial compression state. Although the maximum and minimum principal stresses were all much larger than the yield stress of the strip, the equivalent stress became lower than that, and no further plastic strain, even a small elastic springback occurred in the central flat region. That was the problem of ‘hydrostatic pressure’ in thin strip temper rolling.
Material
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  Application of Rietveld Refinement to Investigate the High Chromium White Cast Iron Austempered at Different Temperatures

  HOU Qingyu;HUANG Zhenyi;WANG Jingtao

  中国钢铁期刊网. 2009, 16(4): 33-0.

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  The effect of austempering temperature on the microstructure and properties of a high chromium white cast iron was investigated with the Rietveld refinement method. The result shows that the upper bainite exists in the sample austempered at 623 K and the martensite, lower bainite, M7C3, and retained austenite exist in the samples austempered at 563 K and 593 K. The relative content of the retained austenite increases with increasing the austempering temperature from 563 K to 623 K. The higher hardness, impact toughness and impact abrasive wear resistance can be obtained for the specimen austempered at 593 K.
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  Properties of 3Cr2W8V Die Steel With Striations Processed by Laser

  CHEN Li;ZHOU Hong;ZHANG Zhihui;REN Luquan

  中国钢铁期刊网. 2009, 16(4): 39-0.

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  The striations on the surface of 3Cr2W8V die steel were processed by laser. The microstructure, hardness, wear resistance and thermal fatigue behavior of the specimens processed by laser were measured. The appearance and mechanism of thermal fatigue crack propagation in the zone processed by laser were observed and discussed. The results show that the wear resistance and thermal fatigue resistance of materials processed by laser are all better than those of the unprocessed material. The processed zone by laser plays a role in baffling wearing process and crack propagation. The pilenail effect of processed zone is the main factor for improving the wear resistance and thermal fatigue resistance of material.
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  Fatigue Property of Low Cost and High Strength Wheel Steel for Commercial Vehicle

  WANG Ning;LI Yi;DU Linxiu;WU Di;LIU Xianghua

  中国钢铁期刊网. 2009, 16(4): 44-0.

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  The fatigue properties of the newly developed wheel steel used for commercial vehicles were studied using pushpull axial loading fatigue tests with stress ratio R=-1. Q235B steel, which is conventionally applied to commercial vehicle wheels, was also analyzed for comparison. Although the chemical composition and microstructure (ferrite and pearlite) of newly developed wheel steel were similar to those of Q235B, the 107 cycles fatigue limit of the new wheel steel was 260 MPa, which is 24% higher than that of Q235B (210 MPa). The improvement of the fatigue strength of the new wheel steel can be attributed to grain refinement. In order to investigate the effect of the decrease in thickness of the wheel steel on the fatigue property of the wheel, dynamic cornering fatigue tests were conducted on full scale wheels with the model of 825×225. The results indicated that the newly developed wheel steel had outstanding fatigue life even if the mass loss was 10% in comparison with Q235B.
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  Evaluation of Dry Sliding Wear Behaviour of Plasma Transferred Arc Hardfaced Stainless Steel

  C S Ramachandran;V Balasubramanian;R Varahamoorthy

  中国钢铁期刊网. 2009, 16(4): 49-0.

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  The effects of different experimental conditions on the dry sliding wear behavior of stainless steel surface produced by plasma transferred arc (PTA) hardfacing process were studied. The wear test was conducted in a pinonroller wear testing machine, at constant sliding distance of 1 km. Mathematical models were developed to estimate wear rate incorporating with rotational speed, applied load and roller hardness using statistical tools such as design of experiments, regression analysis and analysis of variance. It is found that the wear resistance of the PTA hardfaced stainless steel surface is better than that of the carbon steel substrate.
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  Effect of WarmRolled Pearlite Microstructural Features on Austenitic Transformation

  YAO Shengjie;DU Linxiu;LIU Xianghua;WANG Guodong

  中国钢铁期刊网. 2009, 16(4): 55-0.

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  The austenite transformation characteristics for various warmrolled pearlite during rapid heating were investigated. The results indicate that the start temperature (Ts) is sensitive to the microstructural feature of pearlite, whereas the dislocation plays an important role in the transformation rate; at the same time, the uniformity of austenite grains is more or less affected by the amount of spheroidized pearlite. A critical effect on the state of austenite grain is created through the influence of initial microstructures on the start temperature of transformation.
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  Precipitates in Steels With Ti Additive Produced by CSP Process

  LOU Yanzhi;LIU Delu;NI Xiaoqing

  中国钢铁期刊网. 2009, 16(4): 60-0.

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  Hot strips of low carbon steels with Ti additive [contain C 004%-007%, Si≤06%, Mn≤06%, Ti 006%-014% (mass percent)] produced by EAFCSP (Electric Arc FurnacesCompact Strip Production) process were examined by TEM, HREM and XRD. Carbonitrides with different N/C ratio were found in the samples. The varying composition of the Ticarbonitrides resulted from the supersaturation of Ti and temperature at which the compound was formed. In the tested steel, total mass fraction of the precipitates including cementite, carbonitride and a small quantity of Fe3O4, Al2O3, Ti2CS and AlN was about 0305%. XRD results showed that about a quarter of the powder extracted by electrolysis was titanium nitrides, carbonitrides and carbides. Particle arrays formed by interphase precipitation could be observed either in slabs or in hot strips. The dominant reaction mechanisms were discussed. Compared with the conventional cold charge process, small amount of Ti addition would be more effective for precipitation of fine precipitates in the steels produced by CSP process.
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  Effect of Dissolved and Precipitated Niobium in Microalloyed Steel on Deformation Induced Ferrite Transformation (DIFT)

  LIU Qingyou;DENG Suhuai;SUN Xinjun;DONG Han;WENG Yuqing

  中国钢铁期刊网. 2009, 16(4): 67-0.

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  Hot deformation processing was designed to study the effects of niobium (Nb) on DIFT. A prestrain of 051 at 880 ℃ for different isothermal time was used for adjusting the deformed austenite constitution and Nb existing state, followed by a secondary heavy deformation at 780 ℃ for inducing the ferrite transformation. The volume fraction and grain size of deformation induced ferrite (DIF) obtained at different isothermal time between double hits were investigated. It was found that Nb dissolved in austenite is adverse to DIFT; however, the precipitation of Nb is beneficial to DIFT. As Nb plays the role in the conventional TMCP, Nb retards the recrystallization of deformed austenite and enhances the deformation stored energy in the multipass deformation, and in result, Nb promotes DIFT.
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  Development of NbVTi HotRolled High Strength Steel With Fine Ferrite and Precipitation Strengthening

  YI Hailong;DU Linxiu;WANG Guodong;LIU Xianghua

  中国钢铁期刊网. 2009, 16(4): 72-0.

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  A hotrolled steel with high yield strength of 700 MPa, good elongation of about 20% and low ductilebrittle transition temperature (DBTT) lower than -70 ℃ has been developed in laboratory. The results show that adopting finishing rolling temperature of around 800 ℃ is rational, and coiling temperature is between 400 and 500 ℃. The strength of developed 700 MPa hotrolled high strength steel is derived from the cumulative contribution of fine grain size, dislocation hardening and precipitation hardening. The fine grain strengthening and precipitation hardening are the dominant factors responsible for such high strength, and good elongation and toughness are predominantly due to fine grain ferrite.
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  Evolution of Texture in Grain Oriented Silicon Steels

  Constantin Gheorghies;Ana Doniga

  中国钢铁期刊网. 2009, 16(4): 78-0.

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  Goss texture or (110)[100] crystallographic orientation of the grains is typical grain structure of grain oriented silicon steel used for transformer. This type of texture is one of the most important parameters determining the magnetic properties of the laminated steel plates. The formation and growth of Goss texture in three steel samples are investigated. Two of them are prepared under laboratory conditions and one under industrial conditions. The emphasis is put on the effects of hot lamination temperature and time, primary and secondary recrystallization temperatures during cold lamination on developing of the Goss texture in correlation with other texture components. Also in all steel processing stages, the influence of the chemical composition on the occurrence of Goss texture is examined.
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  Effect of Co on Microstructure and Interfacial Properties of FeBased Laser Cladding

  GAO Lili;BIAN Xiufang;TIAN Yongsheng;FU Chunxia

  中国钢铁期刊网. 2009, 16(4): 84-0.

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  The coatings consisting of Fe064Ni036 dendrites as matrix and (Fe,Cr)7(C,B)3 interdendritic compounds as reinforcement were fabricated on the medium steel substrate by laser cladding using the Febased powders with different Co content, and Co is uniformly dissolved in the coatings. Compared with the coatings containing 1% and 5% Co, the coating containing 3% Co increases in the area fraction of the interdendritic region by about 5%, in the microhardness nearby the interface by about HV 55 and in the interfacial bond strength by about 30 MPa. The interface fracture morphology exhibits the tear appearance, which can be characterized as the ductile fracture.
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  Formation Characteristic of CO2 Corrosion Product Layer of P110 Steel Investigated by SEM and Electrochemical Techniques

  ZHAO Guoxian;LU Xianghong;XIANG Jianmin;HAN Yong

  中国钢铁期刊网. 2009, 16(4): 89-0.

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  Formation characteristic of CO2 corrosion product layer on the surface of P110 steel was investigated in simulated oilfield environment using massloss experiment, potentiodynamic polarization curve, impedance spectroscopy, and SEM micrograph analysis. Samples of different times up to 240 h were tested during exposure. Corrosion product was primarily composed of Fe(Ca,Mg)(CO3)2, which was distinguished by two layers. With an increase in the exposure time, the charge transfer resistance and polarization resistance increased progressively, the uniform corrosion rate decreased, and the corrosion reaction was controlled by the diffusion process instead of the activation process. All phenomena were attributed to the formation of the protective corrosion product layer. More compact and lower porosity of the layer made it more difficult to transfer and diffuse through the corrosion product layer for the charges and ions. Similar results were obtained by electrochemical test and massloss experiment.